Open AccessNitrate Isotopic Composition in Precipitation at a Chinese Megacity: Seasonal Variations, Atmospheric Processes, and Implications for Sources
Author(s) -
Li Zhengjie,
Walters Wendell W.,
Hastings Meredith G.,
Zhang Yanlin,
Song Linlin,
Liu Dongwei,
Zhang Wenqi,
Pan Yuepeng,
Fu Pingqing,
Fang Yunting
Publication year - 2019
Publication title -
earth and space science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.843
H-Index - 23
ISSN - 2333-5084
DOI - 10.1029/2019ea000759
Subject(s) - coal combustion products , fractionation , combustion , environmental chemistry , deposition (geology) , environmental science , seasonality , nitrate , isotope fractionation , atmospheric sciences , nitrogen , precipitation , coal , pollution , chemistry , meteorology , geology , paleontology , ecology , statistics , physics , mathematics , organic chemistry , sediment , biology
Abstract Nitrogen stable isotope composition (δ 15 N) of nitrate (NO 3 − ) deposition can aid in source apportionment of its precursor emissions, nitrogen oxides (NO x ), with implications in mitigation policy to address serious air pollution. However, potential δ 15 N fractionation during atmospheric NO 3 − formation may hinder accurate quantification of NO x contributions. Previously, NO x photochemical reactions have been suggested to be the dominant δ 15 N fractionation process in NO 3 − formation. Here, we have quantified the potential fractionation effects associated with NO x photochemical reactions based upon δ 15 N‐NO 3 − measured in 1 year of daily‐based bulk deposition samples in Shenyang, a megacity with distinct seasonal fossil fuel combustion in northeastern China. The mean δ 15 N was 0.9 ± 4.0‰ and ranged from −4.9 to 8.3‰, with the lowest and highest values observed during summer and winter, respectively. Calculated NO x photochemical equilibrium fractionation may account for up to 42% of the observed seasonal δ 15 N change in NO 3 − deposition. However, the relative NO x source contribution trends, estimated based upon a δ 15 N Bayesian mixing model, were insensitive to NO x photochemical fractionation considerations. Overall, NO x source partitioning based upon averaged year‐long δ 15 N of bulk NO 3 − deposition estimated the following relative trend in NO x emission sources: coal combustion > biomass burning = vehicle emissions ≫ soil emissions. Seasonally, the increase of coal combustion emissions from summer to winter drives the seasonality of δ 15 N in NO 3 − deposition, indicating a necessity to control NO x emissions from coal combustion to improve wintertime air quality.