Atmospheric effects on winter SO2 pollution in Lanzhou, China

Lanzhou is one of the most polluted cities in China. Sulfur dioxide (SO2) concentrations have shown evident seasonal variability. Pollution was generally within the second-level criterion (< 0.15 mg m− 3) in spring, summer, and fall but was much higher than the second-level criterion and sometimes reaches mid-level pollution (API > 200) in winter. Meteorological conditions (low winds, stable stratification) were found to be important for SO2 pollution. Observational and modeling studies conducted in the present study showed a close connection between static stability and SO2 pollution in Lanzhou, China, during winter.