Urban development and air pollution: Evidence from a global panel of cities

Study examines air pollution concentration in 75 urban areas between 2005 and 2011. Focuses specifically on the impacts of changes in the urban environment and transportation mode on pollution. A surprising finding of the research is that increasing car and population densities significantly reduce air pollution concentration in city centers where air pollution induced health risks are greatest. These effects are largely confined to cities in non-OECD countries. Two possible mechanisms for the negative effect of car density are explored: (i) increasing car density permits a decentralization of residential and economic activity; and (ii) car usage substitutes for motorbike usage. We find limited evidence in favour of (i) and no evidence in favour of (ii). We also observe a complex relationship between income and pollution concentration as well as a general downward-trend in pollution concentration over time. Overall, our findings are indicative that densely populated polycentric cities may be �greener� and �healthier� than comparable monocentric ones.