Short-lived halocarbon species in the Oceans and Atmosphere

This study aimed to improve current understanding of the emissions and distributions of very short-lived halocarbons (VSLH), thus their impact on atmospheric halogen chemistry.
VSLH measurements were made during the TROMPEX campaign over the tropical Atlantic Ocean and Mauritanian upwelling region. This produced the first reported measurements of \ce{CH2ICl} by a research aircraft and identified an open-ocean source, likely linked to phytoplankton. VSLH emissions over the upwelling, implicated as a major localised source, were similar to previously measured coastal emissions which globally cover a much larger area. Thus it is likely that coastal upwelling systems in themselves are not strong global sources of VSLH.

Ship-borne VSLH measurements were taken in the East Tropical Pacific (ETP) during the TORERO campaign. High sensitivity and frequency sampling gave new information regarding the distribution of VSLH, including a photolytically driven diurnal cycle of \ce{CH2I2}. Fluxes were calculated using simultaneous seawater and air measurements spanning a large area of the ETP where very few other measurements exist.
Although individual VSLH depth profiles showed covariance with Chlorophyll-a (Chl-a), cross sections revealed differences in their latitudinal distributions. In fact there was little bulk correlation with surface water concentrations of Chl-a.
\ce{CH2I2} and \ce{CH2ICl} displayed a negative relationship with Chl-a, attributed to physical and mixing processes. \ce{CHBr3}, \ce{CH2Br2} and \ce{CHBr2Cl} showed a relationship between surface and deep maxima concentrations suggesting that if a proxy for their production was found that this would negate the use of water column models to parameterise the surface concentrations of these species.

Wind speed controls VSLH distribution in the ocean mixed layer and may even influence oceanic lifetimes of the shortest-lived species via increased turbidity and solar attenuation. It also exerts a strong control on \ce{CH3I}, \ce{CH2ICl}, \ce{CH2I2} and \ce{CHCl3} emissions and could form a link between emissions and future changes in climate.