资源环境科技发展态势分析平台

We examine relationships between day-to-day variations in the large-scale atmospheric circulation and the occurrence, intensity, and duration of haze during several recent winters, beginning with a focused examination of Beijing in 2013-2017 and then evaluating the extent to which the findings applied to other urban areas in China in 2015-2017. Composite analysis for Beijing indicates that haze preferentially occurred when the East Asian winter monsoon (EAWM; based on potential vorticity) and Siberian High (SH; based on sea level pressure) were weak. Daily variations in EAWM and SH are cross-correlated but have different relationships with conditions that affect haze development. EAWM is more strongly anticorrelated with boundary layer humidity, suggesting a greater influence on particulate growth. SH, by contrast, has stronger relationships with thermodynamic stability and near-surface wind speed. A linear combination of these two indices provides a simple but effective indicator of heightened pollution risk over much of central eastern China. The particular value of the EAWM index is supported by its applicability to a broader area and its links to air quality in Beijing during the winter of 2017-2018. Clean conditions during November-February coincided with a persistent strong EAWM despite the SH deviating little from its climatology. The EAWM weakened in March, when air quality reverted to conditions typical of the previous four winters. These results confirm and help to clarify links between the large-scale circulation and air quality at daily to weekly time scales and provide an empirical foundation for evaluating models used to simulate air quality in this region.