Quantifying major NOx sources of aerosol nitrate in Hangzhou, China, by using stable isotopes and a Bayesian isotope mixing model
Quantifying major NOx sources of aerosol nitrate in Hangzhou, China, by using stable isotopes and a Bayesian isotope mixing model
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使用稳定同位素和贝叶斯同位素混合模型量化中国杭州硝酸盐气溶胶的主要氮氧化物来源
DOI：
10.1016/j.atmosenv.2020.117979
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发表时间：
2021-01-01
影响因子：
5
通讯作者：
Li, Feili
中科院分区：
文献类型：
--
作者：
Jin, Zanfang;Qian, Lijing;Li, Feili
人为排放的氮氧化物（NOx）氧化形成硝酸盐（NO3），在大气污染中起着关键作用。以华东典型城市杭州为研究对象，对其氮氧化物来源及其季节变化规律进行了研究。为此，研究人员在2018年12月至2019年11月收集的细颗粒物（PM2.5）和总悬浮颗粒（TSP）气溶胶样本中测量了水溶性无机离子（WSIIs）的化学特征和NO3-的稳定同位素（δ N-15-NO3-和δ O-18-NO3-）。结果发现，杭州PM2.5年平均浓度（69.28 +/- 34.69 μ g/m(3)）超过了中国空气质量标准35.00 μ g/m(3)。结果表明：PM2.5和TSP中WSIIs中NO3-所占比例最大，主要离子主要以NH4NO3、（NH4）(2)SO4、Ca(NO3)(2)、CaSO4等形式存在于气溶胶颗粒中；PM2.5和TSP中NO3-/SO42-比值较高，表明机动车尾气排放已成为杭州市日益重要的气溶胶污染源。杭州的N-15-NO3- δ值在PM2.5中为+1.1 ~ +9.2‰，在TSP中为-1.0 ~ +8.5‰。采用贝叶斯同位素混合模型（SIAR）对杭州地区NOx源进行了定量分析。机动车尾气排放、燃煤和生物质燃烧是PM2.5和TSP的主要NOx来源。研究区PM2.5和TSP中N-15-NO3- δ值的季节变化与不同来源NOx贡献的季节变化有关。SIAR模型结果表明，中国北方冬季煤炭燃烧增加与采暖有关（冬季PM2.5和TSP分别为38.4%和36.4%，夏季PM2.5和TSP分别为30.6%和29.8%），微生物N循环增加与夏季作物施肥量增加有关（冬季PM2.5和TSP分别为5.3%和5.6%，夏季PM2.5和TSP分别为10.7%和11.6%）。与SIAR模型相比，改进的SIAR模型与平衡分馏相结合，煤燃烧的贡献较低（15.5-20.2%），微生物N循环的贡献较高（22.9-29.3%）。δ O-18-NO3-值的季节变化受NO2通过O-3氧化（形成HNO3）的差异影响，冬季以N2O5途径为主，夏季以OH途径为主。
Nitrogen oxides (NOx) from anthropogenic emissions oxidized to form nitrate (NO3) and play a key role in air pollution. The aim of this study is to identify the NOx sources and their seasonal variations in Hangzhou, a typical city in East China. To achieve this, the chemical characteristics of water-soluble inorganic ions (WSIIs) and the stable isotopes of NO3- (delta N-15-NO3- and delta O-18-NO3-) were measured in fine particulate matter (PM2.5) and total suspended particle (TSP) aerosol samples that were collected between December 2018 and November 2019. It was found that the annual average concentration of PM2.5 (69.28 +/- 34.69 mu g/m(3)) in Hangzhou exceeded the Chinese air quality limit of 35.00 mu g/m(3). The results showed that NO3- accounted for the largest proportion of the WSIIs in both PM2.5 and TSP, and that major ions were mainly in the form of NH4NO3, (NH4)(2)SO4, Ca(NO3)(2), CaSO4 in aerosol particles. High ratios of NO3-/SO42- in PM2.5 and TSP indicated that vehicle emissions became increasingly important source of aerosol pollution in Hangzhou during the study period. The delta N-15-NO3- values ranged from +1.1 parts per thousand to +9.2 parts per thousand in PM2.5 and from -1.0 parts per thousand to +8.5 parts per thousand in TSP in Hangzhou. A Bayesian isotopic mixing model (stable isotope analysis in R (SIAR)) was applied to quantify the NOx sources in Hangzhou. This revealed that vehicle emissions, coal combustion and biomass burning were the main NOx sources of PM2.5 and TSP. The seasonal variation of the delta N-15-NO3- values in PM2.5 and TSP in the study area were due to seasonal changes in the NOx contributions from different sources. The SIAR model results indicated that coal combustion increased in association with heating in north China during the winter (winter: 38.4% for PM2.5 and 36.4% for TSP, summer: 30.6% for PM2.5 and 29.8% for TSP) and the microbial N cycle increased with a higher application of fertilizer to crops during the summer (winter: 5.3% for PM2.5 and 5.6% for TSP, summer: 10.7% for PM2.5 and 11.6% for TSP). The improved SIAR model combined with the equilibrium fractionation reported the lower contributions from coal combustion (15.5-20.2%) and the higher contributions from Microbial N cycle (22.9-29.3%), as compared to the SIAR model. The seasonal variation of the delta O-18-NO3- values was influenced by differences in the oxidation of NO2 via O-3 (forming HNO3), whereby the N2O5 pathway dominated during the winter and the OH pathway dominated during the summer.