This paper assesses whether air quality influences public transportation ridership in the city of Chicago. Urban air pollution is a serious health risk, and a priority of urban municipalities. Public transportation is an attractive option for governments attempting to curb urban air emissions. I use data from the Chicago Transit Authority (CTA) and the EPA’s Air Quality Index (AQI) to explore the relationship between a day’s air quality and CTA ridership. I employ three different model specifications, rail, bus and total ridership, to test whether high AQI values (poor air quality) result in increased public transportation ridership in the city of Chicago. My results provide several statistically significant estimates, however, the results to not match across my models, suggesting that there are complex underlying differences between rail and bus ridership. My results reveal the value and possibilities of continued research into the differences between rail and bus ridership in Chicago, or public transportation systems in other American cities.



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