HR: 0800h
AN: A51C-0586    [Abstracts]
TI: Modeling the halogen chemistry in the Antarctic boundary layer
AU: Piot, M
EM: mpiot@iup.uni-heidelberg.de
AF: IUP, Heidelberg, Institute of Environmental Physics University of Heidelberg Im Neuenheimer Feld 229, Heidelberg, 69120, Germany
AU: * von Glasow, R
EM: R.Von-Glasow@uea.ac.uk
AF: UEA, Norwich, School of Environmental Sciences University of East Anglia, Norwich, NR4 7TJ, United Kingdom
AB: Since the mid-1980s, events of drastic losses of ozone have been reported in the Arctic boundary layer in spring. Subsequently, similar ozone depletions have been observed in the Antarctic boundary layer. It is now recognized that reactive halogens play a major role in these ozone depletion events. Interestingly, significant levels of iodine oxides (IO) have been reported from stations near the Antarctic coast, while no such levels have yet been measured in the Arctic. The importance of these levels of IO in the Antarctic remains unclear as regard to the chemical mechanisms associated with ozone depletions and the bromine chemistry. We investigated the potential sources of iodine for the Antarctic boundary layer using the model MISTRA in the one-dimensional mode. The relative contributions of sea salt aerosols, frost flowers, and organoiodine species for the release of reactive iodine to the gas phase were assessed. Typical, as well as increased sea salt aerosol number concentrations, do not contain enough iodine ions to account for a significant source of iodine. Modeling the presence of frost flowers containing increased concentrations of iodide compared to seawater also showed no relevant release of reactive iodine species. Model runs investigating typical levels of organoiodine (2 ppt CH₃I, 1 ppt C₃H₇I) showed mean mixing ratios of IO and OIO nearly 10³ times higher than modeled sea salt or frost flower aerosols, but reaching levels of only ~10^-1 ppt. The rapid photodissociation of CH₂I₂ was found important for the release of reactive iodine. A prescribed flux of CH₂I₂ from the surface (set to maintain observed levels of ~0.5 ppt in the Antarctic) induced IO and OIO mixing ratios approximating 1 ppt. In order to release observed mean levels of reactive iodine to the boundary layer (5-10 ppt IO), a prescribed flux of molecular iodine from the surface had to be set to nearly 1.0×10⁹ molec~cm^-2~s^-1. Modeled vertical distribution of IO within the boundary layer is not consistent with observations of well-mixed IO. Interactions between the bromine and iodine chemistry are investigated and possible model improvements are presented.
DE: 0365 Troposphere: composition and chemistry
DE: 3307 Boundary layer processes
DE: 3349 Polar meteorology
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting