Air Pollution and Cardiovascular Health: Evidence from Agricultural Fires in India

Abstract:

Recent medical literature suggests that a potential mechanism through which air pollution exposure can lead to adverse health outcomes is by increasing hypertension and cardiovascular stress. However, causal evidence to this effect is limited. In this study, we show that both short-term and long-term exposure to poor air quality harms adults' cardiovascular health in low-income settings. Using satellite data, we exploit variation in daily agricultural fires and wind direction to construct a measure of plausibly exogenous variation in pollution exposure across India. Using data from pollution monitoring stations across 250 cities, we first show that up-wind fires increase particulate pollution. In contrast, fires located downwind do not affect air quality. Second, matching fire exposure to nationally representative health data for more than 0.8 million individuals, we find that short-term exposure to up-wind fires (within 24 hours of the health test) significantly raises the risk of high blood pressure. Our results suggest a ten-unit increase in PM10 results in an 8.3 percentage point increase in the likelihood of elevated blood pressure. We also find that accumulated long-term exposure over a one-year horizon to poor air quality results in high blood pressure and an increase in the risk of obesity. Using a machine learning model to classify high-risk subgroups, we characterize the substantial heterogeneity in effect sizes across the population. We find that the most-affected individuals experience an impact of more than double the average effect. Overall, our results suggest that, first, the cost of the health damages from air pollution in developing countries is likely to be much higher than that implied by previous estimates. Second, these adverse health outcomes are concentrated among high-risk and vulnerable groups, thereby amplifying preexisting health inequities.