Ozone Production Efficiency in the Baltimore-Washington Urban Plume: Evaluating CMAQ with aircraft (DISCOVER-AQ) and satellite (OMI) observations

Elevated levels of tropospheric ozone have detrimental effects on human health and the ecosystem. A comprehensive set of atmospheric observations from the NASA DISCOVER-AQ (D-AQ) campaign conducted in the Baltimore-Washington region during July 2011 as well as observations of column NO₂ and HCHO from the Ozone Monitoring Instrument (OMI) on the NASA Aura satellite are used to quantify the ozone production efficiency (OPE) of urban plumes and the distribution of ozone precursors in the mid-Atlantic region. We assess the accuracy of the representation of ozone photochemistry as well as the magnitude and distribution of NO_x and VOCs within the Community Multi-scale Air Quality (CMAQ) model via comparison with values of OPE inferred from the D-AQ data, as well as many other species measured either by aircraft or satellite instrumentation. We show that CMAQ tends to overestimate measured abundances of reactive nitrogen species and underestimates both ambient OPE as well as the reactivity of HO₂ + RO₂ with NO. Therefore, future levels of surface ozone could exhibit stronger declines to further reductions of NO_x emissions than projected by the CMAQ model that is presently being used by air quality agencies to quantify the response of ozone to various emission reduction scenarios.