Summertime aerosol volatility measurements in Beijing, China

Xu, Weiqi; Xie, Conghui; Karnezi, Eleni; Zhang, Qi; Wang, Junfeng; Pandis, Spyros N.; Ge, Xinlei; Zhang, Jingwei; An, Junling; Wang, Qingqing; Zhao, Jian; Du, Wei; Qiu, Yanmei; Zhou, Wei; He, Yao; Li, Ying; Li, Jie; Fu, Pingqing; Wang, Zifa; Worsnop, Douglas R.; Sun, Yele

Volatility plays a key role in affecting mass concentrations and the lifetime of aerosol particles in the atmosphere, yet our knowledge of aerosol volatility in relatively polluted environment, e.g., north China, remains poor. Here aerosol volatility in Beijing in summer 2017 and 2018 was measured using a thermodenuder (TD) coupled with an Aerodyne high-resolution aerosol mass spectrometer (AMS) and a soot particle AMS. Our results showed overall similar thermograms for most non-refractory aerosol species compared with those reported in previous studies. However, high mass fraction remaining and inline-formula M1inlinescrollmathml chem normal NO + / normal NO normal 2 + 53pt15ptsvg-formulamathimg9a7b3e522d33b88dadb3ad7fd815cb87 acp-19-10205-2019-ie00001.svg53pt15ptacp-19-10205-2019-ie00001.png ratio for chloride and nitrate, each above 200 inline-formulaC, indicated the presence of considerable metallic salts and organic nitrates in Beijing. The volatility distributions of organic aerosol (OA) and four OA factors that were resolved from positive matrix factorization were estimated using a mass transfer model. The ambient OA comprised mainly semi-volatile organic compounds (SVOCs; 63 %) with an average effective saturation concentration (inline-formulaC*) of 0.55 inline-formulaµg minline-formula−3, suggesting overall more volatile properties than OA in megacities of Europe and the US. Further analysis showed that the freshly oxidized secondary OA was the most volatile OA factor (SVOC inline-formula= 70 %) followed by hydrocarbon-like OA (HOA). In contrast, the volatility of more oxidized oxygenated OA (MO-OOA) was comparable to that of cooking OA with SVOC on average accounting for 60.2 %. We also compared the volatility of ambient and black-carbon-containing OA. Our results showed that the BC-containing primary OA (POA) was much more volatile than ambient POA (inline-formula M7inlinescrollmathml C * = normal 0.69 48pt11ptsvg-formulamathimgf8ea7fc5732a22e5dd89967e0f3cad81 acp-19-10205-2019-ie00002.svg48pt11ptacp-19-10205-2019-ie00002.png inline-formulaµg minline-formula−3 vs. 0.37 inline-formulaµg minline-formula−3), while the BC-containing SOA was much less volatile, highlighting the very different composition and properties between BC-containing and ambient aerosol particles.

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Xu, Weiqi / Xie, Conghui / Karnezi, Eleni / et al: Summertime aerosol volatility measurements in Beijing, China. 2019. Copernicus Publications.

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