Relationships between submicrometer particulate air pollution and air mass history in Beijing, China, 2004–2006

[摘要] The Chinese capital Beijing is one of the global megacities where the effects of rapid economicgrowth have led to complex air pollution problems that are not well understood. In this study,ambient particle number size distributions in Beijing between 2004 and 2006 are analysed as afunction of regional meteorological transport. An essential result is that the particle sizedistribution in Beijing depends to large extent on the history of the synoptic scale air masses. Afirst approach based on manual back trajectory classification yielded differences in particulatematter mass concentration by a factor of two between four different air masscategories, including three main wind directions plus the case of stagnant air masses. A backtrajectory cluster analysis refined these results, yielding a total of six trajectory clusters.Besides the large scale wind direction, the transportation speed of an air mass was found to playan essential role on the PM concentrations in Beijing. Slow-moving air masses were shown to beassociated with an effective accumulation of surface-based anthropogenic emissions due to both, anincreased residence time over densely populated land, and their higher degree of verticalstability. For the six back trajectory clusters, differences in PM₁ mass concentrations by afactor of 3.5, in the mean air mass speed by a factor of 6, and in atmospheric visibility by afactor of 4 were found. The main conclusion is that the air quality in Beijing is not only degradedby anthropogenic aerosol sources from within the megacity, but also by sources across the entireNorthwest China plain depending on the meteorological situation.

[学科分类] 大气科学