Assessing Global Terrestrial Sources of Methyl Halides - Ozone Regulating Gases

Methyl bromide (CH3Br) and methyl chloride (CH3Cl) play significant roles in the depletion of the stratospheric ozone layer. The vast portion of methyl halide sources and sinks sources and sinks are natural in origin. The sources are poorly constrained, leading to unbalanced budgets. Budget closure for both methyl halides is of considerable importance as it is essential in forecasting the future of the ozone layer. The objective of this project is to close the gap between known sources and sinks. In order to achieve this objective, GIS techniques are employed. Spatial global datasets of land cover, climatic zones and growing periods are combined with methyl halide emission values in an ArcGIS context. Fluxes are derived from methyl halide emission inventories compiled during this project. The amount of annual emissions from natural and agricultural sources is estimated in this study to be 65Gg and 2887 Gg yr-1 for CH3Br and CH3Cl, respectively. Tropical forest is identified as the highest emitter of methyl bromide and methyl chloride, contributing 58% and 81% to the total estimated emissions, indicating tropical ecosystems play an important role in budget closure. By applying the results of this study against the emission estimations by WMO, it is shown that the missing source for CH3Br decreases to 10 Gg yr-1 while sources of CH3Cl outweigh sinks by 550 Gg, annually. This study determines that grassland ecosystem is not a sink, but rather a small source of CH3Br