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Global-scale chemical transport model simulationsindicate lightning NOx dominates upper tropospheric O3 productionabove Eastern North America during summertime but vary in their estimates.To improve our understanding, a regional-scale model (REAM) with higherresolution is applied. To examine the uncertainties in modeling the impactof convective transport and lightning NOx production on uppertropospheric chemical tracer distributions, REAM simulations of chemicaltracers are driven by two meteorological models, WRF and MM5, with differentcumulus convective parameterizations. The model simulations are evaluatedusing INTEX-A aircraft measurements and satellite measurements of NO2columns and cloud top pressure, and we find that mid and upper tropospherictrace gas concentrations are affected strongly by convection and lightningNOx production. WRF with the KF-eta convection scheme simulates largerconvective updraft mass fluxes below 150 hPa than MM5 with the Grell scheme.The inclusion of the entrainment and detrainment processes leads to moreoutflow in the mid troposphere in WRF than MM5. The ratio ofC2H6/C3H8 is found to be a sensitive parameter toconvective outflow; the simulation by WRF-REAM is in closer agreement withINTEX-A measurements than MM5-REAM, implying that convective mass fluxes byWRF are more realistic. WRF also simulates lower cloud top heights (10–12 km)than MM5 (up to 16 km), and hence smaller amounts of estimated(intra-cloud) lightning NOx and lower emission altitudes. WRF simulatedcloud top heights are in better agreement with GOES satellite measurementsthan MM5. Simulated lightning NOx production difference (due primarilyto cloud top height difference) is mostly above 12 km. At 8–12 km, themodels simulate a contribution of 60–75% of NOx and up to 20 ppbv ofO3 from lightning, although the decrease of lightning NOx effectfrom the Southeast to Northeast and eastern Canada is overestimated. Themodel differences and biases found in this study reflect some majoruncertainties of upper tropospheric NOx and O3 simulations drivenby those in meteorological simulations and lightning parameterizations

atmospheric chemistry and physics

Summertime impact of convective transport and lightning NO&amp;lt;sub&amp;gt;x&amp;lt;/sub&amp;gt; production over North America: modeling dependence on meteorological simulations