Simulation of carbon monoxide redistribution over central Africa during biomass burning events (Experiment for Regional Sources and Sinks of Oxidants(EXPRESSO))

The Regional Atmospheric Modeling System (RAMS) is used to assess a realist ic estimate of emissions by savanna fires from NOAA advanced very high reso lution radiometer (AVHRR) satellite imagery during the Experiment for Regio nal Sources and Sinks of Oxidants (EXPRESSO) campaign. The daily amounts of gases released by biomass burning depend on burnt biomaterial, the mass of which is estimated from two independent methods: classification of vegetat ion formations (CV) or net primary productivity (NPP). The area of the burn t zone is derived from satellite imagery. The percent of burnt biomass or c ombustion factor (alpha) is determined by an adjustment procedure using two model runs and assumed to be 40%, a value consistent with the biomass wetn ess. The simulated CO redistribution is compared with aircraft measurements (tracks and profiles). Two events of 4 and 5 days are examined, where flig hts above forest and savanna zones have been performed. In this study we sh ow that the main mechanisms of the chemical species spatial redistribution originates from mesoscale features. The RAMS results are in rather good agr eement with the aircraft measurements (vertical profiles or horizontal legs ) over forest and savanna. The difference between the CO simulated fields o btained from CV or NPP is weak (about 20% or 30%), and it is difficult to d iscriminate the best method because this difference is generally inferior t o the gap between model and observations. One may consider this study as a preliminary approach to improve the estimate of released gases by biomass b urning with the help of mesoscale modeling and the knowledge of the real so urces.