The formation and evolution of secondary organic aerosol during haze events in Beijing in wintertime

Jie Li; Zhiwei Han; Jiawei Li; Ruiting Liu; Yunfei Wu; Lin Liang; Renjian Zhang

doi:10.1016/j.scitotenv.2019.134937

The formation and evolution of secondary organic aerosol during haze events in Beijing in wintertime

Sci Total Environ. 2020 Feb 10:703:134937. doi: 10.1016/j.scitotenv.2019.134937. Epub 2019 Nov 2.

Authors

Jie Li¹, Zhiwei Han², Jiawei Li³, Ruiting Liu⁴, Yunfei Wu³, Lin Liang¹, Renjian Zhang³

Affiliations

¹ Key Laboratory of Regional Climate-Environment for Temperate East Asia (RCE-TEA), Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS), Beijing 100029, China; University of Chinese Academy of Sciences, Beijing 100049, China.
² Key Laboratory of Regional Climate-Environment for Temperate East Asia (RCE-TEA), Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS), Beijing 100029, China; University of Chinese Academy of Sciences, Beijing 100049, China. Electronic address: hzw@mail.iap.ac.cn.
³ Key Laboratory of Regional Climate-Environment for Temperate East Asia (RCE-TEA), Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS), Beijing 100029, China.
⁴ Institute of Urban Meteorology, China Meteorological Administration, Beijing 100089, China.

PMID: 31767292
DOI: 10.1016/j.scitotenv.2019.134937

Abstract

A regional air quality model system (RAQMS) with a volatility basis set approach for secondary organic aerosol (SOA) formation and an emission inventory of semi-volatile (SVOC) and intermediate volatile organic compounds (IVOC) are applied to investigate the distribution and evolution of organic aerosols over the Beijing-Tianjin-Hebei (BTH) region in winter 2014, with focus on Beijing. Model validation demonstrates the model is capable of reproducing meteorological variables and major aerosol components, and the model significantly improves SOA and organic aerosol (OA) simulations by taking S/IVOCs (SVOC + IVOC) and relevant aging processes into account. SVOC and IVOC emissions in the BTH region are estimated to be 0.47 Tg and in a range of 0.09-0.36 Tg, respectively, which are about 18% and 4-14% of the emission amounts of volatile organic compounds (VOCs). The distribution of mean organic aerosols is characterized by a high concentration belt oriented southwest-northeast from southern Hebei to Beijing, with the maximum concentration up to 50 μg m^-3 in Beijing and Shijiazhuang. The simulated SOA concentration is comparable in magnitude to primary organic aerosol (POA) concentration, and the SOA/OA ratio is around 50% in most areas of the BTH region. In terms of domain average, the percentage contributions to SOA mass concentration from anthropogenic volatile organic compounds (AVOCs), SVOCs, IVOCs and biogenic VOCs are estimated to be 46.1%, 40.1%, 9.4% and 4.4%, respectively, in the BTH region during the study period, which indicates an important role of S/IVOCs in SOA formation. From clean to haze periods, both POA and SOA concentrations apparently increase, with an increasing (decreasing) trend of the SOA/OA (POA/OA) ratio. SOA dominates over POA in fine organic aerosols during the haze periods. The increase of POA in hazy days is mainly due to the weakened vertical diffusion and accumulation near the surface, whereas the increase of SOA is likely attributed to both the reduced diffusivity and a series of competing chemical processes, in which the decreased photolysis rate by aerosol attenuation tends to decrease SOA concentration by about 6% during the most severe haze day, whereas the lower surface air temperature and higher POA and S/IVOC concentrations in haze days both enhance gas to particle partition, and consequently lead to higher SOA concentration.

Keywords: Beijing; Gas-particle partition; Photolysis rate; S/IVOCs; SOA/OA ratio; Secondary organic aerosol.