10 Mar 2023
 | 10 Mar 2023
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Fine particle chemistry under a special dust transport event: impacts from unusually enhanced ozone and air mass backflows over the ocean

Da Lu, Hao Li, Guochen Wang, Xiaofei Qin, Na Zhao, Juntao Huo, Fan Yang, Yanfen Lin, Jia Chen, Qingyan Fu, Yusen Duan, Xinyi Dong, Congrui Deng, Sabur Abdullaev, and Kan Huang

Abstract. A five-days long-lasting dust event was observed with a synergy of field measurements techniques in Shanghai in the autumn of 2019. Different from most dust events, this dust was an unusual one characterized of low wind speed, high relative humidity, high concentrations of gaseous precursors, and contrasting wind vectors between low and high altitudes. Three dust stages were identified and the first stage was a normal dust invasion with high particulate concentrations and short duration. In contrast, unusual enhancement of ozone was observed in the second stage, due to compound causes of weak synoptic system, transport from the ocean, and subsidence of high-altitude O3 down drafted by dust. As a result, sulfate and nitrate moderately correlated with O3 while had almost no correlation with aerosol liquid water content, indicating the dominant role of gas phase oxidations. During the third stage of dust, a special phenomenon of dust backflow was observed that the dust plume drifted from the Shandong Peninsula and travelled slowly over the Yellow Sea and the East China Sea, finally returning to Shanghai. The dust backflow was evidenced by the enrichment of marine vessel emissions (V and Ni) and increased solubility of calcium. Under the humid oceanic breezes, the formation of nitrate was dominated by aqueous processing, while the strong correlation between SO42- and Na+ suggested that a considerable part of sulfate was aged and directly transported. Based on the thermodynamic modeling, sea salts probably involved more in the secondary aerosol formation than the dust heterogeneous reactions. By developing an upstream-receptor relationship method, the amounts of transported and secondarily formed aerosol species were separated. This study highlights that the transport pathway of dust and environmental conditions could significantly modify the aerosol properties, especially at the complex land-sea interface.

Da Lu et al.

Status: open (until 27 Apr 2023)

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Da Lu et al.


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Short summary
Environmental conditions during dust are usually not favorable for the secondary aerosol formation. While in this study, an unusual dust event was captured in a Chinese mega-city and showed the “anomalous” meteorology and a special dust backflow transport pathway. The underlying formation mechanisms of secondary aerosols are probed in the context of this special dust event. This study shows significant implications on the varying dust aerosol chemistry in the future changing climate.