Conservation cobenefits from air pollution regulation: Evidence from birds.

Massive wildlife losses over the past 50 y have brought new urgency to identifying both the drivers of population decline and potential solutions. We provide large-scale evidence that air pollution, specifically ozone, is associated with declines in bird abundance in the United States. We show that an air pollution regulation limiting ozone precursors emissions has delivered substantial benefits to bird conservation. Our estimates imply that air quality improvements over the past 4 decades have stemmed the decline in bird populations, averting the loss of 1.5 billion birds, ∼20% of current totals. Our results highlight that in addition to protecting human health, air pollution regulations have previously unrecognized and unquantified conservation cobenefits.

Air pollution and visitation at U.S. national parks.

Hundreds of millions of visitors travel to U.S. national parks every year to visit America's iconic landscapes. Concerns about air quality in these areas have led to strict, yet controversial pollution control policies. We document pollution trends in U.S. national parks and estimate the relationship between pollution and park visitation. From 1990 to 2014, average ozone concentrations in national parks were statistically indistinguishable from the 20 largest U.S. metropolitan areas. Further, relative to U.S. cities, national parks have seen only modest reductions in days with ozone concentrations exceeding levels deemed unhealthy by the U.S. Environmental Protection Agency. We find a robust, negative relationship between in-park ozone concentrations and park visitation. Still, 35% of all national park visits occur when ozone levels are elevated.