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 anthropogenic contribution to atmospheric CH3Br. An even spatial distribution 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 interhemispheric ratio, lead to the conclusion that the total emission source of CH3Br 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 strength of 91 ktonnes yr-1, with a 54% anthropogenic contribution of 49 ktonnes yr-1. The sensitivity of these results are discussed with respect to OH concentration, transport, seasonality, altitude, and the representative nature of the latitudinal spread of data and spatial distribution of emissions.