The Campaigns of Air Quality Research in Beijing and Surrounding Region 2006 (CAREBeijing-2006) were mainly focused on the influence of the regional aerosol on the air pollution in Beijing. The urban aerosol was characterized in detail. The particle size distributions were also compared to those measured at a regional site (Yufa) approximately 50 km south of the urban site at Peking University (PKU). At PKU, total particle number and volume concentrations were (1.8 +/- 0.8) x 10(4) cm(-3) and 83.5 +/- 57.9 mu m(3) cm(-3), respectively. Days in three consecutive summers of 2004, 2005, and 2006 were classified as polluted days with PM10 over 150 mu g m(-3) and nonpolluted days with lower PM10. On nonpolluted days, particle number size distributions showed a maximum at about 60 nm with Aitken mode particles dominating number concentration. On polluted days, the contribution of accumulation mode particles increased, shifting the maximum of the number size distribution to over 80 nm. On polluted days with stagnant meteorological conditions, secondary aerosol dominated, with SO42-, NO3-, and NH4+ accounting for over 60% of accumulation mode particle mass. Particle number size distributions at both sites were similar. Number and volume concentrations of total particles at Yufa were 6% and 12% lower, respectively; those of accumulation mode particles were 2% and 15% lower. This means that air pollution in Beijing is mainly a regional problem. The regional accumulation mode particles are a metric for assessing the air quality since they influence most the visibility and total mass concentration. Their number and volume concentrations on polluted days were 5 x 10(3) cm(-3) and 30 mu m(3) cm(-3), respectively. Five new particle formation (NPF) events with continuous smooth growth were observed at both PKU and Yufa during CAREBeijing-2006. These NPF events are regional or semiregional. Growth rates at PKU ranged from 1.2 to 5.6 nm h(-1), and formation rates ranged from 1.1 to 22.4 cm(-3) s(-1). SO42-, NH4+, and oxalate might be important contributors to NPF events.

Fine particles (PM2.5, i.e., particles with an aerodynamic diameter of <= 2.5 mu m) were collected from the air in August 2005, August-September 2006, and January-February 2007, in Beijing, China. The chemical compositions of particulate organic matter in the ambient samples were quantified by gas chromatography/mass spectrometry. The dominant compounds identified in summertime were n-alkanoic acids, followed by dicarboxylic acids and sugars, while sugars became the most abundant species in winter, followed by polycyclic aromatic hydrocarbons, n-alkanes, and n-alkanoic acids. The contributions of seven emission sources (i.e., gasoline/diesel vehicles, coal burning, wood/straw burning, cooking, and vegetative detritus) to particulate organic matter in PM2.5 were estimated using a chemical mass balance receptor model. The model results present the seasonal trends of source contributions to organic aerosols. Biomass burning (straw and wood) had the highest contribution in winter, followed by coal burning, vehicle exhaust, and cooking. The contribution of cooking was the highest in summer, followed by vehicle exhaust and biomass burning, while coal smoke showed only a minor contribution to ambient organic carbon.

To further understand and improve air quality for the 2008 Beijing Olympic Games, the Campaigns of Air Quality Research in Beijing and Surrounding Region 2006 (CAREBeijing-2006) were carried out in an urban and a suburban area from 10 August to 12 September 2006. As a part of an intensive series of measurements, the optical and physical properties of the aerosol were monitored together with identification of the chemical species involved. A method to calculate the hygroscopic factor for aerosol scattering f(RH), defined as the ratio of the aerosol scattering coefficient at given relative humidity (RH) to that at 35% RH, is proposed on the basis of the optical parameters. Over the course of the study f(80%) = 1.63 +/- 0.19. The observation that the molar ratio of NH4+ to (2*SO42- plus NO3-) was very close to 1 implies that the chemical form of the sulfate aerosol may be ammonium sulfate (NH4)(2)SO4 and that nitrate possibly existed as NH4NO3. On the basis of the measurements of size-resolved chemistry, RH, and published functional relationships between the chemical composition and water uptake, the aerosol scattering coefficients could be calculated by the Mie theory for the major particle species (ammonium sulfate, ammonium nitrate, sodium chloride, particulate organic matter, elemental carbon, and residual material). This retrieval method synthesizes the high temporal resolution of mass concentration measurements and low temporal resolution size distribution for water soluble ionic components and carbonaceous aerosols. A local closure experiment is obtained by comparing the measured f(RH) with model calculations using aerosol chemical composition and chemical thermodynamics. Results from the closure study show that the measured and the predicted values of f(RH) agree within measurement uncertainties.