AN ESTIMATE OF THE ANTHROPOGENIC CONTRIBUTION TO ATMOSPHERIC METHYL-BROMIDE

A global, 2-D, atmospheric chemistry model of latitude versus altitude , employing a prescribed hydroxyl field, is used to estimate the anthr opogenic contribution to atmospheric CH3Br. An even spatial distributi on is applied to natural emissions, whilst an anthropogenic source is assumed for the northern hemispheric mid-latitudes. Model calculations , constrained by observed concentrations of CH3Br and its interhemisph eric ratio, lead to the conclusion that the total emission source of C H3Br has a strength of 75-105 ktonnes yr-1 with a 33-74% anthropogenic contribution of 25-80 ktonnes yr-1. The best estimate is a total stre ngth of 91 ktonnes yr-1, with a 54% anthropogenic contribution of 49 k tonnes yr-1. The sensitivity of these results are discussed with respe ct to OH concentration, transport, seasonality, altitude, and the repr esentative nature of the latitudinal spread of data and spatial distri bution of emissions.