Regional Characteristics of Air Pollutants during Heavy Haze Events in the Yangtze River Delta, China

Abstract

There were 6 severe haze events over a large area of the Yangtze River Delta (YRD) region in January 2013. In this study, based on the hourly concentrations of trace gases and PM_(2.5) at 10 observation stations (8 city stations, 1 regional background station and 1 island station) during Jan. 1-31, 2013 as well as the concentrations of water-soluble ions at 5 stations (4 city stations and 1 regional background station) during Jan. 18-24, 2013 in the YRD region, the regional characteristics of the air pollutants during heavy haze episodes were investigated in combination with the atmospheric circulation patterns. The concentrations of PM_(2.5) on haze days were 1.6-2.4-fold higher than on clear days. The concentration of PM_(2.5), SO_2, NO_2 and CO increased significantly, with average values of 128.6, 48.5, 78.1 μg m^(-3) and 1.5 mg m^(-3) on haze days, and were 64.6, 36, 52.5 μg m^(-3) and 1.1 mg m^(-3) on clear days. The PM_(2.5) concentration of ten observation sites had positive correlations with CO and NO_2, and had weakly negative correlations with O_3. The sources of PM_(2.5), SO_2, NO_2 and CO were strong in inland cities and weak in coastal cities, and the sources of O_3 were mainly from Wuxi, Suzhou and southeast of An'hui. The mass and water-soluble ion concentrations were both centralized in PM_(2.1) during the haze events; additionally, the NH_4^+, SO_4^(2-) and NO_3^- ions were dominant, constituting 86-90.9% of the total ion concentrations in PM_(2.1). The mass spectra of NH_4^+, K^+, Cl^-, SO_4^(2-), F^-, NO_2^- and NO_3^- had unimodal distributions. The secondary formations of sulfate dominated on haze days, and the nitrate oxidation rates were relatively high for inland cities and low for coastal cities.