Urbanization exacerbates disparities in exposure to air pollution in China.

Prolonged exposure to fine particulate matter (PM2.5) is associated with harmful impacts on human health and population growth in urban areas has exacerbated this exposure. In this study, we compare the exposure between cities at a national level and between different regions within cities considering the population in situ. We estimate the impacts of pollution and population on exposure by spatial and time series analysis from 2000 to 2018 based on 1-km grid data. Our results show that the exposure significantly increases with an increase in city size but is not necessarily related to higher PM2.5 concentrations. Notably, nonurban areas within most prefecture cities have a higher exposure than urban areas. The exposure follows an inverted U-shaped pattern over time across all cities, which are at varying stages within this trend. Nationally, it grows by 0.9 billion person-levels/year during the increasing stage and reduces by 1.0 billion person-levels/year during the decreasing stage. For urban areas, population growth is the dominant factor that determines the exposure during the increasing phase, while changes in air pollution dominate during the decreasing phase. In nonurban areas, however, the change in air pollution plays a more decisive role during both stages. Understanding the spatial distribution and the driving process of exposure provided directions for the country and each prefecture city to balance the benefits of air pollution control, mitigation costs, addressing disparities, and increasing national welfare.