| Methyl chloride (CH3Cl) is the most abundant halocarbon in the atmosphere, with about 16% of organic chlorine in the troposphere in the form of this trace gas. Motivated by the potential, but unstudied, seasonality in net sea-air fluxes, marine CH3Cl concentrations were measured in the northwest Atlantic during the spring, summer, and fall. These measurements showed that seasonality and surface temperature play a role in surface production of CH3Cl, and consequently net fluxes. The main source of marine CH3Cl could not be identified, but production of CH3Cl by transhalogenation accounted for less than 10% of the net efflux, which, combined with the seasonality in net production, suggests a biogenic source. Data from the current and earlier studies were combined to examine the relationship between concentration anomaly and sea surface temperature. This anomaly-temperature relationship, along with remotely-sensed sea surface temperature and wind speed, allowed the calculation of a global annual net flux of CH3Cl to the atmosphere of (5+/-1)x109 moles/y (210-330 Gg/y). |
