Isotopic source analysis of nitrogen-containing aerosol: A study of PM2.5 in Guiyang (SW, China)

The source of fine particulate matter (PM2.5) has been a longstanding subject of debate, the nitrogen-15 isotope (delta N-15) has been used to identify the major sources of atmospheric nitrogen. In this study, PM2.5 samples (n = 361) were collected from September 2017 to August 2018 in the urban area of Guiyang (SW, China), to investigate the chemical composition and potential sources of PM2.5. The results showed an average PM2.5 of 33.0 mu g m(-3) +/- 20.0 mu g m-3. The concentration of PM2.5 was higher in Winter, lower in Summer. The major water resolved inorganic ions (WSIIs) were Ca-2(+), NH4+, Na+, SO42 -, NO3-, Cl-. Nitrogen-containing aerosols (i.e., NO3- and NH4+) suddenly strengthened during the winter, when NO3- became the dominant contributor. Over the sampling period, the molar ratio of NH4+/(NO-3 + 2 x SO42 -) ranged from 0.1 to 0.9, thus indicating the full fixation of NH4+ by existing NO3- and SO42 - in PM2.5. The annual value of NOR was 0.1 while rised to 0.5 inWinter. The variations ofNOR (Nitrogen oxidation ratio) (0.1-0.5) values suggest that the secondary formation of NO3- occurred every season and was most influential during the winter. The total particulate nitrogen (TN) gamma N-15 value of PM2.5 ranged from-5.9% to 25.3% over the year with annualmean of+11.8%+/- 4.7%, whereas it was between -5.9% and 14.3% during the winter with mean of 7.0% +/- 3.8%. A Bayesian isotope mixing model (Stable Isotope Analysis in R; SIAR) was applied to analyze the nitrogen sources. The modeling results showed that 29%, 21%, and 40% of TN in PM2.5 during the winter in Guiyang was due to nitrogen-emissions fromcoal combustion, vehicle exhausts, and biomass burning, respectively. Our results demonstrate that biomass burningwas themain contributor to PMduring thewinter, 80% of the airmass comes fromrural areas of Guizhou border, this transport process can increase the risk of particulate pollution in Guiyang. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The study in Guiyang, China revealed that biomass burning is the main contributor to PM2.5, with major water-soluble inorganic ions being dominated by NH4+. In winter, NO3- becomes the major nitrogen contributor, with emissions from coal combustion, vehicle exhaust, and biomass burning identified as the key sources.