AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Characteristics and Formation Mechanism of Severe Winter Hazes in Beijing
TAO MA, Fengkui Duan, Kebin He, Tsinghua University
Abstract Number: 261 Working Group: Urban Aerosols
Abstract We observed four severe haze episodes in Beijing from December 16, 2015 to January 9, 2016 with hourly-based continuous gas and particulate measurements. These episodes were frequent (intervals between episodes were usually less than 1 day) and durations were from 2 to 7 days. Overall, the PM2.5 concentration varied from 2.7 μg m-3 to 506.3 μg m-3, with an average of 125.0 (±106.5) μg m-3. During clean periods, organic compounds were dominant. With the deterioration of pollution, SNA increased quickly to be major components while the ratio of organic compounds decreased slowly. High concentration of SO2 and NO2 promoted the formation of sulfate and nitrate, and high concentration of CO reflected primary emission and boundary layer height. Low concentration of O3 during episode indicated weak photochemical reaction. Meteorological conditions have a strong impact on pollution level. High PM2.5 concentrations usually appeared under the condition of low wind speed and high humidity, which were in favor of the accumulation of pollutants and secondary transformation. PM1/PM2.5 increased with RH when RH was below 50%, and kept stable when RH was between 50% and 80%, and decreased when RH was larger than 80%, indicating PM1-2.5 was dominant during severe hazes. PM2.5/PM10 was discrete when RH was below 50%, and kept stable around 0.9 when RH was larger than 50%. The oxidation ratio of sulfur and nitrogen increased with RH, indicating the importance of aqueous reaction on secondary inorganics formation during severe hazes. These results suggested that stable synoptic conditions, formation of secondary species and hygroscopic growth contributed to the formation of the severe winter hazes.