Nitrate debuts as a dominant contributor to particulate pollution in Beijing: Roles of enhanced atmospheric oxidizing capacity and decreased sulfur dioxide emission

• Published in: Atmospheric environment (1994) Vol. 244; p. 117995
• Main Authors: Feng, Tian, Bei, Naifang, Zhao, Shuyu, Wu, Jiarui, Liu, Suixin, Li, Xia, Liu, Lang, Wang, Ruonan, Zhang, Xiu, Tie, Xuexi, Li, Guohui
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.01.2021
• Subjects: aerosols; air; Atmospheric oxidizing capacity; autumn; China; environment; Nitrate; nitrates; Ozone; Sulfate; sulfates; sulfur dioxide; WRF-Chem; China; Ozone; Nitrate; Sulfate; WRF-Chem; Atmospheric oxidizing capacity
• ISSN: 1352-2310; 1873-2844
• DOI: 10.1016/j.atmosenv.2020.117995

Implementation of strict emission mitigation measures since 2013 has significantly changed air pollutants in the Beijing-Tianjin-Hebei region (BTH), China. Observations show that ozone (O3) concentrations have increased by 62.40% (27.84%) and SO2 concentrations have decreased by 56.42% (35.07%) during particulate pollution episodes in Beijing (BTH) in the autumn from 2013 to 2015. The measured nitrate concentration in Beijing has increased markedly, which to a large degree offsets the sulfate decrease caused by SO2 emission mitigation. Using the WRF-Chem model, we demonstrate that the enhanced nitrate formation is primarily attributed to increasing atmospheric oxidizing capacity (AOC) and decreasing sulfate competition for base ions. A 9.41–46.24% (7.58–40.97%) decrease in OH radical (O3) concentrations in October 2015 reduces nitrate and fine particulate matters (PM2.5) concentrations by 2.51–18.18% and 3.15–18.90% in Beijing, respectively. Based on the scenario in October 2015, if the SO2 emission increases by 20.00–100.00%, the PM2.5 concentration increases by 3.02–11.21%, but the nitrate level decreases by 2.48–21.87% simultaneously. Our results suggest that the nitrate aerosol has become a dominant contributor to particulate pollution in Beijing and that decreasing AOC is critical to mitigate nitrate and PM2.5 concentrations. ●Increasing nitrate concentration largely offsets the sulfate decrease since 2013.●Increasing nitrate is mainly due to enhanced AOC and weakened sulfate competition.●Decreasing AOC is beneficial to mitigate nitrate and PM2.5 concentrations.