PM2.5, aerosol optical coefficients, CCN activation were monitored in Shanghai during spring 2012.
Organic matter, sulfate, nitrate, ammonium were major components of PM2.5.
Diurnal variations of aerosol optical coefficients had a typical bimodal pattern.
Aerosol particle chemistry contributed significantly to CCN activation.
The semi-diurnal mean aerosol mass concentration, chemical composition, and optical properties of PM2.5 were investigated in Shanghai during the spring of 2012. Slight pollution was observed during the study period. The average PM2.5 concentration was 64.11 ± 22.83 μg/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 albedo 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.