Characteristics of atmospheric pollution during 2001⌼2009 in Lanzhou, northwest China

The annual tendency, monthly and seasonal distribution of main air pollutants SO₂, NO₂ and PM₁₀ and the characteristics of atmospheric pollution in Lanzhou have been analyzed based on the atmospheric monitoring data from 2001 to 2009. The results indicate that Lanzhou is one of the most heavily polluted cities in China, which have more heavy pollution weather number and less fine weather compared with other large cities in China. During the last nine years, there have been remarkable decrease in PM₁₀ and SO₂, and a slight increase in NO₂ mass concentrations. However, the concentrations of the three pollutants were relatively high. PM₁₀ was the dominant pollutants while the mass concentration of SO₂ and NO₂ were relatively low. The pollution of PM₁₀, SO₂ and NO₂ presented obvious seasonal change: air pollution was severer in winter and milder in summer. PM₁₀ exceeded the second level of the national ambient air quality standard (NAAQS) all the years, the SO₂ exceeded the standard in part years, and the concentration of NO₂ no exceeded the standard, so they showed a coal smoke pollution typically. The meteorological conditions had a vital influence on the concentration of pollutants. A comparison of the mass concentrations of the three pollutants under different meteorological conditions has revealed that a negative correlation existed between the concentrations of pollutants and wind speed. Precipitation had important cleanup effect on pollutants. A negative correlation also existed between the visibility and the three pollutants.