Chronic exposure to ambient ne particulate matter (PM2.5) represents one of the largest global public health risks, leading to millions of premature deaths annually. For a country facing high and spatially variable exposures, prioritizing where to reduce PM2.5 concentrations leads to an inherent tradeoff between saving the most lives and reducing inequality of exposure. This tradeoff results from the shape of the concentration-response function between exposure to PM2.5 and mortality, which indicates that the additional lives saved per unit reduction in PM2.5 declines as concentrations increase. We estimate this concentration-response function for urban areas of India, nding that a 10 unit reduction in PM2.5 in already-clean locations will reduce the mortality rate substantially (4.2% for a reduction from 30 to 20 µgm-3), while a 10 unit reduction in the dirtiest locations will reduce mortality only modestly (1.2% for a reduction from 90 to 80 µgm-3). We explore the implications of this PM2.5/mortality relationship by considering a thought experiment. If India had a xed amount of resources to devote to PM2.5 concentration reductions across urban areas, what is the lives saved/inequality of exposure tradeoff from three different methods of employing those resources? Across our three scenarios-1) which reduces exposures for the dirtiest districts, 2) which reduces exposures everywhere equally, and 3) which reduces exposures to save the most lives-scenario 1 saves 18,000 lives per year while reducing the inequality of exposure by 65%, while scenario 3 saves 126,000 lives per year, but increases inequality by 19%.
Signi cance StatementDesigning policies to reduce exposure to PM 2.5 is complicated by the apparent supralinear relationship between PM 2.5 and premature mortality. This relationship-which we estimate for Indian urban areasindicates that more lives can be saved by reducing exposures in the already-clean locations than in the dirtiest locations. Thus, policymakers face a troubling tradeoff, between maximizing lives saved and reducing the inequality of exposure to pollution. Many air policies impose an upper limit on exposure, thereby cleaning the dirtiest locations while reducing exposure inequality. We illustrate the tradeoff between lives saved and inequality, highlighting the challenge facing policy makers charged with protecting human health equitably.