“…The expansion of built-up area has a significant positive effect on urban haze pollution, but unlike population size, the secondary indicator of built-up area does not have a significant effect on haze pollution, indicating that the impact of urban area expansion on haze pollution is mainly monotonic and increasing. Possible reasons are that, on the one hand, the expansion of built-up areas will generate a large number of pollution sources, and also crowd the surrounding agricultural land, wetlands and woodlands, etc., breaking the ecological balance and reducing the ability of the environment to recover itself, on the other hand, the urbanization of people in China obviously lags behind the urbanization of land, and the continuous expansion of built-up areas further increases the problem of incompatible development between the two, indirectly aggravating haze pollution (Li et al, 2021;Zhang et al, 2022).…”