Changes in ammonia and its effects on PM2.5 chemical property in three winter seasons in Beijing, China

Zhaoyang Meng; Lingyan Wu; Xiangde Xu; Wanyun Xu; Renjian Zhang; Xiaofang Jia; Linlin Liang; Yucong Miao; Hongbing Cheng; Yulin Xie; Jianjun He; Junting Zhong

doi:10.1016/j.scitotenv.2020.142208

Changes in ammonia and its effects on PM_2.5 chemical property in three winter seasons in Beijing, China

Sci Total Environ. 2020 Dec 20:749:142208. doi: 10.1016/j.scitotenv.2020.142208. Epub 2020 Sep 9.

Authors

Affiliations

¹ State Key Laboratory of Severe Weather & Key Laboratory of Atmospheric Chemistry of China Meteorological Administration, Institute of Atmospheric Composition, Chinese Academy of Meteorological Sciences, Beijing, China. Electronic address: mengzy@cma.gov.cn.
² State Key Laboratory of Severe Weather & Key Laboratory of Atmospheric Chemistry of China Meteorological Administration, Institute of Atmospheric Composition, Chinese Academy of Meteorological Sciences, Beijing, China.
³ Key Laboratory of Middle Atmosphere and Global Environment Observation, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China; Xianghe Observatory of Whole Atmosphere, Institute of Atmospheric Physics, Chinese Academy of Sciences, Xianghe, China. Electronic address: zrj@mail.iap.ac.cn.
⁴ CMA Meteorological Observation Centre, Beijing, China.
⁵ Baotou Steel Group Mining Research Institute, Baotou, China.

PMID: 33370901
DOI: 10.1016/j.scitotenv.2020.142208

Abstract

NH₃, SO₂, NO_x and the inorganic ions of PM_2.5 in winter 2009, 2014 and 2016 were examined to investigate the change in NH₃ and aerosol chemistry in Beijing, China. NH₃ concentrations showed an increase by 59% on average, in contrast to the decrease of SO₂ by 63% from winter 2009 to 2016. The mean mass ratio of NH₃/NH_x was 0.83 ± 0.12 in 2016, which is higher than those obtained in 2009 and 2014, implying more NH_x remaining as free NH₃ in 2016 winter. Our findings suggest that vehicles exhaust emissions are an important NH₃ source in urban central atmosphere of Beijing in winter. Despite the observed NO_x presenting declining trends from 2014 to 2016, nitrate concentrations even exhibited a significant increasing trend, which may be largely attributable to high NH₃ levels. An in-depth analysis of measured NH₃ and aerosol species in a heavy pollution episode in December 2016, combined with the acidity predicted by ISORROPIA II model demonstrated abundant NH₃ most of the time in air, where NH₃ is not only a precursor for NH₄⁺ but also effect the neutralization of SO₄^2- and NO₃^- in PM_2.5. With high RH and low photochemical activity, elevated NO₃^- concentration was attributed to an enhanced heterogeneous conversion of NO_x to HNO₃ to form NH₄NO₃ in pollution transport stage. The decrease in NO_x from high level and the increase in NH₃, with peaks of SO₄^2- occurring were observed in pollution cumulative stage. The aqueous-phase oxidation of SO₂ by NO₂ to sulfate might play an important role with high pH values. Our results suggested that the simultaneous control of NH₃ emissions in conjunction with SO₂ and NO_x emissions would be more effective in reducing particulate matter PM_2.5 formation.

Keywords: Aerosol chemistry; Ammonia; PM(2.5) pollution; Three winter seasons; Urban Beijing.