1. Isotopic evaluation on relative contributions of major NOx sources to nitrate of PM2.5 in Beijing.
- Author
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Song, Wei, Wang, Yan-Li, Yang, Wen, Sun, Xin-Chao, Tong, Yin-Dong, Wang, Xue-Mei, Liu, Cong-Qiang, Bai, Zhi-Peng, and Liu, Xue-Yan
- Subjects
COAL combustion ,BIOMASS burning ,AIR pollutants ,CARBONACEOUS aerosols ,NITRIC oxide ,NITROGEN isotopes ,SEASONAL temperature variations - Abstract
Nitrate (NO 3
− ) is a key component of secondary inorganic aerosols and PM 2.5. However, the contributions of nitrogen oxides (NO x) emission sources to NO 3− in PM 2.5 remain poorly constrained. This study measured nitrogen (N) isotopes of NO 3− (hereafter as δ15 N-NO 3- ) in PM 2.5 collected at Beijing in 2014. We observed that δ15 N-NO 3- values in PM 2.5 (−2.3‰ − 19.7‰; 7.3 ± 5.4‰ annually) were significantly higher in winter (11.9 ± 4.4‰) than in summer (2.2 ± 2.5‰). The δ15 N differences between source NO x and NO 3− in PM 2.5 (hereafter as Δ values) were estimated by a computation module as 7.8 ± 2.2‰ − 10.4 ± 1.6‰ (8.8 ± 2.4‰). Using the Δ values and δ15 N values of NO x from major fossil (coal combustion, vehicle exhausts) and non-fossil sources (biomass burning, microbial N cycle), contributions of major NO x sources to NO 3− in PM 2.5 were further estimated by the SIAR model. We found that seasonal variations of δ15 N-NO 3- values in PM 2.5 of Beijing were mainly caused by those of NO x contributions from coal combustion (38 ± 10% in winter, 20 ± 9% in summer). Annually, NO x from coal combustion, vehicle exhausts, biomass burning, and microbial N cycle contributed 28 ± 12%, 29 ± 17%, 27 ± 15%, and 16 ± 7% to NO 3− in PM 2.5 , respectively, showing actually comparable contributions between non-fossil NO x (43 ± 16%) and fossil NO x (57 ± 21%). These results are useful for planning the reduction of NO x emissions in city environments and for elucidating relationships between regional NO x emissions and atmospheric NO 3− pollution or deposition. Image 1 • δ15 N-NO 3- values of PM 2.5 in Beijing were higher in winter than in summer. • Seasonal δ15 N-NO 3- variations of PM 2.5 were mainly caused by those of NO x emission from coal combustion. • Fossil and non-fossil NO x sources contributed equally to NO 3− of PM 2.5 in Beijing. Isotope partitioning of major nitrate sources in PM 2.5 [ABSTRACT FROM AUTHOR]- Published
- 2019
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