Enhancement of secondary aerosol formation by reduced anthropogenic emissions during Spring Festival 2019 and enlightenment for regional PM_2.5 control in Beijing

• Main Authors: Y. Wang, Z. Li, Q. Wang, X. Jin, P. Yan, M. Cribb, Y. Li, C. Yuan, H. Wu, T. Wu, R. Ren, Z. Cai
• Format: Article
• Language: English
• Published: Copernicus Publications 2021-01-01
• Series: Atmospheric Chemistry and Physics
• Online Access: https://acp.copernicus.org/articles/21/915/2021/acp-21-915-2021.pdf

<p>A comprehensive field experiment measuring aerosol chemical and physical properties at a suburban site in Beijing around the 2019 Spring Festival was carried out to investigate the impact of reduced anthropogenic emissions on aerosol formation. Sharply reduced sulfur dioxide (<span class="inline-formula">SO₂</span>) and nitrogen dioxide (<span class="inline-formula">NO₂</span>) concentrations during the festival holiday resulted in an unexpected increase in the surface ozone (<span class="inline-formula">O₃</span>) concentration caused by the strong <span class="inline-formula">O₃</span>-titration phenomenon. Simultaneously, the reduced anthropogenic emissions resulted in massive decreases in particle number concentration at all sizes and the mass concentrations of organics and black carbon. However, the mass concentrations of inorganics (especially sulfate) decreased weakly. Detailed analyses of the sulfur oxidation ratio and the nitrogen oxidation ratio suggest that sulfate formation during the holiday could be promoted by enhanced nocturnal aqueous-phase chemical reactions between <span class="inline-formula">SO₂</span> and <span class="inline-formula">O₃</span> under moderate relative humidity (RH) conditions (40 % <span class="inline-formula">&lt;</span> RH <span class="inline-formula">&lt;</span> 80 %). Daytime photochemical reactions in winter in Beijing mainly controlled nitrate formation, which was enhanced a little during the holiday. A regional analysis of air pollution patterns shows that the enhanced formation of secondary aerosols occurred throughout the entire Beijing–Tianjin–Hebei (BTH) region during the holiday, partly offsetting the decrease in particle matter with an aerodynamic diameter less than 2.5 <span class="inline-formula">µ</span>m. Our results highlight the necessary control of <span class="inline-formula">O₃</span> formation to reduce secondary pollution in winter under current emission conditions.</p>