Air pollution and morbidity: evidence from internet search behavior in a panel of 100 Chinese cities

We provide linear and nonparametric 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 upwind 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. Among pollutants, the effect can be tied specifically to particulate matter (PM2.5\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$PM_{2.5}$$\end{document}). The results prove resilient in a series of robustness tests and falsification exercises.