Optical properties and chemical composition of PM_(2.5) in Shanghai in the spring of 2012

The semi-diurnal mean aerosol mass concentration, chemical composition, and optical properties of PM2.s were investigated in Shanghai during the spring of 2012. Slight pollution was observed during the study period. The average PM2.s concentration was 64.11± 22.83μg/m3. The mean coefficients of extinction, scattering, and absorption at 532 nm were 125.9 ± 78.5, 91.1 ± 56.3, and 34.9 ±23.6 Mm-1, respectively. A relatively low mean single scattering alhedo at 532 nm （0.73 ±0.04） and low level of elemental carbon （EC, 2.67± 1.96 μg/m3） suggested that the light absorption was enhanced due to the internal mixing of the EC. Sulfate contributed the most to aerosol light scattering in Shanghai. The chemical composition of PM2.5 was dominated by particulate organic matter, sulfate, nitrate, ammonium, and EC. Anthropogenic sources made a significant contribution to the emission and loading of the particulate pollutants. A relatively good correlation between the aerosol chemical composition and the cloud condensation nuclei （CCN） activation indicated that aerosol chemistry is an important factor that influences the saturated hygroscopicity and growth of the aerosol.

Impacts of aerosol chemical compositions on optical properties in urban Beijing,China

The optical properties of aerosols and their chemical composition, including water-soluble ions, organic carbon （OC）, and elemental carbon （EC） in PM2.5 and PM10, were measured from 26 May to 30 June of 2012 at an urban site in Beijing. The daily average concentrations of PM2.5 and PM10 were 103.2 and 159.6 μg/m^3, respectively. On average, the OC and EC contributed 20.1% and 4.3%, respectively, to PM2.5 and 16.3% and 3.9%, respectively, to PM10. Secondary ions （SO4^2-, NO3-, and NH4^＋） dominated the water-soluble ions and accounted for 57.9% and 62.6% of PM2.5 and PM10, respectively. The wind dependence of PM2.5, OC, SO4^2-, and NO3 implied that the pollution sources mainly came from south and southeast of Beijing during the summer. The monthly mean values of the scattering coefficient （σsc） and absorption coefficient （σab） at 525 nm were 312.9 and 28.7 Mm^-1, respectively, and the mean single-scattering albedo （ω） was 0.85. The wind dependence of σsc revealed that this value was mainly influenced by regional transport during the summer, and the relationship between aab and wind indicated that a high crab resulted from the joint effects of local emissions and regional transport. The reconstructed σsc that was derived from the revised IMPROVE equation agreed well with the observations. The contribution of different chemical species to crsc was investigated under different pollution levels, and it was found that secondary inorganic aerosols accounted for a large part of σsc during pollution episodes （35.7%）, while organic matter was the main contributor to σsc under clean conditions （33.6%）.