Comparison of Measurements of Hydroxyl Radicals in the Tropical Troposphere during GABRIEL with the Box Model MECCA

Hydroxyl radicals play a major role in the chemistry of the troposphere and dominate its oxidation capacity during daytime. Their main source in the unpolluted troposphere is the photolysis of O3 and following reactions with water vapour. The largest contribution to the global oxidation capacity occurs in the tropical region. The GABRIEL campaign, Oct 2005, took place in equatorial South America (Suriname) to gain basic understanding of the dominant processes over the tropical rainforest and their influence on the HOx budget. Global models predict that the emissions of hydrocarbons from the rainforest reduce the amount of HOx and therefore the selfcleaning capacity significantly. The poster concentrates on understanding the HOx budget and its interdependence with other species measured during the campaign. Since OH and HO2 have very short lifetimes, MECCA, a box model, is applied in steady state mode and used for detailed analysis. Hereby all measured species like radiation, O3, isoprene, NO, HCHO, CO, hydrocarbons are used as constraint parameters to model OH and HO2.