Isoprene and soil NOx impacts on nonattainment ozone from GEOS-CHem

Abstract

Ozone (O3) is a criteria air pollutant that continues to pose a threat to more than one hundred million Americans each year, despite progress in regulating precursor emissions. In many O3-polluted areas, the role of natural emissions of isoprene in the production of ground-level O3 has been well recognized, but this chemistry depends strongly on local anthropogenic emissions which have been changing rapidly. We use an updated estimate of anthropogenic emissions to demonstrate that many areas that remain in nonattainment of the federally mandated O3 standard are now much less sensitive to natural isoprene emissions, with biogenic nitrogen oxide emissions from soils becoming more and more important. The role of these soil emissions on O3 in nonattainment areas has not been well characterized, but, as we show in our companion article in JGR-Atmospheres, this will become increasingly necessary for good O3 policy in nonattainment areas.