Chemical ionization mass spectrometry method for off-line organic aerosol sample

Abstract

The invention discloses a chemical ionization mass spectrometry method for an off-line organic aerosol sample, and aims to realize rapid and accurate measurement of a polar atmospheric organic aerosol sample. The method comprises the following steps: firstly, treating an off-line atmospheric particulate sample, intercepting a sample with the size of 2-7mm, and clamping the sample between two clean filter membranes to fix the sample; then, heating the sample by adopting a nonlinear temperature rising program, and collecting data after heating; a thermal background signal is deducted through a thermal background multiplication method or a thermal background inference method, so that the accuracy of data is ensured; and finally, after hot nitrogen purging desorption, analyzing mass spectrum signals of various organic components of the sample at different temperatures through chemical ionization mass spectrometry to obtain molecular composition information and a thermal desorption curve of compounds in the sample aerosol. The method is simple and convenient to operate, can effectively analyze the chemical components of the polar organic aerosol, is suitable for off-line sample analysis of atmospheric aerosol, and has relatively high popularization and application values.

Description

Technical Field

[0001] The invention belongs to the technical field of mass spectrometry analysis, and in particular relates to a chemical ionization mass spectrometry analysis method for off-line organic aerosol samples. Background Art

[0002] Chemical ionization mass spectrometry (CIMS) coupled with thermal desorption is currently a widely used method for online analysis of the molecular composition of organic aerosols. This method collects particles on a Teflon filter and uses high-purity nitrogen to perform thermal desorption under linear heating conditions from room temperature to 200°C. The molecular composition information of the evaporated inorganic and organic aerosol compounds is then analyzed using a chemical ionization mass spectrometer. Although this technology can provide high-resolution molecular composition information, its design, which is mainly used for online analysis, limits its wide application.

[0003] Online CIMS technology requires the deployment of complex mass spectrometers at stable observation sites, and its long-term maintenance requires a lot of human and financial resources. Therefore, this technology can usually only be deployed at a specific location for a short period of time (usually lasting a few weeks to a few months), and it is difficult to achieve long-term monitoring or simultaneous measurement at multiple locations.

[0004] Based on this, the development of a suitable offline filter membrane analysis method is of practical significance for the analysis of organic aerosols using chemical ionization mass spectrometry. However, the analysis of offline filter membrane samples using chemical ionization mass spectrometry coupled thermal desorption method needs to overcome the following problems: (1) Although the offline Teflon filter membrane can effectively reduce gas phase interference, it is inconvenient to cut and is very easy to clog under high concentration sampling conditions, which limits its application in offline analysis; (2) The online sampling time is short, and the sample amount is usually less than 1μg, while the offline sampling time of urban atmospheric particulate matter is usually more than 12h, and the sample amount can reach more than 10mg. The existing methods are difficult to directly apply to offline sample analysis; (3) A large amount of ammonium nitrate in urban atmospheric particulate matter decomposes during the thermal desorption process, which will consume the reagent ions of chemical ionization mass spectrometry and seriously affect the analysis results of organic aerosols; (4) The thermal background signal is significantly increased during the offline thermal desorption analysis, and an effective background subtraction method needs to be developed to obtain accurate analysis results. Summary of the invention

[0005] In view of the deficiencies of the prior art, the present invention provides a chemical ionization mass spectrometry analysis method for off-line organic aerosol samples, which can achieve rapid and accurate measurement of polar atmospheric organic aerosol samples.

[0006] The present invention is achieved through the following technical solutions:

[0007] A chemical ionization mass spectrometry analysis method for off-line organic aerosol samples comprises the following steps:

[0008] Step 1) Sample processing: Take the offline 47mm quartz filter atmospheric particulate matter sample and use a filter gun heated at 500℃ to cut a sample of 2-7mm size on the quartz filter; select two clean unused filter membranes with a diameter of 25mm and heated at 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 nonlinear temperature ramp program. After the heating stage, the sample is kept at 200°C for 20 minutes for constant temperature desorption so that the signal returns to the background level.

[0010] Step 3) Data processing: Data processing is performed on the sample heated in step 2). Considering the nonlinear relationship between signal and desorption concentration caused by nonlinear heating, for each species i obtained by chemical ionization mass spectrometry, the signal needs to be corrected by desorption and then re-obtained, as shown in the following formula I:

[0011]

[0012] In formula I: I 样品,i,j It represents the signal intensity of compound i at temperature j minus the signal intensity of blank sample during the non-uniform heating process; I 脱附修正,i,j Represents the integral of the correction signal from the temperature range T-ΔT to T; dT ​​is the small temperature interval of the integral unit within the temperature integral range, which is 0.1-0.2°C; ΔT is the temperature interval, which is 2-3°C;

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

[0014] Step 5) After the background is subtracted in step 4), the sample is desorbed by hot nitrogen purge, and the mass spectrometry signals of various organic components of the sample at different temperatures are analyzed by chemical ionization mass spectrometry to obtain the molecular composition information and thermal analysis curve of the compounds in the sample aerosol.

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

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

[0017] Preferably, the thermal background multiplication method in step 4) is as follows: the last 1.5 to 3 minutes of the heating cycle is used as a reference time period, and the blank signal of the environmental sample is multiplied to the thermal background concentration of the sample signal according to the ratio between the mass spectrometry signal ratios in the reference time period, to obtain the sample signals with thermal background removed in different time periods, as shown in the following formula II:

[0018]

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

[0020] Preferably, the thermal background inference method in step 4) is as follows: a background thermal image is determined for each thermal image of each compound, called thermal baseline Is 热基线 The pre-average time of the thermal image data was set to 4 to 6 data points of the original time resolution to reduce noise in the thermal baseline calculation; the field blank was processed in the same way; the blank of compound i was subtracted from the signal Is 扣除基线,i As shown in the following formula III:

[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 is the concentration signal of species i in the sample at time j; I 环境空白,i,j Is is 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 are the total baselines integrated during the entire heating analysis for the i-species sample and the ambient blank, respectively.

[0025] The present invention provides a method for analyzing an offline filter membrane with high load, high sampling time and high inorganic ion interference using a gas aerosol chemical ionization mass spectrometer, which has significant technical advantages and practical application effects. The specific beneficial effects are as follows:

[0026] (1) High repeatability and stability: When using quartz filter membrane, the repeatability of integrated signal intensity can be controlled within ±9%; when using 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 gas aerosol mass spectrometry concentration-signal response relationship, and is suitable for the analysis of samples with an organic aerosol concentration range of 0.05 to 0.1 μg, and can meet the detection requirements 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 organic aerosol, sulfate and nitrate chemical components measured by the aerosol mass spectrometer, and the correlation coefficient Rsp reaches 0.94-0.95, which verifies the accuracy and reliability of the method.

[0029] (4) Optimized thermal desorption performance: A non-uniform ramp-up program was used to calibrate the highest signal temperature (T) of the desorption thermogram. 最高信号温度 ), compared with the T of the traditional uniform rising heating method 最高信号温度 There is a high correlation (correlation coefficient Rsp: 0.72-0.84). For species that account for more than 50% of the total compounds, T 最高信号温度 The error of the value can be controlled within 5°C (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 time (such as 12h and 24h), which is much longer than the sampling time 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 avoiding interference: The method of the present invention can effectively avoid interference from inorganic ion signals and thermal background effects by optimizing filter membrane selection, temperature rise program and background subtraction method, thereby significantly improving the accuracy and applicability of offline sample analysis.

[0032] In summary, the method of the present invention shows significant advantages in repeatability, linear response, accuracy, thermal desorption performance and applicability, and provides an efficient and reliable technical means for the analysis of offline filter membrane samples with high load and long sampling time, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1This is a schematic diagram of the “sandwich method” aerosol sample injection in Example 1;

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

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

[0036] Figure 3 It is a schematic diagram of converting the nonlinear temperature program heating curve in Example 1 into a linear temperature program curve;

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

[0038] Figure 5 is the repetition rate of the sample when the organic aerosol concentration is 1 μg (A) and 0.1 μg (B) in Example 2;

[0039] Figure 6 This is a graph showing the relationship between different cross-sectional areas and their signals on the same Teflon filter membrane sample in Example 3. DETAILED DESCRIPTION

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

[0041] Example 1

[0042] A chemical ionization mass spectrometry analysis method for off-line organic aerosol samples, the specific steps are as follows:

[0043] (1) Sample preparation

[0044] like Figure 1 As shown, the sample can be selected as an offline 47mm quartz filter atmospheric particulate matter sample, and a filter gun 1 heated at 500°C is used to intercept a 2-7mm sample 3 (the organic aerosol injection amount is 0.1-1μg) on ​​the quartz filter 2, and the filter load is reduced by intercepting a small amount of the filter. Two clean unused Teflon or quartz filter membranes with a diameter of 25mm and heated at 200°C for 30 minutes are selected, and the intercepted sample 3 is sandwiched between two clean filter membranes 4 to fix the filter membrane (this method is named "sandwich method" in the present invention). The entire "sandwich method" sample 5 after fixation will desorb the organic aerosol in the sample 3 by heating.

[0045] (2) Sample heating

[0046] Since ammonium nitrate accounts for a high proportion of atmospheric particulate matter, the large amount of nitric acid produced after thermal decomposition will greatly interfere with the analysis of organic aerosols. The "sandwich method" will not use the traditional linear heating method when heating samples, but will use nonlinear heating of organic matter. The nonlinear heating method is used to reduce the consumption of chemical ionization mass spectrometry reagent ions by secondary inorganic ions in fine particles. The main principle is: when the ammonium nitrate decomposition temperature is 60-105°C, a lower heating rate is used to reduce the large consumption of reagent ions by nitric acid gas caused by the decomposition of a large amount of ammonium nitrate. For example Figure 2 As shown, the specific heating program is:

[0047] The temperature was raised from room temperature (about 25°C) to 60°C at a rate of 5°C / min, which took 8 minutes; then from 60°C to 105°C at a rate of 3°C / min, which took 15 minutes; and finally from 105°C to 200°C at a rate of 8°C / min, which took 12 minutes. After the temperature rise stage, the desorption was kept at 200°C for 20 minutes to allow the signal to return to the background level.

[0048] (3) Data processing

[0049] The heated samples are processed, such as Figure 3 As shown, the nonlinear temperature program heating curve is converted into a linear temperature program curve, and the temperature integration method is used to reconstruct the thermal desorption curve under the nonlinear temperature program. Considering the nonlinear relationship between signal and desorption concentration caused by nonlinear temperature increase, for each species i obtained by chemical ionization mass spectrometry, the signal needs to be corrected by desorption and then re-obtained, as shown in the following formula I:

[0050]

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

[0052] (4) Background subtraction

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

[0054] (4-1) Thermal background multiplication method

[0055] like Figure 4As shown in A, the thermal background signal is deducted by the doubling method. In order to scale the thermal background signal to the ratio of the environmental sample and blank sample signals during the reference period, the environmental sample blank signal can be multiplied to the thermal background concentration of the sample signal according to the ratio between the mass spectrometry signal ratios during the reference period after the constant temperature desorption process (for example, the last 1.5 to 3 minutes of the heating cycle) as the reference time period, and the thermal background sample signal is removed at different time periods. The specific formula is shown in the following formula II:

[0056]

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

[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 the background concentration based on the concentration time series of the pollutant (by determining the background spline at different time intervals). The background baseline of the thermal image can be determined by referring to the literature of Wang et al. (DOI: 10.1021 / acs.est.8b01914). In the specific implementation of determining the background, the pre-averaging time of the thermal image data can be set to 4 to 6 data points of the original time resolution (for example, 1.8 minutes) to reduce the noise in the thermal baseline calculation. The field blank is processed in the same way (such as Figure 4 Therefore, the blank of compound i is subtracted from the signal Is 扣除基线,i As shown in the following formula III:

[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,jis the concentration signal of species i in the sample at time j; I 环境空白,i,j Is is 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 are the total baselines integrated during the entire heating analysis for the i-species sample and the ambient blank, respectively.

[0064] (5) After background subtraction, Figure 1 As shown, after purging and desorption with hot high-purity nitrogen 6, the mass spectral signals of various organic components of the sample at different temperatures are analyzed by chemical ionization mass spectrometry, and the molecular composition information and thermal analysis curves of more than 1000 compounds in the sample aerosol can be analyzed.

[0065] Example 2

[0066] A chemical ionization mass spectrometry analysis method for off-line organic aerosol samples, the specific steps are as follows:

[0067] (1) Sample preparation

[0068] Similar to Example 1, two 47 mm quartz filter membrane atmospheric particulate matter samples with different organic aerosol loads were selected, and three groups of 2 mm size samples were intercepted, and the intercepted organic aerosol samples were 0.1 μg and 1 μg respectively. The whole fixed sample was heated to desorb the organic aerosol in the sample using the "sandwich method".

[0069] Two 47 mm Teflon filter membrane atmospheric particulate matter samples with different organic aerosol loads of 0.1 μg and 1 μg were selected, and three groups of 2 mm size samples were intercepted and the same operation was performed ("sandwich method").

[0070] (2) Sample heating

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

[0072] (3) Data processing

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

[0074] (4) Background subtraction

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

[0076] (5) Repeatability test data analysis

[0077] In data analysis, more than 1000 species signals from three repeated tests were compared with their average values ​​to obtain the frequency distribution of sample repeatability.

[0078] like Figure 5 As shown, it was detected that when the organic aerosol concentration in the sample was 1 μg ( Figure 5 In A), using quartz filter membrane as sampling filter membrane can achieve the repeatability of integrated signal intensity within ±9%, and using Teflon filter membrane as sampling filter membrane can achieve the repeatability within 18%; under the condition of sample organic aerosol concentration of 0.1μg ( Figure 5 In B), using a quartz filter membrane as a sampling filter membrane can achieve a repeatability of the integrated signal intensity within ±25%, and using a Teflon filter membrane as a sampling filter membrane can achieve a repeatability of 31%.

[0079] Example 3

[0080] A chemical ionization mass spectrometry analysis method for off-line organic aerosol samples, the specific steps are as follows:

[0081] (1) Sample preparation

[0082] As in Example 1, an organic aerosol 47mm Teflon filter atmospheric particulate matter sample was selected, and samples of 2mm, 3mm, 4mm, and 7mm sizes were intercepted, and the corresponding intercepted organic aerosol sample amounts were 1.2μg, 2.7μg, 4.8μg, and 15μg, respectively. The "sandwich method" was used to heat the fixed whole sample to desorb the organic aerosol in the sample.

[0083] (2) Sample heating

[0084] The same heating program as in Example 1 was selected to heat the Teflon filter membrane samples respectively.

[0085] (3) Data processing

[0086] The same data processing method as in Example 1 was selected to process data of more than 1000 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 perform background subtraction on the Teflon filter membrane samples. This example uses the thermal background inference method.

[0089] (5) Experimental results

[0090] The relationship between the signal of different interception areas and their signals on the same Teflon filter membrane sample, namely 3mm (2.7μg), 4mm (4.8μg) and 7mm (15μg) and 2mm (1.2μg) samples is shown in the figure. Figure 6 As shown, it is shown that when the injection concentration changes by more than one order of magnitude, the concentration-signal still has a good linear response relationship (the Spearman rank correlation coefficient Rsp is above 0.95).

[0091] Example 4

[0092] In this embodiment, when analyzing offline samples, conventional means and the method of the present invention are used for comparison in the sample heating procedure and data processing, respectively. The specific steps are as follows:

[0093] (1) Sample preparation

[0094] As in Example 1, an organic aerosol 47 mm Teflon filter atmospheric particulate matter sample was selected, and two 2 mm size samples (corresponding to 1.2 μg of organic aerosol sample) were intercepted, divided into sample A and sample B. The two fixed samples were heated and desorbed from the organic aerosol using the "sandwich method".

[0095] (2) Sample heating

[0096] ① Sample A adopts a nonlinear heating program, that is, the same heating program as Example 1 is selected to heat Sample A.

[0097] ② Sample B adopts a linear heating program, that is, sample B is heated from room temperature to 200°C at a constant heating rate of 6°C / min.

[0098] (3) Data processing

[0099] ① The same background subtraction method as in Example 1 was used to perform background subtraction on sample A. That is, the temperature integration method was used to reconstruct the thermal desorption curve under the nonlinear temperature increase program. Considering the nonlinear relationship between signal and desorption concentration caused by nonlinear temperature increase, for each species i obtained by chemical ionization mass spectrometry, the signal needs to be corrected by desorption and then re-obtained, as shown in the following formula I:

[0100]

[0101] In formula I: ΔT is 2°C, dT is 0.1°C.

[0102] ② A linear temperature ramp program was used to directly analyze sample B, and the relationship between 1000 organic aerosol signals at different temperatures.

[0103] (4) Background subtraction

[0104] The same data processing method as in Example 1 was selected to perform background subtraction processing on more than 1000 organic aerosol species in Sample A and Sample B. This example uses the thermal background multiplication method.

[0105] (5) Experimental results

[0106] The maximum signal temperature (T 最高信号温度 ) is usually used to characterize the volatility of a species. In previous studies, it has been shown that there is an exponential relationship between it and the saturated vapor pressure of the species. In this example, the non-uniform heating program (sample A) is compared with the corrected T 最高信号温度 T with uniform rising heating program (sample B) 最高信号温度 After correction, the nonlinear temperature program and the linear temperature program (correlation coefficient Rsp: 0.72-0.84) were compared in more than 1000 organic species, and more than 50% of them could be compared in repeated tests. 最高信号温度 The value error is within 5°C (correlation coefficient Rsp: 0.87~0.93).

[0107] The embodiments described above are only some embodiments of the present invention, rather than all embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. The scope of protection of the present invention shall be subject to the scope required by the claims. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work shall fall within the scope of protection of the present invention.

Claims

1. A chemical ionization mass spectrometry method for off-line organic aerosol samples, characterized in that: The following steps are involved: Step 1) Sample processing: Take the offline 47mm quartz filter atmospheric particulate matter sample and use a filter gun heated at 500℃ to cut a sample of 2-7mm size on the quartz filter; select two clean unused filter membranes with a diameter of 25mm and heated at 200℃ for 30min, 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 nonlinear temperature ramp program. After the heating stage, the sample is kept at 200°C for 20 minutes for constant temperature desorption so that the signal returns to the background level. Step 3) Data processing: Data processing is performed on the sample heated in step 2). Considering the nonlinear relationship between signal and desorption concentration caused by nonlinear heating, for each species i obtained by chemical ionization mass spectrometry, the signal needs to be corrected by desorption and then re-obtained, as shown in the following formula I: In formula I: I 样品,i,j It represents the signal intensity of compound i at temperature j minus the signal intensity of blank sample during the non-uniform heating process; I 脱附修正,i,j Represents the integral of the correction signal from the temperature range T-ΔT to T; dT ​​is the small temperature interval of the integral unit within the temperature integral range, which is 0.1-0.2°C; ΔT is the temperature interval, which is 2-3°C; Step 4) Background subtraction: subtract the thermal background signal using the thermal background multiplication method or the thermal background inference method; Step 5) After the background is subtracted in step 4), the sample is desorbed by hot nitrogen purge, and the mass spectrometry signals of various organic components of the sample at different temperatures are analyzed by chemical ionization mass spectrometry to obtain the molecular composition information and thermal analysis curve of the compounds in the sample aerosol.

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

3. The chemical ionization mass spectrometry analysis method for off-line organic aerosol samples according to claim 1, characterized in that: The heating procedure of step 2) is as follows: from room temperature to 60°C, the heating rate is 5°C / min, and it takes 8 minutes; then from 60°C to 105°C, the heating rate is 3°C / min, and it takes 15 minutes; finally, from 105°C to 200°C, the heating rate is 8°C / min, and it takes 12 minutes.

4. The chemical ionization mass spectrometry analysis method for off-line 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, and the blank signal of the environmental sample is multiplied to the thermal background concentration of the sample signal according to the ratio of the mass spectrometry signal ratio in the reference time period to obtain the sample signal with the thermal background removed in different time periods, as shown in the following formula II: In formula II: I 样品,i,j is the signal intensity of sample compound i at temperature j; I 环境空白,i,j Is is the signal intensity of compound i in the environmental blank sample at temperature j; 环境样品,i is the total integrated signal intensity of compound i in the environmental sample from time t1 to t2; Is 空白样品,i is the total integrated signal intensity of compound i in the blank sample from t1 to t2.

5. The chemical ionization mass spectrometry analysis method for off-line organic aerosol samples according to claim 1, characterized in that: Step 4) The thermal background inference method is as follows: a background thermal image is determined for each thermal image of each compound, called the thermal baseline Is 热基线 ,The pre-averaging time of the thermal image data was set to 4 to 6 data points of the original time resolution to reduce noise in the thermal baseline calculation; the field blanks were processed in the same way; Blank minus signal Is of compound i 扣除基线,i As shown in the following formula III: In formula III: I 样品,i,j is the concentration signal of species i in the sample at time j; I 环境空白,i,j Is is 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 are the total baselines integrated during the entire heating analysis for the i-species sample and the ambient blank, respectively.

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