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

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.