Air pollution is a very big deal. Its adverse effects on numerous health outcomes and general mortality are widely documented. However, our understanding of its cognitive costs is more recent and those costs are almost certainly still significantly under-emphasized. For example, cognitive effects are not mentioned in most EPA materials.

World Bank data indicate that 3.7 billion people, about half the world's population, are exposed to more than 50 µg/m³ of PM2.5 on an annual basis, 5x the unit of measure for most of the findings below.