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Understanding Variability of Haze in Eastern China

Xuexi Tie and Junji Cao

In recent years, there are heavy aerosol pollutions in eastern China. For example, in the Northern China Plain (NCP) and the capital city of Beijing, the concentrations of PM2.5 (particle matter <2.5 μm in diameter) often reached to the levels of more than 200-400 μg/m3. In contract, the World Health Organization (WHO) identifies a safe level of air quality as containing 10-25 μg/m3. In addition to the high levels of aerosol pollutions, there is a largely temporal variability of the concentrations. This study discusses the major factors, which control the short-term variability (days to weeks) of the aerosol pollutions in eastern China. The results suggest that the meteorological parameters, including wind direction, wind speed, and vertical diffusion in the planetary boundary layer (PBL) have important effects on the short-term variability. The secondary formation of aerosols, especially during heavy haze periods, has also important contribution to the large variability. Because the secondary aerosols (SA) have a large portion in the composition of the total aerosols during the haze period, the formation of SA amplifies the magnitude of the variation, causing significant increase in the concentrations of PM2.5 during the heavy haze periods in eastern China.