Mountains of Evidence: The Effects of Abnormal Air Pollution on Crime

We find that air pollution increases crime in a city that ranks in the worst two percentiles worldwide for dirty winter air. Our identification strategy employs distinct geographic features of Almaty, Kazakhstan: cleaner mountain winds and frequent temperature inversions. Using these variables to instrument for PM2.5 air pollution, we estimate a PM2.5 elasticity of the expected crime rate more than four times as large as similar estimates from cleaner cities. Among crime types, we estimate statistically significant effects of air pollution on property crime, and we find no evidence of an effect on violent crime. These results are consistent with theory that air pollution induces higher discounting rather than aggression. We extend this theory and find that whether air pollution has distinct effects on crimes of varying severity depends on whether the population is more heterogenous in the outside option or in the discount factor. Using microdata on crime severity, we find statistically significant increases in both major and minor crime rates from air pollution, and we fail to reject common PM2.5 elasticities of minor and major crime rates. The greater scale of major crimes implies that they contribute more to the total crime rate increase from air pollution.