Atmos. Chem. Phys. Discuss., 9, 2289-2317, 2009
© Author(s) 2009. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Impact of convective transport and lightning NOx production over North America: dependence on cumulus parameterizations
C. Zhao1, Y. Wang1, Y. Choi2, and T. Zeng1
1School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
2Jet Propulsion Laboratory, Pasadena, CA, USA

Abstract. 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 chemical tracer distributions. 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 and satellite measurements of NO2 columns and cloud top pressure, and we find that mid and upper tropospheric trace gas concentrations are affected strongly by convection and lightning NOx productions. A major improvement of the KF-eta scheme is its inclusion of cloud entrainment and detrainment processes. KF-eta scheme simulates larger convective updraft mass fluxes below 150 hPa than the Grell scheme, resulting in more outflow of pollutants in the mid troposphere. The ratio of C2H6/C3H8 is found to be a sensitive parameter to convective outflow; the simulation by WRF-REAM is in closer agreement with INTEX-NA measurements than MM5-REAM, implying that convective mass fluxes by KF-eta scheme are more realistic. The inclusion of entrainment and detrainment processes in the KF-eta scheme also leads to lower cloud top heights (10–12 km) than the Grell scheme (up to 16 km), and hence smaller amounts of estimated (intra-cloud) lightning NOx and lower emission altitudes. WRF simulated cloud top heights are in better agreement with GOES satellite measurements than MM5. The model divergence on lightning NOx mostly is above 12 km. As a result, both models suggest that lightning NOx production enhances the concentrations of upper tropospheric NO2 by a factor of >5 (~100 pptv) and increases O3 by up to ~20 ppbv at 8–12 km.

Citation: Zhao, C., Wang, Y., Choi, Y., and Zeng, T.: Impact of convective transport and lightning NOx production over North America: dependence on cumulus parameterizations, Atmos. Chem. Phys. Discuss., 9, 2289-2317, doi:10.5194/acpd-9-2289-2009, 2009.
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