Vertical distributions of SO2 and NO2 in the lower atmosphere in Beijing urban areas, China

Measurements of SO2 and NO2 were conducted from January to March 2001 and August 2003 at a 325 m meteorological tower in Beijing. The concentrations of SO2 and NO2 observed by passive samplers at ten heights showed complex vertical distributions in winter and summer. The vertical profiles of pollutants were influenced by source emissions, meteorological conditions, urban canopy and other factors. The comparison analysis of winter and summer pollutant concentrations suggests that the decrease in SO2 concentration was significant in summer, and the reduction of NO2 was relatively not distinctive. Domestic heating and industrial sources were major sources of SO2 in urban areas of Beijing. Differing from SO2, urban NO2 was closely related to traffic emission. Meteorological evidence suggests that strong temperature inversions influence vertical distribution of air pollutants over urban Beijing. The high levels of SO2 and NO2 concentrations were due to the accumulation of pollutants resulting from the stable atmosphere prevalent during the measurement period. The vertical distributions of air pollutants were controlled and affected by atmospheric dynamical characteristics.