Air Pollution and Morbidity: Evidence from Internet Search Behavior in a Panel of 100 Chinese Cities

We provide linear and non-parametric estimates of the causal impact of short-term exposure to polluted air on the prevalence of cough in a panel of a hundred Chinese cities. In our central estimate, which exploits plausibly-exogenous variations in the number of agricultural fires burning in the vicinity as an instrument, we find that a one standard deviation increase in airborne pollution causes a roughly 6% increase in the prevalence of cough in the affected city. Amongst pollutants the effect can be tied specifically to particulate matter (PM_2.5). The results prove resilient in a series of robustness tests and falsification exercises.