Relationships between submicrometer particulate air pollution and air mass history in Beijing, China, 2004–2006 B. Wehner1, W. Birmili1, F. Ditas1, Z. Wu2, M. Hu2, X. Liu3, J. Mao3, N. Sugimoto4, and A. Wiedensohler1 1Leibniz-Institute for Tropospheric Research, 04318 Leipzig, Germany 2State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, P. R. China 3Department of Atmospheric Sciences, College of Physics, Peking University, Beijing 100871, P. R. China 4Atmospheric Environment Division, National Institute for Environmental Studies, Tsukuba, Japan
Abstract. The Chinese capital Beijing is one of the global megacities where the effects of rapid economic
growth 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 a
function of regional meteorological transport. An essential result is that the particle size
distribution in Beijing depends to large extent on the history of the synoptic scale air masses. A
first approach based on manual back trajectory classification yielded differences in particulate
matter mass concentration by a factor of two between four different air mass
categories, including three main wind directions plus the case of stagnant air masses. A back
trajectory 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 play
an essential role on the PM concentrations in Beijing. Slow-moving air masses were shown to be
associated with an effective accumulation of surface-based anthropogenic emissions due to both, an
increased residence time over densely populated land, and their higher degree of vertical
stability. For the six back trajectory clusters, differences in PM1 mass concentrations by a
factor of 3.5, in the mean air mass speed by a factor of 6, and in atmospheric visibility by a
factor of 4 were found. The main conclusion is that the air quality in Beijing is not only degraded
by anthropogenic aerosol sources from within the megacity, but also by sources across the entire
Northwest China plain depending on the meteorological situation.
Citation: Wehner, B., Birmili, W., Ditas, F., Wu, Z., Hu, M., Liu, X., Mao, J., Sugimoto, N., and Wiedensohler, A.: Relationships between submicrometer particulate air pollution and air mass history in Beijing, China, 2004–2006, Atmos. Chem. Phys., 8, 6155-6168, doi:10.5194/acp-8-6155-2008, 2008.