Sefi will be discussing his research on air quality in US cities.


We study whether urban density affects the exposure of city dwellers to ambient air pollution by using satellite-derived measures of air quality for the contiguous United States. For identification, we rely on an instrumental variable strategy, which induces exogenous variation in density without affecting pollution directly. For this purpose we use three variables measuring geologic characteristics, earthquake risks, soil drainage capacity, and the presence of aquifers, as instruments for density. Overall, we find a positive and statistically significant relationship between density and exposure to ambient air pollution. Our main estimates report a pollution-density elasticity of 0.13. Using EPA costing estimates, we find that a doubling of density on an average city increases health costs by as much as USD 370 per capita. Our results suggest that despite the common claim that denser cities tend to be more environmentally friendly, air pollution exposure is actually higher in denser cities. This in turn highlights the possible trade-off between reducing global greenhouse gas emissions and preserving the environmental quality within the city, and the need to incorporate the effect on air quality when estimating the impact of densification policies.

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