Modeling the impacts of convective transport and lightning NOx production over North America: Dependence on cumulus parameterizations

A 3-D regional chemical transport model (REAM) is applied to examine the uncertainties in modeling the effects of convective transport and lightning NOx production on upper tropospheric O3 and its precursors. To assess the model uncertainties, two different cumulus convective parameterizations, KF-eta and Grell, are adopted in REAM from the respective meteorological models, WRF and MM5. The model simulations are evaluated using INTEX- NA aircraft measurements. A major improvement of the KF-eta scheme (in WRF) is its inclusion of entrainment and detrainment processes. It simulates larger convective updraft mass fluxes below 300 hpa than the Grell scheme (in MM5), resulting in better simulations of vertical profiles of the concentrations of CO, C3H8, and C4H10 in the middle and upper troposphere. More efficient scavenging from entrainment and detrainment also results in better simulations of highly soluble pollutant HNO3 in the free troposphere in WRF-REAM. The inclusion of entrainment and detrainment processes in the KF-eta scheme also leads to lower cloud top heights (10-12 km in WRF) than the Grell scheme (13-16 km in MM5) and hence smaller amounts of estimated intra- cloud lightning flashes. WRF simulated cloud top heights are in better agreement with GOES satellites measurements over the southeastern United States and the Atlantic Ocean. The WRF-REAM model better simulates lightning NOx distributions than the MM5-REAM, especially over the Atlantic Ocean. Lightning NOx production enhances the concentration of upper tropospheric NO2 by a factor of > 2 (~50 pptv) and increases O3 by up to 20 ppbv.