Characteristics and sources of air-borne particulate in Urumqi, China, the upstream area of Asia dust
A sampling campaign of aerosols over Urumqi from 2004 to 2007 with detailed and systematic analysis was carried out to investigate the severe air pollution in Urumqi, China, which is located nearby the upstream area of Asia dust. It was found that Urumqi city was the severest polluted city over the world. The average PM 2.5 and TSP concentrations in the winter of 2007 were 187 and 385 μg m -3 with maximum of 487 and 1313 μg m -3, respectively, 12 times higher than USA standard for PM 2.5 and 3 times the National Ambient Air Quality Standard of China for TSP. The city's industrial emissions of sulfur dioxide were converted to sulfate in the air, and sulfate-rich soil dust was transported to Urumqi's air from agricultural fields south of Jungger Basin and surrounding salt lake areas. The mixing of the local anthropogenic aerosol with the transported soil dust from outside the city was the main sources of the high concentration of sulfate, one of the main factors causing the heavy air pollution over Urumqi. The high concentration of ammonium and sulfate salts in the aerosol from both inside and outside city and the low wind speed might be the main factors to form the heavy haze over the Urumqi.