Gaseous pollutants in the city of Urumqi, Xinjiang: spatial and temporal trends, sources and implications

Nitrogen oxides (NO2 and NOx), ozone (O3), sulphur dioxide (SO2), benzene, toluene, ethylbenzene and xylenes (BTEX) and ammonia (NH3) were determined in ambient air in Urumqi, the capital of Xinjiang in NW China, from 2010 to 2012 by applying the diffusive sampling approach. Principal component analysis (PCA) was used to identify the major contributions to atmospheric pollution. Four extensive measurement campaigns were performed in the city, where very few investigations had been made on ambient pollution. The impacts of pollutants in four city districts were assessed. Considerably high mean annual concentrations were observed in Urumqi for all toxicants; these latter ranged between 46 and 158 ?g m-3 (SO2), 33-126 ?g m-3 (NO2), 83-141 ?g m-3 (NOx), and 46-82 µg m-3 (BTEX). Nitrogen oxides and BTEX were overall released by industrial plants and motor vehicles. Huge consumption of fossil fuels for energy generation and domestic heating purposes looked as the principal factors causing the high pollution levels recorded. In the winter, coal burning in houses was recognized as a major contributor to SO2 and BTEX budgets. Important ammonia loads were found in the district hosting slaughter and meat treatment facilities. Other primary factors influencing the pollution patterns were variously related to diffusion of chemicals across the atmosphere, i.e.: wind speed and direction, air stagnation and occurrence of inversion events; besides, important roles were played by relevant emission sources (especially for BTEX and NOx), seasonality and photochemistry.