10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Effects of Aqueous-phase and Photochemical Chemistry on Winter Haze Formation and Evolution in Beijing, China
TAO MA, Fengkui Duan, Hiroshi Furutani, Michisato Toyoda, Takashi Kimoto, Lidan Zhu, Yongliang Ma, Kebin He, Tsinghua University
Abstract Number: 718 Working Group: Air Quality in Megacities: from Sources to Control
Abstract In recent years, severe hazes with high PM2.5 concentrations have been serious problems in China due to the rapid economic growth and urbanization. To better understand the severe winter hazes in Beijing, a suite of strengthened observations was conducted in Tsinghua University from December 21, 2015 to January 8, 2016 with hourly-based continuous gas and particle measurements including a single particle mass spectrometer (ATOFMS). Four continuous severe haze episodes were observed and PM2.5 concentration varied from 2.7 µg m-3 to 506.3 µg m-3 during the campaign. We classified air quality into three types: clean (PM2.5 ≤ 75 µg m-3), dry-haze (PM2.5 > 75 µg m-3 and RH < 80%) and wet-haze (PM2.5 > 75 µg m-3 and RH ≥ 80%). Based on ART-2a method, we classified all single particles into 7 groups: OC-day, OC-night, K-rich, Na-rich, K/Na-rich, K/Na-CN and Metal-rich. During clean and dry-haze periods, organic compounds were dominant, while SNA (sulfate, nitrate and ammonium) increased quickly to be major components during wet-haze periods. The oxidation ratio of sulfur and nitrogen increased with RH, indicating the importance of aqueous reaction on secondary inorganics formation during severe hazes. OC/EC showed bimodal diurnal variation, consistent with OC-day and OC-night particle types. The phenomenon indicated the effect of photochemical and aqueous chemistry on secondary organic aerosol formation in daytime and nighttime, respectively. Meteorological conditions also have a strong impact on haze formation. High PM2.5 concentrations usually appeared under the condition of low wind speed and high humidity, which were in favor of the pollutants accumulation and secondary transformation.