Inequality amplifies the negative association between life expectancy and air pollution: A cross-national longitudinal study

Ambient air pollution, in the form of fine particulate matter (PM2.5), poses serious population health risks. We estimate cross-national longitudinal models to test whether the negative relationship between life expectancy and PM2.5 concentration is larger in nations with higher levels of income inequality. The dependent variable is average life expectancy at birth, and the focal predictor variables include PM2.5 concentration, income inequality, and the two-way interaction between them. We also estimate the average marginal effects of PM2.5 concentration from low to high values of income inequality, and the predicted values of life expectancy from low to high values of PM2.5 concentration and income inequality. Results indicate that the negative relationship between life expectancy and PM2.5 concentration is larger in nations with higher levels of income inequality, and the reductions in predicted life expectancy are substantial when both PM2.5 concentration and income inequality are high. We suggest that the theoretical principles of Power, Proximity, and Physiology help explain our findings. This study underscores the importance in considering the multiplicative impacts of environmental conditions and socioeconomic factors in the modeling of population health.