Effect of hydrolysis of N2O5 on nitrate and ammonium formation in Beijing China: WRF-Chem model simulation

Xing Su; Xuexi Tie; Guohui Li; Junji Cao; Rujin Huang; Tian Feng; Xin Long; Ruiguang Xu

doi:10.1016/j.scitotenv.2016.11.125

Effect of hydrolysis of N₂O₅ on nitrate and ammonium formation in Beijing China: WRF-Chem model simulation

Sci Total Environ. 2017 Feb 1:579:221-229. doi: 10.1016/j.scitotenv.2016.11.125. Epub 2016 Nov 24.

Authors

Xing Su¹, Xuexi Tie², Guohui Li³, Junji Cao³, Rujin Huang⁴, Tian Feng⁵, Xin Long³, Ruiguang Xu¹

Affiliations

¹ Key Laboratory of Aerosol Science and Technology, State Key Laboratory of Loess Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China; University of Chinese Academy of Sciences, Beijing 100049, China.
² Key Laboratory of Aerosol Science and Technology, State Key Laboratory of Loess Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China; Center for Excellence in Urban Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China; National Center for Atmospheric Research (NCAR), Boulder 80303, USA. Electronic address: tiexx@ieecas.cn.
³ Key Laboratory of Aerosol Science and Technology, State Key Laboratory of Loess Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China.
⁴ Key Laboratory of Aerosol Science and Technology, State Key Laboratory of Loess Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China; Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), Villigen 5232, Switzerland.
⁵ Key Laboratory of Aerosol Science and Technology, State Key Laboratory of Loess Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China; School of Human Settlements and Civil Engineering, Xi'an Jiaotong University, Xi'an 710049, China.

PMID: 27890411
DOI: 10.1016/j.scitotenv.2016.11.125

Abstract

Beijing, the capital of China, is a mega city with a population of >20 million. In recent years, the city has experienced heavy air pollution, with particulate matter (PM) being one of its top pollutants. In the last decade, extensive efforts have been made to characterize the sources, properties, and processes of PM in Beijing. Despite progress made by previous studies, there are still some important questions to be answered and addressed. The focus of this research is to study the impact of the heterogeneous hydrolysis of N₂O₅ on the formation of nitrate (NO₃^-) and ammonium (NH₄⁺) in Beijing. The results show that during heavy pollution days (e.g., during 14-17 September 2015, with PM_2.5 concentration over 100μg/m³), the concentrations of NO₂ and O₃ were high, with maxima of 90 and 240μg/m³, respectively, providing high precursors for the formation of N₂O₅. In addition, the aerosol and sulfate concentrations were also high, with maxima of 201μg/m³ and 23μg/m³ respectively, providing reacting surface for the heterogeneous reaction. As a result, the hydrolysis of N₂O₅ led to 21.0% enhancement of nitrate (NO₃^-) and 7.5% enhancement of ammonium (NH₄⁺). It is worth to note that this important effect only occurred in high pollution days (PM_2.5 concentration over 100μg/m³). During low-pollution periods (PM_2.5 concentration <100μg/m³), the effect of hydrolysis of N₂O₅ on the formation of nitrate and ammonium was insignificant (variation rate <5%). This study suggests that during heavy pollution periods, the hydrolysis of N₂O₅ enhances the level of aerosol pollution in Beijing, and needs to be further studied in order to perform efficient air pollution control and mitigation strategies.

Keywords: Beijing; Hydrolysis of N(2)O(5); Nitrate and ammonium; WRF-Chem.