Bromoform in tropical Atlantic air from 25oN to 25oS

Atmospheric mixing ratios of bromoform (CHBr3) measured over the eastern Atlantic Ocean were enhanced (4 to 13 pptv) between 8–25°N, 17–21°W, in air masses advected over the NW African coast/upwelling zone. The highest mixing ratios at 8–10°N were associated with a biomass burning plume from the African savannah belt. Airborne samples taken over Nigeria showed however that biomass burning here is not a source of CHBr3. Previously reported water samples taken near to the NW African upwelling zone do not support the very high levels of atmospheric CHBr3 observed, unless there is significant surface stratification of the atmospheric boundary layer. Other potential explanations include coastal macroalgae and/or sources within continental Africa. It is important to ascertain the nature of tropical sources of CHBr3 in order to establish the mechanisms of suggested feedbacks between organic bromine and climate change.