Ozone denuder and method for collecting atmospheric organic compound

Abstract

To provide an ozone denuder which can remove ozone without causing loss or organic compounds in the atmosphere or contamination of a sample, and a method for collecting a sample in the atmosphere by using the ozone denuder.SOLUTION: By immobilizing an organic iodine compound onto a carrier such as ceramics through a silane coupling reaction, an ozone denuder capable of removing ozone without causing loss of an atmospheric organic compound due to decomposition or adsorption can obtained. This makes it possible to suppress exposure to ozone when a sample is being collected and to collect the sample onto a collection material without affecting a structure or concentration of an organic compound in the atmosphere.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an ozone denuder for removing ozone contained in an air sample, and a method for collecting organic compounds in the air using an ozone denuder. [Background technology]

[0002] Organic compounds in the atmospheric environment are generated from various sources and affect climate change by promoting the formation of cloud particles and absorbing solar radiation, as well as affecting human health through harmful effects such as carcinogenicity and mutagenicity. Understanding the behavior and functions of organic compounds in the atmosphere is required to predict and control future climate change and health effects.

[0003] There are two methods for measuring organic compounds in the air: the online method, in which air samples are introduced into a measuring device on the spot, and the offline method, in which samples are collected on a carrier such as a filter and then extracted and measured in a laboratory. However, at present, the online method requires expensive measuring equipment and is not suitable for multi-point observation, and the detection sensitivity of compounds is not sufficient.

[0004] On the other hand, offline samplers are relatively inexpensive and already in widespread use. They offer a high degree of freedom in setting flow rates and sampling times, and the filters can be divided to be used for a variety of measurement methods; therefore, they are expected to enable accurate measurement of a wide variety of organic compounds.

[0005] However, in the offline method, organic compounds captured on a carrier such as a filter during collection of an air sample may be exposed to ozone present in the air and be oxidized and degraded. Non-Patent Document 1 reports that benzo[a]pyrene, a polycyclic aromatic hydrocarbon (PAHs), is decomposed by oxidation with ozone on the filter.

[0006] Furthermore, there are many organic compounds in the atmosphere that are oxidized by ozone, hydroxyl radicals, and nitrate radicals. In order to observe the chemical reaction processes of these reactive organic compounds in the atmosphere, it is necessary to collect the organic compounds in the atmosphere while preserving their structure and concentration. Therefore, when measuring such compounds, it is necessary to suppress ozone oxidation on the collection material used to collect air samples.

[0007] In order to suppress ozone oxidation during air sample collection, ozone denuders (or ozone scrubbers) that remove ozone from the atmosphere have been developed. Currently used ozone denuders use potassium iodide (KI), inorganic oxides (manganese dioxide, etc.), and activated carbon (Non-Patent Documents 1 to 3). However, as described below, these ozone denuders affect the state of organic compounds in the atmosphere, so they are mainly used for observing inorganic compounds.

[0008] In recent years, attempts have been made to develop an ozone denuder suitable for capturing organic compounds, and a denuder in which an iodine-based ionic liquid is supported on a ceramic honeycomb has been proposed (Non-Patent Document 4). [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] “Polycyclic Aromatic Hydrocarbons in Urban Air Particulate Matter: Decadal and Seasonal Trends, Chemical Degradation, and Sampling Artifacts” Environmental and Science Technology, 37 (13), 2861 (2003) [Non-Patent Document 2] “Removal of atmospheric oxidants with annular denuders” Environmental and Science Technology, 24 (6), 811 (1990) [Non-Patent Document 3] “Oxidant denuder sampling for analysis of polycyclic aromatic hydrocarbons and their oxygenated derivatives in ambient aerosol: Evaluation of sampling artefact” Chemosphere, 62 (11), 1889 (2006) [Non-Patent Document 4] “A new ozone denuder for aerosol sampling based on an ionic liquid coating” Analytical and Bioanalytical Chemistry, 396 (2), 857 (2010) Summary of the Invention [Problem to be solved by the invention]

[0010] However, these conventional ozone removal techniques are unable to collect samples without affecting a wide variety of organic compounds, including volatile organic chemicals (VOCs) and semi-volatile substances.

[0011] For example, KI is deliquescent, and condensation occurs during collection, causing clogging of the flow path and sample contamination, so dehumidification by heating is necessary. However, there are drawbacks in that it is difficult to heat the sample sufficiently with a high flow rate sampler, and heating causes the volatilization of semi-volatile organic compounds.

[0012] It is also known that in ozone denuders using inorganic oxides, organic compounds such as VOCs are oxidized and decomposed by the active oxygen formed on the surface. Furthermore, in ozone denuders using activated carbon, not only ozone but also VOCs and semi-volatile substances are adsorbed and removed, resulting in the loss of these organic compounds. These mechanisms of decomposition and removal of organic compounds by inorganic oxides and activated carbon are already widespread as VOC removal technologies, and it is clear that they affect the state of existence of organic compounds.

[0013] An ozone denuder using an iodine-based ionic liquid has been proposed as an ozone denuder suitable for reducing such effects and capturing organic compounds (Non-Patent Document 4). This ozone denuder removes ozone by impregnating a carrier with a compound in which iodine is bound to an ionic liquid with a low vapor pressure. However, although it was thought that ionic liquids hardly volatilize at room temperature, when actually used to capture air samples, there was a problem that the ionic liquid desorbs from the carrier and contaminates the air sample.

[0014] Therefore, the present invention aims to overcome the problems of conventional ozone denuders and to make it possible to remove ozone during air sample collection without causing loss of organic compounds in the air or contamination of the sample. Another aim is to provide a collection method for clarifying the structure and abundance of organic compounds actually present in the air by suppressing ozone oxidation of organic compounds collected on air sample collection materials such as filters and polyurethane foams. [Means for solving the problem]

[0015] The present invention is an ozone denuder characterized in that an organic iodine compound is immobilized on a carrier by a silane coupling reaction.

[0016] The ozone denuder uses an alkoxysilylalkylpyridinium iodide represented by the following formula (1) as the organic iodine compound.

[0017] Formula (1): [ka] (In the formula, R represents a substituent, n is an integer of 0 to 5, m is an integer of 1 to 18, and Ak is an alkyl group of C1 to C3.)

[0018] The ozone denuder uses 3-trimethoxysilylpropyldimethylpyridinium iodide represented by the following formula (2) as the organic iodine compound.

[0019] Formula (2): [ka]

[0020] Also, the ozone denuder is formed by bonding the above-mentioned organic iodine compound to a carrier having hydroxyl groups on the surface, such as ceramics or cellulose, by a silane coupling reaction. Effect of the Invention

[0021] According to the present invention as described above, it is possible to provide an ozone denuder that can remove ozone without affecting organic compounds through decomposition, sorption, oxidation, etc. Specifically, it is possible to remove ozone during collection of an air sample using a collection device as shown in Figure 1, and to collect the organic compounds in the air while suppressing their loss and denaturation. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is an explanatory diagram showing a method for collecting air samples using an ozone denuder of the present invention. [Diagram 2] FIG. 1 is an explanatory diagram showing an air sample collection method used in the examples. [Diagram 3] FIG. 13 shows the ozone concentration when the ozone denuder of the present invention is not used. [Figure 4] FIG. 2 shows the ozone concentration when the ozone denuder of the present invention is used. [Diagram 5]FIG. 1 is a graph showing a concentration ratio obtained by dividing the organic compound concentration when an ozone denuder is not used by the organic compound concentration when an ozone denuder is used. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The present invention relates to an ozone denuder characterized by immobilizing an organic iodine compound on a carrier by a silane coupling reaction, and also to a method for collecting air samples by mounting the ozone denuder on various air samplers.

[0024] As the organic iodine compound, an alkoxysilylalkylpyridinium iodide having an alkoxysilyl group for undergoing a silane coupling reaction with a hydroxyl group can be used.

[0025] When 3-trimethoxysilylpropyldimethylpyridinium iodide is used as the organic iodine compound, it can be produced as follows.

[0026] 2.2 g of dimethylpyridine and 6.65 g of potassium iodide (KI) are mixed with 60 mL of dehydrated acetonitrile, and 7.5 mL of 3-chloropropyltrimethoxysilane is added while stirring the solution and refluxed for 24 hours. After cooling, the solution is filtered and the filtrate is concentrated under reduced pressure, and 25 mL of diethyl ether is added to the concentrated solution to obtain a yellow precipitate. The precipitate is washed several times with diethyl ether and further dried in vacuum to obtain 7.5 g of 3-trimethoxysilylpropyldimethylpyridinium iodide (yield: approximately 95%). It is possible to produce organic iodine compounds with any alkyl chain length by using chloroalkyltrimethoxysilanes with different alkyl chain lengths.

[0027] The organic iodine compound produced as described above is immobilized on a carrier such as ceramics such as cordierite or alumina, silica gel, cellulose, etc., by a silane coupling reaction. When using ceramics as a carrier, it is effective to increase the amount of surface hydroxyl groups by boiling it in an acidic aqueous solution. In addition, substances other than those mentioned above can also be used as carriers as long as they have hydroxyl groups and can be used in a silane coupling reaction.

[0028] The shape of the carrier can be particulate, granular, porous, cylindrical, honeycomb, etc., and there is no limitation on the shape as long as the air sample is breathable. When used to collect airborne particle samples, a honeycomb-shaped carrier is suitable because it reduces the loss of particles.

[0029] When cordierite is used as the carrier and 3-trimethoxysilylpropyldimethylpyridinium iodide is used as the organic iodine compound, immobilization can be carried out by a silane coupling reaction as follows.

[0030] The cordierite is boiled in 2 mol / L hydrochloric acid for 2 hours, washed with water, and then dried. In addition, 2.5 g of 3-trimethoxysilylpropyldimethylpyridinium iodide is dissolved in 100 mL of a 2-butanol:water (8:2) solution, and stirred at room temperature for 2 hours. The dried cordierite is immersed in the solution, and stirred at room temperature for 24 hours. After the reaction, the cordierite is taken out and the solvent is removed, and dehydration condensation is performed by vacuum drying (100°C, 2 hours). The cordierite is allowed to cool, washed with 2-butanol overnight using a Soxhlet extractor, and then vacuum dried (room temperature).

[0031] The carrier on which the organic iodine compound is immobilized as described above is packed into a cylindrical or cartridge-shaped container made of metal, glass, plastic, etc. to prepare an ozone denuder. The material and shape of the container can be selected arbitrarily depending on the target air sample.

[0032] The ozone denuder manufactured as described above is attached to various air samplers. Depending on the purpose, air samplers use adsorption materials such as filters, polyurethane foam, activated carbon fiber, solid-phase fillers, etc., and by attaching the ozone denuder upstream of these adsorption materials, it is possible to suppress ozone exposure to the air sample collected on the adsorption materials.

[0033] By subjecting the collected air samples to extraction, pretreatment, and measurement methods appropriate for the target compound, it is possible to determine the structure and amount of the compound in a state that has not been oxidized by ozone during sample collection. EXAMPLES

[0034] The following examples are specifically described, but the present invention is not limited thereto. In the following examples, a fine particulate matter (PM2.5) collector (FRM2025) manufactured by Thermo was used as an air sampler, an ozone concentration meter (OA683) manufactured by Kimoto Electronics was used as an ozone concentration meter, and a Sciex LC-Triple Quad 4500 system manufactured by Sciex was used as a liquid chromatograph mass spectrometer.

[0035] The ozone denuder used was a honeycomb-shaped cordierite that was immobilized with 3-trimethoxysilylpropyldimethylpyridinium iodide as an organic iodine compound by a silane coupling reaction. The honeycomb had a diameter of 38 mm, a length of 40 mm, and a cell density of 400 cpsi. As shown in Figure 2, the honeycomb was packed into a cylindrical stainless steel tube and installed in the PM2.5 collection device.

[0036] Two PM2.5 collection devices were prepared, one of which was equipped with the above-mentioned ozone denuder, and the other was not, and air samples were collected in parallel. Quartz fiber filter paper (PALLFLEX, 2500QAT-UP) was used as the collection material for the PM2.5 collection device. Air samples were collected in Osaka City from September to October 2020 at 16.7 L / min for 24 hours from midnight, and then continuous collection was performed by automatically replacing the quartz fiber filter paper. A portion of the air was drawn from the rear of the quartz fiber filter paper of each PM2.5 collection device, and the ozone concentration was measured.

[0037] Figure 3 shows the ozone concentration downstream of the quartz fiber filter when the ozone denuder of the present invention was not used. The average ozone concentration during the two-week observation period was 30.4 ppb, and typical ozone concentration fluctuations were observed, with high concentrations during the day and low concentrations at night.

[0038] Figure 4 shows the ozone concentration after the quartz fiber filter paper when the ozone denuder of the present invention was used. When the ozone denuder of the present invention was used, the average ozone concentration during the two-week observation period was 0.7 ppb, and almost all of the ozone was removed (removal rate 97.5%). This result shows that ozone in the atmosphere can be removed continuously for more than two weeks at a flow rate of 16.7 L / min. Furthermore, when the ozone denuder and the collected samples were checked after use, there was rainfall during the collection period and high humidity conditions, but deliquescence and sample contamination like those observed with KI were not observed.

[0039] The concentrations of azelaic acid, p-nitrophenol, pinonic acid, 4-nitrocatechol, 4-methyl-5-nitrocatechol, phthalic acid, 3-methyl-1,2,3-butanetricarboxylic acid, and levoglucosan were measured using a liquid chromatography mass spectrometer for each of the seven-day samples collected by the two PM2.5 samplers. These organic compounds are used as indicator compounds of the source of PM2.5 in the analysis of the behavior of PM2.5.

[0040] FIG. 5 shows the concentration ratio obtained by dividing the organic compound concentration when the ozone denuder was not used by the organic compound concentration when the ozone denuder was used. For phthalic acid, 3-methyl-1,2,3-butanetricarboxylic acid, and levoglucosan, there was no difference in the measured concentration depending on whether or not the ozone denuder was used (average concentration ratio = 1.0). On the other hand, the measured concentrations of azelaic acid, p-nitrophenol, and pinonic acid were significantly lower when the ozone denuder was used (average concentration ratio = 3.3 to 57). In addition, the measured concentrations of 4-nitrocatechol and 4-methyl-5-nitrocatechol were higher when the ozone denuder was used (average concentration ratio = 0.62 to 0.54). In other words, in the conventional collection method of the present invention that does not use the ozone denuder, it was found that azelaic acid, p-nitrophenol, and pinonic acid were generated on the collection material by ozone in the atmosphere, and 4-nitrocatechol and 4-methyl-5-nitrocatechol were decomposed on the collection material.

[0041] The ozone denuder of the present invention can remove ozone when collecting an air sample, suppressing exposure of the air sample to ozone and preventing the denaturation of organic compounds by ozone. By measuring an air sample that has not been denatured by ozone, it is possible to grasp the structure and amount of organic compounds actually present in the air. This allows more accurate knowledge of the dynamics and functionality of organic compounds in the air. Furthermore, the device can be applied not only to outdoor air samples, but also to indoor air samples and exhaust gas samples, and can be used for accurate measurement of organic compounds in gas in a wide range of fields. [Explanation of symbols]

[0042] 1 Air sample inlet 2. Air sample introduction tube 3 Stainless steel tube for holding ozone denuder 4. Honeycomb ozone denuder 5 PM2.5 sampler body

Claims

1. An ozone denuder in which an organic iodine compound is immobilized on a carrier.

2. 2. The ozone denuder according to claim 1, wherein the organic iodine compound is an alkoxysilylalkylpyridinium iodide.

3. The ozone denuder according to claim 1, wherein the organic iodine compound is 3-trimethoxysilylpropyldimethylpyridinium iodide.

4. A method for producing the ozone denuder according to any one of claims 1 to 3, comprising immobilizing an organic iodine compound on a carrier by a silane coupling reaction.

5. A method for capturing organic compounds using the ozone denuder according to any one of claims 1 to 3.

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