The implication of carbonaceous aerosol to the formation of haze: Revealed from the characteristics and sources of OC/EC over a mega-city in China

The characteristics and sources of organic carbon (OC) and elemental carbon (EC) in PM2.5 in 2006-2007 as well as their impact on the formation of heavy haze in Shanghai were investigated. Daily average concentrations of OC and EC ranged from 1.8 to 20.1 μg m−3 and 0.5-7.8 μg m−3 with averages of 7.2 and 2.8 μg m−3, respectively. The carbonaceous aerosol (OC plus EC) contributed to ∼27.2% of the total mass of PM2.5 on annual average. Obvious seasonal variation was observed in both OC and EC. The percentage of secondary organic carbon (SOC) contributed to OC was in a range of 2.4-66.8%, with an average of 40.1%. Three types of haze were classified based on their chemical composition. OC, EC, SO2/NO2 (in turn, SO42−/NO3−) were responsible for the formation of the three types of haze, respectively. The carbonaceous aerosol was one of the key factors in the formation of haze. Local emissions were the dominant sources of OC and EC in warm seasons, and long-range transport had a significant contribution to OC and EC in PM2.5 in spring and winter in Shanghai.