Trends of Urban Air Pollution in Zhengzhou City in 1996-2008

Urban air pollution is a commonly concerned environmental problem in the world. Identification of air quality trend using long-term monitoring data is helpful to understand the effectiveness of pollution control strategies. This study, using data from six monitoring stations in Zhengzhou City, analyzed the changing trend in concentrations of SO2, NOx/NO2 and TSP/PM10 in 1996-2008, based on non-parametric Mann-Kendall test and Sen's slope estimator, and evaluated the comprehensive air pollution level using Multi-Pollutant Index (MPI). It was found that the concentration of each pollutant exceeded obviously the World Health Organization (WHO) guideline value, but the changing trend varied: SO2 and NO2 were significantly increased mainly due to an increase in coal consumption and vehicle number, while NOx, TSP and PM10 decreased. The air pollution was serious, and differed markedly among the three functional regions: it is the most severe in the Industrial and Residential Area (IRA), followed by the Transportation Hub and Business District (THBD), and then the High-tech, Cultural and Educational Area (HCEA). Different from NO2 concentration that had a similar change trend/rate among the function regions, the change rate of PM10 concentration differed spatially, decreased much more obviously in THBD than other two regions. For the whole city, the comprehensive air pollution level declined gradually, illustrating that the air quality in Zhengzhou was improved in the last decade.