Long-term ambient air pollution levels in four Chinese cities: inter-city and intra-city concentration gradients for epidemiological studies
Journal of Exposure Science and Environmental Epidemiology
The field data collection of an air pollution epidemiologic study was carried out from 1993 to 1996 in four Chinese cities of Lanzhou, Chongqing, Wuhan, and Guangzhou. In each city, an urban district and a suburban district were selected. Ambient concentrations of total suspended particles ( TSP ) , size -fractionated particulate matter including PM 2.5 , PM 2.5 -10 , and PM 10 , sulfur dioxide ( SO 2 ) , and oxides of nitrogen ( NO x ) were measured in these districts. The results indicate the
... esults indicate the presence of wide inter -city and intra -city gradients in long -term ambient levels of these measured pollutants. Across the eight districts, the 1993 -1996 4 -year means of TSP, SO 2 , and NO x ranged from 198 to 659 g / m 3 , from 14.6 to 331 g / m 3 , and from 31.5 to 239 g / m 3 , respectively, and the 1995 -1996 2 -year means of PM 2.5 , PM 2.5 -10 , and PM 10 ranged from 51.5 to 142 g / m 3 , from 29.2 to 107 g / m 3 , and from 80.7 to 232 g / m 3 , respectively. These pollution ranges substantially extended the upper end of the pollution ranges of previous air pollution epidemiologic studies conducted in North America and Europe. In each district, significant correlations among the measured pollutants were observed for daily concentrations. However, the gradient patterns in longterm means of different pollutants were different across the eight districts. ( e.g., PM 2.5 -10 and TSP were highest in the Lanzhou urban district, PM 2.5 and PM 10 were highest in the Guangzhou urban district, SO 2 was highest in the Chongqing urban district, and NO x was highest in the Guangzhou urban district ) . In general, seasonal variations were present in the ambient concentrations with high levels often occurring in winter months. The eight districts may be classified into four district clusters based on integrated levels of all measured pollutants. These features of the ambient air pollution have important implications for epidemiological studies and may provide unique opportunities to study exposure -effects relationships in the four Chinese cities.