Regional transport has been identified as an important contributor to air pollution. Yet, understanding evolution of aerosol components associated with synoptic systems remains limited, particularly in China, where most of the measurement studies were conducted at ground-surface. In this study, an intensive campaign was designed with an aircraft measurement in Northeast China (NEC) together with ground-surface measurements in North China Plain (NCP), to investigate the role that the mid-latitude cyclone plays in transporting air pollution, specifically in changing aerosol components during the transport. During a flight on 30 July 2018, high concentrations of aerosols dominated by sulfate were observed in the free troposphere (FT), despite low aerosol loadings dominated by organics in the planetary boundary layer. Model simulations indicated that pollution in the lower free troposphere (LFT) 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 the transport, sulfate concentrations stayed 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.
