AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Impacts of Water Partitioning and Polarity of Organic Compounds on Secondary Organic Aerosols over Eastern China
JINGYI LI, Qi Ying, Jianlin Hu, Jianjun Chen, Haowen Zhang, Nanjing University of Information Science & Technology
Abstract Number: 107 Working Group: Aerosol Chemistry
Abstract Secondary organic aerosol (SOA) is a very important component of fine particular mater (PM2.5), accounting for 20-50% in urban and rural areas of China[1]. Most air quality models used an equilibrium partitioning method along with estimated saturation vapor pressure of semi-volatile organic compounds (SVOCs) to predict SOA formation. However, this method ignored partitioning of water vapor to the condensed phase as well as the polarity of SVOCs, and might result in significant underestimate of SOA[2]. Here, we used the Community Multi-scale Air Quality model (CMAQv5.0.1) to investigate the above impacts on SOA formation during winter (January) and summer (July) of 2013 over eastern China. The organic aerosol module was updated followed Pankow et al.[2] by incorporating water co-condensation and molecular structure of SVOCs. We also considered the polarity of primary organic aerosols by assuming a bulk composition of 10 surrogate species with different mass fractions following Li et al.[3]. Our model can well reproduce the mass concentration and diurnal variation of PM2.5 and major components. SOA concentration shows significant seasonal and spatial variation, with high levels in North China Plain (NCP), Central China and Sichuan basin areas during winter (up to 16 μg m-3) and in Yangtze River Delta (YRD) during summer (up to 10 μg m-3). By including water co-condensation, we see SOA increases by 20-40% in winter in Eastern China. This process leads to a relatively higher increase of SOA in summer by about 40%-80% in YRD. The polarity of SVOCs and POA exhibits negative effects on SOA formation, resulting in about 20% decrease in both summer and winter. Overall, SOA concentration varies from -10~20% to 20-40% in the high regions in winter and summer, respectively. Condensed water into the SOA portion reaches to 3 and 1.2 μg m-3 in the highly concentrated areas in winter and summer, accounting for 15-30% and up to 15% of the total SOA, respectively. Such variation in both SOA and water content will further alter the physical and chemical properties of aerosols.
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