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

Abstract

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 PM 1 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.

Chemical characteristics of inorganic ammonium salts in PM<sub>2.5</sub> in the atmosphere of Beijing (China)

“…Thus, the presence of high concentration of primary precursors in the southern regions, such as NH 3 , SO 2 and NO x , led to the high particulate ammonium, sulfate and nitrate concentrations in the atmosphere of Beijing. The indication that the areas to the south of Beijing are major sources of particulate matter for Beijing have been reported in other studies (Xia et al, 2007;Streets et al, 2007;Wehner et al, 2008;Zhao et al, 2009;Wu et al, 2009). In addition, the urban area itself is a major source for traffic emission.…”

A parameterization of low visibilities for hazy days in the North China Plain

“…The volume concentration is representative of the aerosol pollution as it affects visibility and is much more easily measured compared to the aerosol number or surface concentration. The volume concentration is closely related to the mass concentration and can be derived from the mass concentration divided by an average particle density of 1.7 g cm −3 (Wehner et al, 2008). In contrast to insufficient PNSD measurements, long-term measurements of aerosol mass concentration are common in China.…”

Analysis of extinction properties as a function of relative humidity using a <i>κ</i>-EC-Mie model in Nanjing

“…We obtained the mass of each pure species according to the pairing method. Supposing a dry particle density of 1.7 g cm −3 (Wehner et al, 2008), we calculated the volume of the dry particles. Aside from the WSOC and the four types of inorganic components in Table 1, we assumed that other components do not contribute to the hygroscopic properties of the aerosols.…”