Influence of regional pollution outflow on the concentrations of fine particulate matter and visibility in the coastal area of southern China

The Pearl River Delta (PRD) is a fast developing region in China that has experienced serious air pollution. In this study, we present the measurement results of fine particulate matter (PM2.5) mass, major ions, and carbonaceous concentrations at a rural site in southern PRD during November to December 2002. The aims of this study are to characterize the temporal variation of PM2.5 mass and chemical composition in winter, which is typically a season of high pollution, and to estimate the contribution of sources from PRD inland and coastal cities (Hong Kong and Shenzhen) on the levels of fine particles observed in the downwind area. The average concentration of 24-h PM2.5 filter samples (N=24) was 41.3 (±17.1) μg m−3 (±standard deviation), with the concentration of individual samples ranging from 10.1 to 89.9 μg m−3. Particulate organic matter (POM) and non-sea-salt sulfate (nss-SO42−) were the major components of PM2.5 accounting for 42% and 25% of the total mass, respectively. Examination of the ratio of secondary organic carbon to total organic carbon suggests that approximately 34% of organic carbon was of secondary origin. The temporal variations of PM2.5 concentrations were strongly influenced by synoptic wind flow. The regional outflows from PRD inland and coastal cities made significant contributions to the ambient concentrations in the study site, which accounted for 48–57% for PM2.5, 66–72% for POM, and 18–20% for nss-SO42−, respectively. An application of a formula developed in the IMPROVE study showed that POM accounted for 44%, 42% and 22% of the light extinction under northeasterly, northerly, and easterly winds, respectively, whereas ammonium sulfate contributed 45%, 47%, and 70%, respectively. This highlights the significance of fine sulfate in visibility impairment in region with humid climates.