Method for quantifying the contribution of urbanization on population exposure to air pollution

Rapid urbanization has negative effects on the ecological environment, especially the air pollution in some areas of China, where the air has been widely polluted by the major pollutant known as fine particulate matter (PM2.5) in recent decades. The population exposure in the contaminated area is generally due to the expansion of the contaminant’s area, but is also highly attributed to the population migration caused by rapid urbanization. In this study, we established a quantitative model for evaluating the contribution of urbanization on the population exposed to air pollution, and selected the Beijing Tianjin-Hebei urban agglomeration, which has been suffering the most severe PM2.5 pollution in China and undergoing rapid urbanization. By using PM2.5 concentration, population raster data,and population natural growth rate data from 2000 to 2015, we quantitatively explored the contribution of urbanization on the population exposed to air pollution. The results showed that:（1） the Beijing-Tianjin-Hebei area affected by pollution and population changed significantly, resulting in alarge number of people exposed to PM2.5 pollution.（2） Contribution of population migration and natural growth caused by urbanization were varied: in general, the total population migration contribution rate, which is the percentage of migrated population in the total increased population that exposed to PM2.5 pollution, of the Beijing-Tianjin-Hebei urban agglomeration was 48%, the total population migration contribution rate of Beijing and Tianjin were 94% and 88% respectively, and that of Hebei Province was-32% from 2000 to 2015. In the continuously polluted area, the contribution rates of population migration in Beijing and Tianjin were close to 100% in 2000-2015, while the contribution rate of migration in Hebei was-26%; in Hengshui City, Hebei Province, the contribution rate of population migration was-6613% in 2010-2015. In the areas into which pollution expanded, the contribution of population migration in Beijing and Tianjin were 86% and 84% respectively, while the contribution rate of population migration in Hebei province was-757% in 2000-2015. This study establishes a quantitative approach to reveal the quantitative contribution of population exposure to air pollution caused by urbanization.