A method for the chemical ionization mass spectrometric analysis of off-line organic aerosol samples

Abstract

The application discloses a method for chemical ionization mass spectrum analysis of offline organic aerosol samples, aiming at realizing fast and accurate measurement of polar atmospheric organic aerosol samples. The method firstly processes offline atmospheric particulate matter samples, intercepts 2-7mm-sized samples, and clamps the samples between two clean filter membranes to fix the samples; then, the samples are heated by using a nonlinear temperature program, and data are collected after heating; the thermal background signal is deducted by using a thermal background multiplication method or a thermal background inference method to ensure the accuracy of the data; finally, the mass spectrum signals of various organic components of the samples at different temperatures are analyzed by chemical ionization mass spectrum after desorption by hot nitrogen blowing, so that the molecular composition information and thermal analysis curves of the compounds in the sample aerosol are obtained. The method is simple in operation, can effectively analyze the chemical components of polar organic aerosols, is suitable for offline sample analysis of atmospheric aerosols, and has high popularization and application value.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of mass spectrometry, and particularly relates to a chemical ionization mass spectrometry analysis method for offline organic aerosol samples. BACKGROUND

[0002] The chemical ionization mass spectrometry (CIMS) technology coupled with a thermal desorption method is a widely used method for online analysis of molecular composition of organic aerosols. In this method, particulate matter is collected on a Teflon filter, and thermal desorption is performed under linear heating conditions from room temperature to 200 DEG C using high-purity nitrogen. Subsequently, the molecular composition information of the evaporated inorganic and organic aerosol compounds is analyzed using a chemical ionization mass spectrometer. Although this technology can provide high-resolution molecular composition information, its design for online analysis limits its wide application.

[0003] The online CIMS technology requires deployment of a complex mass spectrometer at a stable observation site, and a large amount of human and financial resources are required for long-term maintenance. Therefore, this technology can only be deployed for a short period of time (usually several weeks to several months) at a specific location, and it is difficult to achieve long-term monitoring or simultaneous measurement at multiple locations.

[0004] Therefore, it is of practical significance to develop a suitable offline filter membrane analysis method for analyzing organic aerosols using chemical ionization mass spectrometry. However, the use of chemical ionization mass spectrometry coupled with thermal desorption method for analyzing offline filter membrane samples needs to overcome the following problems: (1) offline Teflon filter can effectively reduce gas phase interference, but it is not easy to cut, and it is easy to block under high concentration sampling conditions, which limits its application in offline analysis; (2) the sampling time is short, and the sample amount is usually less than 1 ug, while the sampling time of urban atmospheric particulate matter is usually more than 12 h, and the sample amount can reach more than 10 mg, and the existing method is difficult to be directly applied to offline sample analysis; (3) a large amount of ammonium nitrate in urban atmospheric particulate matter decomposes in the thermal desorption process, which consumes the reagent ions of chemical ionization mass spectrometry, and seriously affects the analysis results of organic aerosols; (4) the thermal background signal is significantly elevated during offline thermal desorption analysis, and an effective background subtraction method needs to be developed to obtain accurate analysis results. SUMMARY

[0005] In view of the deficiencies of the prior art, the application provides a chemical ionization mass spectrometry analysis method for offline organic aerosol samples, which realizes rapid and accurate measurement of polar atmospheric organic aerosol samples.

[0006] The application is realized by the following technical solutions:

[0007] A chemical ionization mass spectrometry analysis method for offline organic aerosol samples, comprising the following steps:

[0008] Step 1) Sample preparation: Take an offline 47mm quartz filter membrane atmospheric particulate matter sample and cut a 2-7mm sample from the quartz filter membrane using a filter membrane punch heated to 500℃; select two clean, unused filter membranes with a diameter of 25mm that have been heated to 200℃ for 30min, and sandwich the cut sample between the two clean filter membranes to fix the filter membranes.

[0009] Step 2) Sample heating: The sample treated in Step 1) is heated to 200°C using a non-linear heating program. After the heating phase, it is kept at 200°C for 20 minutes for isothermal desorption so that the signal returns to the background level.

[0010] Step 3) Data Processing: The sample heated in Step 2) is processed. Considering the nonlinear relationship between signal and desorption concentration caused by nonlinear heating, the signal of each species i obtained by chemical ionization mass spectrometry needs to be corrected for desorption before being re-obtained, as shown in Equation I below:

[0011]

[0012] In formula I: I 样品,i,j This represents the difference between the signal intensity of compound i at temperature j and the signal intensity of the blank sample during non-uniform heating; I 脱附修正,i,j dT represents the integral of the correction signal from the temperature range T-ΔT to T; dT ​​is the unit minute temperature interval of the integral within the temperature integration range, which is 0.1 to 0.2℃; ΔT is the temperature interval, which is 2 to 3℃.

[0013] Step 4) Background subtraction: Subtract the hot background signal using the hot background multiplication method or the hot background inference method;

[0014] Step 5) After background subtraction in step 4), the sample is desorbed by hot nitrogen purging. Then, the mass spectrometry signals of various organic components in the sample at different temperatures are analyzed by chemical ionization mass spectrometry. This allows us to obtain the molecular composition information and thermal desorption curves of the compounds in the sample aerosol.

[0015] Preferably, the material of the clean, unused filter membrane in step 1) is Teflon or quartz.

[0016] Preferably, the heating procedure in step 2) is as follows: heating from room temperature to 60°C at a rate of 5°C / min for 8 minutes; heating from 60°C to 105°C at a rate of 3°C / min for 15 minutes; and finally heating from 105°C to 200°C at a rate of 8°C / min for 12 minutes.

[0017] Preferably, the thermal background multiplication method in step 4) is as follows: The last 1.5–3 minutes of the heating cycle is used as a reference time period. Based on the ratio between the mass spectrometry signals during the reference time period, the environmental sample blank signal is multiplied to the thermal background concentration of the sample signal to obtain sample signals with removed thermal background at different time periods, as shown in Equation II below:

[0018]

[0019] In formula II: I 样品,i,j I represents the signal intensity of sample compound i at temperature j. 环境空白,i,j Is represents the signal intensity of compound i in the environmental blank sample at time j; 环境样品,i Is represents the total integrated signal intensity of compound i in the environmental sample during the time interval t1 to t2; 空白样品,i The total integrated signal intensity of compound i in the blank sample during the time period from t1 to t2 is denoted as t1.

[0020] Preferably, the thermal background inference method in step 4) is as follows: a background thermal image, called the thermal baseline Is, is determined for each thermal image of each compound. 热基线 The pre-averaging time for thermal image data is set to 4–6 data points of the original temporal resolution to reduce noise in thermal baseline calculation; field blanks are processed in the same way; the blank of compound i is reduced by the signal Is. 扣除基线,i As shown in Equation III below:

[0021] Is 扣除基线,i =Is 样品扣除基线,i -Is 环境空白扣除基线,i

[0022] =(∫I 样品,i,j -Is 样品拟合基线,i )-(∫I 环境空白,i,j -Is 环境空白拟合基线,i )

[0023] Formula III;

[0024] In Formula III: I 样品,i,j I represents the concentration signal of species i in the sample at time j; 环境空白,i,j Is represents the concentration signal of species i at time j in the environmental blank. 样品拟合基线,i Is 环境空白拟合基线,i The total baseline is obtained by integrating the i-species sample and the environmental blank throughout the entire heating analysis process.

[0025] This invention provides a method for analyzing offline filter membranes with high loading capacity, long sampling time, and high inorganic ion interference using a gas aerosol chemical ionization mass spectrometer, which has significant technical advantages and practical application effects. Specific beneficial effects are as follows:

[0026] (1) High repeatability and stability: When using a quartz filter membrane, the repeatability of the integrated signal intensity can be controlled within ±9%; when using a Teflon filter membrane, the repeatability can be controlled within ±18%, which significantly improves the stability and reliability of offline sample analysis.

[0027] (2) Wide concentration range and high linear response: The method of the present invention exhibits excellent linear correlation (Spearman rank correlation coefficient Rsp≥0.95) in the concentration-signal response relationship of gas aerosol mass spectrometry, and is suitable for the analysis of samples with organic aerosol concentration range of 0.05~0.1μg, which can meet the detection needs of high-load samples of urban atmospheric particulate matter.

[0028] (3) High accuracy and consistency: The total organic matter signal, inorganic sulfate and nitrate signal measured by the method of the present invention are highly consistent with the chemical composition of organic aerosols, sulfate and nitrate measured by aerosol mass spectrometry, with a correlation coefficient Rsp of 0.94 to 0.95, which verifies the accuracy and reliability of the method.

[0029] (4) Optimized thermal desorption performance: The highest signal temperature (T) of the desorption thermogram is corrected using a non-uniform temperature rise program. 最高信号温度 ), compared with the traditional uniform upward heating method T 最高信号温度 It exhibits a high correlation (correlation coefficient Rsp: 0.72–0.84). For species comprising more than 50% of the total compounds, T in repeated tests... 最高信号温度 The error of the value can be controlled within 5℃ (correlation coefficient Rsp: 0.87~0.93), which significantly improves the accuracy and repeatability of thermal desorption analysis.

[0030] (5) Suitable for long-term sampling: The method of the present invention can analyze filter membrane samples with typical offline sampling durations (such as 12h and 24h), which far exceeds the sampling duration of traditional online methods (usually 30min), providing an efficient and economical solution for long-term monitoring and simultaneous measurement at multiple locations.

[0031] (6) Effectively avoid interference: The method of the present invention can effectively avoid interference from inorganic ion signals and thermal background by optimizing the selection of filter membrane, heating program and background subtraction method, which significantly improves the accuracy and applicability of offline sample analysis.

[0032] In summary, the method of the present invention exhibits significant advantages in repeatability, linear response, accuracy, thermal desorption performance, and applicability, providing an efficient and reliable technical means for offline filter membrane sample analysis with high loading capacity and long sampling time, and has broad application prospects. Attached Figure Description

[0033] Figure 1This is a schematic diagram of the aerosol sample introduction using the "sandwich method" in Example 1;

[0034] Figure 1 In the middle: 1. Filter membrane gun; 2. Quartz filter membrane; 3. Sample; 4. Clean filter membrane; 5. "Sandwich method" sample; 6. Hot high-purity nitrogen;

[0035] Figure 2 This is a schematic diagram of the nonlinear heating program in Example 1;

[0036] Figure 3 This is a schematic diagram illustrating the transformation of the nonlinear heating program curve in Example 1 into a linear heating program curve.

[0037] Figure 4 The background subtraction methods in Example 1 are: A is the hot background multiplication method, and B is the hot background inference method;

[0038] Figure 5 The repeatability of samples in Example 2 with organic aerosol concentrations of 1 μg (A) and 0.1 μg (B);

[0039] Figure 6 This is a graph showing the relationship between different cut-off areas and their signals on the same Teflon filter membrane sample in Example 3. Detailed Implementation

[0040] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0041] Example 1

[0042] A chemical ionization mass spectrometry method for offline analysis of organic aerosol samples, the specific steps of which are as follows:

[0043] (1) Sample preparation

[0044] like Figure 1 As shown, the sample can be an offline 47mm quartz filter membrane for atmospheric particulate matter. Using a filter membrane gun 1 heated to 500℃, a 2-7mm sample 3 (organic aerosol injection volume of 0.1-1μg) is cut from the quartz filter membrane 2. This method of cutting a small amount of filter membrane reduces the filter membrane load. Two clean, unused Teflon or quartz filter membranes with a diameter of 25mm, heated to 200℃ for 30min, are selected. The cut sample 3 is sandwiched between the two clean filter membranes 4 to fix the filter membrane (this method is named the "sandwich method" in this invention). The entire "sandwich method" sample 5, after fixation, will desorb the organic aerosol from the sample 3 by heating.

[0045] (2) Sample heating

[0046] Because ammonium nitrate constitutes a high proportion of atmospheric particulate matter, its thermal decomposition produces a large amount of nitric acid, which significantly interferes with the analysis of organic aerosols. The "sandwich method" sample heating does not use the traditional linear heating method, but instead employs nonlinear heating of the organic matter. This nonlinear heating method reduces the consumption of reagent ions by secondary inorganic ions in fine particles for chemical ionization mass spectrometry. The main principle is to use a lower heating rate within the ammonium nitrate decomposition temperature range of 60–105℃, thereby reducing the large consumption of reagent ions by nitric acid gas generated during ammonium nitrate decomposition. Figure 2 As shown, the specific heating procedure is as follows:

[0047] The temperature was increased from room temperature (approximately 25°C) to 60°C at a rate of 5°C / min over 8 minutes; then increased from 60°C to 105°C at a rate of 3°C / min over 15 minutes; finally, increased from 105°C to 200°C at a rate of 8°C / min over 12 minutes. After the temperature increase phase, the temperature was maintained at 200°C for 20 minutes for desorption to allow the signal to return to background levels.

[0048] (3) Data processing

[0049] Data processing is performed on the heated sample, such as... Figure 3 As shown, the nonlinear heating program curve is transformed into a linear heating program curve, and the thermal desorption curve under the nonlinear heating program is reconstructed using the temperature integration method. Considering the nonlinear relationship between signal and desorption concentration caused by the nonlinear heating, the signal of each species i obtained by chemical ionization mass spectrometry needs to be corrected for desorption before being obtained again, as shown in Equation I below:

[0050]

[0051] In formula I: I 样品,i,j This represents the difference between the signal intensity of compound i at temperature j and the signal intensity of the blank sample during non-uniform heating; I 脱附修正,i,j dT represents the integral of the correction signal from the temperature range T-ΔT to T; dT ​​is the unit minute temperature interval of the integral within the temperature integration range, typically 0.1 to 0.2 °C; considering that the reproducibility of the thermal desorption curve in the online gas aerosol chemical ionization mass spectrometry study report varies by about 2 °C, the usable temperature interval ΔT is 2 to 3 °C.

[0052] (4) Background subtraction

[0053] In this embodiment, background subtraction can be achieved using either of the following two methods:

[0054] (4-1) Thermal Background Multiplication Method

[0055] like Figure 4As shown in Figure A, the thermal background signal is subtracted using a multiplication method. To scale the thermal background signal to the ratio of the environmental sample and blank sample signals during the reference period, a reference time period can be used after the isothermal desorption process ends (e.g., the last 1.5–3 min of the heating cycle). Based on the ratio between the mass spectrometry signals during the reference time period, the environmental sample blank signal is multiplied to the thermal background concentration of the sample signal, thus obtaining the sample signals with removed thermal background at different time periods, as shown in Equation II below:

[0056]

[0057] In formula II: I 样品,i,j I represents the signal intensity of sample compound i at temperature j. 环境空白,i,j Is represents the signal intensity of compound i in the environmental blank sample at time j; 环境样品,i Is represents the total integrated signal intensity of compound i in the environmental sample during the time interval t1 to t2; 空白样品,i The total integrated signal intensity of compound i in the blank sample during the time period from t1 to t2 is denoted as t1.

[0058] (4-2) Thermal Background Inference Method

[0059] like Figure 4 As shown in Figure B, in this method, we determine a background thermal image for each thermal image of each compound, called the thermal baseline (I). 热基线 This algorithm is used to determine background concentrations based on the time series of pollutant concentrations (by identifying background splines at different time intervals). The background baseline of the thermal image can be determined by referring to the work of Wang et al. (DOI: 10.1021 / acs.est.8b01914). In the specific implementation of background determination, the pre-averaging time of the thermal image data can be set to 4–6 data points (e.g., 1.8 min) of the original time resolution to reduce noise in the thermal baseline calculation. Field blanks are handled in the same way (e.g., ...). Figure 4 (As shown in B). Therefore, the blank of compound i minus the signal Is 扣除基线,i As shown in Equation III below:

[0060] Is 扣除基线,i =Is 样品扣除基线,i -Is 环境空白扣除基线,i

[0061] =(∫I 样品,i,j -Is 样品拟合基线,i )-(∫I 环境空白,i,j -Is 环境空白拟合基线,i )

[0062] Formula III

[0063] In Formula III: I 样品,i,jI represents the concentration signal of species i in the sample at time j; 环境空白,i,j Is represents the concentration signal of species i at time j in the environmental blank. 样品拟合基线,i Is 环境空白拟合基线,i The total baseline is obtained by integrating the i-species sample and the environmental blank throughout the entire heating analysis process.

[0064] (5) After completing the background removal, as follows Figure 1 As shown, after purging and desorption with hot high-purity nitrogen 6, the mass spectrometry signals of various organic components in the sample at different temperatures are analyzed by chemical ionization mass spectrometry. This allows for the analysis of molecular composition information and thermal desorption curves of more than 1,000 compounds in the sample aerosol.

[0065] Example 2

[0066] A chemical ionization mass spectrometry method for offline analysis of organic aerosol samples, the specific steps of which are as follows:

[0067] (1) Sample preparation

[0068] Similar to Example 1, two 47mm quartz filter membrane atmospheric particulate matter samples with different organic aerosol loadings were selected. Three groups of 2mm samples were cut from each sample, with organic aerosol sample amounts of 0.1μg and 1μg, respectively. The entire fixed sample was then subjected to a "sandwich method" to desorb the organic aerosols by heating.

[0069] Two 47 mm Teflon filter membrane samples with organic aerosol loadings of 0.1 μg and 1 μg were selected. Three groups of 2 mm samples were cut from each sample and the same operation was performed ("sandwich method").

[0070] (2) Sample heating

[0071] The same heating program as in Example 1 was used to heat the three groups of quartz filter membranes and the three groups of Teflon filter membranes respectively.

[0072] (3) Data processing

[0073] The same data processing method as in Example 1 was used to process the data of the three groups of quartz filter membranes and the three groups of Teflon filter membranes.

[0074] (4) Background subtraction

[0075] The same background subtraction method as in Example 1 was used to perform background subtraction on the three groups of quartz filter membranes and the three groups of Teflon filter membranes. This example uses the thermal background multiplication method.

[0076] (5) Repeatability test data analysis

[0077] In data analysis, the signals of more than 1,000 species in three repeated tests were compared with their average values ​​to obtain the frequency distribution of sample repeatability.

[0078] like Figure 5 As shown, the concentration of organic aerosols in the sample was 1 μg, which, according to the test results, resulted in a high concentration of organic aerosols. Figure 5 In section A), using a quartz filter membrane as the sampling membrane can achieve repeatability of the integrated signal intensity within ±9%, while using a Teflon filter membrane as the sampling membrane can achieve repeatability within 18%; under the condition that the concentration of organic aerosol in the sample is 0.1 μg ( Figure 5 In section B), using a quartz filter membrane as the sampling filter membrane can achieve repeatability of the integrated signal intensity within ±25%, while using a Teflon filter membrane as the sampling filter membrane can achieve repeatability of 31%.

[0079] Example 3

[0080] A chemical ionization mass spectrometry method for offline analysis of organic aerosol samples, the specific steps of which are as follows:

[0081] (1) Sample preparation

[0082] Similar to Example 1, atmospheric particulate matter samples from a 47mm Teflon filter membrane containing organic aerosols were selected. Samples of 2mm, 3mm, 4mm, and 7mm in size were cut off, corresponding to organic aerosol sample amounts of 1.2μg, 2.7μg, 4.8μg, and 15μg, respectively. The entire fixed sample was then subjected to a "sandwich method" to desorb the organic aerosols by heating.

[0083] (2) Sample heating

[0084] The Teflon filter membrane samples were heated using the same heating program as in Example 1.

[0085] (3) Data processing

[0086] The same data processing method as in Example 1 was used to process data on more than 1,000 organic aerosol species in the Teflon filter membrane sample.

[0087] (4) Background subtraction

[0088] The same background subtraction method as in Example 1 was used to subtract the background from the Teflon filter membrane samples. This example uses the thermal background inference method.

[0089] (5) Experimental Results

[0090] The relationship between different cut-off areas and their signals on the same Teflon filter membrane sample, namely the signals of 3 mm (2.7 μg), 4 mm (4.8 μg), and 7 mm (15 μg) samples and 2 mm (1.2 μg) samples, is as follows:Figure 6 As shown, the method of the present invention still exhibits a good linear response relationship between concentration and signal when the change in injection concentration is more than one order of magnitude (Spearman rank correlation coefficient Rsp is above 0.95).

[0091] Example 4

[0092] In this embodiment, when analyzing offline samples, conventional methods and the method of the present invention are compared in terms of sample heating procedures and data processing. The specific steps are as follows:

[0093] (1) Sample preparation

[0094] Similar to Example 1, an atmospheric particulate matter sample with a 47mm Teflon filter membrane was selected as an organic aerosol. Two 2mm samples were taken (each corresponding to 1.2μg of organic aerosol sample), and these were designated as Sample A and Sample B. The two fixed samples were desorbed from the organic aerosol by heating using the "sandwich method".

[0095] (2) Sample heating

[0096] ① Sample A was heated using a non-linear heating program, that is, the same heating program as in Example 1 was selected to heat sample A.

[0097] ②Sample B was heated using a linear heating program, i.e., at a constant heating rate of 6℃ / min, sample B was heated from room temperature to 200℃.

[0098] (3) Data processing

[0099] ① The same background subtraction method as in Example 1 was used to subtract the background from sample A. That is, the thermal desorption curve under the nonlinear heating program was reconstructed using the temperature integration method. Considering the nonlinear relationship between signal and desorption concentration caused by the nonlinear heating, the signal for each species i obtained by chemical ionization mass spectrometry needs to be corrected for desorption before being re-obtained, as shown in Equation I below:

[0100]

[0101] In Equation I: ΔT is 2℃, and dT is 0.1℃.

[0102] ② The signal relationships of 1000 organic aerosols at different temperatures were directly analyzed using a linear heating program for sample B.

[0103] (4) Background subtraction

[0104] The same data processing method as in Example 1 was used to perform background subtraction on more than 1,000 organic aerosol species in samples A and B. This example uses the thermal background multiplication method.

[0105] (5) Experimental Results

[0106] The highest signal temperature (T) of the desorption thermogram 最高信号温度 Volatility is often used to characterize the volatility of a species, and previous studies have shown an exponential relationship between it and the saturated vapor pressure of that species. In this embodiment, a non-uniform heating program (sample A) is compared at a corrected T0. 最高信号温度 T compared to uniform rising heating program (sample B) 最高信号温度 The corrected nonlinear heating program and the linear heating program (correlation coefficient Rsp: 0.72–0.84) showed that over 50% of the more than 1000 organic species could be replicated in T1 tests. 最高信号温度 The error is within 5℃ (correlation coefficient Rsp: 0.87~0.93).

[0107] The embodiments described above are only some, not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. The scope of protection of the present invention is determined by the scope claimed in the claims. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A chemical ionization mass spectrometry method for offline organic aerosol sample analysis, characterized in that, Includes the following steps: Step 1) Sample preparation: Take an offline 47 mm quartz filter membrane atmospheric particulate matter sample and cut a 2-7 mm sample from the quartz filter membrane using a filter membrane punch heated to 500℃; select two clean, unused filter membranes with a diameter of 25 mm that have been heated to 200℃ for 30 min, and sandwich the cut sample between the two clean filter membranes to fix the filter membranes. Step 2) Sample heating: The sample treated in Step 1) is heated to 200°C using a non-linear heating program. After the heating phase, it is kept at 200°C for 20 min for isothermal desorption so that the signal returns to the background level. Step 3) Data Processing: The sample heated in Step 2) is processed. Considering the nonlinear relationship between signal and desorption concentration caused by nonlinear heating, the signal for each species i obtained by chemical ionization mass spectrometry needs to be corrected for desorption before being re-obtained, as shown in Equation I below: Equation I; In formula I: I 样品,i,j This represents the difference between the signal intensity of compound i at temperature j and the signal intensity of the blank sample during non-uniform heating; I 脱附修正,i,j dT represents the integral of the correction signal from the temperature range T-ΔT to T; dT ​​is the unit minute temperature interval of the integral within the temperature integration range, which is 0.1~0.2℃; ΔT is the temperature interval, which is 2~3℃. Step 4) Background subtraction: Subtract the hot background signal using the hot background multiplication method or the hot background inference method; Step 5) After background subtraction in step 4), the sample is desorbed by hot nitrogen purging. Then, the mass spectrometry signals of various organic components in the sample at different temperatures are analyzed by chemical ionization mass spectrometry. This allows us to obtain the molecular formula information of the compounds in the sample aerosol and the corresponding thermal desorption curves.

2. The chemical ionization mass spectrometry analysis method for offline organic aerosol samples according to claim 1, characterized in that, Step 1) The material of the clean, unused filter membrane is Teflon or quartz.

3. The chemical ionization mass spectrometry analysis method for offline organic aerosol samples according to claim 1, characterized in that, Step 2) The heating program is as follows: from room temperature to 60°C, the heating rate is 5°C / min, and the time is 8min; then from 60°C to 105°C, the heating rate is 3°C / min, and the time is 15min; finally, from 105°C to 200°C, the heating rate is 8°C / min, and the time is 12min.

4. The chemical ionization mass spectrometry analysis method for offline organic aerosol samples according to claim 1, characterized in that, Step 4) The thermal background multiplication method is as follows: The last 1.5 to 3 minutes of the heating cycle is used as a reference time period. Based on the ratio between the mass spectrometry signals in the reference time period, the ambient blank signal is multiplied to the thermal background concentration of the sample signal to obtain the sample signal after removing the thermal background at different time periods, as shown in Equation II below: Formula II; In formula II: I 环境样品,ij I represents the signal intensity of compound i in the environmental sample at temperature j. 环境空白,ij The signal intensity of compound i in the environmental blank sample at temperature j; the time range t1 to t2 refers to the entire thermal desorption phase of the sample; the time range t3 to t4 refers to the reference time period, i.e. the last 1.5 to 3 minutes of the heating cycle; The integral signal intensity of compound i in the environmental sample during the entire thermal desorption phase is denoted as . The integral signal intensity of compound i in the environmental blank sample during the entire thermal desorption phase is given. The integral signal intensity of compound i in the environmental sample over the reference time period; The integral signal intensity of compound i in the environmental blank sample during the reference time period is given.

5. The chemical ionization mass spectrometry analysis method for offline organic aerosol samples according to claim 1, characterized in that, Step 4) The thermal background inference method is as follows: For each thermal image of each compound, a background thermal image is determined, called the thermal baseline. The pre-averaging time of the thermal image data is set to 4 to 6 data points of the original time resolution to reduce noise in the thermal baseline calculation. The field blank is handled in the same way; the signal Is after background subtraction of compound i 扣除基线,i As shown in Equation III below: Formula III; In Formula III: I 环境样品,ij I represents the concentration signal of species i in the environmental sample at time j. 环境空白,ij The concentration signal of species i at time j in the environmental blank; the time range t1 to t2 refers to the sample throughout the entire thermal desorption phase; The integral signal intensity of compound i in the environmental sample during the entire thermal desorption phase is denoted as . The integral signal intensity of compound i in the environmental blank sample during the entire thermal desorption phase is given. Is 样品拟合基线,i Is 环境空白拟合基线,i The total baseline signal intensity is obtained by integrating species i throughout the entire thermal desorption phase in the environmental sample and the environmental blank sample, respectively.

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