HR: 08:40h
AN: A41G-03 INVITED    [Abstracts]
TI: Sea-air Fluxes of Organic Iodine Compounds and Evidence for Their Large-Scale Effects in the Tropical Marine Boundary Layer
AU: * Carpenter, L
EM: ljc4@york.ac.uk
AF: University of York, Department of Chemistry, University of York, Heslington, York, YO105DD, United Kingdom
AU: Jones, C
EM: cej103@york.ac.uk
AF: University of York, Department of Chemistry, University of York, Heslington, York, YO105DD, United Kingdom
AU: Dunk, R
EM: rmd502@york.ac.uk
AF: University of York, Department of Chemistry, University of York, Heslington, York, YO105DD, United Kingdom
AU: Hornsby, K
EM: keh114@york.ac.uk
AF: University of York, Department of Chemistry, University of York, Heslington, York, YO105DD, United Kingdom
AU: Read, K
EM: km519@york.ac.uk
AF: University of York, Department of Chemistry, University of York, Heslington, York, YO105DD, United Kingdom
AU: Lewis, A
EM: acl5@york.ac.uk
AF: University of York, Department of Chemistry, University of York, Heslington, York, YO105DD, United Kingdom
AU: Lee, J
EM: jdl3@york.ac.uk
AF: University of York, Department of Chemistry, University of York, Heslington, York, YO105DD, United Kingdom
AU: Moller, S
EM: sjm133@york.ac.uk
AF: University of York, Department of Chemistry, University of York, Heslington, York, YO105DD, United Kingdom
AU: Mendes Neves, L
EM: lulumendescv@yahoo.com.br
AF: Instituto Nacional de Meteorologia e Geofisca, CP15 Mindelo, São Vicente, Cabo Verde, Mindelo, CP15, Cape Verde
AU: Faria, B
EM: vigil.isecmar@cvtelecom.cv
AF: Instituto Nacional de Meteorologia e Geofisca, CP15 Mindelo, São Vicente, Cabo Verde, Mindelo, CP15, Cape Verde
AU: Young, D
EM: dickon.young@bristol.ac.uk
AF: University of Bristol, School of Chemistry, University of Bristol, Cantocks Close, Bristol, BS8 1TS, United Kingdom
AU: O'Doherty, S
EM: s.odoherty@bristol.ac.uk
AF: University of Bristol, School of Chemistry, University of Bristol, Cantocks Close, Bristol, BS8 1TS, United Kingdom
AB: Whilst it is now clear that iodine has an important atmospheric impact in coastal regions, particularly as a precursor to new aerosol particles, the global impact is as yet unknown. This is mainly a result of the paucity of observations over the open ocean. Here we present sea-air fluxes of the organic iodine compounds CH₃I, C₂H₅I, 1-C₃H₇I, CH₂ICl, CH₂IBr and CH₂I₂ calculated from simultaneous surface seawater and air measurements in/over the mid-latitude and tropical eastern North Atlantic Ocean during summer 2006 and 2007. Average combined dihalomethane (CH₂IX where X is I, Br, Cl) fluxes were around 40 nmol m^-2d^-1 in the mid-latitude and tropical eastern North Atlantic and reached up to 120 nmol m^-2d^-1 in upwelling regions. Globally, the dihalomethane fluxes are extrapolated to be a factor of about 2 higher than those of CH₃I alone. A box model incorporating gas phase reactions and reactions in and on sea salt aerosol, driven by the measured open ocean organic iodine fluxes, predicts a daytime maximum of around 1 pmol/mol of the iodine oxide radical (IO) in the tropical MBL. Evidence for the large-scale effects of such halogen chemistry is apparent in the trace gas measurements at the Cape Verde Atmospheric Observatory in the tropical eastern North Atlantic Ocean. Measurements of ozone from October 2006 to October 2007 reveal daily net photochemical destruction averaging 3.2 nmol/mol between 9am and 5pm; aircraft measurements in summer show that these destruction rates are sustained throughout the boundary layer. Photochemical losses of ozone caused by photolysis in the presence of water vapour combined with reactions of ozone with OH and HO₂ (together, "odd-hydrogen" losses) are sufficient to explain only 55% of the photochemical ozone destruction. However, model calculations show that the observed photochemical losses can be simulated by including halogen-catalysed ozone destruction reactions, assuming 1 pmol/mol IO combined with BrO concentrations of a few pmol/mol (midday maxima).
DE: 0312 Air/sea constituent fluxes (3339, 4504)
DE: 0365 Troposphere: composition and chemistry
DE: 1610 Atmosphere (0315, 0325)
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting