| dc.description | Methyl chloride (CH3Cl), methyl bromide (CH3Br), and methyl iodide (CH3I) are trace gases of interest in atmospheric chemistry as carriers of halogen atoms. Chlorine, bromine, and iodine atoms are effective to varying degrees in catalyzing the destruction of stratospheric ozone. Knowledge of the sources and sinks of these compounds in the atmosphere can be used to improve the overall understanding of how halogens cycle between the atmospheric, terrestrial, and oceanic environments, and to determine the effects of anthropogenic activities on the natural cycle. In this work, the net annual air-sea flux of three methyl halide compounds (CH3X) has been estimated based on field measurements made with an equilibrator and a mass selective detector over a wide range of latitudes and oceanic regions in several seasons. The global flux estimates have been calculated by using the monthly mean sea surface temperature as a proxy variable to predict the concentration anomalies of the methyl halides at each point on a 2° x 2° map of the global ocean. The piston velocity at each grid point was calculated from climatological wind speeds. The primary conclusion of this thesis is that the global ocean represents a source of ∼0.55 Tg y --1 (range 0.31 to 0.59 Tg y--1) of methyl chloride and ∼0.32 Tg y--1 (0.18 to 0.34 Tg y --1) of methyl iodide to the atmosphere, and a sink of ∼7 Gg y--1 (4 to 10 Gg y--1) of methyl bromide from the atmosphere. When taken in the context of the tropospheric budgets of these three gases, the results suggest that the ocean is not the main source of methyl chloride to the atmosphere, but the ocean is apparently the main source of atmospheric methyl iodide. The atmospheric budgets of methyl chloride and methyl bromide remain significantly out of balance, with sinks exceeding sources, while the budget of methyl iodide may be balanced. Other significant sources of methyl chloride and methyl bromide to the atmosphere are predicted to exist, probably in the terrestrial environment. There is production of all three methyl halides in ocean surface waters, and the source of that production is not yet understood. | en_US |
