Figure 2:
Population size amplifies empirically derived marginal health benefits (MB) of PM2.5 reduction, which deviate from classical assumptions.
The MB of reducing annual mean PM2.5 (thick solid curve, representing monetized regional total health benefits per µg/m3 reduction) is typically nonlinear, with substantial benefits persisting at low concentrations. Unlike classical models (cf. Fig. 1) that often assume diminishing returns, this empirically informed curve can exhibit steeper slopes (greater perunit benefit) when further abating pollution in cleaner environments. Critically, regional total health benefits, and thus the MB curve’s position, are significantly higher in regions with a large total population (upper dashed lines) compared to regions with a small total population (lower dashed lines) for any given PM2.5 level. This reflects the larger number of individuals benefiting from air quality improvements in regions with a larger total population.