HR: 0800h
AN: A51C-0578    [Abstracts]
TI: Destruction of Iodocarbons in Surface Seawater - Implications for Sea-Air Flux Calculations and the Atmospheric Iodine Budget
AU: * Jones, C E
EM: cej103@york.ac.uk
AF: Department of Chemistry, University of York, York, YO10 5DD, United Kingdom
AU: Dunk, R M
EM: rmd502@york.ac.uk
AF: Department of Chemistry, University of York, York, YO10 5DD, United Kingdom
AU: Hornsby, K E
EM: keh114@york.ac.uk
AF: Department of Chemistry, University of York, York, YO10 5DD, United Kingdom
AU: McFiggans, G
EM: g.mcfiggans@manchester.ac.uk
AF: School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, M60 1QD, United Kingdom
AU: Carpenter, L J
EM: ljc4@york.ac.uk
AF: Department of Chemistry, University of York, York, YO10 5DD, United Kingdom
AB: Although it is now widely accepted that CH₃I is the major volatile organic source of iodine from the surface ocean to the atmosphere, CH₃I emissions alone cannot balance the global iodine budget, which implies that there must be some additional source(s). Seawater and air measurements made during two cruises in the Atlantic Ocean during summer 2006 and spring 2007 suggest that other iodocarbons, in particular the dihaloalkanes CH₂I₂, CH₂IBr and CH₂ICl, may provide a combined global iodine atom source which is comparable to that of CH₃I. However, deriving sea-to-air fluxes of these volatile gases is not straightforward. Established flux parameterizations are based on air and surface water concentrations, but seawater samples from ship campaigns are typically taken from at least 2-6 m depth (since there are technical difficulties associated with sampling closer to the surface). Given its relatively long lifetime in the oceans, sea-air fluxes of CH₃I may be adequately approximated directly from concentrations measured a few metres below the surface, however for the dihalomethanes this is likely to give rise to considerable inaccuracies due to their short lifetimes with respect to photolysis in surface waters. Consequently, we have used a one-dimensional oceanic mixed layer model to constrain the extent of dihalomethane photodecay within the top few metres of the water column such that we can extrapolate surface seawater concentrations from sub-surface measurements, which in turn allows more accurate sea-air fluxes to be determined for these gases. A number of mono-iodinated alkanes were also detected in Atlantic seawater, including C₂H₅I and 1- C₃H₇I. Laboratory based studies have been carried out in order to parameterize the temperature- dependent chemical destruction of a number of mono-iodinated alkanes in saltwater, such that the oceanic lifetimes of these species may be predicted as a simple function of the surface seawater temperature. In light of these results we also consider the potential impact of rising global seawater temperatures on emissions of these iodocarbons to the marine boundary layer.
DE: 0312 Air/sea constituent fluxes (3339, 4504)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting