Elevated Formation of Particulate Nitrate From N2O5 Hydrolysis in the Yangtze River Delta Region From 2011 to 2019. Issue 9 (29th April 2022)

• Record Type: Journal Article
• Authors: Zhou, Min; Nie, Wei; Qiao, Liping; Huang, Dan Dan; Zhu, Shuhui; Lou, Shengrong; Wang, Hongli; Wang, Qian; Tao, Shikang; Sun, Peng; Liu, Yawen; Xu, Zheng; An, Jingyu; Yan, Rusha; Su, Hang; Huang, Cheng; Ding, Aijun; Chen, Changhong
• Is Part Of: Geophysical research letters. Volume 49:Issue 9(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-04-29
• Subjects: aerosol nitrate -- long‐term trend -- N2O5 hydrolysis; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2021GL097393
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Aerosol nitrate has become the most abundant compound during aerosol pollution in eastern China. The Chinese government implemented a stringent policy during 2013–2017 to tackle aerosol pollution. However, the response of nitrate to nitrogen oxides (NOx ) reduction is unclear owing to the limitation of long‐term measurement. Here, we performed a 9‐year continuous measurement of aerosol compositions in Shanghai and confirmed a decrease in most species except nitrate. The contribution of nitrate to fine particulate matter (PM2.5 ) increased significantly, reaching up to 35% in pollution episodes after 2017. This is in contrast to the evident reduction in NOx emissions. We found that the elevated dinitrogen pentoxide (N2 O5 ) hydrolysis is responsible for the observed nitrate trend. Increased ozone and decreased nitrogen dioxide (NO) facilitated the formation of N2 O5, and increased nitrate proportion promoted the uptake of N2 O5 and eventually enhanced the conversion efficiency of NO2 to nitrate. Our results highlight the importance of synergic control of aerosol and ozone pollution. Plain Language Summary: To tackle severe particulate matter (PM) pollution, the Chinese government tried to reduce the primary emission of pollutants, especially a stringent policy during 2013 and 2017, named Air Pollution Prevention and Control Action Plan. A particular need is to understand the respond of the chemical composition of PM2.5 to primary emission reductions, which supports the PM2.5 pollution control more effectively and scientifically. In this work, we performed a 9‐year online measurement of PM2.5 and its chemical compositions in the Yangtze River Delta from 2011 to 2019. We confirmed a significant decreasing trend for most species except nitrate, which remained unchanged in contrast to the evident reduction of nitrogen oxides. After ruling out the potential influences of meteorological parameters, we demonstrated the elevated dinitrogen pentoxide (N2 O5 ) hydrolysis is responsible for the observed nitrate trend. Increased ozone and decreased nitrogen dioxide (NO) promoted the formation of N2 O5, and increased nitrate proportion promoted the uptake of N2 O5 and eventually promoted the conversion efficiency of NO2 to nitrate. Overall, the primary emission reduction strategies feedback to the elevated formation of nitrate mainly via the increased O3 production, highlighting the need for the synergic control of aerosol and atmospheric oxidation capacity in mitigating PM2.5 pollutions. Key Points: A 9‐year observation of fine particulate matter (PM2.5 ) chemical compositions in Shanghai from 2011 to 2019 confirmed a decrease in most species except nitrate The conversion rate of nitrogen dioxide (NO2 ) to nitrate was promoted by dinitrogen pentoxide hydrolysis, resulting in a nonlinear response of nitrate to NO2 reduction Increased ozone concentration, decreased NO concentration, and increased nitrate proportion played a key role in enhancing nitrate formation