Abstract: | While a growing literature in economics has established the harmful health effects of longstanding criteria air pollutants such as ozone and carbon monoxide, fine particulate air pollution is relatively understudied. This paper provides evidence on the harmful effects of fine particulate pollution for Ontario, where municipalities enjoy particulate levels well below US Environmental Protection Agency (EPA) standards and predominantly below Canada‐wide standards. Results provide strong evidence for the detrimental effect of fine particulate pollution for the respiratory health of children, with a one standard deviation change in particulate pollution, leading to a 4% increase in respiratory admissions. While these results inform the stringency of current pollution standards, they also highlight the importance of an international approach to air quality. For instance, the paper also shows that particulate levels in Ontario municipalities are strongly influenced by southerly winds from US jurisdictions, which adhere to more lenient EPA standards. |