Method and apparatus for collecting and analyzing aerosol particles - Patents.com

Abstract

The apparatus (200) for collecting and analyzing aerosol particles includes a fluid storage tank (206) for generating a condensed fluid (256) having a first temperature, and an aerosol collection port (202) having a vapor inlet (212) for receiving the condensed fluid and an aerosol inlet (222) for receiving an aerosol stream having a second temperature lower than the first temperature. The condensed fluid (256) is mixed with the aerosol stream in the aerosol collection port (202) to generate a mixed stream. The apparatus also includes a growth tube (204) configured to receive the mixed stream and condense the aerosol particles to form a gas stream containing grown droplets that include the aerosol particles, and a converging nozzle (248) in fluid communication with the growth tube (204). The apparatus allows for semi-continuous measurement of an aerosol sample, where a measurement cycle may include i) collection of particles on a substrate (238), ii) analysis using a spectroscopic technique, and iii) removal of the sample and preparation for the next measurement.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 63 / 304,260, filed January 28, 2022, the contents of which are incorporated by reference in their entirety herein. Statement of government support This invention was made in part with Government support from the Centers for Disease Control and Prevention. The Government has certain rights in this invention.

[0002] 1. Field of the invention The present invention generally relates to methods and apparatus for concentrating aerosol particles from an air sample and collecting them on a substrate, allowing the collected sample to be subsequently chemically analyzed using a variety of spectroscopic techniques, thereby enabling automated, semi-continuous analysis. [Background technology]

[0003] 2. Brief description of the technology Exposure to harmful airborne particles can pose significant health risks to people routinely exposed to the air environment and in industrial settings. Measuring the chemical composition and concentration of aerosols is important to prevent exposure and protect human health.

[0004] Currently, widely used methods for environmental and workplace aerosol chemistry measurements involve particle collection on filters over several hours, followed by laboratory analysis. These methods can provide time-averaged air concentrations, but cannot capture transient exposures. They are time and resource intensive, and provide analytical results days after exposure has occurred. Therefore, low-cost, portable, real-time aerosol chemistry analysis instruments are needed to effectively assess and prevent human exposure to harmful airborne particles. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US Patent Application Publication No. 2002 / 0124664 [Patent Document 2] US Patent Application Publication No. 2011 / 0159596 Summary of the Invention [Means for solving the problem]

[0006] In one aspect, the invention is directed to an apparatus for collecting and analyzing aerosol particles, the apparatus including: a fluid storage tank for generating a condensed fluid comprising vapor, the condensed fluid having a first temperature; an aerosol collection port having a vapor inlet for receiving the condensed fluid generated from the fluid storage tank and an aerosol inlet for receiving an aerosol stream comprising aerosol particles and having a second temperature lower than the first temperature, where the condensed fluid mixes with the aerosol stream in the aerosol collection port to generate a mixed stream; a growth tube configured to receive the mixed stream from the aerosol collection port and condense the aerosol particles to form a gas stream containing grown droplets comprising the aerosol particles; and a focusing nozzle in fluid communication with the growth tube for focusing the condensed fluid into an aerosol beam comprising grown droplets.

[0007] A method for analyzing aerosol particles using the above apparatus includes generating a condensed fluid containing vapor, mixing the condensed fluid with an aerosol stream in an aerosol collection port to generate a mixed stream, introducing the mixed stream into a growth tube, condensing the aerosol particles in the growth tube to form a gas stream containing grown droplets containing the aerosol particles, and focusing the gas stream containing the grown droplets into an aerosol beam.

[0008] In another aspect, an apparatus for collecting and analyzing aerosol particles includes a converging nozzle for emitting an aerosol stream containing aerosol particles, a collecting substrate positioned downstream of the converging nozzle for collecting the aerosol particles from the aerosol stream, a controller coupled to the collecting substrate for controlling rotation of the collecting substrate, and a means for ablating the aerosol particles on the collecting substrate.

[0009] A method of analyzing aerosol particles includes collecting aerosol particles on a collecting substrate in an initial orientation, rotating the collecting substrate to a new ablation orientation, ablating the aerosol particles on the collecting substrate in the new ablation orientation, rotating the collecting substrate back to the initial orientation, and subsequently collecting a next sample of aerosol particles. Optionally, ablating the aerosol particles produces atomic emission, and the method further includes analyzing the atomic emission to characterize the aerosol particles on the collecting substrate.

[0010] In yet another aspect, a method of analyzing aerosol particles includes analyzing first aerosol particles on a first surface of a collecting substrate, ablating second aerosol particles on a second surface of the collecting substrate to generate atomic emission, and analyzing the atomic emission to characterize the second aerosol particles on the collecting substrate, optionally wherein the first aerosol particles and the second aerosol particles are collected from the same or different aerosol streams. [Brief description of the drawings]

[0011] The illustrations, by way of example and not limitation, are as follows: [Figure 1A] FIG. 2 is a three-dimensional view of one embodiment of an apparatus for collecting and analyzing aerosol particles, the apparatus including a spot sample mixed-flow condensation aerosol concentrator, i.e., a spot sample MCAC, for collecting spot samples. [Figure 1B] FIG. 1B is a cross-sectional view of the device of FIG. 1A taken along line AA. [Diagram 2]FIG. 13 is a cross-sectional view of another embodiment of an apparatus for collecting aerosol particles (also called a liquid sample MCAC for collecting a liquid sample). [Figure 3A] FIG. 2 is a three-dimensional view of another embodiment of an apparatus for analyzing aerosol particles. [Figure 3B] FIG. 3B is a cross-sectional view of the device of FIG. 3A taken along line AA. [Figure 3C] FIG. 3B is a schematic diagram showing a measurement procedure using the device of FIG. 3A. [Figure 4] FIG. 1 illustrates an example of an apparatus for collecting and analyzing aerosol particles. [Figure 5A] Figure 1 shows the theoretical saturation rate calculated for 25 nm particles of NaCl in comparison with the experimental activation efficiency measured in spot sample MCAC (>1,400 nm) at a saturator temperature of 70 °C, respectively. The dashed line represents the fitting curve of the experimentally measured growth efficiency, and the error bars indicate the standard deviation calculated from three replicates. [Figure 5B] Figure 1 shows the theoretical saturation rate calculated for 25 nm particles of NaCl in comparison with the experimental activation efficiency measured in spot sample MCAC (>1,400 nm) at a saturator temperature of 75 °C, respectively. The dashed line represents the fitting curve of the experimentally measured growth efficiency, and the error bars indicate the standard deviation calculated from three replicates. [Figure 5C] Figure 1 shows the theoretical saturation rate calculated for 25 nm particles of NaCl in comparison with the experimental activation efficiency measured in spot sample MCAC (>1,400 nm), respectively, at a saturator temperature of 80 °C. The dashed line represents the fitting curve of the experimentally measured growth efficiency, and the error bars indicate the standard deviation calculated from three replicates. [Figure 5D] Figure 1 shows the theoretical saturation rate calculated for 25 nm particles of NaCl in comparison with the experimental activation efficiency measured in spot sample MCAC (>1,400 nm) at a saturator temperature of 85 °C, respectively. The dashed line represents the fitting curve of the experimentally measured growth efficiency, and the error bars indicate the standard deviation calculated from three replicates. [Figure 6A]FIG. 13 shows the activation efficiency of spot samples MCAC based on >300 nm, >700 nm, and >1,400 nm for Tsat=70° C. [Figure 6B] FIG. 1 shows activation efficiency based on droplet size fraction above 1400 nm measured with spot sample MCAC, where Tsat is set at 70° C., 75° C., 80° C., and 85° C., respectively, with aerosol flow at 22° C. and 100% humidity, and error bars indicate standard deviation calculated from three replicates. [Figure 7A] FIG. 1 shows the activation efficiency of spot sample MCAC based on droplet size fractions of >300 nm, >700 nm, and >1,400 nm measured as a function of saturator temperature for 25 nm NaCl particles and (a) 100% aerosol inlet humidity, with aerosol flow at a temperature of 22° C. and error bars indicating standard deviation extracted from three replicates. [Figure 7B] Figure 1 shows the activation efficiency of spot sample MCAC based on droplet size fractions of >300 nm, >700 nm, and >1,400 nm measured as a function of saturator temperature for (a) 25 nm NaCl particles and (b) 25% aerosol inlet humidity, with aerosol flow at a temperature of 22 °C, and error bars indicate standard deviation extracted from three replicates. [Figure 7C] Figure 1 shows the activation efficiency of spot sample MCAC based on droplet size fractions of >300 nm, >700 nm, and >1,400 nm measured as a function of saturator temperature for (a) 25 nm NaCl particles and (b) 15% aerosol inlet humidity, with aerosol flow at a temperature of 22°C, and error bars indicate standard deviation extracted from three replicates. [Figure 7D] (a) Activation efficiency of spot sample MCAC based on droplet size fractions of >300 nm, >700 nm, and >1,400 nm measured as a function of saturator temperature for 25 nm NaCl particles and (b) an aerosol inlet humidity of 11%. The aerosol flow was at a temperature of 22° C., and error bars indicate standard deviation extracted from three replicates. [Figure 8]Figure 1 shows the activation efficiency of spot sample MCAC measured using different fractions of grown droplet diameters, >300 nm, >700 nm, and >1,400 nm, as a function of operating time (minutes, min) for 25 nm particles of NaCl. The aerosol flow was at a temperature of 22°C and 100% humidity, the measurement started when the saturator temperature reached 80°C, a flow rate of 4 L / min was used for the aerosol flow and a flow rate of 0.4 L / min was implemented for the water vapor flow. [Figure 9A] Scanning electron microscope (SEM) image of an aerosol sample area with deposited 20 nm diameter polystyrene spheres, where droplet collection was achieved via spot sample MCAC with Tsat=75°C, Qh=0.6 L / min, Qc=4 L / min, Taerosol=23°C, RHaerosol=59-65%, and Tsubstrate=90-100°C. [Figure 9B] Scanning electron microscope (SEM) image of an aerosol sample area with deposited 150 nm diameter polystyrene spheres, where droplet collection was achieved via spot sample MCAC with Tsat=75°C, Qh=0.6 L / min, Qc=4 L / min, Taerosol=23°C, RHaerosol=59-65%, and Tsubstrate=90-100°C. [Figure 9C] Scanning electron microscope (SEM) image of an aerosol sample area with deposited 1,900 nm diameter polystyrene spheres, where droplet collection was achieved via spot sample MCAC with Tsat=75°C, Qh=0.6 L / min, Qc=4 L / min, Taerosol=23°C, RHaerosol=59-65%, and Tsubstrate=90-100°C. [Figure 10A] FIG. 9A is an axial distribution of the deposited aerosol sample area of ​​20 nm diameter polystyrene spheres. [Figure 10B] FIG. 9B is the axial distribution of the deposited aerosol sample area of ​​150 nm diameter polystyrene spheres. [Figure 10C] Figure 9C is the axial distribution of the deposited aerosol sample area of ​​1,900 nm diameter polystyrene spheres. [Figure 11]Figure 1 shows the activation efficiency of spot sample MCAC based on grown droplet diameters >300 nm, >700 nm, and >1,400 nm as a function of aerosol number concentration of monodisperse test aerosol (diameter 25 nm). The aerosol flow was at a temperature of 22°C and 100% humidity, a flow rate of 4 L / min was used for the aerosol flow, a flow rate of 0.6 L / min was implemented for the water vapor flow, and the saturator temperature was set at 75°C. [Figure 12] FIG. 14 shows the activation efficiency of liquid sample MCAC as a function of saturator temperature, where sodium chloride aerosol with an aerodynamic diameter of 100 nm (Taerosol=23.6-24.9°C, RHaerosol=45.8-51.5%) was used, the temperature of the growth tube was fixed at 0°C, and the error bars indicate the standard deviation calculated from three replicate measurements. [Figure 13A] FIG. 1 shows the activation efficiency of liquid sample MCAC as a function of aerosol aerodynamic diameter (nm). [Figure 13B] FIG. 13 shows the activation efficiency of liquid sample MCAC as a function of operating time (min) using sodium chloride aerosol (Taerosol=22.5-25.3° C., RHaerosol=46.6-56%). [Figure 14] FIG. 13 shows the activation efficiency of growing droplets in liquid sample MCAC as a function of growth tube temperature (°C) using sodium chloride aerosol with an aerodynamic diameter of 100 nm (Taerosol=23.7-24.9°C, RHaerosol=46.5-52.2%). [Figure 15] FIG. 1 shows the activation efficiency of grown droplets in a liquid sample MCAC as a function of the relative humidity (%) of the inlet aerosol-containing stream, where a sodium chloride aerosol having an aerodynamic diameter of 100 nm was used, the inlet aerosol-containing stream had a temperature of 25° C., and the saturator temperature was set at 85° C. [Figure 16] Figure 14 shows the number concentration dependent collection efficiency of respirable silica particles in liquid sample MCAC, where the inlet particle flow rate was 10 L / min and the temperatures of the saturator and growth tube wall were maintained at 85 °C and 0 °C, respectively. [Figure 17]FIG. 11 compares particle mass collected through the liquid sample MCAC and the reference filter, where the dashed line represents the linear fitting curve corresponding to the experimental data and the error bars represent the standard deviation of three weight replicate measurements of the filter. [Figure 18A] A calibration curve for crystalline silica is shown, which shows the Raman peak signal intensity as a function of mass measurements obtained from a Quartz Crystal Microbalance (QCM) MOUDI™ impactor and two types of nozzles were used for collection: a single stage nozzle (SSN) and a multi-stage nozzle (MSN). [Figure 18B] 1 shows a calibration curve for rutile titanium dioxide / titania, which shows Raman peak signal intensity as a function of mass measurements obtained from a QCM MOUDI™ impactor, where only SSN was used for collection. [Figure 19A] FIG. 13 shows measurements of crystalline silica / quartz mass in fracking dust samples collected on electrodes for 2, 3, and 4 hours. [Figure 19B] FIG. 13 shows the measurement of titania mass in a 5:1:1 mixture of titania, Arizona road dust, and diesel particulate matter. The estimated titania mass and the measured mixture mass from QCM MOUDI were used to determine the titania percentage as shown in the pie chart. [Figure 20] Figure 4 shows the results of short-term measurements of crystalline silica using Raman techniques in transient aerosols simulating work activities in an aerosol collection and analysis device (Figure 4), where total aerosol concentrations were kept high to allow for shorter collection times. [Figure 21A] FIG. 1 illustrates detection of diesel particulate matter (DPM) using the disclosed Raman instrument. [Figure 21B] FIG. 1 illustrates the detection of graphene using the disclosed Raman instrument. [Figure 21C] FIG. 1 illustrates detection of single-walled carbon nanotubes (SWCNTs) using the disclosed Raman instrument. [Figure 21D] FIG. 1 illustrates detection of chromium (VI) using the disclosed Raman instrument. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The above and other features are illustrated by the following detailed description and examples. Disclosed herein is a sampling and analysis device that can be used to collect and analyze aerosol particles from ambient (outdoor) or indoor air atmospheres in real time. The sampling and analysis device includes an aerosol collection port in fluid communication with a growth tube and a fluid storage tank. The aerosol collection port is effective to capture aerosols at a much higher fluid velocity than the condensation fluid delivered to the collection port from the fluid storage tank. This allows a high concentration of aerosol particles to be collected as the condensation fluid is removed from the combination of aerosol particles and condensation fluid.

[0013] The growth tube is downstream of the aerosol collection port and promotes nucleation and growth of the aerosol particles after they mix with the condensation fluid. In one embodiment, the growth tube is immediately downstream of the aerosol collection port. The fluid storage tank is downstream of the aerosol collection port and the growth tube. In one embodiment, the fluid storage tank is in direct contact with the growth tube. The fluid storage tank is in a recirculation loop with the aerosol collection port via a tube that fills the aerosol collection port with the condensation fluid. Thus, the fluid storage tank is both upstream and downstream of the aerosol inlet port.

[0014] 1A and 1B, an analyzer (200) includes an aerosol collection port (202) having a vapor inlet (212) for receiving a condensed fluid generated from a fluid storage tank (206) and an aerosol inlet (222) for receiving an aerosol stream containing aerosol particles. At the aerosol collection port (202), the condensed fluid and the aerosol stream may instantaneously and adiabatically mix to form a mixed stream.

[0015] In one embodiment, the condensing fluid is in vapor form and at a higher temperature than the aerosol stream before entering the aerosol collection port 202. In one embodiment, the condensing fluid is at a first temperature and the aerosol stream is at a second temperature lower than the first temperature before they contact each other. The temperature of the condensing fluid can be 75-95°C or 75-85°C and the aerosol stream can be at room temperature, for example 15-30°C. The condensing fluid and the aerosol stream contact each other at the aerosol collection port 202. Upon instantaneous adiabatic mixing, the vapor molecules can attach to the aerosol particles. In one embodiment, the vapor condenses on the aerosol particles.

[0016] A variety of fluids can be used as the condensing fluid. Examples of fluids include aqueous solvents, organic solvents, or combinations thereof. Organic solvents that are non-toxic to living organisms are preferred.

[0017] Examples of organic solvents include aprotic polar solvents, polar protic solvents, non-polar solvents, or combinations thereof. Examples of liquid aprotic polar solvents include propylene carbonate, ethylene carbonate, butyrolactone, acetonitrile, benzonitrile, nitromethane, nitrobenzene, sulfolane, dimethylformamide, N-methylpyrrolidone, and the like, or combinations thereof. Examples of polar protic solvents include water, alcohols such as methanol, ethanol, propanol, isopropanol, and butanol, acetonitrile, nitromethane, and the like, or combinations thereof. Examples of non-polar solvents include benzene, toluene, methylene chloride, carbon tetrachloride, hexane, diethyl ether, tetrahydrofuran, and the like, or combinations thereof. Co-solvents comprising at least one aprotic polar solvent and at least one non-polar solvent may also be utilized to modify the swelling power of the solvent of the aerosol particles. In an exemplary embodiment, the condensing fluid is water in vapor form. In another exemplary embodiment, the condensing fluid is water and alcohol in vapor form.

[0018] The aerosol stream may have a relative humidity of 9-100% or 25-100%. For example, in the case of the spot sample MCAC shown in FIG. 1A, the inlet aerosol stream may have a relative humidity of 25-100%. In the case of the liquid sample MCAC shown in FIG. 2, the inlet aerosol stream may have a relative humidity of 9-100%.

[0019] The device (200) allows for the collection of aerosol particles at relatively high aerosol flow rates. In one embodiment, the aerosol flow is introduced into the aerosol collection port (202) at a flow rate of 1-20 liters / min, 1-10 liters / min, or 2-8 liters / min. Compared to the aerosol flow, the condensing fluid is introduced into the aerosol collection port (202) at a slower flow rate, for example, 0.08-1.5 liters / min or 0.1-1 liters / min. The flow rate ratio of the condensing fluid to the aerosol flow can be 0.01-0.5, preferably 0.05-0.5, more preferably 0.07-0.3.

[0020] To accommodate high flow rates, the aerosol collection port (202) may be a "T-shaped" port, where the aerosol flow can enter from the top and the condensing fluid can enter from the side. In one embodiment (not shown), the aerosol flow can meet the incoming condensing fluid in the aerosol collection port (202) at an angle of 30-150°, preferably 60-120°. This configuration can minimize particle loss inside the aerosol collection port (202).

[0021] The aerosol collection port (202) may be in the form of a tube with a volume of 0.1 to 5 cubic centimeters. The residence time of the aerosol flow and condensed fluid in the aerosol collection port (202) may be in the range of 1 to 5 milliseconds.

[0022] The apparatus (200) also includes a growth tube (204) that is in fluid communication with and located downstream of the aerosol collection port (202) such that the temperature of the mixed stream generated from the aerosol collection port (202) is reduced, causing vapor molecules to condense onto the aerosol particles, thereby allowing the aerosol particles to act as seeds and promote growth into droplets.

[0023] The growth tube (204) may have a larger volume than the aerosol collection port (202). Optionally, the mixed stream enters the growth tube (204) through an orifice, which has a smaller diameter than the growth tube (204). Thus, upon entering the growth tube (204), the mixed stream expands in volume, and the temperature of the mixed stream may decrease due to this expansion. As the temperature decreases within the growth tube 204, the vapor of the condensing fluid may condense on the aerosol particles, which may act as nucleation sites to form droplets containing the aerosol particles. In one embodiment, the droplets may be referred to as particle-containing droplets. The droplets may grow within the growth tube, and then the grown droplets are collected, and the aerosol particles within the droplets are analyzed, as described in more detail below. Optionally, the inner walls of the growth tube may be coated with a liner, such as a porous filter paper liner, on which the excess vapor within the condensing fluid condenses. A pump located outside the growth tube may be used to remove condensed fluid from the liner to prevent excess fluid accumulation on the inner walls of the growth tube.

[0024] The temperature reduction can also occur by the contact of the mixed stream with the walls of the growth tube (204). In one embodiment, no cooling device is coupled to the growth chamber (204). Without "active" cooling, the temperature of the walls of the growth tube (204) can be 15-25°C. Alternatively, the growth tube (204) is cooled by one or more cooling devices to reduce the temperature of the walls of the growth tube (204) to less than 15°C, preferably 0°C-13°C, 0°C-10°C, or about 0°C. "Active" cooling of the growth tube can enhance particle growth and is beneficial for achieving higher aerosol flow rates.

[0025] The inner wall of the growth tube (204) may be coated with a filter membrane, and the excess of steam that condenses on the inner wall of the growth tube (204) may be collected on the filter and then removed by a pump through an outlet (214) in the side wall of the growth tube (204).

[0026] The inner diameter and length of the growth tube (204) may be 10-25 millimeters and 40-50 millimeters, respectively. Other dimensions are possible.

[0027] Aerosol particles with initial aerodynamic diameters of about 3 nm to 1 micrometer or greater in diameter can be grown to sizes greater than 1 micrometer, greater than 1.5 micrometers, or greater than 2 micrometers in the growth tube (204). The wider the temperature "gap" between the condensing fluid and the aerosol stream, the larger the enlarged or grown droplets will be.

[0028] Condensable fluid that promotes the growth of the aerosol particles is generated in a fluid storage tank (206). The storage tank (206) contains a condensable fluid (256). Condensable fluid (e.g., water) may be added to the tank (206) via a liquid inlet (226). The fluid storage tank (206) includes a heater (246) that is operative to heat the condensable fluid in the tank (206) to generate steam. Optionally, the tank includes a temperature sensor (not shown). Both the temperature sensor and the heater (246) may be connected to a temperature controller, as desired. Preferably, the steam is generated at a temperature of 75-95°C or 75-85°C.

[0029] The interior of the fluid storage tank (206) may be equipped with a permeable tube, which is formed of a proton exchange membrane that is permeable to the condensed vapor. An example of such a tube is NAFION™ tube, available from Perma Pure LLC. The inlet (216) and outlet (236) of the permeable tube may be attached to the wall of the fluid storage tank (206). In use, a gas stream, for example a particle-free air stream at room temperature, may enter the permeable tube via the inlet (216). Vapor generated in the tank (206) is then transferred to the interior of the permeable tube, forming a vapor-containing gas stream, which is discharged from the outlet (236) of the tank (206). The vapor-containing gas stream is then introduced into the aerosol collection port (202) as a condensed fluid. The condensed fluid may be particle-free.

[0030] As discussed herein, vapor in the condensing fluid condenses on the aerosol particles within the growth tube (204), and the aerosol particles may act as nucleation sites to form droplets containing the aerosol particles. The droplets grow within the growth tube, forming a gas stream containing the grown droplets. Optionally, an orifice is located just before the exit of the growth tube (204) to ensure that the grown droplets are concentrated near the central axis of the tubular member (266) that connects the growth tube (204) to the converging nozzle (248).

[0031] In Figures 1A and 1B, at least a portion of the connecting tubular member (266) is surrounded by the fluid storage tank (206) and the walls of the connecting tubular member (266) are heated by the surrounding fluid storage tank (206) to avoid condensation of steam on the walls of the connecting tubular member (266). The connecting tubular member (266) is optional. The growth tube (204) is in direct fluid communication with the convergent nozzle (248). In this case, the fluid storage tank (206) may be located next to the water vapor inlet (212).

[0032] In the converging nozzle (248), the gas stream containing the grown droplets containing the aerosol particles can be focused into a small aerosol particle beam. The length of the converging nozzle (248) can be 10-30 millimeters or 15-25 millimeters. The converging nozzle has an outlet for emitting the expanded particles, and the outlet can have a diameter of 0.5-5 millimeters, 0.5-3 millimeters, or 1-2 millimeters.

[0033] The aerosol particles in the aerosol particle beam are then collected on a collecting substrate (238) located downstream of the converging nozzle (248) for subsequent optical spectroscopic analysis. The collecting substrate (238) can be heated to evaporate the condensed fluid upon impact, and the heated condensed fluid can be ejected from the device (200) via the aerosol outlet (258). The distance between the converging nozzle outlet and the collecting substrate (238) is preferably between 1 mm and 10 mm, or between 2 mm and 8 mm. Because the aerosol sample can be collected as a spot on the substrate, the aerosol collection port (202), the growth tube (204), the converging nozzle (248), and the collecting substrate (238) can be together referred to as a spot sample mixed-flow condensation aerosol concentrator, i.e., spot sample MCAC.

[0034] The collecting substrate (238) may have a cross-sectional profile that is circular, rectangular, or any shape that allows efficient collection of grown droplets containing aerosol particles. In one embodiment, the collecting substrate (238) is an electrode, for example a tungsten electrode. The electrode may be coated with silver nanoparticles, gold nanoparticles, copper nanoparticles, or a combination thereof. The coating may have a thickness between 1 nanometer and 100 nanometers. Preferably, the collecting substrate (238) is rotatable about the substrate axis, thereby allowing collection and measurement from various independent angles. The collecting substrate may also be a rotating disk (rotating about an azimuthal axis) or a large diameter cylinder (rotating about a longitudinal axis), allowing the collected particle sample to be collected, analyzed, and ablated in different independent areas, so that all three processes of collection, analysis, and ablation can be performed independently and / or simultaneously.

[0035] Using the converging nozzle 248, extremely small aerosol deposition areas can be achieved on the collection substrate 238 as spots of 0.1-5 mm, 0.1-3 mm, or 1-2 mm diameter, either small or large enough to be coupled with optical or laser spectroscopy devices that can be used to analyze the chemical composition of the aerosol particles.

[0036] Although Figures 1A and 1B show an apparatus that collects grown droplets containing aerosol particles onto a collection substrate using a converging nozzle, it will be appreciated that other techniques may also be used, such as traditional inertial impaction, aerodynamic lens focusing collection, or electrostatic collection, which may not involve condensation growth.

[0037] FIG. 2 shows an apparatus (300) for direct liquid sample collection. The apparatus includes two thermoelectric coolers (340) located on opposite sides of the growth tube (204) to enhance cooling. A pair of heat sinks (310) and fans (320) are located on opposite sides of the coolers (340) to quickly dissipate heat and increase cooling efficiency. The thermoelectric coolers (340), heat sinks (310), and fans (320) operate to reduce the temperature of the growth tube (204) to less than 15° C., preferably 0° C. to 13° C., 0° C. to 10° C., or about 0° C. The “active” cooling of the growth chamber enhances the expansion of the droplets, which is effective for higher flow rates, and can be easily collected by impaction. In addition, the converging nozzle (248) can be coupled with a connector for an impactor (350) and an easily replaceable container (330) to concentrate the aerosol-containing water droplets. Collection of aerosols in liquid solutions can be achieved at flow rates up to 15 L / min or up to 10 L / min. Nanoparticles with initial aerodynamic diameters of 5-500 nm, 5-250 nm, or 5-50 nm can be scaled up to optical sizes of over 1,400 nm.

[0038] The collected aerosol particles described herein can be analyzed by an offline analytical device. In one embodiment, the device (200) shown in Figures 1A and 1B includes an analytical component (208), which can be coupled to a fluid storage tank (206) or growth tube (204) via a tubular member (266) and a converging nozzle (248).

[0039] The analytical component (208) may facilitate characterization of the aerosol particles deposited on the collection substrate by optical or laser spectroscopy. Examples of optical or laser spectroscopy include Raman spectroscopy, reflectance or absorption spectroscopy (UV-VIS or infrared range), fluorescence spectroscopy, or emission spectroscopy. The analytical component (208) may include a probe (218), such as a Raman probe, an infrared probe, or a combination thereof. When the collection substrate (238) is the collection electrode, the analysis device (200) may further include a counter spark electrode (228) spaced apart from the collection electrode (238) to define a spark gap. When a voltage pulse is applied between the collection electrode (which may function as a cathode, 238) and the counter spark electrode (which may function as an anode, 228), a pulsed spark discharge is generated, enabling chemical analysis of the deposited aerosol particles via spark emission spectroscopy (SES). This method has been referred to by various names, such as spark microplasma spectroscopy or spark induced breakdown spectroscopy. Alternative plasma discharges, such as pulsed laser, pulsed microplasma, atmospheric or low pressure radio frequency glow discharge, laser, laser induced plasma, or microwave induced plasma, may also be used.

[0040] 3A and 3B, an apparatus (400) for collecting and analyzing aerosol particles includes a converging nozzle (248) for emitting an aerosol stream containing aerosol particles, a collecting substrate (238) disposed downstream of the converging nozzle (248) for collecting the aerosol particles from the aerosol stream, a controller (268) coupled to the collecting substrate (238) for controlling the rotation of the collecting substrate (238), and a means for ablating the aerosol particles on the collecting substrate (238). The converging nozzle (248) and the collecting substrate (238) of the apparatus (400) can be the same as the converging nozzle (248) and the collecting substrate (238) described in connection with the apparatus (200). In one embodiment, the converging nozzle is a multi-stage converging nozzle having 2 to 10 connected sections, each section having a diameter that decreases in a direction from the inlet of the converging nozzle to the outlet of the converging nozzle.

[0041] The means for ablating the aerosol particles on the collecting substrate may include a means for generating a plasma discharge. Examples of the plasma discharge include a pulsed laser, a pulsed microplasma, a pulsed spark discharge, a laser, a high frequency glow discharge, a laser induced plasma, or a microwave induced plasma. Multiple plasma discharges may be used. In one aspect, the means for ablating the aerosol particles on the collecting substrate may include a counter spark electrode (228) spaced apart from the collecting substrate (238) to define a spark gap, and a means for applying a voltage pulse between the collecting substrate (238) and the counter spark electrode (228) to generate a pulsed spark discharge that ablates the aerosol particles on the collecting substrate. Optionally, the apparatus further includes a Raman probe, an infrared probe, or a combination thereof.

[0042] Optionally, the device (400) further comprises one or more components to facilitate collection of the aerosol particles. The components are not limited and any suitable components may be used. In one embodiment, the device (400) further comprises a fluid storage tank, an aerosol collection port, and a growth tube as described herein in connection with the device (200). The aerosol outlet (258) discharges excess fluid exiting the collection substrate (238).

[0043] A method of analyzing aerosol particles using the devices described herein includes depositing grown droplets containing aerosol particles emitted from a converging nozzle onto a collecting substrate and analyzing the aerosol particles deposited on the collecting substrate with an analytical device.

[0044] Aerosols can also be analyzed by using tandem spectroscopy on the same particulate deposits: Raman spectroscopy (or any other laser spectroscopy, e.g., quantum cascade laser (QCL) reflectance spectroscopy) and spark emission spectroscopy (SES) can be used for chemical analysis of aerosol samples by identifying molecular species, and for elemental analysis of aerosols.

[0045] In one aspect, a method of analyzing aerosol particles includes collecting the aerosol particles on a collecting substrate. The collecting substrate is then rotated to any desired angle that allows for independent and / or simultaneous spectroscopic analysis. The method of collecting the aerosol particles is not particularly limited. Optionally, the aerosol particles may be collected using a condensation growth method as described herein. The aerosol particles may be analyzed by multiple methods. For example, a method of analyzing aerosol particles may include collecting the aerosol particles on a collecting substrate (238) and rotating the collecting substrate (238) to any desired angle that allows for independent and / or simultaneous spectroscopic analysis. The deposited aerosol particles may be analyzed using a first analysis method, followed by rotating the collecting substrate (238) and analyzing the deposited aerosol particles using a second, third, or additional analysis method. One analysis method may include ablating the particles deposited on the collecting substrate to generate atomic emissions and analyzing the atomic emissions. Other analysis methods may include Raman-based fluorescence, reflectance, or absorption measurements.

[0046] 3A-3C, in one embodiment, a method for analyzing aerosol particles includes collecting aerosol particles on a collecting substrate (238) in an initial orientation. The collecting substrate (238) is rotated to a new ablation orientation. The aerosol particles on the collecting substrate (238) are ablated in the new ablation orientation, optionally generating atomic emission, and then analyzed to characterize the aerosol particles on the collecting substrate (238) as desired. The substrate may then be rotated to the initial orientation to continue collecting the next sample of aerosol particles. The method for ablating the aerosol particles is not particularly limited. For example, the aerosol particles on the collecting substrate (238) may be ablated with a plasma discharge, optionally comprising at least one of a pulsed laser, a pulsed microplasma, a pulsed spark discharge, a high frequency glow discharge, a laser, a laser induced plasma, or a microwave induced plasma. The collecting substrate (238) may be rotated to any desired angle, for example, 90° or 180°. In one embodiment, the collecting substrate (238) is rotated to face the counter spark electrode (228), which functions as the anode. A voltage pulse can be applied between the collecting electrode (238) and the counter spark electrode (228) to generate a pulsed spark discharge (480) that ablates aerosol particles on the collecting substrate.

[0047] In another embodiment, the aerosol particles on a single substrate can be subjected to multiple ablation and analysis steps: the aerosol particles collected on the substrate can be subjected to a first ablation, then analyzed, and then a second ablation and a second analysis.

[0048] An exemplary method for analyzing aerosol particles as shown in Figure 4 includes collecting aerosol particles on a collecting substrate, e.g., depositing grown droplets containing aerosol particles emitted from a converging nozzle (248) on a collecting electrode (238), rotating the collecting electrode (238) to face a laser beam generated from a laser source (260), irradiating the deposited aerosol particles with the laser beam to enable Raman, reflectance, or absorption measurements by a spectrometer (261) via a probe, e.g., a Raman or IR probe (218), rotating the collecting electrode (238) to face the deposited aerosol particles to a counter spark electrode (228), and applying a voltage pulse between the collecting electrode (238) and the counter spark electrode (228). The voltage pulse can generate a pulsed spark discharge (480) that ablates the aerosol particles on the collecting substrate. Optionally, ablating the aerosol particles on the collecting substrate may produce atomic emission, and the method further includes analyzing the deposited aerosol particles using spark emission spectroscopy. Once the analysis is performed, the collecting electrode (238) is rotated to face the focusing nozzle (248) to allow a second cycle of particle collection and measurement. The voltage discharge may be generated by a high voltage pulse generator (269). The operation of each component may be controlled using a microcontroller and data acquisition system (265), which are powered using an on-board DC power supply (289). The aerosol flow may be driven by a pump (264) and maintained at a specific flow rate using a controller with feedback from a flow meter (263). After the aerosol particles are collected, the remaining particle stream may be optionally filtered through a filter (262) before exhausting.

[0049] In one embodiment, the rotatable collecting substrate (238) has three or four collecting surfaces. Initially, no aerosol particles are deposited on any of the collecting surfaces. Once the aerosol particles are collected on a first surface, the collecting substrate (238) can be rotated to deposit the aerosol particles on its second surface. Thus, the collecting substrate (238) has a first and a second or additional surface, each surface on which aerosol particles are deposited, and also another new / fresh surface free of aerosol particles. In this case, the method includes analyzing the aerosol particles initially deposited on the first surface of the collecting substrate (238) by optical analysis, e.g. Raman spectroscopy, reflectance or absorption spectroscopy (UV-VIS or infrared range), fluorescence spectroscopy, and ablating the second aerosol particles on the second surface of the collecting substrate (238) and analyzing the second aerosol particles by atomic emission spectroscopy. The method may further include collecting the aerosol particles on a third surface of the collecting substrate. The method of collecting the aerosol particles is not particularly limited. The first and second aerosol particles can be collected from the same or different aerosol samples. Optionally, the aerosol particles can be collected using the condensation growth method described herein, but any other suitable collection method can also be used. In other words, the aerosol sample can be collected at one collection surface, while the sample collected at another surface (e.g., at 90°) is spectroscopically analyzed, and the sample collected at another surface facing the opposing spark electrode is simultaneously ablated and analyzed. Thus, this method allows the parallelization of three processes: i) particle collection, ii) spectroscopic analysis, and iii) ablation / removal of the collected aerosol particles.

[0050] The method and apparatus described herein have several advantageous features for personal aerosol sampling and aerosol chemical analysis. The method and apparatus allow for space-saving and compact design, allowing for easy integration into portable devices. The apparatus and methods also allow for near real-time measurement of aerosol samples. In addition, the apparatus and methods described herein allow for aerosol sample collection as small spots (e.g., 0.5-1.5 mm diameter, or even 1 mm diameter) that can then be efficiently interfaced with laser spectroscopy detection / analysis, followed by removal of the collected sample, improving detection sensitivity, shortening aerosol sampling time, and allowing for improved measurement time resolution. Furthermore, the apparatus and methods allow for continuous automated measurement of aerosol samples. In the disclosed method according to one embodiment, each measurement cycle can include i) collection of particles on a substrate, ii) analysis using a spectroscopy technique, and iii) removal of the sample and preparation for the next measurement. As all three steps can be completed automatically, the method allows for smooth near real-time measurements on portable devices. The apparatus and methods further allow for simultaneous elemental and molecular analysis of aerosol samples via various spectroscopy techniques. Vibrational spectroscopy such as Raman spectroscopy and near- or mid-infrared spectroscopy provide molecular information, and atomic emission spectroscopy provides elemental composition of the aerosol sample. EXAMPLES

[0051] Spot sample MCAC A low volume medical nebulizer (Salter 8900 series, Salter Labs, Irvine, CA, USA) was used to generate aerosols of sodium chloride to characterize the concentrator or spot sample MCAC described herein. A diffusion dryer was used in turn to dry the aerosolized stream. The aerosol stream subsequently entered an Aerodynamic Aerosol Classifier (AAC, Cambustion Ltd, Cambridge, UK) to generate a monodisperse nano- or microscale particle-containing flow. A low flow rate through the AAC was selected to increase the resolution of the classification. Dry particle-free dilution air was additionally supplied to reach a flow rate of 4 L / min for the cold particle-containing flow (aerosol flow). Simultaneously, the dry, dust particle-free flow entered a saturator (fluid storage tank) and a hot water vapor saturated flow (condensed fluid) was generated at the outlet. The temperature in the saturator was varied in the range of 70–85 °C and the flow rate of the hot water vapor gas was adjusted to 0.2–1.2 L / min.

[0052] Humidification of the aerosol stream was performed by a MH-110-12F-4 series (Perma Pure LLC, New Jersey, USA) to achieve full saturation (RH = 100%). In additional experiments, the relative humidity of the aerosol stream was adjusted in the range of 11-100%. Downstream of the concentrator, the particle / droplet concentration of the mixture was measured by two optical meters. The first was an Ultrafine Water-based Condensation Particle Counter (UWCPC, model 3786, TSI Inc., Shoreview, MN, USA), which can provide the total particle concentration of particles with sizes up to 2.5 nm. In addition, an Optical Particle Sizer (model 3330, TSI Inc., Shoreview, MN, USA) was used to classify the particles into 16 different channels with a minimum detectable size of 300 nm. As a result, condensation growth of particle sizes down to a few nanometers can be investigated experimentally by comparing measurements from the two instruments.

[0053] The aerosol activation and growth efficiency of the spot sample MCAC was measured under the influence of five variables: (1) the hot to cold flow rate ratio (Q h / Q c ), (2) Saturator temperature (T sat ), (3) the relative humidity of the aerosol stream, (4) the aerosol size, and (5) the aerosol number concentration.

[0054] Finally, the aerosol samples were deposited on a heated collecting plane to obtain the aerosol deposition area. In this set of experiments, polystyrene nanospheres with diameters of 20 nm and 150 nm (NIST traceable particle size standard, Thermo Fisher Scientific) and Fluoromax green beads with diameters of 1.9 μm (Thermo Fisher Scientific) were used. Nanospheres and microspheres were generated by aerosolization of liquid suspensions. Aerosol samples were collected on a heated plane at 90–100 °C with an optimal nozzle-to-plate distance found experimentally. An aluminum-backed carbon tape (Ted Pella Inc., Redding, CA, USA) was implemented for the collection of samples and the acquisition of images using a scanning electron microscope (SEM). The spot diameter of the formed deposits was calculated using the application of ImageJ software.

[0055] Optimal Mix Ratio Figures 5A-5D show the theoretically estimated saturation change of the mixed flow and the experimentally measured activation efficiency of 25 nm sodium chloride particles as a function of the mixing ratio at four saturator temperatures (70, 75, 80, and 85 °C). At all saturator temperatures tested, the saturation rate exceeded 1 after mixing, which portends particle activation and droplet growth. When water vapor was generated at 70 °C, about 60% of the particles were activated and the droplets grew to a diameter of more than 1.4 μm. When the saturator temperatures were set at 75, 80, and 85 °C, the particles were fully activated and the droplets grew to a diameter of more than 1.4 μm.

[0056] According to Figures 5A-5D, the saturation rate and activation efficiency are proportional to the temperature difference (ΔT) between the water vapor and the aerosol flow. The larger ΔT, the higher the saturation rate and activation efficiency. The minimum particle size that can be activated and the final droplet size that can be achieved depend on the absolute value of the saturation rate, among other parameters. A good agreement is observed between the calculated saturation rate and the experimental activation efficiency peaks. However, the mixing ratios corresponding to the saturation and / or activation efficiency peaks are different for various ΔT. For a vapor temperature of 70 °C, the saturation rate approaches a maximum value at 1.6, corresponding to a mixing ratio of 0.2. In the experimentally measured activation efficiency curve, a plateau is reached for a mixing ratio range of 0.15-0.25. This range includes the theoretically predicted optimal mixing ratio values. When the vapor temperature was set at 75, 80, and 85 °C, the calculated maximum saturation values ​​were 1.67, 1.74, and 1.8 for mixing ratios of 0.155, 0.115, and 0.08, respectively. Therefore, in the following experiments, different mixing ratios were selected based on the water vapor temperature to obtain optimal performance of the concentrator.

[0057] particle size T sat The activation efficiency of 25 nm diameter NaCl particles introduced into the spot sample MCAC at = 70 °C is shown in Figure 6A. The activation efficiency based on three different droplet size fractions is shown: (i) > 300 nm, (ii) > 700 nm, and (iii) > 1400 nm. The activation efficiency based on the fraction larger than 300 nm is above 90% for NaCl seed particle diameters up to 50 nm and nearly 100% above that. However, the activation efficiency falls below 60% when the activation efficiency is based on the droplet size fraction > 1400 nm, indicating that the majority of the particles (~55%) do not grow beyond 1.4 μm.

[0058] Various T values ​​of 70, 75, 80, and 85°C based on the fraction greater than 1400 nm satThe activation efficiencies at 75°C, 80°C, and 85°C are shown in Figure 6B. Good activation efficiencies of over 86%, 92%, and 93% can be obtained for seed aerodynamic particle sizes in the range of 25-300 nm at 75°C, 80°C, and 85°C, respectively. Based on these measurements, saturator temperatures in the range of 75-85°C were used in this study.

[0059] Wall losses and transport losses due to diffusion and inertial collisions were calculated in the spot sample MCAC. The transport efficiency throughout the spot sample MCAC is expected to be over 90% for nanoparticles with diameters up to 2 nm. Diffusion deposition is expected to be negligible in the mixed condensation growth collector (Kim et al., J. Aerosol Sci. 33(10), 1389-1404, (2002)) due to the relatively high flow rate. Particle losses due to inertial deposition in the spot sample MCAC were experimentally measured. Negligible losses (≦10%) were measured in the growth tube for particle sizes up to 10 μm. When using a converging nozzle with an exit diameter of 1.7 mm, the measured total wall losses were less than 15% for particle sizes smaller than 5 μm and less than 20% for particle sizes smaller than 10 μm.

[0060] Relative humidity The performance of the spot sample MCAC was tested at various relative humidity values ​​of the aerosol flow. As shown in Figures 7A-7D, superior performance of the spot sample MCAC was observed when the aerosol-containing stream was fully saturated (RH = 100%). A fully saturated aerosol stream contains more water masses than a partially saturated stream. Thus, the stream mixture produced by mixing a hot vapor stream with a cold aerosol-containing stream contains more water masses corresponding to higher partial vapor pressures, thus producing higher supersaturation values. The performance of the spot sample MCAC was also observed at a relative humidity of 25% in the aerosol stream, T sat = 75, 80, and 85 °C. However, performance was poor even when activation efficiency was based on droplet size fractions of > 300 nm. sat It decreased when the temperature was ≦75°C and the RH was less than 25%.

[0061] When the relative humidity reaches 11%, the lowest value tested, partial activation occurs at the maximum temperature in the saturator (T sat = 85 °C) (activation efficiencies of 68% and 57% based on droplet size fractions of >300 nm and >1400 nm, respectively). Thus, the optimal inlet relative humidity range may be 25-100% when the saturator temperature is above 75 °C.

[0062] Performance stability The activation efficiency of 25 nm diameter NaCl seed particles facilitated by spot sample MCAC as a function of continuous operation time is presented in Figure 8. Full activation and growth at detectable droplet diameters (>300 nm) was observed for at least up to 60 min. The activation efficiency remains constant, approaching approximately 87%, for final droplet diameters above 1400 nm.

[0063] The mixed condensation growth technique is based on the instantaneous adiabatic mixing of a hot vapor stream with a cold aerosol-containing gas. The mixing chamber of the spot sample MCAC is not actively cooled, but despite the lack of active cooling, the desired temperature difference between the hot and cold flows is maintained over long periods of operation, indicating that steady-state temperatures of the flows and the mixing chamber walls are reached relatively quickly and without performance degradation. Similar performance is expected for longer periods of operation.

[0064] Spot sample characteristics Spot Samples To investigate the properties of the spot samples obtained from MCAC, experiments were performed using polystyrene latex particles as test aerosols. The particles were collected directly on an aluminum-backed carbon substrate and easily analyzed using a scanning electron microscope to obtain the spot diameter and distribution characteristics. Figures 9A-9C show scanning electron micrographs of spot samples obtained with test PSL aerosols with particle sizes of 20, 150, and 1900 nm. The deposition diameter D90 was defined as the diameter of a circle containing 90% of the deposited particles and was calculated from the radial position distribution of the projected area of ​​the particles shown in Figures 10A-10C. The D of the spot samples 90was found to be 1.4 mm for all tested PSL spheres, independent of the seed particle size entering the spot sample MCAC. Spot sample characteristics of 150 nm diameter PSL nanospheres at saturator temperatures of 80 and 85 °C were also obtained. Similar deposition areas were formed, with spot diameters equal to about 1.4 mm and 1.2 mm at 80 and 85 °C. Smaller spot deposition was obtained when water vapor was generated at 85 °C, possibly due to the higher saturation rate generated, resulting in the formation of slightly larger droplets with a focus closer to the nozzle exit.

[0065] Several tests were performed to obtain the optimal nozzle-to-plate distance, which would result in similar ultra-small spot deposits over a wide range of diameters of PSL spheres. Large droplets are expected to have a focal point closer to the nozzle exit than small droplets, but at longer distances where small droplets converge closer to the central axis, larger droplets are expected to cross the axis, resulting in a dispersed spot deposit (Hari et al., Aerosol Sci. Technol. 41(11), 1040-1048 (2007)). Thus, a distance of 4 mm may be the optimal nozzle-to-plate distance that can meet the scope of this study.

[0066] Samples collected on the tiny deposition areas can then be analyzed using laser spectroscopy, e.g. Raman spectroscopy, reflection or absorption spectroscopy (UV-VIS or infrared range), fluorescence spectroscopy, and emission spectroscopy, with enhanced sensitivity and enhanced detection limits (Wei et al., Sci. Rep. 7(1), 1-8(2017); J. Aerosol Sci. 150(August, 2020); Ann. Work Expo. Heal. 1-15(2021); Zheng et al., J. Aerosol Sci. 104, 66-78(2017); Anal. Chem. 90(10), 6229-6239(2018)). Good sampling statistics are associated with effective sample microconcentration, increasing the mass density on the surface.

[0067] Aerosol number concentration effect The effect of particle number concentration on the activation efficiency of 25 nm diameter NaCl seed particles is shown in Figure 11. The condensation aerosol concentrator can achieve a maximum of 3 × 10 4 / cm 3 For a number concentration range of 1.6×10, about 85% of the particles can be effectively activated and grown into droplets with sizes exceeding 1400 nm, while 3.6×10 4 / cm 3 Approximately 60% of the nanoparticles are expected to be collected. A similar trend is observed for droplet sizes above 300 nm and 700 nm. This indicates that as the number concentration increases, the activation efficiency decreases along with the growth efficiency. Therefore, it can be assumed that vapor condensation into particles begins during mixing, leading to an increase in temperature and subsequently a decrease in the supersaturation rate.

[0068] Counting statistics for fiber concentration measurements. Fiber counting by phase contrast microscopy (PCM) is often used to quantify fiber concentration collected on a substrate. Although fiber collection on a 25 mm filter is proposed in NIOSH Method 7400 for PCM analysis (NIOSH 2019), other collection techniques may be used to concentrate fiber samples in small spot deposits, reducing counting uncertainty. Comparison of the estimated Poisson counting statistics of fiber concentration measurements using PCM may be facilitated with various collection methods, e.g., spot sample MCAC, Sequential Spot Sampler, and filter-based collection methods. Sampling a large number of fibers, N, to be counted may reduce counting uncertainty (σ%=1√N). NIOSH Method 7400 specifies a substrate area for microscopic analysis of 0.785 mm 2 (Am), the fiber density on the microscopic analysis area is 100 to 1300 / mm 2 A fiber concentration of 0.1 / cm is recommended to achieve optimal and unbiased counting (σ=2.8-10%, NIOSH 2019). 3 Assuming (Cf), the estimated sampling time (tc) required to achieve the target counting uncertainty of 3–10% was calculated as follows: tc=N Ad / AmCfQη where Ad is the spot deposition area for each collection technique, Q is the sample flow rate used for each collection method, and η is the collection efficiency. The area of ​​the spot sample generated from the spot sample MCAC was approximately 1.54 mm 2 However, the effective area over which samples were collected using a continuous spot sampler and a 25 mm filter was 0.785 mm 2 and 385mm 2 It was.

[0069] The spot deposits formed by the spot sample MCAC and the continuous spot sampler improved sampling time at the same target counting uncertainty (σ = 3-10%) or counting uncertainty at the same sample collection time by about 2-3 orders of magnitude compared to 25 nm filter collection. To achieve a target uncertainty of 3%, about 6 min of fiber sampling was required for the spot sample MCAC, 8 min for the continuous spot sampler, and 2725 min of fiber sampling for the 25 nm filter collection.

[0070] Liquid sample MCAC After each collection run, the impactor and collection vial were removed from the collector for sample acquisition. The impactor was rinsed with isopropyl alcohol, after which the suspension was vacuum filtered.

[0071] Saturator Temperature Effects First, we evaluated the effect of the temperature in the saturator, where high-temperature steam is generated, on the detection efficiency of grown droplets containing sodium chloride particles (Figure 12). The highest detection efficiency (≥90%) was obtained at all aerosol flow rates when the highest saturator temperature (85°C) was used. Good detection efficiency (≥89%) was measured when an aerosol flow rate of 8 L / min was used and the saturator temperature was set at 75°C or higher.

[0072] When higher aerosol flow rates were used, higher saturator temperatures were required for near perfect detection. In particular, when an aerosol flow rate of 9 L / min was used, detection efficiencies of over 92% were achieved for saturator temperature settings of 80°C and above. In addition, when an aerosol flow rate of 10 L / min was used, a detection efficiency of 90% was measured only when the vapor temperature was equal to 85°C.

[0073] The correlation between aerosol flow rate, saturator temperature, and efficiency of liquid sample MCAC obtained here may be due to the residence time of the particles inside the collector. In particular, it has been shown that lower vapor temperatures can be used when using lower aerosol flow rates. For example, when an aerosol flow rate of 8 L / min is implemented and the generated vapor temperature is set to 75 °C, the total throughput through the growth tube is 9.2 L / min with a particle residence time of 0.19 s. On the other hand, a sample flow rate of 10 L / min requires instantaneous mixing with 1.5 L / min of hot vapor, resulting in a residence time of 0.15 s, which was found to be insufficient for aerosol activation and droplet growth at optical sizes above 1400 nm.

[0074] Effect of particle size and operating time The effect of particle size on the performance of the liquid sample MCAC was also investigated for three aerosol flow rates: 8, 9, and 10 L / min (Figure 13A). The saturator temperature used for each aerosol flow rate was the lowest temperature required for near perfect detection (T for Q = 8 L / min). sat = 75℃, Q = 9 L / min, T sat = 80℃, Q = 10 L / min, T sat = 85 °C). Detection efficiencies of over 80% are obtained for the smallest particle size generated, 25 nm, and can reach values ​​of over 90% for larger particle sizes, regardless of the aerosol-containing flow rate.

[0075] Due to the temperature differential used in the collector and the need for adiabatic mixing of the hot vapor with the particle-carrying stream, the effect of the operation time of the liquid sample MCAC on the collection efficiency was also evaluated (FIG. 13B). The collector operated successfully for up to 60 minutes to collect sodium chloride aerosols with an aerodynamic diameter of 100 nm. The measured detection efficiency was nearly 80% or higher over time, especially at high flow rates of the aerosol sample. Thus, the collector can be operated continuously for at least 60 minutes, without heat being transferred through the various sections contained within the collector that could reduce the collection efficiency.

[0076] Growth tube temperature effect Growth tube temperature (T gt The effect of the temperature of the growth tube on the detection efficiency obtained via the liquid sample MCAC is shown in Figure 14. The highest detection efficiency was measured at the lowest temperature set on the growth tube wall, 0 °C, for all particle flow rates used, as expected. However, for the lower aerosol sample flow rates, i.e., 8 or 9 L / min, the effect of the growth tube temperature was larger than when a higher aerosol sample flow rate was implemented (10 L / min). This is probably because a lower saturator temperature was used when the lower flow rates were used (T sat <85 °C). The particle activation and droplet growth efficiency, and therefore the detection efficiency, is proportional to the saturation value reached at the mixing point of the cold aerosol-containing flow and the hot vapor stream. The saturation depends only on the temperature difference between the two streams and the vapor-to-heat flow ratio, and not on the individual flow rates of the streams, and therefore the highest detection efficiency is achieved at the highest saturator temperature (T sat = 85°C) is expected to be obtained.

[0077] Relative Humidity Effects The detection efficiency of the enlarged droplets detected by the OPS as a function of the relative humidity of the inlet aerosol flow is shown in Figure 15. Higher supersaturation rates can be achieved with higher water vapor content of the aerosol flow, and therefore better particle activation and growth efficiency is expected for higher relative humidity values ​​of the aerosol-containing flow. Furthermore, an inverse relationship is observed between the inlet flow rate used and its relative humidity value. The lower the inlet aerosol-containing flow rate, the higher the detection efficiency even at low humidity levels. At an aerosol flow rate of 8 L / min, the detection efficiency is greater than 90% for relative humidity values ​​of 20% and above. In addition, good detection efficiency (greater than 80%) is achieved even for relative humidity values ​​of 9%.

[0078] Excellent detection efficiency is obtained up to a 30% relative humidity drop with an aerosol flow rate of 9 L / min. If the maximum aerosol flow rate is implemented at 10 L / min, good detection efficiency is obtained at relative humidity values ​​of 40% and above. Efficiency may decrease at lower relative humidity values.

[0079] Number concentration effect Respirable silica was generated and used to evaluate the effect of particle number concentration on the MCAC of liquid samples (Figure 16). Complete airborne particle collection occurred at a particle number concentration of approximately 1.8 x 105 particles / cm. 3 The larger respirable silica particle sizes are the largest contributors to the total particle mass of the sample and are efficiently collected to high concentrations.

[0080] Particle mass collection The particle mass collection obtained via the liquid sample MCAC was measured and compared to the traditional air filtration particle collection method (Figure 17). In general, good agreement was found between the two particle collection techniques, with small deviations of approximately 7% (Figure 17). A linear fit curve corresponding to the experimental data was plotted, with a slope of 0.93, indicating high linearity (R 2 =0.997).

[0081] The deviations in the collected mass measured through the liquid collector and the filter may be due to the insolubility of the collected aerosols used here, respirable silica, the activation and growth efficiency that can be achieved with the liquid collector, possible particle or droplet losses that occur with the condensation growth device, and / or particle sample loss due to sample deposition from the suspension onto the filter. The high agreement between the two collection techniques indicates that the liquid collector device developed here can be successfully used for aerosol collection directly as a liquid suspension.

[0082] Measurement of atmospheric aerosols in the workplace Experimental Method In this section, methods for detecting multi-component aerosols in the workplace are discussed. An in situ portable instrument based on Raman spectroscopy with near real-time measurement of aerosols is presented in this section.

[0083] Equipment setup A portable prototype Raman aerosol spectrometer is used, as shown in Figure 4. Components within the instrument are electronically controlled using an embedded microcontroller, and a data acquisition system allows automated measurements.

[0084] Aerosol collection The suspended particles are focused through a converging nozzle onto a tungsten electrode for a predefined time. Two types of nozzles are used for particle deposition: (i) multi-stage nozzle (MSN) and (ii) single-stage nozzle (SSN), with exit diameters of 0.8 mm and 0.5 mm, respectively.

[0085] Flow rates of 2 l / min and 0.5 l / min were used for the MSN and SSN, respectively.

[0086] The electrode (1.5 mm diameter, 56 mm long) is held by a geared stepper motor (model 42M048C2B-R21, Portescap, West Chester, PA) with a rotational step size of 0.75°. One end of the cylindrical electrode is machined to create a 6 mm flat surface for particle aerosol collection. The aerosol flow through the aerosol collection system was driven by a small pump (Allied Motion (Premotec) BL30EB) and maintained at a specific flow rate using a proportional-integral-derivative (PID) controller with feedback from a flow meter. The remaining particle flow is exhausted after filtering.

[0087] Raman spectrometer After rotating the electrode at a given angle, e.g., 90°, to another orientation of the planar collection surface relative to the nozzle axis, the particle sample deposited on the electrode is analyzed using a Raman system consisting of an integrated Raman probe, a laser source, and a spectrometer (model WP785, Wasatch Photonics, Morrisville, NC). The Raman probe is integrated with an ACS so that the excitation laser is incident perpendicularly to the planar collection surface of the electrode. The working distance between the probe and the collection surface is 22 mm. The laser source has an excitation wavelength of 785 nm, a maximum power of 450 mW, and a focal spot diameter of 120 μm. The spectrometer measures the Raman intensity at a wavelength of 6 cm. -1 Spectral resolution of 235-2000 cm -1 The measurements are made over a wavenumber range of

[0088] Raman spectra were collected at maximum power (450 mW) of the excitation laser. A detector integration time of 3 seconds was used to optimize the signal-to-noise ratio for the materials used in this study. Dark and blank spectrum subtraction and baseline correction were applied to each spectrum. For baseline removal, a standard rolling circle filter (RCF) algorithm coupled with a Savitzky-Golay filtering step, known as the Savitzky-Golay adaptive rolling circle filter (SCARF), was employed. Lines drawn tangentially to the background correction curve on either side of the peak were used as baselines for calculating the peak height at a specific Raman frequency shift.

[0089] Pulse Spark Generation System After Raman analysis, the electrode is rotated another 90° and the particle sample deposited on the electrode is ablated using a series of pulsed spark discharges generated by a high-voltage pulse generator (Firefly, Cascodium Inc., Andover, MA) with an output energy of 200 mJ / pulse. The electrode without the sample is then available for the next measurement cycle.

[0090] The overall measurement scheme used in this study consists of the following cyclic steps: (i) collection of particles on the electrode at a given time, (ii) rotation of the electrode by 90° counterclockwise, (iii) acquisition of Raman spectra at a given signal integration time followed by determination of the aerosol mass by spectral analysis and classification, (iv) further rotation of the electrode by 90° counterclockwise, (v) sample removal by ablation, and (vi) return to the initial position.

[0091] In addition, the instrument can perform tandem Raman spark optical emission spectroscopy. This method consists of collection of aerosolized particles onto a small electrode tip, followed by ablation of the particles by a spark generated using a high voltage (HV) pulse generator. Emission from excited atomic and ionic species in the spark-induced plasma was collected using a broadband spectrometer (wavelength range 200-900 nm, and resolution 0.1 nm, LIBS2500Plus, Ocean Optics Inc., Dunedin, FL) for spectrochemical analysis.

[0092] Equipment Calibration Calibration aerosols were generated from aqueous suspensions using a Collison nebulizer (BGI, Butler, NJ, USA) and then passed through a diffusion dryer (TSI Inc., Shoreview, MN, USA). Aqueous suspensions of α-quartz respirable crystalline silica (RCS) materials, Min-U-Sil5 and rutile titanium dioxide (C35R4, DuPont Chemicals, Wilmington, DE, USA) were prepared in ultrafiltered deionized water (CAS7732-18-5, Thermo Fisher Scientific, Rochester, NY, USA). For RCS measurements, Min-U-Sil5 was used instead of the NIST standard reference material, SRM1878, because larger amounts of analyte were required to generate the calibration curve. Note that SRM1878 is based on Min-U-Sil532. Aerosol generated from the nebulizer at an air flow rate of 5 l / min was split between a quartz crystal microbalance micro-orifice uniform deposition impactor (QCM MOUDI impactor model 140, TSI Inc., Shoreview, MN, USA) and the Raman instrument. For collection of analytes on the electrodes using MSNs, a flow rate of 2 l / min was used, whereas for collection with SSNs, a flow rate of 0.5 l / min was used. Simultaneously, the nebulized aerosol was delivered to the QCM at 0.5 l / min. To compensate for the QCM impactor's operating flow rate of 10 l / min, the nebulized aerosol was diluted with 9.5 l / min of filtered air, adjusted using a mass flow controller. The QCM impactor measures the mass of particulate aerosol with aerodynamic sizes between 0.045 μm and 2.44 μm (≦PM2.5) in real time. For the quartz and titania analytes aerosolized in this study, this PM2.5 fraction accounts for more than 90% of the total mass. The size-based distribution of mass concentration was estimated from an aerodynamic aerosol classifier (AAC, Cambustion Ltd, Cambridge, UK) and a condensation particle counter, Ultrafine Water-based Condensation Particle Counter (Model 3786UCPC, TSI Inc., Shoreview, MN, USA) working in tandem. The total mass of the aerosol was measured by QCM over a specific collection time on the electrode, followed by the acquisition of the Raman spectrum on the instrument.

[0093] Quantification of hazardous aerosols Quartz RCS in fracking dust Fracking dust samples were collected at oil and gas extraction sites. The dust was aerosolized using nebulization and then collected in a Raman instrument.

[0094] Prior to aerosol deposition, a thin layer of silver nanoparticles (576832, Sigma-Aldrich Inc., Atlanta, GA) was coated onto the electrode. Fracking dust samples were then collected on the electrode for 2, 3, and 4 hours for spectral acquisition. In addition, X-ray diffraction (XRD) analysis of frack dust samples deposited on a silver filter with a diameter of 25 mm and a pore size of 0.45 μm (catalog no. 225-1802, lot no. 20191202, SKC Inc., PA, USA) was performed on an Empyrean diffractometer (Malvern PANalytical BV, Almelo, The Netherlands) according to NIOSH method 750041 to determine the concentration of quartz RCS. Bulk frack dust samples were also imaged using a Phenom XL 12 SEM (Thermo Fisher Scientific, Waltham, MA, USA) equipped with a backscattered electron (BSE) detector. The micrographs were analyzed using MIPARTM software version 3.4.2 to determine the particle size distribution.

[0095] Titanium dioxide in mixture A mixture of titanium dioxide, Arizona road dust (ARD), and diesel particulate matter (DPM) in a mass ratio of 5:1:1 was prepared. The mixture was aerosolized using nebulization and then collected on the electrodes of the Raman instrument. Aerosols were collected at 10-second intervals over a period of 10 to 60 seconds.

[0096] Common hazardous aerosol detection Other aerosols of interest in the workplace air, such as elemental carbon-based compounds and toxic metals such as chromium(VI) (hexavalent chromium), were evaluated using the Raman instrument. Carbon-based compounds, such as single-walled carbon nanotubes (P7-SWNT, Carbon Solutions Inc., Riverside, CA), DPM (NIST SRM 2975, US Department of Commerce, NIST, Gaithersburg, MD), and chromium(VI) oxide (675644, Sigma-Aldrich Inc., Atlanta, GA) were sprayed and then collected on an electrode. The collected samples were analyzed to see if these harmful aerosols could be detected with the Raman instrument.

[0097] Calibration curves for quartz RCS and rutile titania For crystalline silica, 465 cm -1 The peak Raman shift of 465 cm is associated with the Si-O-Si symmetric stretch bending mode. The vertical axis of the quartz calibration curve in FIG. 18A plots the baseline Raman intensity at 465 cm. -1 The peak heights shown in the figures were determined by subtracting the peak intensity of the QCM impactor from the peak height of the QCM impactor. The horizontal axis of the calibration curve contains the corresponding mass of crystalline silica obtained from the QCM impactor. The vertical error bars for each data point in Figures 18A and 18B represent the standard deviation of the mean value obtained by averaging three measurements.

[0098] FIG. 18A shows the calibration curves using MSNs (mass loading less than 20 μg) and SSNs (mass loading less than 5 μg). The MSNs have a larger aperture, allowing a larger amount of analyte to be collected. The SSNs have a smaller aperture, resulting in a smaller amount of detectable analyte. COMSOL™ simulations of particles of various aerodynamic sizes collected through a nozzle show that a narrower spot can be obtained using MSNs at 2 l / min. However, a significant portion of the particles is concentrated at the periphery rather than the center, resulting in a higher limit of detection (LOD). The particles are more spread out during collection through SSNs at 0.5 l / min, but the majority is deposited in the center. The nonlinearity at higher mass loadings for collection through SSNs was attributed to the increasing thickness of the spot sample. The Raman signal saturates at a certain thickness of deposit, beyond which it no longer increases. Using SSNs, the nonlinear portion of the curves up to 1 μg appears to provide acceptable uncertainty.

[0099] The LODs were calculated using the 3 sigma criteria defined by the International Union of Pure and Applied Chemistry (IUPAC). With a signal integration time of 3 s, the mass LODs for crystalline silica were 0.98 μg and 0.2 μg for MSN and SSN, respectively. These detection limits are significantly lower compared to the standard XRD method41 (5 μg) and may enable short-term and full-shift measurements below the new permissible exposure limits.

[0100] Two types of nanosized titanium dioxide, anatase and rutile, are widely used in industrial, commercial, and biological systems. The Raman spectrum of rutile TiO2 has a peak at 445 cm -1 and 610cm -1 The Raman system can also measure the other titanium dioxide polymorph, anatase, which has a peak at 390 cm -1 , 510cm -1 , and 640 cm -1 Using the SSN, TiO2 (rutile) powder was collected and analyzed using a Raman spectrometer. The calibration curve was shown in Figure 18B with a peak at 445 cm after baseline correction. -1The data was generated by plotting the peak heights of TiO2 as a function of the corresponding TiO2 mass obtained from the QCM impactor. The vertical error bars around each data point in Figure 18B represent the standard deviation around the mean value obtained by averaging three replicate measurements.

[0101] The LOD was calculated using the 3 sigma criteria defined by the International Union of Pure and Applied Chemistry (IUPAC). With a signal integration time of 3 seconds, the mass LOD for TiO2 (rutile) was ~0.027 μg. The drastic improvement in sensitivity of the system described herein is achieved by collecting the particles on a small spot on the ACS, which allows for effective coupling to the Raman excitation laser. The LOQ for the anatase polymorph is expected to be similar to that observed for the rutile polymorph (~0.09 μg), since both polymorphs have similar sensitivity for Raman analysis. This demonstrates the excellent sensitivity of the instrument to detect different polymorphs of a particular analyte when they have different Raman peaks.

[0102] Quantifying particulate aerosols in field samples and mixtures Figure 19A shows the mass of quartz RCS in fracking dust aerosolized and collected on an electrode over 2, 3, and 4 hours using the MSN. The RCS content was determined using the calibration curve in Figure 18A. At least 2 hours of collection was required for the RCS content in the samples to exceed the LOD. Longer collection times were expected because only a small fraction of the bulk fracking dust consisted of PM2.5 particles. The RCS content in the bulk fracking dust was estimated to be 60 (±20)% from the quartz SRM1878b calibration curve. Although not attempted, the percentage of RCS in fracking dust from the Raman instrument is expected to be comparable to the XRD method if fluorescence can be minimized.

[0103] FIG. 19B shows the mass of titania in an aerosolized mixture of titania (5 parts), ARD (1 part), and DPM (1 part) collected at 10 second intervals using the SSN. The titania content was determined using the calibration curve shown in FIG. 18B. A minimum of 30 seconds of collection was required for the titania content in the mixture to exceed the LOD. The composite Raman spectrum from the mixture included the signature peak of TiO2 and the carbon "D" and "G" modes of DPM. Using a Raman instrument, it is possible to detect different components simultaneously. The pie chart in FIG. 19B shows that the titania content in the mixture was 64.1% by mass, based on the Raman measurements, which is nearly the same as the titania mass in the prepared mixture (71.4%). Since the aerosol generated is not the same component ratio as the prepared mixture, slight discrepancies are expected.

[0104] Evaluating the near real-time measurement capabilities of the device A quartz RCS test aerosol (Min-U-Sil5) was used to evaluate the short-term measurement capabilities of the disclosed Raman instrument. Figure 20 shows continuous measurements of simulated transient quartz aerosol mass concentration. The concentration of the test aerosol was purposefully varied periodically to mimic a transient exposure over 180 minutes. The total mass concentration of the aerosol was monitored by an optical particle sizer (Model 3330, TSI Inc., Shoreview, Minnesota, USA). Continuous 30-minute spot samples were collected for Raman analysis. This collection time was sufficient to measure the RCS above the LOQ of the Raman method. In Figure 20, the curve marked with o shows the real-time total aerosol mass concentration air concentration measured by the TSI OPS. The curve marked with Δ shows the RCS concentration measured using the Raman instrument. As can be seen from Figure 20, the transient measurement capabilities of the Raman instrument are in good agreement with the TSI OPS measurements. These measurements clearly demonstrate the ability of the disclosed approach to obtain continuous, automated, near real-time measurements.

[0105] Elemental carbon-based materials and chromium(VI) 21A, 21B, and 21C show the spectra of carbon-based compounds using a Raman instrument. All carbon-based materials, whether amorphous or crystalline, have a peak at about 1380 cm -1 and 1580cm -1 DPM shows characteristic first order peaks at 166 cm and 170 cm, commonly referred to as the D and G bands, respectively. The G band arises due to the stretching of the bond connecting two sp2 sites arranged in an olefin chain or aromatic ring. The D band arises due to the breathing vibration of a hexa-fold aromatic ring. Figure 21A shows the characteristic Raman spectrum of DPM showing two peaks associated with the D and G bands. Similar peaks were observed in graphene, as shown in Figure 21B, and in single-walled carbon nanotubes (SWCNTs) in Figure 21C. SWCNTs also exhibit radial breathing modes (RBM, 166 cm). -1 ), but this peak is in the range of the detector (235–2000 cm -1 ) could not be detected due to the limitations.

[0106] Chromium exists in nine valence states (from -2 to +6). Among them, Cr(VI) and Cr(III) are predominant in the environment due to their stability. Cr(VI) compounds are carcinogenic and mutagenic, and can cause serious damage to living organisms, including allergies, inflammation, and respiratory disorders. Figure 21D shows the 894 cm -1 The characteristic Raman spectrum of Cr(VI) with a peak at 0.05 is shown. The LOD for Cr(VI) using a Raman instrument is expected to be ~20ng to ~30ng (similar to rutile titania) since it is extremely sensitive to the Raman signal.

[0107] Uncertainty analysis The relative standard deviation of the aerosol sampling flow rate of the pump in the instrument was estimated to be 5%-10%. Misalignment of the electrode during collection and measurement may underestimate the amount of analyte being detected by the laser. Therefore, the rotational movement of the electrode was repeated 100, 500, and 1000 times to check if steps were missing from the stepper motor. Negligible uncertainty was detected from the rotational movement of the electrode. Additionally, the electrode was intentionally misaligned up to about 5° to determine the uncertainty. It was found that such misalignment can result in an uncertainty of 10%-15%. Overall, the relative uncertainty of the Raman instrument for aerosol concentration measurement was estimated from the standard error of the average concentration measured over the maximum time used in this study and ranged from 8%-15%. Using the formula, m=C total Through uncertainty propagation using Qt, the relative uncertainties associated with the mass measurements were estimated to be in the range of 12%–18%.

[0108] The measurements described herein clearly demonstrate the capability of Raman instruments to obtain continuous, automated, near real-time measurements of a variety of aerosols. Previously, few studies have reported real-time measurements of aerosols using Raman spectroscopy. Raman scattering is orders of magnitude weaker than elastic scattering, and probing aerosols in suspension results in extremely poor sampling statistics and detection limits (typically >1 mg / m 3 ). Furthermore, large lasers with high power density are required along with precisely designed optics to generate a focal spot to analyze suspended particles within aerosols, making this approach unsuitable for use with field-portable instruments. The Raman instrument presented in this work offers excellent time resolution and detection limits and is portable.

[0109] Portable Raman instruments are useful for making rapid field measurements of short exposures where it is not possible using laboratory techniques such as XRD. Spot sample collection is necessary to achieve low detection limits, but may not be necessary for higher detection limits or where full shift collection is sufficient.

[0110] One advantage of the disclosed approach is that heating of the sample is negligible or reduced due to efficient heat transfer to the metal electrodes of the aerosol collection system.

[0111] This study indicates that Raman instruments may be more widely adopted as an on-site or in-situ method by unskilled experts (professionals not trained in Raman spectroscopy). This approach is also cost-effective, allowing users to collect short-term samples or multiple samples as needed. By using this instrument judiciously, it may be possible to design an effective aerosol exposure monitoring program, which may help reduce the number of compliance samples and their analytical costs. Even if the measurement uncertainty using Raman instruments is in an unacceptable range for certain workplace samples, the technique may still be useful in some applications, such as the evaluation of engineering controls, by providing rapid, on-site, semi-quantitative or qualitative measurements.

[0112] The terms "a" and "an" do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. The term "or" means "and / or." The open-ended transitional phrase "comprising" includes the intermediate transitional phrase "consisting essentially of" and the closed-ended phrase "consisting of." Claims having one of these three transitional phrases, or alternative transitional phrases such as "containing" or "including," may be written using any other transitional phrase unless clearly precluded by context or art. The recitation of ranges of values ​​is merely intended as a shorthand method of individually referring to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually set forth herein. All range endpoints are included within the ranges and are independently combinable. All methods described herein may be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any examples or exemplary language (e.g., "etc.") is merely to better describe the disclosure and does not limit its scope unless specifically claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention as used herein. Unless otherwise defined, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

Claims

1. 1. An apparatus for collecting and analyzing aerosol particles, comprising: a fluid storage tank for producing a condensed fluid comprising vapor, the condensed fluid having a first temperature; 1. An aerosol collection port, comprising: a vapor inlet for receiving the condensed fluid produced from the fluid storage tank; an aerosol inlet for receiving an aerosol stream containing aerosol particles, the aerosol stream having a second temperature lower than the first temperature; and the condensed fluid is mixed with the aerosol stream in the aerosol collection port to form a mixed stream. an aerosol collection port; a growth tube configured to receive the mixed stream from the aerosol collection port and condense the aerosol particles to form a gas stream containing grown droplets that include the aerosol particles; a converging nozzle in fluid communication with the growth tube, the converging nozzle focusing the condensed fluid into an aerosol beam containing the grown droplets; An apparatus comprising:

2. 10. The apparatus of claim 1, wherein the convergent nozzle has an outlet for emitting the grown droplets containing aerosol particles, the outlet having a diameter of 0.5 to 5 millimeters, or 0.5 to 3 millimeters, or 1 to 2 millimeters.

3. 10. The apparatus of claim 1, further comprising a tubular member connecting the growth tube to the convergent nozzle, wherein at least a portion of the tubular member is surrounded by the fluid storage tank, such that a wall of the tubular member is heated by the fluid storage tank to prevent condensation of vapor on the wall of the tubular member.

4. 10. The apparatus of claim 1, further comprising a collecting substrate positioned downstream of the converging nozzle for collecting the grown droplets comprising aerosol particles emitted from the converging nozzle, optionally the collecting substrate being rotatable.

5. 5. The apparatus of claim 4, wherein the collecting substrate is a collecting electrode, and further comprising an opposing spark electrode spaced apart from the collecting electrode to define a spark gap.

6. 5. The apparatus of claim 4, further comprising an analytical component for facilitating characterization of the aerosol particles collected on the collection substrate, optionally the analytical component comprising a Raman probe, or an infrared probe, or a combination thereof.

7. 10. The apparatus of claim 1, further comprising a cooling device operative to reduce the temperature of the growth tube wall to below 15°C, preferably between 0°C and 13°C, or between 0°C and 10°C, or about 0°C.

8. an impactor coupled to the convergent nozzle; a container connected to the impactor via a connector for collecting the grown droplets comprising aerosol particles in a liquid suspension; Further provided with as needed, the cooling device includes a thermoelectric cooler disposed on an outer surface of the growth tube, and a heat sink disposed between a fan and the thermoelectric cooler.

8. The apparatus of claim 7.

9. 1. An apparatus for collecting and analyzing aerosol particles, comprising: a converging nozzle for emitting an aerosol stream containing aerosol particles; a collecting substrate positioned downstream of the converging nozzle for collecting aerosol particles from the aerosol stream; a controller coupled to the collecting substrate for controlling rotation of the collecting substrate; a means for ablating the aerosol particles on the collecting substrate; An apparatus comprising:

10. the means for ablating the aerosol particles on the collecting substrate comprises means for generating a plasma discharge, preferably the plasma discharge comprises at least one of a pulsed laser, or a pulsed microplasma, or a pulsed spark discharge, or a laser, or a radio frequency glow discharge, or a laser induced plasma, or a microwave induced plasma; Optionally, the means for ablating the aerosol particles on the collecting substrate comprises: opposing spark electrodes spaced apart from the collecting substrate to define a spark gap; and means for applying a voltage pulse between the collecting substrate and the opposing spark electrode to generate a pulsed spark discharge that ablates the aerosol particles on the collecting substrate.

10. The apparatus of claim 9.

11. The apparatus of claim 9 further comprising a Raman probe, or an infrared probe, or a combination thereof.

12. a fluid storage tank for producing a condensed fluid comprising vapor, the condensed fluid having a first temperature; 1. An aerosol collection port, comprising: a vapor inlet for receiving the condensed fluid produced from the fluid storage tank; an aerosol inlet for receiving an aerosol stream containing aerosol particles, the aerosol stream having a second temperature lower than the first temperature; and the condensed fluid is mixed with the aerosol stream in the aerosol collection port to form a mixed stream. an aerosol collection port; a growth tube configured to receive the mixed stream from the aerosol collection port and condense the aerosol particles to form a gas stream containing grown droplets that include the aerosol particles; a converging nozzle in fluid communication with the growth tube, the converging nozzle focusing the condensing fluid into an aerosol beam including the grown droplets containing aerosol particles; The apparatus of claim 9 further comprising:

13. 9. A method for collecting and analysing aerosol particles using the device of any one of claims 1 to 8, comprising the steps of: producing the condensed fluid comprising the vapor; mixing the condensed fluid with the aerosol stream in the aerosol collection port to form a mixed stream; introducing the mixed flow into the growth tube; condensing the aerosol particles in the growth tube to form the gas stream containing grown droplets comprising the aerosol particles; focusing the gas stream containing the grown droplets into the aerosol beam; A method comprising:

14. The following conditions: the aerosol stream is introduced into the aerosol collection port at a flow rate of 1 to 20 liters per minute; or The vapor is generated in the fluid storage tank at a temperature between 75°C and 90°C; or the aerosol stream has a relative humidity of 9 to 100%, or the condensing fluid is adiabatically mixed with the aerosol stream in the aerosol collection port; or the temperature of the growth tube wall is reduced to less than 15°C or between 0 and 13°C; The method of claim 13, wherein one or more of the conditions are applied.

15. depositing the grown droplets containing aerosol particles emitted from the convergent nozzle onto a collecting substrate; analyzing the deposited aerosol particles; 14. The method of claim 13 further comprising:

16. 13. A method for analyzing aerosol particles using the device according to any one of claims 9 to 12, comprising the steps of: collecting the aerosol particles on a collection substrate at an initial orientation; rotating the collecting substrate to a new ablation orientation; ablating the aerosol particles on the collecting substrate at the new ablation orientation; rotating the collecting substrate back to the initial orientation and subsequently collecting a next sample of aerosol particles; A method comprising:

17. generating atomic emission; analyzing the atomic emission to characterize the aerosol particles on the collecting substrate; 17. The method of claim 16 further comprising:

18. 17. The method of claim 16, wherein the aerosol particles on the collecting substrate are ablated using a plasma discharge, the plasma discharge comprising at least one of a pulsed laser, or a pulsed microplasma, or a pulsed spark discharge, or a radio frequency glow discharge, or a laser, or a laser induced plasma, or a microwave induced plasma.

19. 17. The method of claim 16, wherein the aerosol particles on the collecting substrate are ablated using a pulsed spark discharge, the method further comprising applying a voltage pulse between the collecting substrate and an opposing spark electrode to generate a pulsed spark discharge and ablate the aerosol particles on the collecting substrate.

20. 17. The method of claim 16, further comprising ablating the aerosol particles on the collecting substrate after rotating the collecting substrate in a measurement direction, and analyzing the aerosol particles on the collecting substrate by optical spectroscopy, optionally including irradiating the collected aerosol particles on the collecting substrate with a laser beam to enable Raman, reflectance, or absorption measurements.

21. 1. A method for analyzing aerosol particles, comprising: analyzing the first aerosol particles on the first surface of the collection substrate; ablating second aerosol particles on a second surface of the collecting substrate to produce atomic emission; analyzing the atomic emission to characterize the second aerosol particles on the second surface of the collecting substrate; Including, Optionally, the first aerosol particles and the second aerosol particles are collected from the same or different aerosol streams. method.

22. 22. The method of claim 21, further comprising collecting third aerosol particles on a third surface of the collecting substrate, wherein at least two of the collecting, analyzing, and ablating are performed simultaneously.

23. The collecting the aerosol particles or the collecting the third aerosol particles may include: generating a condensed fluid comprising vapor; mixing the condensed fluid with the aerosol flow in an aerosol collection port to form a mixed flow; introducing the mixed flow into a growth tube; condensing the aerosol particles in the growth tube to form a gas stream containing grown droplets comprising the aerosol particles; focusing the gas stream containing the grown droplets into the aerosol beam; depositing the grown droplets containing aerosol particles emitted from the convergent nozzle onto a collecting substrate; 14. The method of claim 13, comprising:

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