One day at a time: heterogeneous impact evaluation of air pollution peaks.

With Tarik Benmarhnia

Abstract: We develop a novel approach to assess the heterogeneity of air pollution peaks and how their impact on mortality varies depending on their characteristics. Combining the Generalised Synthetic Control Method and a two-stage staggered design, we construct a synthetic control group to estimate average treatment effects for each peak, one by one, and conduct a meta-analysis on pooled results. We exploit daily data on pollution, weather and health in 18 French urban areas between 2008 and 2015. We find that both air pollution peaks and their mortality effects are highly heterogeneous. We identify policy threshold, seasonality, weather and pollutant concentrations as drivers of this variability. We believe this study can help address the ‘One size (does not) fit(s) all’ issue: the potential mismatch between these homogeneous policies, triggered by a binary criterion on pollutant concentrations, and the heterogeneous pollution peaks they target. More broadly, this methodology can study the heterogeneity of any extreme weather events, help understand the conditions for effective counter-measures, and thus contribute to policy fine-tuning.