Size- and time-resolved chemical particle characterization during CAREBeijing-2006: Different pollution regimes and diurnal profiles

Beijing, the capital of China, faces severe air pollution problems, resulting from a steep economic growth during the past decades. To better characterize the processes leading to the frequently observed high concentrations of air pollutants on a regional scale, the international field campaign "Campaigns of Air Quality Research in Beijing and Surrounding Region 2006'' (CAREBeijing-2006) was conducted in summer 2006. In this contribution, we present chemical data of size-resolved particles, obtained by a five-stage Berner impactor during 3 weeks at both an urban and suburban site in the area of Beijing, China. The samples were analyzed for inorganic ions (Cl-, SO42-, NO3-, NH4+, K+, Ca2+, Na+, and Mg2+), carbon sum parameters (OC, EC, and WSOC), and a variety of organic compounds such as dicarboxylic acids, alkanes, PAHs, and, for the first time in China, nitrooxy-organosulfates. On average, the observed PM10 (where PM is particulate matter) mass concentrations were 133 mu g m(-3) and 112 mu g m(-3) at the urban and suburban site, respectively. A high influence of meteorology on the PM pollution was observed and is discussed. The highest concentrations of both PM mass and particle constituents were observed when sampled air masses originated south of Beijing and moved over the area with low wind speeds. During such periods, a strong increase of daytime concentrations of the secondary ions sulfate, nitrate, ammonium, and also some dicarboxylic acids could be observed. A strong diurnal variation of particle sulfate concentration with increasing values from morning to afternoon was observed during an intensive period, which could be attributed to regional production. Similar observations were made for oxalic acid. Generally, water-soluble organic carbon concentrations were enhanced by a factor of 2 in fine particles during the studied period of intense photochemistry. Elemental carbon, alkanes, and PAHs showed clear nighttime concentration maxima obviously due to enhanced emissions and a relatively low mixing volume during night. For the newly studied compound group of nitrooxy-organosulfates, qualitative data can be presented indicating an influence of nighttime chemistry and/or anthropogenic activities on their concentrations. The investigation of an intense nucleation and particle growth event revealed that the youngest particles largely consist of ammonium sulfate and primary carbonaceous material, with a possible contribution of secondary organic compounds.