Does income inequality influence health vulnerability to pollution? Evidence from France

This study investigates whether income inequality within a population influences the health effects of pollution. Specifically, we empirically estimate the causal impact of particulate matter (PM10) on mortality in France, using wind direction as an instrumental variable, and explore how income inequality modifies this relationship. Our findings reveal a statistically and economically significant impact of pollution exposure on the mortality of individuals aged 50 or older, which intensifies in municipalities with higher levels of income inequality. More precisely, while the effect of PM10 is not significant in municipalities with the lowest levels of disparities, it is significant for the others and increases with the level of inequality within the municipalities. The impact of PM$_{10}$ on the mortality of individuals aged 50 or older in the top 33% of municipalities with the highest inequality is up to twice as large as in municipalities with intermediate levels of inequality. This result is particularly striking given that it concerns a country like France, which has relatively low income inequality. To provide a comprehensive understanding of the potential underlying mechanisms, we develop a theoretical model and empirically test its predictions. We conclude that the observed variation in vulnerability to pollution across municipalities, stratified by inequality levels, could have been but is not attributable to differences in public health expenditure, pollution exposure (between and within municipalities), or poverty prevalence and intensity. Our results suggest that inequality plays a significant role in environmental health, worthy of further research.