COVID-19, Urban Transportation, and Air Pollution

Quantifying the effect of transportation on urban air pollution is challenging because decisions to travel are endogenous to air quality. The spread of COVID-19 offers a unique opportunity for causal identification, as the pandemic directly affects decisions to travel and choices of transportation modes but has little direct effect on air pollution. Leveraging the number of COVID-19 infections and COVID-19-related queries to search engines as instruments, we quantify the effects of three public transportation subsectors (buses, railways, and taxis) and private vehicles on six primary air pollutants in 36 central cities of China. The results demonstrate that the negative effects of urban transportation on air quality are likely to be significantly underestimated without addressing endogeneity in the observational data. After addressing endogeneity, the findings show that every 1% increase in the passenger volume of public transportation and in the congestion index results in a 0.039% and 0.368% increase in the synthesized air pollution index. Further, our estimates indicate that the effects are heterogeneous across transportation modes and air pollutants. Notably, our work shows that air pollution shifts the demand from mass transportation (i.e., buses) to taxis, which tends to further aggravate pollution