Impacts of Transboundary Transport on Coastal Air Quality of South China

Transboundary transport plays an important role in air pollution formation in China. The coastal area of south China (CA-SCHN) frequently experiences air pollution in spring and autumn, but the contribution of transboundary transport to the air quality is still not clear. Meteorological field analyses reveal that large-scale synoptic patterns over east China in spring and autumn provide favorable situations facilitating southward transport of air pollutants originated from the North China Plain (NCP) and Yangtze River Delta (YRD). A springtime case study using the WRF-Chem model shows that trans-boundary transport of air pollutants from the NCP and YRD contributes to 27% and 46% of ozone (O₃) and fine particulate matter (PM_2.5) concentrations in the CA-SCHN, respectively. In the autumn case, the contribution is around 11% for O₃ and 24% for PM_2.5. In the spring, air pollutants in the NCP and YRD are transported over seas by large-scale synoptic systems to the South China Sea and re-circulated by the sea breeze to the CA-SCHN during daytime. In the autumn, the transport is driven by northerly winds over the land induced by large-scale synoptic systems, and is also modulated by the local mountain-valley breeze circulation. The results provide support for design and implementation of air pollutants control strategies in the CA-SCHN.