High Contribution of Anthropogenic Combustion Sources to Atmospheric Inorganic Reactive Nitrogen in South China Evidenced by Isotopes

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Atmospheric inorganic nitrogen concentrations and stable nitrogen isotopes in South China

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PM2.5 samples (n=66) were collected from May 2017 to June 2018 in Guangzhou (23.13°N, 113.27°E). Water-soluble ions: NH4+and NO3- were measured by ion chromatography. The blank samples were also analyzed following the same procedure for samples. Reagent blanks (ultrapure water) and quality control standards were measured every 10 samples to detect contamination and drift. The δ15N-NO3- values in PM2.5 was analyzed by methods of nitrous oxide (N2O). Briefly, NO3- was reduced to NO2- using cadmium powder and imidazole solution, and N2O was made by adding NaN3 to NO2- solution. The production of 75nmol N2O gas was needed to measure. The N2O gas produced by above processes was measured by MAT253 stable isotope mass spectrometer. The values of δ15N were expressed in ‰. The δ15N-NO3- values (‰) were corrected by multi-point correction (r2=0.999) based on international standards (IAEA-NO3, USGS32, USGS34, and USGS35). The δ15N-NH4+ was measured by methods of hypobromite oxidation coupled with reduction of hydroxylamine hydrochloride. Briefly, NH4+ was oxidated to NO2- using alkaline hypobromite (BrO-), and N2O was made by adding sodium arsenite and hydrochloric acid to NO2- solution. The production of 120 nmol N2O gas was needed to measure. The N2O gas produced by above processes was measured by MAT253 stable isotope mass spectrometer. The values of δ15N were expressed in ‰. δ15N-NH4+ was corrected by international standards (IAEA-N1, USGS25, and USGS26).

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