Probing the severe haze pollution in three typical regions of China: Characteristics, sources and regional impacts

PM2.5 with its major chemical components were measured and analyzed during a concurrent haze in Jan. 1-19, 2013 at three sites (Shanghai, Beijing, and Huaniao, a remote isle over the East China Sea) to probe the sources and formation process of such a severe haze over three typical regions in China. The mean PM2.5 concentrations during the severely polluted days reached 180.8 μg m−3, 299.2 μg m−3, and 131.1 μg m−3 in Shanghai, Beijing, and the Huaniao Isle, respectively. The mass ratio of the sum of SO42−, NO3−, and NH4+ to PM2.5 were over 1/3 during the polluted days at all the three sites. Promoted gas-to-particle transformations from acidic SO2 and NOx to SO42− and NO3− under high relative humidity conditions played a major role in the formation of this severe haze. Significant contribution of traffic emissions to the haze formation over China was suggested to be one of the major sources in triggering the heavy haze over China. Specifically, there was a more contribution from traffic in Shanghai than in Beijing as indicated by the higher NO3−/SO42− ratio in Shanghai. In Beijing, the enhanced coal combustion for winter heating along with the traffic emission was suggested to be the major two sources of this haze episode. Typical pollution elements such as As, Cd, and Pb as well as Cl− and K+ were substantially enhanced in the severely polluted days. Although the Huaniao Isle is located in the remote oceanic area as a background site, pollution elements, secondary ions, and K+ all increased substantially during the polluted days. As visualized by the backward air mass trajectories associated with the potential source region identification technique, air masses that passed over Northern China and Yangtze River Delta evidently invaded the offshore areas of Eastern China. The ratios of As, Cd, Cu, Zn, and K+ to Al at the Huaniao Isle were closer to those of Beijing rather than Shanghai, indicating that the marine aerosol over the East China Sea had been significantly polluted via the long-range transport of anthropogenic pollutants originating from Northern China.