Impact of Summertime Weather System Activity on Air Quality Variations Over Beijing and the Implications

It is very known that there is a clear relationship between air quality (in particular, PM sub(10) concentrations) and meteorological parameters (prevailing wind conditions) in Beijing. In this study, by analyzing the PM sub(10) concentrations and wind characteristics at Peking University monitoring station and the large-scale wind patterns during summertime over Beijing, we found the PM sub(10) levels show repeated cycles at the synoptic scale that can be expressed by a new component meteorological index defined by the meteorological parameters. By reviewing the summertime air quality variations in 2006 and 2007, we found that activity of mid- latitude baroclinic waves and the subtropical high of the western pacific are major contributors to air quality variability over Beijing in the summer. This should be good news for air quality forecasting in Beijing as our understanding of mid-latitude baroclinic waves is quite good, and these systems are predicted rather well by most state-of-the-art numerical weather prediction models. We further studied an inter-annual variation of Air pollution Index (API) recorded at 39 monitoring stations over eastern China, and its relationship with the monthly mean atmospheric circulation at an intra-seasonal scale. A physical pattern showing an anti-correlation of north and south of eastern China was identified by empirical orthogonal function and singular value decomposition analyses. Analysis of the monthly mean circulation fields and API showed that there is a clear relationship between the inter-annual variability of monthly averaged air quality over eastern China and the large scale circulations, including inter-annual movement of the western pacific subtropical high, the strength of the low-level winds, and the location of the Meiyu front over China