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Aircraft Study of Secondary Aerosols in Long‐Range Transported Air Masses From the North China Plain by a Mid‐Latitude Cyclone.

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Title: Aircraft Study of Secondary Aerosols in Long‐Range Transported Air Masses From the North China Plain by a Mid‐Latitude Cyclone.
Authors: Sun, Peng1,2 sunpeng@nju.edu.cn, Nie, Wei1,2, Chi, Xuguang1,2, Huang, Xin1,2, Ren, Chuanhua1,2, Xue, Likun2,3, Shan, Ye3, Wen, Liang3,4, Li, Hongyong3, Chen, Tianshu3, Qi, Yanbin5,6, Gao, Jian7, Zhang, Qi8, Ding, Aijun1,2 dingaj@nju.edu.cn
Source: Journal of Geophysical Research. Atmospheres. 2/27/2022, Vol. 127 Issue 4, p1-16. 16p.
Subject Terms: *Atmospheric aerosols, *Air masses, *Cyclones, *Troposphere
Geographic Terms: North China Plain (China)
Abstract: Regional transport has been identified as an important contributor to air pollution. Yet, understanding the evolution of aerosol components associated with synoptic systems remains limited, particularly in China, where most of the measurement studies were conducted at the ground surface. In this study, an intensive campaign was designed with aircraft measurements in Northeast China together with ground‐surface measurements in the North China Plain (NCP) to investigate the role that the mid‐latitude cyclone plays in transporting air pollution, specifically in changing aerosol components during transport. During a flight on 30 July 2018, high concentrations of aerosols dominated by sulfate were observed in the free troposphere, despite low aerosol loadings dominated by organics in the planetary boundary layer. Model simulations indicated that pollution in the lower free troposphere was transported directly from North Hebei by warm and moist air masses, while pollution in the higher free troposphere (HFT) was influenced by the warm conveyor belt (WCB), which transported aerosols from the (NCP) and lifted them into the HFT. Both particulate nitrate and sulfate were formed productively due to strong emissions and high atmospheric oxidizing capacity in the NCP. During transport, sulfate concentrations remained relatively constant, while nitrate decreased readily due to evaporation losses, resulting in an increasing contribution of sulfate but a decreasing contribution of nitrate to secondary aerosols along the transport path. Plain Language Summary: Atmospheric chemical processes may occur inside an air mass plume as it moves continuously along the trajectory. This challenges single‐site‐based investigations in understanding changes in aerosol composition. Here, we organized a campaign using an aircraft in Northeast China (NEC) and multiple ground observations in the North China Plain (NCP) to investigate aerosol chemistry during regional transport from the NCP to NEC influenced by a mid‐latitude cyclone. High loadings of aged secondary aerosols observed in the free troposphere (FT) in NEC were attributed to the regional transport from the NCP. Both sulfate and nitrate formed strongly in the NCP but behaved differently during transport to the north in that sulfate remained constant, while nitrate decreased readily due to evaporation losses. Key Points: Aircraft measurements recorded high loadings of sulfate‐dominated secondary aerosols in the free troposphere of Northeast ChinaStrong changes in secondary aerosols occurred in the front‐induced air masses transported by a mid‐latitude cycloneThe increased sulfate contribution to PM2.5 was mainly caused by evaporation‐induced nitrate losses during transport [ABSTRACT FROM AUTHOR]
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Abstract:Regional transport has been identified as an important contributor to air pollution. Yet, understanding the evolution of aerosol components associated with synoptic systems remains limited, particularly in China, where most of the measurement studies were conducted at the ground surface. In this study, an intensive campaign was designed with aircraft measurements in Northeast China together with ground‐surface measurements in the North China Plain (NCP) to investigate the role that the mid‐latitude cyclone plays in transporting air pollution, specifically in changing aerosol components during transport. During a flight on 30 July 2018, high concentrations of aerosols dominated by sulfate were observed in the free troposphere, despite low aerosol loadings dominated by organics in the planetary boundary layer. Model simulations indicated that pollution in the lower free troposphere was transported directly from North Hebei by warm and moist air masses, while pollution in the higher free troposphere (HFT) was influenced by the warm conveyor belt (WCB), which transported aerosols from the (NCP) and lifted them into the HFT. Both particulate nitrate and sulfate were formed productively due to strong emissions and high atmospheric oxidizing capacity in the NCP. During transport, sulfate concentrations remained relatively constant, while nitrate decreased readily due to evaporation losses, resulting in an increasing contribution of sulfate but a decreasing contribution of nitrate to secondary aerosols along the transport path. Plain Language Summary: Atmospheric chemical processes may occur inside an air mass plume as it moves continuously along the trajectory. This challenges single‐site‐based investigations in understanding changes in aerosol composition. Here, we organized a campaign using an aircraft in Northeast China (NEC) and multiple ground observations in the North China Plain (NCP) to investigate aerosol chemistry during regional transport from the NCP to NEC influenced by a mid‐latitude cyclone. High loadings of aged secondary aerosols observed in the free troposphere (FT) in NEC were attributed to the regional transport from the NCP. Both sulfate and nitrate formed strongly in the NCP but behaved differently during transport to the north in that sulfate remained constant, while nitrate decreased readily due to evaporation losses. Key Points: Aircraft measurements recorded high loadings of sulfate‐dominated secondary aerosols in the free troposphere of Northeast ChinaStrong changes in secondary aerosols occurred in the front‐induced air masses transported by a mid‐latitude cycloneThe increased sulfate contribution to PM2.5 was mainly caused by evaporation‐induced nitrate losses during transport [ABSTRACT FROM AUTHOR]
ISSN:2169897X
DOI:10.1029/2021JD036178