Long-term ambient air pollution levels in four Chinese cities: inter-city and intra-city concentration gradients for epidemiological studies

Abstract

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 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.

Children's respiratory morbidity prevalence in relation to air pollution in four Chinese cities.

“…The details on the air pollution measurements can be found in the previous report by Qian et al (6). Briefly, concentrations of TSP, SO 2 , and NO x were obtained from municipal air pollution monitoring stations, because these regulated pollutants were routinely measured in all the study districts.…”

“…The schoolyard measurements, however, were made for only 2 years (1995 and 1996) because of financial and logistical limitations. The TSP, SO 2 , and NO x measurements at the municipal monitoring stations strictly followed the standard methods set by the State Environmental Protection Administration of China (6,7). In the schoolyards, concentrations of PM 2.5 and PM 10-2.5 were measured using dichotomous samplers (model 241; Sierra-Anderson, Atlanta, GA) provided by U.S. EPA with certification as reference sampling devices.…”

“…The study districts were selected with the aims of maximizing the between-city and within-city concentration gradients in the ambient air pollutants of interest and of minimizing the correlation between district-specific ambient particulate and sulfur dioxide pollution. These aims were achieved by selecting an urban district and a suburban district in each of the four cities (6). Elementary school students and their families were chosen to provide the subject pool.…”

“…The study included multiyear measurements of four size fractions of ambient PM-total suspended particulates (TSP), particles with aerodynamic diameter ≤ 10 µm (PM 10 ) and ≤ 2.5 µm (PM 2.5 ), and the coarse fraction of PM 10 (diameters between 2.5 and 10 µm, PM 10-2.5 )-and of SO 2 and oxides of nitrogen (NO x ). Ambient concentrations of these pollutants measured in each of the eight districts, along with geographic locations, climate, population density, and major indoor and outdoor pollution sources, have been reported in detail elsewhere (6). The Four Chinese Cities Study also provides an opportunity to study air pollution effects in urban and suburban residents of Chinese ethnicity.…”

“…These cities were chosen because they exhibited wide between-city gradients and within-city differences of ambient pollutant levels, thus offering a valuable epidemiologic opportunity for exposureresponse assessment (6). The study included multiyear measurements of four size fractions of ambient PM-total suspended particulates (TSP), particles with aerodynamic diameter ≤ 10 µm (PM 10 ) and ≤ 2.5 µm (PM 2.5 ), and the coarse fraction of PM 10 (diameters between 2.5 and 10 µm, PM 10-2.5 )-and of SO 2 and oxides of nitrogen (NO x ).…”