WRF-Chem Estimates of Lightning Nitrogen Oxide and Biomass Burning Contributions to Middle and Upper Tropospheric Ozone During the AEROSE II Cruise

Abundant tropospheric ozone is observed over Equatorial Africa and the Atlantic Ocean by the Second Cruise of the Aerosols and Ocean Science Expeditions; the Southern Hemisphere Additional Ozonesonde Network; and the Ozone Measuring Instrument during June 2006. Biomass burning (bb) fires and enhanced carbon moNOxide are observed by the Moderate Imaging Spectrometer and the Measurements of Pollution in the Troposphere Satellite, respectively. Convection and lightning flashes are observed by the Tropical Rainfall Measuring Mission Satellite and the Worldwide Lightning Location Network (WWLLN). The European Center for Medium Range Weather Forecasting reanalyses is used to depict the large-scale dynamics over Equatorial Africa.;The research questions are: how much do bb and LNOx emissions contribute to ozone in the Equatorial Africa and the Atlantic Ocean? For first order estimates of NOx and ozone this study uses the WRF-Chem model at a 20 km resolution for the period 20 May--1 July 2006. The first model simulation is a control simulation that contains anthropogenic and biogenic emissions; the second simulation is a bb simulation; and the third simulation replaces bb emissions with LNOx emissions. For time and location of LNOx emissions, hourly WWLLN lightning flashes are scaled up to the total cloud-to-ground and intracloud lightning flashes using a detection efficiency based on TRMM/Lightning Imaging Sensor climatology. Then 250 mol of NO per flash is distributed vertically based on profiles from cloud-resolving model simulations. A fourth simulation combines bb and LNOx emissions.;The LNOx emissions produce more ozone than bb emissions despite numerous fires over Southern Hemisphere (SH) Africa particularly in the upper troposphere (UT). Ozone enhancement from bb in the UT is 2--3 ppbv and nearly 1 ppbv in the MT. The bb emissions remain in the lower troposphere (LT) as they are transported from the SH Africa to the Gulf of Guinea (GoG) by the active AEJ-S. Ozone enhancement from LNOx emissions is 8--12 ppbv in the UT and 3--7 ppbv in the MT. The LNOx emissions are transported in a counterclockwise trajectory around an anticyclonic gyre to Ascension Island and the UT of SH Africa.