US-12618815-B2 - Atmospheric aerosol inorganic and organic nitrogen quantification method and system

Abstract

A method of atmospheric inorganic and organic nitrogen quantification is disclosed. The ambient air is sampled by drawing it through an inlet followed by a denuder to reduce positive artifacts. After artifact removal, the air sample is collected onto a filter. The filter is subjected to thermal evolution under stepwise temperature program to generate a gaseous product mixture. In the presence of oxygen-containing carrier gas, the gaseous product mixture is oxidized to form oxidized gaseous products of CO 2 and nitrogen oxides. Then, the nitrogen oxides products are processed to form an NO product and reacted with ozone to form an excited NO 2 * molecule. By quantifying the intensity of fluorescence, the concentration of NO 2 * molecule is measured, which determines the nitrogen content in the aerosol sample. The differentiation of inorganic and organic nitrogen is achieved through processing the thermally evolved carbon and nitrogen signals using multivariate curve resolution data treatment.

Inventors

• Jianzhen YU
• Xu Yu
• Jinjian LI
• Qianfeng LI
• Xiaohui HUANG

Assignees

• THE HONG KONG UNIVERSITY OF SCIENCE AND TECHNOLOGY

Dates

Publication Date

20260505

Application Date

20221005

Claims (16)

1. 1 . An atmospheric aerosol inorganic and organic nitrogen quantification method, comprising: sampling an ambient air by drawing it though an inlet to obtain an air sample; reducing positive artifacts caused by the adsorption of gas-phase compounds of the air sample by a parallel-plate filter denuder; filtering the air sample to collect an aerosol product; thermally evolving the aerosol product through a stepwise temperature program to obtain a gaseous product mixture, wherein the stepwise temperature program is a heating program with a plurality of progressive heating temperatures; oxidizing the gaseous product mixture with an oxygen-containing carrier gas to generate oxidized gaseous products, wherein the gaseous product mixture is oxidized to the oxidized gaseous products under 840-870° C. in the presence of oxygen and MnO 2 catalyst, and wherein the oxidized gaseous products comprise a CO 2 product and nitrogen oxides products and the oxidized gaseous products are split and subjected into two paths, wherein one path is directed to a carbon detector for detecting a carbon amount and generating a C signal and the other path is directed to a NOx analyzer comprising a NO convertor for transforming the nitrogen oxides products into an NO product; forming the NO product from the nitrogen oxides products in the NO converter; reacting the NO product with ozone to produce an excited NO 2 * molecule for causing a chemiluminescent reaction; and detecting and quantifying a fluorescence emitted during the chemiluminescent reaction to obtain an intensity value of the fluorescence; wherein the intensity value of the fluorescence represents a total nitrogen mass concentration as a N signal of ambient nitrogenous aerosols.
2. 2 . The method of claim 1 , wherein the inlet has an aerosol size cut cyclone and the ambient air is drawn at a flow rate of at least 8.0 L/min.
3. 3 . The method of claim 1 , wherein the plurality of progressive heating temperatures comprises: 150° C., 180° C., 300° C., 400° C., 500° C. and 800° C.
4. 4 . The method of claim 1 , wherein the carbon detector is a non-dispersive infra-red (NDIR) detector that monitors CO2 product and measures the carbon amount of the CO 2 product to generate the C signal or a flame ionization detector (FID) that converts the CO 2 product to a CH 4 product and measures the carbon amount of the CH 4 product to generate the C signal.
5. 5 . The method of claim 4 , wherein a C/N signal ratio is calculated to evaluate whether the N signal is dominated by inorganic nitrogen or organic nitrogen.
6. 6 . The method of claim 5 , wherein the C signal and N signal are processed to resolve overlapping peaks by using a multivariate curve resolution (MCR) tool.
7. 7 . The method of claim 1 , wherein the NO convertor is a molybdenum convertor.
8. 8 . The method of claim 1 , wherein a flow-adjustable needle valve is deployed on the path to the NO x analyzer.
9. 9 . The method of claim 1 , wherein a calibration curve is constructed by a standard solution containing both carbon and nitrogen.
10. 10 . An atmospheric aerosol inorganic and organic nitrogen quantification system, comprising: an inlet for intaking atmospheric air samples; a denuder for reducing positive artifacts caused by the adsorption of gas-phase compounds of the atmospheric air samples to obtain an aerosol product; tandem aerosol sample heating ovens having a front oven for thermally evolving the aerosol product by a stepwise temperature heating program to obtain a gaseous product mixture and a back oven for oxidizing the gaseous product mixture with an oxygen-containing carrier gas to generate oxidized gaseous products, wherein the stepwise temperature program is a heating program with a plurality of progressive heating temperatures; a carbon detector for performing carbon measurement of a portion of the oxidized gaseous products; a NOx analyzer having a NO convertor for converting another portion of the oxidized gaseous products into an NO product; a needle valve for adjusting a flow rate of the oxidized gaseous products subjected to the NO x analyzer; an ozonator for generating ozone; a reaction chamber for reacting the NO product with the ozone to produce excited NO2* molecules which emit fluorescence light for quantification; and a fluorescence quantification module for evaluating and quantifying the fluorescence light to obtain a fluorescence intensity and correlating the fluorescence intensity to a concentration of the excited NO2* molecules; wherein the tandem aerosol sample heating ovens are connected to the carbon detector, the tandem aerosol sample heating ovens are also connected to the NOx analyzer through the needle valve; and wherein the reaction chamber is connected to the ozonator, the NO convertor and the fluorescence quantification module.
11. 11 . The system of claim 10 , wherein the inlet has an aerosol size cut cyclone and intakes the atmospheric air samples at a flow rate of at least 8.0 L/min.
12. 12 . The system of claim 10 , wherein the denuder is a parallel plate filter denuder.
13. 13 . The system of claim 10 , wherein the oxygen-containing carrier gas is He/O 2 .
14. 14 . The system of claim 10 , wherein the NO convertor is a molybdenum catalytic convertor.
15. 15 . The system of claim 10 , wherein the carbon detector is a nondispersive infrared detector or a flame ionization detector.
16. 16 . The system of claim 10 , wherein the system further comprises a data logging module for analyzing, calculating, and saving the fluorescence intensity, a temperature control module for adjusting and controlling the stepwise temperature heating program of the front oven and the temperature of back oven, and a controller to control the data logging module and the temperature control module.

Description

CROSS-REFERENCE OF RELATED APPLICATIONS This present application claims the benefit of U.S. Provisional Patent Application No. 63/252,179 filed on Oct. 5, 2021, which is incorporated by reference herein in its entirety. FIELD OF THE INVENTION The present invention generally relates to environmental science fields. More specifically, the present invention relates to simultaneous quantification of inorganic and organic nitrogenous aerosols in atmosphere. BACKGROUND OF THE INVENTION As an important source of fixed nitrogen and a limiting nutrient in the biogeochemical cycling, nitrogenous aerosols, including inorganic nitrogen (IN) and organic nitrogen (ON), are crucial in controlling primary production in the biosphere (Elser et al., 2007; Gruber and Galloway, 2008). The major inorganic nitrogen species in atmosphere are ammonium (NH4+) and nitrate (NO3−). Organic nitrogen includes a wide variety of nitrogen-containing organics in a reduced form, such as urea, amino acid, alkyl amines, and N-heterocyclic compounds, or in an oxidized form, like organic nitrates and nitro-aromatic compounds. However, excess nitrogen is a serious threat to the ecosystem and biodiversity by causing soil acidification, aquatic eutrophication, and stratospheric ozone depletion (Fenn et al., 1998; Gruber and Galloway, 2008). This is also why the environmental impacts of nitrogenous aerosols have attracted wide attention. Given such importance, quantitative understanding of the ambient abundance and chemical characteristics of atmospheric nitrogenous aerosols is required. While the quantification of aerosol inorganic nitrogen species has been well established and routinely conducted by ion chromatography (IC), accurate and precise determination of the bulk organic nitrogen remains a challenge. In principle, one approach to determine bulk organic nitrogen concentration is to estimate by subtracting the inorganic nitrogen concentration from the total nitrogen concentration, where inorganic nitrogen is the sum of nitrate-nitrogen (NO3−—N) and ammonium-nitrogen (NH4+—N) concentration measured by IC analysis. In practice, the quantification of total nitrogen is executed by using a total nitrogen analyzer to analyze water extraction of aerosol sample. In such a total nitrogen analyzer, all the nitrogen-containing components in the water extract are converted to measurable inorganic forms. By this approach, the total nitrogen value stands for the water-soluble part of the sample. Therefore, the bulk organic nitrogen concentration determined by the above method is the water-soluble organic nitrogen (WSON) concentration. There is a lack of analyzing the water-insoluble part of organic nitrogen. This difference method has two major uncertainties: (1) WSON concentration is a derivative value (Cornell et al., 2003; Russell et al., 2003); and (2) the sampling losses and possible incomplete conversion of organic nitrogen to inorganic components result in bias for WSON quantification (Bronk et al., 2000; Mace and Duce, 2002). And these limitations often lead to a negative value of obtained WSON concentration, which has been reported in many studies covering various geographical locations such as China (Yu et al., 2020), Atlantic Ocean (Lesworth et al., 2010) and the eastern Mediterranean (Tsagkaraki et al., 2021). A few studies determined aerosol water-insoluble organic nitrogen (WION) based on the difference between total nitrogen measured by an elemental analyzer and water-soluble total nitrogen (WSTN) measured by a total nitrogen analyzer (Miyazaki et al., 2011; Pavuluri et al., 2015). However, this method has comparatively large uncertainties in WION quantification (16%) due to the propagated errors (Miyazaki et al., 2011). Due to a lack of a direct method to analyze WION, the majority of current aerosol organic nitrogen studies focus on the WSON fraction despite the contribution of WION to bulk organic nitrogen can be also significant (Bhattarai et al., 2019). Therefore, a reliable quantification of inorganic and organic nitrogenous aerosols without considering water solubility is desired in this field. The present invention addresses this need. SUMMARY OF THE INVENTION In accordance with a first aspect of the present invention, an atmosphere nitrogen quantification method is provided. First, ambient air is sampled by drawing it though an inlet to obtain an air sample. The air sample is further processed to reduce positive artifacts. After artifact removal, the air sample is filtered to collect an aerosol sample. A stepwise temperature program is conducted to thermally desorb the aerosol sample to obtain a gaseous product mixture. Using an oxygen-containing carrier gas, the gaseous product mixture is oxidized to generate oxidized gaseous products, which will be further processed to form an NO product. The NO product is reacted with ozone to produce an excited NO2* molecule for causing a chemiluminescent reaction. The excited NO2* molecule can