Simulation of the tropospheric distribution of carbon monoxide during the 1984 MAPS experiment

A global, three-dimensional tropospheric chemistry model was used to perfor m simulations of the tropospheric distribution of carbon monoxide (CO) coin ciding with NASA's Measurement of Air Pollution from Satellites (MAPS) expe riment which took place during 5-13 October 1984. Archived meteorological d ata for September and October, 1984, were obtained from the European Centre for Medium-Range Weather Forecasting and used to drive the offline chemica l transport model simulations. Base-case CO emissions were generated by app lying emission factors to compiled inventories for related or co-emitted tr ace species. Simulation results from September and October have been compar ed with a recent re-release of the 1984 MAPS data and with in situ correlat ive data taken during the MAPS mission. Because of unrealistically large sp atial variability in N2O mixing ratios measured concurrently by MAPS, model results were also compared with an adjusted CO data set generated by assum ing that errors in N2O measured mixing ratios were correlated with errors i n the MAPS CO data. These comparisons, in conjunction with simulations prob ing model sensitivities, led to the conclusion that biomass burning CO emis sions from central and southern Africa may have been larger during Septembe r and October, 1984, than our initial best estimate based on the CO2 emissi ons data of Hao et al. (1990. Fire in the Tropical Biota; Ecosystem Process es and Global Challenges. Springer, Berlin, pp. 440-462; 1994. Global Bioge ochemical Cycles 8, 495-503). This result is in disagreement with recent es timates of biomass burning emissions from Africa (Scholes et al., 1996, Jou rnal of Geophysical Research 101, 23677-23682) which are smaller than previ ously thought for emissions from this region. Although unknown model defici encies cannot be conclusively ruled out, model sensitivity studies indicate that increased CO emissions from central and southern Africa offer the bes t explanation for reducing observed differences between model results and M APS data for this time period. Our results, in combination with a disparity in recent CO emission estimates from this region (Scholes et al., 1996; Ha o et al., 1996, Journal of Geophysical Research 101, 23577-23584), and in l ight of recent indications of highly variable biomass burning activities fr om the tropical western Pacific (Folkins et al., 1997, Journal of Geophysic al Research 102, 13291-13299), seem to suggest that biomass burning emissio ns exhibit significant year-to-year variability. This large variability of emissions sources makes the accurate simulation of specific time periods ve ry difficult and suggests that biomass burning trace species inventories ma y have to be developed specifically for each simulated time period, employi ng satellite-derived information on fire coverage and flame intensity. (C) 1999 Elsevier Science Ltd. All rights reserved.