Decadal Trends in Air Pollution over the Eastern United States: A Remarkable Success Story

Attacks on air pollution have sometimes been uncoordinated or uninformed by the best available science. Early success in fighting 1950’s London smog did not provide good guidance for 1960’s Los Angeles type smog. Dominance of anthropogenic VOCs as in California did not translate well to the sylvan eastern US. Ozone, once a pervasive, large-scale problem from Boston to Washington, DC, eventually responded well to steady improvements in the American vehicle fleet, and especially to large scale cuts in NOx emissions from point sources upwind, although these actions required intervention by the Supreme Court. Despite broad cuts and dramatic success, many areas in the eastern US still regularly violate clean air standards. We will discuss the challenge before us – how to take advantage of advances in our understanding of hydrocarbon reactivity, nitrogen oxide reservoirs, remote sensing, mesoscale meteorology (such as urban heat islands and sea breezes); different species dominate on different time and spatial scales. The use simultaneous observations of conserved tracers such as CO and the greenhouse gases CO₂ to provide insight into combustion processes and to evaluate emission inventories. Ratios of CO to CO₂ indicate combustion efficiency and ratios of NOx to CO and to CO₂ can help evaluate emissions models while ratios of CH₄ to CO₂ have identified major underestimates in methane emissions. Recent, well-coordinated field and modeling efforts can provide the precise scientific guidance to help States and Cities find specific actions needed to meet their climate and air quality goals.