The impact of natural and anthropogenic hydrocarbons on the tropospheric budget of carbon monoxide

A method to quantify the relative contributions of surface sources and phot ochemical production of atmospheric carbon monoxide has been implemented in a three-dimensional chemical-transport model. The impact of biogenic and a nthropogenic hydrocarbons has been calculated. The oxidation of isoprene co ntributes to about 10% of the global tropospheric burden of carbon monoxide , with a maximum contribution over southern America and Africa. Oxidation o f methane and terpenes contribute to 28 and 2%? respectively, of the tropos pheric burden of CO. The oxidation of the other hydrocarbons, which include ethane, propane, ethylene, propylene and the surrogate hydrocarbon represe nting other hydrocarbons results in 12% of the CO tropospheric burden, amon g which 69% results from the oxidation of hydrocarbons of biologic origin. The overall global CO yield From the oxidation of isoprene is estimated to be 23% on a carbon basis. Comparisons between model results and the Few ava ilable observations of isoprene, terpenes and their oxidation products show that there is no evidence that the current global isoprene emissions propo sed in the IGAC/GEIA emissions data base are substantially overestimated, a s suggested by previous studies. (C) 2000 Elsevier Science Ltd. All rights reserved.