Aircraft study of secondary aerosols in long-range transported air
masses from the North China Plain by a mid-latitude cyclone
Abstract
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.