An apparatus and method for simultaneously measuring the concentrations of formaldehyde and glyoxal in the atmosphere.

Abstract

This invention provides an apparatus and method for simultaneously measuring the concentrations of formaldehyde and glyoxal in the atmosphere. The apparatus includes a sample introduction system, an excitation light source, a main cavity, a spectrometer, a wavelength and power correction system, and a software control system. This method can rapidly and accurately measure the concentrations of formaldehyde and glyoxal in the atmosphere simultaneously with time resolution. This invention utilizes a highly selective and sensitive laser-induced emission spectrometer to achieve real-time monitoring of VOCs in hazy weather. It employs time-division multiplexing technology to achieve multi-level selectivity of the results, eliminating interference from field measurements, providing experimental support for tracing the sources of VOCs emissions, and providing strong technical support for studying the intrinsic mechanisms of atmospheric VOCs reaction kinetics. It boasts higher resolution, faster detection speed, and the ability to obtain more multi-dimensional data, and also has advantages such as low cost, modularity, and miniaturization.

Description

Technical Field

[0001] This invention belongs to the field of spectral detection and provides an apparatus and method for simultaneously measuring the concentrations of formaldehyde and glyoxal, organic pollutants in the atmosphere, using single-photon detection technology. Background Technology

[0002] Formaldehyde is an important component of atmospheric chemical processes, participating in atmospheric cycles such as H₂O₂ and NO₂₃, and serves as a tracer for the oxidation of volatile organic compounds (VOCs). In heavily polluted areas, concentrations can reach as high as 40 ppbv. Under sunlight, formaldehyde decomposes into HCO₃⁻, H₂, and CO₂. These free radicals react with each other in the presence of NO₂ to generate H₂O, which promotes the formation of O₃. It is evident that accurate and rapid measurement of formaldehyde concentration can provide a better understanding of the underlying mechanisms of atmospheric pollution. On the other hand, glyoxal (GDI) is the smallest and most ubiquitous dicarbonyl aldehyde. It participates in atmospheric chemical processes or aerosol formation through photolysis or deposition on the surface of aerosol particles. With a lifetime on the order of hours, GDI can be used to study secondary aerosol processes of organic emissions in small areas over short periods, thus serving as a marker for these processes. In non-urban areas, GDI concentrations range from 0 to 600 ppbv. Using formaldehyde and glyoxal as marker species and measuring their concentrations will help monitor and forecast my country's atmospheric environment, and can provide important information for revealing atmospheric chemical processes and the mechanisms of aerosol formation.

[0003] Based on numerous field experiments, many scholars have proposed that the concentration ratio of formaldehyde to glyoxal can be used to trace the source of pollutant emissions. Formaldehyde and glyoxal originate from different sources. In the atmosphere, they have similar lifetimes, on the order of hours. Among 105 organic pollutants, formaldehyde's main absorption peak is at 353 nm, while glyoxal's is at 440 nm. In contrast, the absorption peaks of benzene and toluene, present in the atmosphere, are below 260 nm, nearly 100 nm different from the strongest absorption spectral bands of formaldehyde and glyoxal. Furthermore, formaldehyde's emission peak is at 390 nm, and glyoxal's at 520 nm, significantly different from the emission peaks of major atmospheric pollutants. Simultaneously, formaldehyde's fluorescence lifetime is 275 ns, and glyoxal's phosphorescence lifetime is as long as 40 μs, while the fluorescence lifetimes of major atmospheric pollutants are extremely short, generally between a few nanoseconds and tens of nanoseconds. This greatly facilitates our selective measurement of formaldehyde and glyoxal concentrations, while avoiding interference from other atmospheric luminescent substances. As long as a suitable excitation light source, detection wavelength, and appropriate time window are selected using the multi-sequence method, it is feasible to measure the concentration ratio of formaldehyde and glyoxal using spectroscopy. To ensure an accurate concentration ratio, we need to measure the concentrations of both in the same chamber, using the same technology, at the same location, and quickly.

[0004] Currently, there are two main types of mature, reliable, rapid, and accurate technologies for measuring the concentration ratio of formaldehyde and glyoxal: Differential Optical Absorption Spectroscopy (DOAS) and Laser-Induced Emission (LIE). LIE includes two sub-methods: Laser-Induced Fluorescence (LIF) and Laser-Induced Phosphorescence (LIP). DOAS and LIE have similar resolutions. DOAS requires a cavity of tens of meters, which is not conducive to instrument integration and portability, but is beneficial for meteorological remote sensing. It is only suitable for large-scale, average pollutant detection. LIF and LIP, on the other hand, can achieve formaldehyde and glyoxal detection at the tens of pptv level within seconds, do not require a long optical cavity, are easier to integrate and portable, and are suitable for "point" testing at the square meter level, meeting my country's current needs for online field measurements. However, to date, there are no reports on high-precision simultaneous monitoring of multiple species.

[0005] Other potential methods for measuring formaldehyde and glyoxal include: mass spectrometry, which detects the mass-to-charge ratio of analytes in ultra-high vacuum to monitor VOCs; however, this requires pretreatment using indirect conversion steps such as deprotonation or ionization. Cavity-enhanced absorption spectroscopy (including Cavity Enhanced Absorption Spectroscopy (CEAS) and Cavity Ring-down Absorption Spectroscopy (CRAS), which are similar in principle) measures the absorption spectrum of VOCs to a relatively broadband light source and then fits the absorption spectrum using known standard absorbance to determine the concentration of the analyte. However, in my country, a large number of different VOC species coexist, and the overlapping absorption spectra of the analytes make concentration inversion difficult. European and American countries have widely adopted spectroscopy and mass spectrometry for practical field measurements. However, the main problem is that the environmental pollution situation in European and American countries is far less complex than in my country. Faced with high particulate matter and high VOC concentration smog in my country, foreign research instruments are difficult to adapt to the specific characteristics of research in my country.

[0006] Domestic institutions have conducted extensive instrument development and field testing, effectively measuring many of the most important atmospheric markers. For example, the Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, uses laser spectroscopy to study the detection of NO2, NO3, and ozone. The University of Science and Technology of China has achieved real-time monitoring of NO3 and NO2 using diode laser cavity ring-down spectroscopy, while Dalian University of Technology has used low-pressure expansion laser-induced fluorescence spectroscopy (FAGE-LIF) to conduct trace detection of reactive species such as OH in plasma.

[0007] Domestically available instruments also exist that can measure formaldehyde and glyoxal separately:

[0008] 1. For example, “Determination of formaldehyde and glyoxal in varenic acid tartrate by derivatization HPLC” (doi: 10.11665 / j.issn.1000-5048.20210310), but it is not measured in the atmosphere and uses liquid chromatography.

[0009] 2. There are also some methods that can detect formaldehyde or glyoxal in the air separately, such as "a gas-sensitive material and element for detecting formaldehyde gas and a preparation method" (application number 201610903286.3), but these require the separate preparation and synthesis of specialized materials and elements.

[0010] 3. For example, “A method for detecting formaldehyde using a diazapyridine structure indicator and its application” (application number 201710253133.3) and “Real-time online formaldehyde detection device and detection method” (application number 201710253133.3) require the use of gas chromatography or liquid chromatography, and also require the preparation of special chemical reagents for calibration and measurement, which are not suitable for field measurement.

[0011] These domestically produced methods and instruments are comparable to imported instruments in terms of both concentration and time resolution. However, it must be said that there are not enough means to measure and study the formaldehyde-glyoxal concentration ratio, which is an important marker for tracing the source of VOCs emissions. In particular, when it comes to tracing the source of pollutants, we need at least two instruments to measure simultaneously for cross-comparison and verification to ensure the accuracy of the measurement results. Summary of the Invention

[0012] This invention is a device for simultaneously measuring the concentrations of formaldehyde and glyoxal, organic pollutants in the atmosphere, using an ultra-narrow linewidth, high repetition rate, and tunable laser detector. It is the first to introduce high-precision time-division multiplexing technology into laser spectroscopy measurement, achieving multi-level selectivity of the results, eliminating interference during field measurements, and enabling simultaneous measurement of multiple species within the same cavity, circuit, and algorithm. It is a device suitable for field measurements in China.

[0013] To achieve the above objectives, the technical solution of the present invention is: a device for simultaneously measuring the concentrations of formaldehyde and glyoxal pollutants in the atmosphere, comprising:

[0014] The excitation light source is connected to the software control system, and a tunable femtosecond to millisecond wide-range laser is output to the main cavity according to the instructions of the software control system.

[0015] The sample introduction system is a tubing channel connected to the main cavity, used to draw atmospheric samples into the main cavity;

[0016] The main cavity is a multi-channel White cell. The sidewalls of the main cavity are provided with an incident chamber surface and an exit chamber surface, and the bottom is provided with a concave reflector. Excitation light enters the White cell from the incident chamber surface along the x-direction, exciting the atmospheric sample inside to produce formaldehyde and glyoxal photons. After being reflected by the concave reflector, the formaldehyde and glyoxal photons change their light path and are emitted from the exit chamber surface along the y and z directions into the spectrometer.

[0017] The spectrometer, connected to the software control system, is used to collect photon signals of formaldehyde and glyoxal, and outputs spectral intensity electrical signals to the software control system.

[0018] The software control system includes a front-end interface and a processing back-end. The processing back-end receives input commands from the front-end interface to control the excitation light source, spectrometer, wavelength and power correction system, collects the spectral intensity electrical signals of formaldehyde and glyoxal, calculates the concentrations of formaldehyde and glyoxal according to the pre-calibrated intensity-concentration relationship, and displays the spectra visually on the front-end interface.

[0019] The wavelength and power correction system is located in the laser output path between the excitation source and the main cavity, connecting the excitation source and the software control system. It includes a wavelength meter and a piezoelectric ceramic actuator, and is used to simultaneously detect the power and wavelength values ​​of the excitation light and feed them back to the excitation source so that it can adjust the laser wavelength and power in real time.

[0020] The excitation source is a high repetition rate, ultra-narrow linewidth pulsed laser with dual-wavelength output; when the software control system receives the start signal, the internal xenon lamp emits excitation light; when the wavelength and power correction system receives the signal, it adjusts the wavelength and power of the excitation light emitted by the xenon lamp in real time.

[0021] The main cavity sidewall is made of aluminum, and the inner surface is coated with a mixture of Teflon and silanizing agent, and then blackened to prevent stray light transmission interference. The incident and exit chamber surfaces of the main cavity sidewall are made of glass to allow the excitation light and formaldehyde and glyoxal photons to pass through. The bottom inner wall of the main cavity is equipped with a heating resistance wire to raise the temperature and prevent formaldehyde and glyoxal photons from being adsorbed on the sidewall.

[0022] The spectrometer includes: a light-collecting lens, a filter, an imaging lens, a preamplifier, and a single-photon detector arranged sequentially on the outgoing light path outside the main cavity; the single-photon detector is placed at the focal point of the imaging lens; the light-collecting lens is used to collect reflected formaldehyde and glyoxal photons and redirect and refract them into the filter; the filter is a dual-wavelength transmission filter used to filter out stray light and allow the excitation photons of formaldehyde and glyoxal to be transmitted to the imaging lens; the imaging lens further refracts the purified and filtered two photon signals into the preamplifier for signal amplification and then outputs them to the single-photon detector; the single-photon detector is a photomultiplier tube used to read the two photon signals and convert them into electrical signals for output to the software control system.

[0023] The wavelength and power calibration system measures the excitation light wavelength in real time and uses piezoelectric ceramics to adjust the laser cavity mirror angle to ensure that the laser wavelength is always at the position of the strongest absorption peak of formaldehyde and glyoxal, thus calibrating the wavelength online in real time.

[0024] The sampling system comprises a gas channel, one side of which is connected to the atmosphere, and the other side is closed with a sampling tube inserted into its end face. The sampling tube is connected to the main cavity. The upper wall of the gas channel has a gas inlet, and the lower wall has a particulate matter channel outlet. A first air pump and a second air pump are respectively installed at the sampling tube inlet and the particulate matter channel outlet. Both the first and second air pumps are connected to a software control system. The first and second air pumps receive control signals from the software control system to turn the air pumps on or off. Atmosphere enters the gas channel through the gas inlet. The first air pump operates, applying a lateral negative pressure in the pipe to cause a portion of the airflow to be sharply turned and drawn into the sampling tube into the cavity. Aerosol particles in the atmosphere maintain their original linear motion due to inertia, and their motion direction changes and deflects as the second air pump operates, exiting through the particulate matter channel outlet, thus achieving the separation of gas and target particles.

[0025] The processing backend includes: a main control module, a sample injection control module, an online calibration module, a laser and spectrometer control module, and a data recording, analysis, and fault tolerance processing module;

[0026] The main control module is used to control the working sequence of each component and upload and store the collected data;

[0027] The injection control module outputs injection flow rate and injection time control signals of the injection system according to the set parameters.

[0028] The online calibration module determines whether spectrometer calibration is needed based on the duration of use and data recordings when the system starts up.

[0029] The laser and spectrometer control module outputs control signals according to set parameters to control the working sequence of the excitation source and the spectrometer, so that the spectrometer can collect formaldehyde and glyoxal photon signals respectively.

[0030] The data recording, analysis, and fault-tolerant processing module is used to graphically process the intensity signals of the measured formaldehyde and glyoxal photons.

[0031] A method for simultaneously measuring the concentrations of formaldehyde and glyoxal in the atmosphere includes the following steps:

[0032] Step 1: Set the injection flow rate and injection time of the atmospheric sample in the front-end interface, and start the gas extraction step: Start the first and second gas extraction pumps to separate and purify the atmospheric sample through the pipeline channel of the injection system and extract it into the main chamber.

[0033] Step 2: Set the wavelength and frequency of the laser output from the excitation source in the front-end interface, and start the wavelength and power calibration steps: Start the excitation source and wavelength and power calibration system. The excitation source emits excitation light into the main cavity, which excites the sample under test to emit photons. The wavelength and power calibration system detects the power and wavelength values ​​of the excitation light in real time and outputs them to the excitation source to adjust the laser wavelength and power in real time.

[0034] Step 3, the steps for starting the excitation source and spectrometer for measurement: control the excitation source to output laser, and start the spectrometer according to the timing output control signal to collect the formaldehyde and glyoxal photon signals excited by the sample to be tested, and convert them into electrical signals;

[0035] Step 4: Visualization Spectrum Display Step: The control system calculates the corresponding formaldehyde and glyoxal photon concentration values ​​according to the intensity signals of the two types of photons received per unit time, based on the concentration-photon intensity function relationship, and generates visualization spectra for display on the front-end interface.

[0036] Before step 3, there is also a step of calibrating the coefficients of the concentration-photon intensity function relationship: a sample of formaldehyde and glyoxal mixed gas with a known standard concentration ρ is drawn into the device, multiple measurement steps are initiated to obtain the photon intensity signals Signal of formaldehyde and glyoxal, and the coefficient A is calibrated according to the formula Signal=A×ρ.

[0037] In step 3, the spectrometer is started according to the timing output control signal to collect the photon signals of formaldehyde and glyoxal excited by the sample to be tested. The timing includes: setting the signal acquisition time window of the spectrometer detector based on the fact that formaldehyde and glyoxal are long-lived fluorescence signals; starting the acquisition of the long-lived fluorescence signal of formaldehyde and glyoxal within the time window; and turning off the detector to not collect photon signals outside the time window. This is used to eliminate the stray short-lived and weak fluorescence signals emitted by other high-concentration particulate interference substances in the atmospheric environment, leaving the long-lived and strong fluorescence signal emitted by the required formaldehyde and glyoxal, and finally obtaining the accurate concentration of formaldehyde and glyoxal in the outside atmosphere.

[0038] The present invention has the following beneficial effects and advantages:

[0039] This invention, based on laser-induced emission spectroscopy (LIF), develops an online monitoring device for measuring trace VOC concentrations in the atmosphere. It integrates ultra-narrow linewidth, high repetition rate, tunable laser technology, single-photon detection technology, and a cutter-in-sample technology. Two lasers emit light synchronously; LIF is used to measure formaldehyde concentration, and LIP (laser-induced phosphorus spectroscopy) is used to measure glyoxal concentration. The relative time delay of the two laser output pulses is adjusted to achieve time-division multiplexing, realizing multi-level selectivity in time resolution and measurement results. This allows for high selectivity and high sensitivity online monitoring of VOC concentrations even under severe interference from extremely high concentrations of particulate matter. It effectively avoids interference from high-concentration particulate matter and environmental noise, resulting in a device suitable for field measurements in China. Notably, this invention is the first to introduce high-precision time-division multiplexing technology into laser spectroscopy measurement, enabling simultaneous measurement of multiple species within the same cavity, circuit, and algorithm. This instrument enables direct monitoring of formaldehyde and glyoxal concentrations without the need for indirect physical or chemical conversion, obtaining their accurate concentration ratios. It solves the technical challenge of tracing the sources of VOCs emissions and provides a basis for research on the causes of air pollution and effective governance in my country. Attached Figure Description

[0040] Figure 1 This is a diagram showing the main components of the present invention.

[0041] Figure 2 A diagram showing the composition of the injection port for the main invention.

[0042] Figure 3 This is a standard calibration curve for standard concentration formaldehyde and glyoxal samples.

[0043] 101 is a single-photon detector, 102 is an imaging lens, 103 is a filter, 104 is a light-collecting lens, 105 is a wavelength meter, 106 is a dual-wavelength output laser, 107 is a piezoelectric ceramic, 108 is a concave mirror, 109 is a sample introduction system, 110 is a waste gas outlet, 111 is a horizontal support, 112 is a base tray, 113 is the main cavity, 201 is a gas inlet, 202 is an accelerating nozzle, 203 is a spectral detection sampling tube, 204 is the first vacuum pump, 205 is a particulate matter channel, 206 is the second vacuum pump, and 207 is a gas channel. Detailed Implementation

[0044] To make the inventive objectives, features, and advantages of the embodiments of the present invention more apparent and understandable, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0045] This invention relates to a device for simultaneously measuring the concentrations of formaldehyde and glyoxal, organic pollutants in the atmosphere, using an ultra-narrow linewidth, high repetition rate, and tunable laser detector. It is the first to introduce high-precision time-division multiplexing technology into laser spectroscopy measurement, enabling simultaneous measurement of multiple species within the same cavity, circuit, and algorithm. This eliminates interference from high-concentration particulate matter in the atmosphere during off-site measurements. The aim is to rapidly and accurately measure the concentrations of formaldehyde and glyoxal in the atmosphere simultaneously.

[0046] This embodiment aims to solve the problem of collecting atmospheric samples from a specific location in the field, simultaneously exciting common pollutants such as formaldehyde and glyoxal using a dual-wavelength output laser to emit fluorescence and phosphorescence, and then measuring and comparing their spectra using a spectrometer. This process eliminates interference from other particulate matter during field measurements, allowing for the determination of the concentrations of formaldehyde and glyoxal in the local atmosphere. The goal is to achieve simultaneous, on-site, and accurate measurements. The instrument in this invention mainly consists of two parts: a sample introduction system and a main detection system.

[0047] A high-precision, modular, time-resolved, multi-level selective simultaneous measurement system for formaldehyde and glyoxal concentrations in the atmosphere includes a sample introduction system, a main chamber, an excitation light source, a spectrometer, a wavelength and power calibration system, a software control system, and a signal connection device.

[0048] The sample introduction system is used to inject the sample and includes a vacuum pump, an accelerator nozzle, and an air conduit. The vacuum pump is electrically connected to the software control system, the accelerator nozzle is connected to the air conduit, and the air conduit is connected to the main chamber. After the instrument is started, the software control system transmits a signal to activate the vacuum pump, drawing the atmospheric sample to be measured into the air conduit through the accelerator nozzle. As the sample passes through the accelerator nozzle, the velocity of the drawn-in atmospheric sample increases, flowing through the conduit at a higher speed. A lateral negative pressure is then applied to the conduit, causing a portion of the airflow to abruptly change direction. Due to inertia, aerosol particles maintain their original linear motion tendency and deflect with the airflow direction. At the same linear velocity, the larger the particle size, the greater its momentum and inertia, and the smaller the deflection distance within a certain range. Particles of a certain size are retained in the original atmospheric flow conduit, thus achieving separation of the gas from the target particles. The separated gas is further drawn into the main chamber and sealed for further measurement.

[0049] The excitation source is used to simultaneously emit dual excitation beams, which are injected into the main cavity to excite the sample under test. The excitation source includes a pulsed laser, a light emission control system, and a signal transmission device. These are connected by electrical signals. The signal transmission device is connected to the software control system by electrical signals, and the nanosecond pulsed laser is connected to the main cavity by optical signals. The pulse half-width is approximately 20 ns, the high repetition rate is 3 kHz, the average power is on the order of tens of mW, the wavelength linewidth is less than or equal to 0.04 cm⁻¹, and the high-precision tunable range is approximately 8 cm⁻¹. It can complete the switching between resonant and non-resonant wavelengths on a time scale of 20 ms with a switching accuracy of 0.001 nm. A single laser outputs dual wavelengths, i.e., simultaneously outputting 353 nm and 440 nm, and the relative time delay of the two laser output pulses can be adjusted to achieve time-division multiplexing technology, simultaneously detecting formaldehyde and glyoxal. When the system starts, the signal transmission device receives the start signal from the software control system and transmits it to the light emission control system. The light emission control system illuminates the pulsed laser, emitting dual-wavelength laser light, which is injected into the main cavity to excite the atmospheric sample under test.

[0050] The main cavity is where the separated atmospheric sample is excited to generate photon signals. It contains a White cell and a curved mirror. The main cavity is a multi-channel White cell. The laser enters the White cell along the x-axis through the glass entrance chamber, opposite which is a highly reflective curved mirror to increase the number of signal photons entering the detector. Two photon signals exit along the y and z-axis through the glass exit chamber and enter the spectrometer. The sampling gas path cuts obliquely into the sample chamber. The interior is chemically blackened to prevent stray light interference. A Teflon coating with a silanizing agent also provides a heating function to prevent formaldehyde and glyoxal adsorption on the sidewalls. After instrument startup, the sample is injected into the main cavity and excited by the laser from the excitation source, producing fluorescence of formaldehyde and phosphorescence of glyoxal. The generated photons are reflected and collected by the curved mirror and enter the detector.

[0051] The wavelength and power calibration system is used for real-time online wavelength calibration to achieve precise wavelength locking. It includes a high-precision wavelength meter and piezoelectric ceramics. The system is located in the laser output path between the laser source and the main cavity components. A prerequisite for high-sensitivity measurement is that the excitation wavelength is accurately locked at the strongest absorption peaks of formaldehyde and glyoxal; therefore, real-time online calibration of the laser's output wavelength is necessary. After the instrument is started, the high-precision wavelength meter measures the excitation wavelength in real time, and the piezoelectric ceramics are used to finely adjust the laser cavity mirror angle, ensuring that the laser wavelength is always at the strongest absorption peaks of formaldehyde and glyoxal, thus calibrating the correct wavelength (A) for accurate simultaneous measurement of formaldehyde and glyoxal concentrations.

[0052] A spectrometer is used to detect photons excited by a sample and convert the detected light signal into an electrical signal. It includes a photomultiplier tube, preamplifier, filter, and main control logic circuit. Its core detector is a photon-counting photomultiplier tube, paired with a 1GHz bandwidth preamplifier. Specific parameters are as follows: detection spectral range 230-700nm, operating temperature 5-40℃. The photomultiplier tube, preamplifier, and main control module are connected by electrical signals. The preamplifier and filter are connected in an optical path configuration. After the instrument starts, an optical imaging device at the front of the detector collects the emitted photons of the analyte in the main cavity. A filter is added to the imaging optical path to allow photons emitted by the analyte to reach the detector, filtering out other stray light. The detector is connected to a photon counter, which reads the number of photons at a specific time gate, eliminating short-lived fluorescence signals left by interfering substances in the atmosphere and ultrafast laser signals, retaining the long-lived, strong fluorescence (phosphorescence) emitted by formaldehyde and glyoxal, achieving multi-level selectivity. The collected signal is then transmitted to the main control logic circuit.

[0053] The software control system handles the timing of various components, processes the acquired electrical signals and converts them into visual graphical signals (the human-machine interface), and performs post-processing on the acquired signals as needed. It includes a main control module, a sample introduction control system, an online calibration system, a laser and spectrometer control system, and a data recording, analysis, and fault-tolerant processing system. The main control module receives instructions from the host human-machine interface, controls the timing of all hardware systems in real time, and uploads and stores experimental data. Its main functions are to synchronize the laser signals output from two lasers, the two photon signals acquired by the counter, and coordinate the main control computer to read spectral data. The main control module sends an external trigger signal to control the lasers to simultaneously emit two laser beams and adjusts the relative time delay of the output light pulses of the two lasers. Simultaneously, it sends a TTL signal with a certain time delay to the photon counter, precisely controlling the start and stop times of counting, achieving an accuracy on the ultrafast timescale. After continuous operation for a period of time, the photon counter transmits the photon count to the host computer for storage. The photon count reflects the molecular luminescence intensity, and the luminescence intensity has a functional relationship with the concentration of the analyte molecule. After all hardware is powered on, the software starts, first initializing the sample injection and calibration system, laser system, and spectrometer system. After confirming these systems are functioning correctly, all hardware is ensured to be in normal operating condition. Then, based on the usage time and data log, it is determined whether spectrometer calibration is required. If calibration is needed, gas chromatography is used to measure the concentration of standard formaldehyde and glyoxal samples for absolute concentration calibration. If no calibration is required, the measurement mode is entered directly. After measurement begins, the time evolution curve is displayed synchronously, data is stored periodically, data anomalies are flagged, and all operational error-tolerant mechanisms are implemented. The measurement process is then stopped according to system instructions or a timer. If spectrometer calibration is required, the chamber is first heated, and high-temperature and vacuum operations are performed to remove any VOCs that may be present on the chamber surface. Then, a standard gas sample is introduced, measurement is conducted, and a new calibration factor is calculated, stored, and the old factor is replaced by the new software. Before completion, the operating status of each hardware component is checked, and any stored anomalies are recorded. In terms of human-computer interaction, even without carefully studying the operation manual, anyone who needs basic education can easily get started. In terms of reliability, in order to cope with complex external conditions, almost every operation needs to be handled with a fault-tolerant mechanism to prevent the program from crashing.

[0054] In this embodiment, the device for detecting formaldehyde and glyoxal concentrations mainly consists of a sample introduction system, an excitation light source, a spectrometer, a main cavity, a wavelength and power calibration system, and a software control system. The sample introduction system is connected to the main cavity, the excitation light source is connected to the main cavity, the wavelength and power calibration system is connected in pairs, the main cavity is connected to the spectrometer, and the spectrometer is connected to the software control system.

[0055] Figure 1This diagram illustrates the specific structure and connection method of the excitation source, spectrometer, main cavity, and wavelength and power calibration system in this invention. The dual-wavelength output laser 106 serves as the excitation source, simultaneously outputting excitation light at 353nm and 440nm wavelengths to excite formaldehyde and glyoxal. The spectrometer consists of a single-photon detector 101, an imaging lens 102, a filter 103, and a light-collecting lens 104. The single-photon detector 101 is a photon-counting type photomultiplier tube that collects photon signals from excited formaldehyde and glyoxal. It is equipped with a 1GHz bandwidth preamplifier, a detection spectral range of 230-700nm, an operating temperature of 5-40℃, and converts the photons into electrical signals for transmission to the software control system. The imaging lens 102 is an optical imaging device that collects and concentrates photons excited by the sample. The filter 103 allows photons emitted by the analyte to reach the detector while filtering out stray light. The light-collecting lens 104, similar to the imaging lens 102, is also an optical imaging device used to initially collect the photons excited by the analyte and introduce them into the spectrometer. The main cavity consists of a concave emission mirror 108, a base tray 112, a main cavity 113, a transverse support 111, and a sample introduction system 109. The base tray 112 secures the entire instrument system. The main cavity 113 is made of aluminum plate, used for sealing the entire device and preventing formaldehyde and glyoxal from adsorbing into the system. Its inner surface is coated with a mixture of Teflon and silanizing reagents, then blackened to mitigate stray light transmission interference. The transverse support 111 supports the overall structure and facilitates instrument transport. The sample introduction system 109 is the sample injection point. The wavelength and power calibration system consists of a high-precision wavelength meter 105 and a piezoelectric ceramic 107. The high-precision wavelength meter 105 is used for wavelength measurement and calibration, while the piezoelectric ceramic 107 is used for power calibration.

[0056] Figure 2This is a schematic diagram of the internal structure and interconnections of the sample introduction system in this invention. The sample introduction system 109 consists of a gas inlet 201, an accelerating nozzle 202, a spectral detection sampling tube 203, a first suction pump 204, a particulate matter channel 205, a second suction pump 206, and a gas channel 207. The gas inlet 201 is the intake port for drawing in atmospheric samples into the sample introduction system. The accelerating nozzle 202 is a gas acceleration device that accelerates the flow rate of the introduced gas by narrowing the inlet. The spectral detection sampling tube 203 is a sealed metal tube inserted into the gas channel 207, through which the sample to be tested is drawn into the main chamber for further measurement. The first suction pump 204 is used to draw the gas to be tested into the sample introduction system and continues to draw gas into the spectral detection sampling tube 203 to separate other particulate matter. The particulate matter channel 205 is the exit channel for separated particulate matter in the sample. The second pump 206 is used for downward gas extraction, drawing the gas to be tested into the sample introduction system on one hand, and extracting particulate matter separated from the sample on the other. Gas channel 207 is the gas passage channel; the separated and purified sample passes through gas channel 207 and enters the main chamber spectrometer for further measurement.

[0057] Figure 3 A standard calibration curve was prepared for formaldehyde and glyoxal samples of standard concentrations. Formaldehyde and glyoxal standard gases were prepared using a pyrolysis method, measured by gas chromatography, and calibrated by a weighing method. The absolute concentrations of the prepared formaldehyde and glyoxal standard gases were then calibrated. The luminescence intensity of formaldehyde and glyoxal at known concentrations was measured under specific experimental conditions, establishing a relationship between formaldehyde and glyoxal concentration and luminescence intensity. This relationship was periodically calibrated. During field measurements, the formaldehyde and glyoxal concentration was inversely deduced using this functional relationship by measuring the luminescence intensity of formaldehyde and glyoxal.

[0058] The calculation method for the simultaneous measurement of formaldehyde and glyoxal concentrations in atmospheric organic pollutants is as follows: Time-division multiplexing (TDM) technology is used. This involves measuring different events using the same cavity, circuit, and algorithm, utilizing only minute time differences to ensure the measurement conditions for both events are as similar as possible. This technology maximizes the accuracy of the formaldehyde-glyoxal concentration ratio. During measurement, the main control circuit sends a TTL external trigger signal to control the synchronous output of two lasers and adjusts the relative time delay of the output pulses. This is the foundation for time-division multiplexing. Simultaneously, a TTL signal with a certain time delay is sent to a photon counter to precisely control its start and stop counting times, achieving nanosecond-level accuracy. After continuous operation for a period, the photon counter transmits the photon count to the host computer for storage. The photon count reflects the luminescence intensity of the molecules, and the luminescence intensity has a functional relationship with the concentration of the analyte molecule.

[0059]

[0060] A non-resonant laser is incident on the cavity, and the photon count A is read. Then, the cavity is switched to a resonant wavelength laser, and the photon count B is read. The process is then repeated for a period of time, and the photon count C is read. The light intensities of A, B, and C are normalized, and then averaged over a second to obtain A1, B1, and C1. The average of A1 and C1 is then taken as D1, which represents the noise in the actual measurement process. A1-D1 is the true number of photons emitted per second by the analyte, where A1 and D1 are the corresponding resonant and non-resonant photon counts in the above figure, respectively. By introducing standard samples of different concentrations and measuring the corresponding photon counts, the correlation function between the analyte concentration and the photon count is obtained. The relationship between the analyte concentration and the photon count is as follows:

[0061] Signal=ρxIxηxqxMxQ

[0062] Wherein, Signal is the luminescence intensity of formaldehyde or glyoxal, ρ is the concentration, I is the intensity of the excitation light, η is the molecular absorption probability, q is the luminescence quantum yield of formaldehyde or glyoxal, M is the system optical transfer function, which includes: the efficiency of collecting luminescence and the transmittance of optical elements, and Q is the photoelectric conversion quantum yield of the detector.

[0063] The formula simplifies to: Signal = A × ρ, where A is a constant. Therefore, there is theoretically a linear relationship between the concentrations of formaldehyde and glyoxal and the photon count. The main task of real-time online sample calibration is to calibrate A correctly in order to measure the concentrations of formaldehyde and glyoxal.

[0064] The steps for measuring the sample are as follows.

[0065] (1) After moving the entire instrument to an outdoor location where measurements are to be taken, assemble all parts of the instrument and turn on the power to the laser, spectrometer, laser wavelength and calibration system, and software control system in sequence. After all hardware is powered on, the software starts and first initializes the sample introduction and calibration system, laser system, and spectrometer system. After confirming that the above systems are in good working order, ensure that all hardware is in normal operating condition and perform spectrometer calibration.

[0066] (2) To ensure measurement accuracy, it is necessary to establish the relationship between the luminescence intensity and concentration of formaldehyde and glyoxal, i.e., to perform spectrometer calibration. This project utilizes a pyrolysis method to prepare formaldehyde and glyoxal standard gases, which are then measured using gas chromatography. The gas chromatography is calibrated using a weighing method, and the absolute concentration of the prepared formaldehyde and glyoxal standard gases is calibrated. Known concentrations of formaldehyde and glyoxal are measured to obtain the luminescence intensity under specific experimental conditions, establishing the relationship between formaldehyde and glyoxal concentration and luminescence intensity. This relationship is then periodically calibrated.

[0067] (3) After startup, open the cover of the gas inlet 201 and the particulate channel 205 of the sample injection system in sequence. Then, input the command through the sample injection control system in the software control system to turn on the first pump 204 and the second pump 206 in sequence to start the sample injection. The atmosphere to be tested is drawn in from the gas inlet 201 by the pumps. After passing through the accelerator nozzle 202, the flow rate increases. Due to the suction force of the two pumps in the cross direction of the horizontal and vertical directions, the particulate matter is gradually separated and extracted from the particulate channel 205. The purified gas to be tested passes through the gas channel 207 and is drawn into the spectroscopic detection sampling tube 203 by the first pump 204. Then, it enters the main chamber for the next test. After the main chamber is filled with the sample to be tested, the software control system will automatically close the valve at the connection between the main chamber and the sample injection system and turn off the first pump and the second pump in sequence.

[0068] (4) After the sample to be tested is drawn into the main cavity, the main control module sends a signal to the laser and spectrometer control system, the spectrometer is started, and the excitation light source 106 is lit, emitting dual-wavelength excitation light of 353nm and 440nm into the main cavity, simultaneously exciting the formaldehyde and glyoxal in the sample. The excited formaldehyde and glyoxal emit photons, which are collected and reflected by the concave mirror 108 at the bottom of the main cavity and enter the light-collecting lens 104. The light-collecting lens 104 collects the reflected photons and directs them to be refracted and directed into the filter 103. The filter 103 is a dual-wavelength transmission filter, which can filter out light of other wavelengths, including the excitation light, except for the maximum emission wavelength required to excite the formaldehyde and glyoxal. The remaining photons are emitted through the filter 103 to the imaging lens 102. The imaging lens 102 further refracts the purified and filtered photons and concentrates them into the single-photon detector 101. The single-photon detector 101 reads the number of photons at a specific time gate, eliminating short-lived fluorescence signals left by interfering substances in the atmosphere and ultrafast laser signals, while retaining the long-lived, strong fluorescence (phosphorescence) emitted by formaldehyde glyoxal, thus achieving multi-level selectivity. Before the single-photon detector 101 receives the photon signal, the photon signal is first amplified by a preamplifier in front of it, and then collected by a photomultiplier tube, converting the optical signal into an electrical signal, which is then transmitted to the logic circuit of the software control system.

[0069] (5) While measuring the sample to be tested in the main cavity, the excitation light emitted by the excitation source 106 is simultaneously detected by the high-precision wavelength meter 105. It detects the wavelength of the excitation light and transmits the sensed signal to the online calibration system in the software control system. The online calibration system calculates the wavelength and power of the excitation light that the excitation source 106 should emit in real time and transmits the signal to the control circuit in the excitation source 106. The wavelength and power of the excitation light are adjusted in real time, and the laser cavity mirror angle is finely adjusted using the piezoelectric ceramic 107 so that the laser wavelength is always at the position of the strongest absorption peak of formaldehyde and glyoxal, ensuring the accuracy of the measured data.

[0070] After the logic circuit of the software control system collects the signal measured by the single-photon detector 101, the logic circuit processes the obtained electrical signal and converts it into a visual graphic signal, which is then transmitted to the human-computer interaction interface and the time evolution curve is displayed simultaneously. The human-computer interaction interface further processes the graphical signal according to actual needs to obtain the final required data, namely the concentration and ratio of formaldehyde and glyoxal in the atmosphere.

[0071] Examples of embodiments have been disclosed herein, and although specific terminology is used, it is used and interpreted in a general and descriptive sense only and is not intended to be limiting. In some instances, as will be apparent to those skilled in the art at the time of filing of this application, features, characteristics, and / or elements described with respect to one particular embodiment may be used alone or in combination with features, characteristics, and / or elements described with respect to other embodiments, unless expressly otherwise indicated. Therefore, those skilled in the art will understand that various changes in form and detail may be made without departing from the spirit and scope of the invention as set forth in the appended claims.

Claims

1. A device for simultaneously measuring the concentrations of formaldehyde and glyoxal, pollutants in the atmosphere, characterized in that, include: An excitation light source is connected to a software control system. According to the instructions of the software control system, a tunable femtosecond to millisecond wide-range laser is output to the main cavity. The excitation light source is a single set of laser dual-wavelength output, that is, simultaneously outputting 353nm and 440nm, which is used to adjust the relative time delay of the two sets of laser output light pulses to complete time-division multiplexing and realize the simultaneous detection of formaldehyde and glyoxal. The sample introduction system is a tubing channel connected to the main cavity, used to draw atmospheric samples into the main cavity; The main cavity is a multi-channel White cell. The side walls of the main cavity are provided with an incident chamber surface and an exit chamber surface, and the bottom is provided with a concave reflector. Excitation light enters the White cell from the incident chamber surface along the x-direction, exciting the atmospheric sample inside to produce formaldehyde and glyoxal photons. After being reflected by the concave reflector, the formaldehyde and glyoxal photons change their light path and are emitted from the exit chamber surface along the y and z directions into the spectrometer. The spectrometer, connected to the software control system, is used to collect photon signals of formaldehyde and glyoxal, and outputs spectral intensity electrical signals to the software control system. The software control system includes a front-end interface and a processing back-end. The processing back-end receives input commands from the front-end interface to control the excitation light source, spectrometer, wavelength and power correction system, collects the spectral intensity electrical signals of formaldehyde and glyoxal, calculates the concentrations of formaldehyde and glyoxal according to the pre-calibrated intensity-concentration relationship, and displays the spectra visually on the front-end interface. The wavelength and power correction system is located in the laser output path between the excitation source and the main cavity, connecting the excitation source and the software control system. It includes a wavelength meter and a piezoelectric ceramic actuator, and is used to simultaneously detect the power and wavelength values ​​of the excitation light and feed them back to the excitation source so that it can adjust the laser wavelength and power in real time.

2. The device for simultaneously measuring the concentrations of formaldehyde and glyoxal in the atmosphere according to claim 1, characterized in that, The excitation source is a high repetition rate, ultra-narrow linewidth pulsed laser with dual-wavelength output; when the software control system receives the start signal, the internal xenon lamp emits excitation light; when the wavelength and power correction system receives the signal, it adjusts the wavelength and power of the excitation light emitted by the xenon lamp in real time.

3. The device for simultaneously measuring the concentrations of formaldehyde and glyoxal in the atmosphere according to claim 1, characterized in that, The main cavity sidewall is made of aluminum, and the inner surface is coated with a mixture of Teflon and silanizing agent, and then blackened to prevent stray light transmission interference. The incident and exit chamber surfaces of the main cavity sidewall are made of glass to allow the excitation light and formaldehyde and glyoxal photons to pass through. The bottom inner wall of the main cavity is equipped with a heating resistance wire to raise the temperature and prevent formaldehyde and glyoxal photons from being adsorbed on the sidewall.

4. The device for simultaneously measuring the concentrations of formaldehyde and glyoxal in the atmosphere according to claim 1, characterized in that, The spectrometer includes: a light-collecting lens, a filter, an imaging lens, a preamplifier, and a single-photon detector arranged sequentially on the outgoing light path outside the main cavity; the single-photon detector is placed at the focal point of the imaging lens; the light-collecting lens is used to collect reflected formaldehyde and glyoxal photons and redirect and refract them into the filter; the filter is a dual-wavelength transmission filter used to filter out stray light and allow the excitation photons of formaldehyde and glyoxal to be transmitted to the imaging lens; the imaging lens further refracts the purified and filtered two photon signals into the preamplifier for signal amplification and then outputs them to the single-photon detector; the single-photon detector is a photomultiplier tube used to read the two photon signals and convert them into electrical signals for output to the software control system.

5. The device for simultaneously measuring the concentrations of formaldehyde and glyoxal in the atmosphere according to claim 1, characterized in that, The wavelength and power calibration system measures the excitation light wavelength in real time and uses piezoelectric ceramics to adjust the laser cavity mirror angle to ensure that the laser wavelength is always at the position of the strongest absorption peak of formaldehyde and glyoxal, thus calibrating the wavelength online in real time.

6. The device for simultaneously measuring the concentrations of formaldehyde and glyoxal in the atmosphere according to claim 1, characterized in that, The sampling system comprises a gas channel, one side of which is connected to the atmosphere, and the other side is closed with a sampling tube inserted into its end face. The sampling tube is connected to the main cavity. The upper wall of the gas channel has a gas inlet, and the lower wall has a particulate matter channel outlet. A first air pump and a second air pump are respectively installed at the sampling tube inlet and the particulate matter channel outlet. Both the first and second air pumps are connected to a software control system. The first and second air pumps receive control signals from the software control system to turn the air pumps on or off. Atmosphere enters the gas channel through the gas inlet. The first air pump operates, applying a lateral negative pressure in the pipe to cause a portion of the airflow to be sharply turned and drawn into the sampling tube into the cavity. Aerosol particles in the atmosphere maintain their original linear motion due to inertia, and their motion direction changes and deflects as the second air pump operates, exiting through the particulate matter channel outlet, thus achieving the separation of gas and target particles.

7. The device for simultaneously measuring the concentrations of formaldehyde and glyoxal in the atmosphere according to claim 1, characterized in that, The processing backend includes: a main control module, a sample injection control module, an online calibration module, a laser and spectrometer control module, and a data recording, analysis, and fault tolerance processing module; The main control module is used to control the working sequence of each component and upload and store the collected data; The injection control module outputs injection flow rate and injection time control signals of the injection system according to the set parameters. The online calibration module determines whether spectrometer calibration is needed based on the duration of use and data recordings when the system starts up. The laser and spectrometer control module outputs control signals according to set parameters to control the working sequence of the excitation source and the spectrometer, so that the spectrometer can collect formaldehyde and glyoxal photon signals respectively. The data recording, analysis, and fault-tolerant processing module is used to graphically process the intensity signals of the measured formaldehyde and glyoxal photons.

8. A method for simultaneously measuring the concentrations of formaldehyde and glyoxal in the atmosphere, said method being implemented based on the apparatus for simultaneously measuring the concentrations of formaldehyde and glyoxal in the atmosphere as described in any one of claims 1-7, characterized in that... Includes the following steps: Step 1: Set the injection flow rate and injection time of the atmospheric sample in the front-end interface, and start the gas extraction step: Start the first and second gas extraction pumps to separate and purify the atmospheric sample through the pipeline channel of the injection system and extract it into the main chamber. Step 2: Set the wavelength and frequency of the laser output from the excitation source in the front-end interface, and start the wavelength and power calibration steps: Start the excitation source and wavelength and power calibration system. The excitation source emits excitation light into the main cavity, which excites the sample under test to emit photons. The wavelength and power calibration system detects the power and wavelength values ​​of the excitation light in real time and outputs them to the excitation source to adjust the laser wavelength and power in real time. Step 3, the steps for starting the excitation source and spectrometer for measurement: control the excitation source to output laser, and start the spectrometer according to the timing output control signal to collect the formaldehyde and glyoxal photon signals excited by the sample to be tested, and convert them into electrical signals; Step 4: Visualization Spectrum Display Step: The control system calculates the corresponding formaldehyde and glyoxal photon concentration values ​​according to the intensity signals of the two types of photons received per unit time, based on the concentration-photon intensity function relationship, and generates visualization spectra for display on the front-end interface.

9. The method for simultaneously measuring the concentrations of formaldehyde and glyoxal in the atmosphere as described in claim 8, characterized in that, Before step 3, the process includes a step of calibrating the coefficients of the concentration-photon intensity function relationship: a sample of a mixture of formaldehyde and glyoxal with a known standard concentration of A is drawn into the device, and multiple measurement steps are initiated to obtain the photon intensity signals AF and AF of formaldehyde and glyoxal are obtained. The coefficients A are calibrated according to the formula AF = A × A.

10. The method for simultaneously measuring the concentrations of formaldehyde and glyoxal in the atmosphere as described in claim 8, characterized in that, In step 3, the spectrometer is started according to the timing output control signal to collect the photon signals of formaldehyde and glyoxal excited by the sample to be tested. The timing includes: setting the signal acquisition time window of the spectrometer detector based on the fact that formaldehyde and glyoxal are long-lived fluorescence signals; starting the acquisition of the long-lived fluorescence signal of formaldehyde and glyoxal within the time window; and turning off the detector to not collect photon signals outside the time window. This is used to eliminate the stray short-lived and weak fluorescence signals emitted by other high-concentration particulate interference substances in the atmospheric environment, leaving the long-lived and strong fluorescence signal emitted by the required formaldehyde and glyoxal, and finally obtaining the accurate concentration of formaldehyde and glyoxal in the outside atmosphere.

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