Atmospheric methylchloride (CH3Cl)

A global time series of atmospheric methylchloride (CH₃Cl) concentrations is reported showing the variability with latitude and season. Springtime concentrations of CH₃Cl at 45°N latitude are 7.5%±3.5% higher than during other seasons. Lowest concentrations were generally observed during fall. CH₃Cl was found to be more abundant by about 6% (±5% NH, ±3% SH) in the tropical regions of both hemispheres. No significant difference in the burdens of CH₃Cl was observed between the two hemispheres. Based on these data the ratio of the average hydroxyl radical (HO) concentration over the southern hemisphere to that over the northern hemisphere was estimated to be 1.3 or less.