Disentangling the effects of air pollutants with many instruments

Air pollution poses a major threat to human health. Far from unidimensional, air pollution is multifaceted, but quasi-experimental studies have been struggling to grasp the consequences of the multiple hazards. By selecting optimal instruments from a novel and large set of altitude-weather instrumental variables, we disentangle the impact of five air pollutants in a comprehensive assessment of their short-term health impact in the largest urban areas of France over 2010-2015. We find that daily higher levels of at least two air pollutants, ozone and sulfur dioxide, lead to more respiratory-related emergency admissions on the same day. Children and elderly are mostly affected. Carbon monoxide increases emergency admissions for cardiovascular diseases while particulate matter and sulfur dioxide are found responsible for increasing the daily mortality rate. Assuming a five air pollutants context, we show that an analyst who ignored the presence of interrelations between air pollutants would have reached partially false conclusions.