Ozone Production Efficiency in the Baltimore-Washington Urban Plume

Elevated levels of tropospheric ozone caused by its precursor emissions of NOx and VOCs have a negative impact on human health and crops. Informed regulatory decisions on how to reduce surface ozone in the Baltimore-Washington region can be made with a thorough understanding of urban plume chemistry and climate. The ozone production efficiency (OPE), which is based on the observed ratio of O3 and various nitrogen species, provides a mechanism for quantitatively assessing air quality representation of a key component of the photochemical evolution of urban plumes. We investigate the representation of ozone precursors within the CMAQ (Community Multi-scale Air Quality) air quality model, with a focus on assessing how well the model represents NOx and HOx chemistry. A comprehensive set of atmospheric observations for which OPE can be found and HO2 and RO2can be inferred, is available from NASA's DISCOVER-AQ campaign for July 2011 in the Baltimore-Washington region. Preliminary results show that the OPE as well as the NOx/NOy ratio in the Baltimore-Washington region derived from measurements is twice as high as within CMAQ, and that isoprene and formaldehyde are too low within CMAQ. Implications for policy will be briefly discussed.