Revisiting PM2.5 pollution along urban-rural gradient and its coupling with urbanization process, a new perspective from urban pollution island analysis

Urbanization leads to widespread urban pollution island effect. Improving our understanding of this phenomenon and its coupling with urbanization is a matter of public concern. In this study, 13 cities in the Beijing-Tianjin-Hebei region experiencing various urbanization and fine particulate matter (PM 2.5 ) pollution were chosen for analysis. We proposed a two-dimensional Gaussian model to index the urban pollution island effect in terms of intensity ( I ) and footprint ( F ). Then, the dynamic of I and F in the case cities during 2000–2015 and their associations with urbanization factors, including Population (POP), Built-up area (BA), and Gross domestic product (GDP), were explored. We found: (1) During 2000–2015, most of the case cities suffered continuous deteriorated urban pollution island effect in both I and F . (2) POP, BA, and GDP all contributed as effective and significant influencers, but their relative contributions to I and F are different. (3) Cities at different urbanization levels not only suffered from their own unique PM 2.5 pollution risks but were also subjected to varying causalities on urban pollution island effect. In the future, multi-index analysis of urban pollution island effect will greatly deepen the understanding of urban air pollution and provide comprehensive references for urban environmental regulation. • Urban pollution island is indexed as intensity and footprint with Gaussian model. • Pollution island provides robust and comprehensive depiction of air pollution risk. • Significant pollution island was found with both raising intensity and footprint. • Urbanization acts as the key driver of urban pollution island effect in BTH region. • Pollution island and its coupling with urbanization varied across cities and times.