This study aims to understand a nuanced intra-urban PM2.5 distribution pattern and provide insights into the environmental consequences of urban development. Inspired by the impact that the urban-rural divide has had on nation-wide urbanization progress, the study approaches urban areas as a series of hotspots and non-hotspots, applying Zipf's law-ruled spatial clustering method on nighttime light data. We found that PM2.5 concentrations and exposures in China decreased notably from 2005 to 2020, affirming the efficacy of that country's air pollution control policies. However, the difference in exposure between hotspot and non-hotspot regions indicates that outside-hotspot PM2.5 exposures across most cities consistently exceeded within-hotspot ones, despite the observed declining trend in exposure disparity during the 15-year time span. The diminishment in exposure disparity primarily stems from the reduction in PM2.5 levels rather than targeted equity measures. All of these outcomes point to the importance of integrating air quality management with broader city planning, economic, and health policies.