Oceanic consumption of CH3CCl3: Implications for tropospheric OH

Strong and extensive negative saturation anomalies for CH 3 CCl 3 were observed in the mid‐Pacific Ocean during the spring of 1990. Anomalies were largest at the equator, where upwelling and biological activity were greatest, but present virtually everywhere in our sampling range of 15°S to 20°N. The mean saturation anomaly for all of our data, corrected for physical effects, was −11.0%, implying that the ocean is a significant sink for CH 3 CCl 3 . The loss rate to maintain this anomaly is supported roughly by known hydrolysis rates, but contributions from other processes cannot be ruled out at this time. If hydrolysis and mixing are the only processes removing CH 3 CCl 3 from seawater, then about 6% of atmospheric CH 3 CCl 3 is removed by consumption in the oceans. Our data show that losses to the ocean most probably would range from 5 to 11% of the CH 3 CCl 3 removed from the atmosphere. This range translates to a partial residence time of 59–128 years for atmospheric CH 3 CCl 3 relative to oceanic consumption. Although these data indicate that the ocean is not an overwhelmingly large sink, its neglect does represent a systematic error in the calculation of tropospheric OH concentration from CH 3 CCl 3 production, growth, and distribution in the atmosphere.