Effects of El Nino on Summertime Ozone Air Quality in the Eastern United States

We investigate the effect of El Nino on maximum daily 8h average surface ozone over the eastern United States in summer during 1980-2016. El Nino can influence the extratropical climate through the propagation of stationary waves, leading to (1) reduced transport of moist, clean air into the middle and southern Atlantic states and greater subsidence, reduced precipitation, and increased surface solar radiation in this region, as well as (2) intensified southerly flow into the south central states, which here enhances flux of moist and clean air. As a result, each standard deviation increase in the Nino 1+2 index is associated with an increase of 1-2ppbv ozone in the Atlantic states and a decrease of 0.5-2ppbv ozone in the south central states. These influences can be predicted 4months in advance. We show that U.S. summertime ozone responds differently to eastern-type El Nino events compared to central-type events.