HR: 0800h
AN: A21A-0822    [Abstracts]
TI: Ozone Depletion Events, in the MBL During Arctic Spring in the Troposphere: a Model Study
AU: Piot, M
EM: mpiot@iup.uni-heidelberg.de
AU: * von Glasow, R
EM: Roland.von.Glasow@iup.uni-heidelberg.de
AB: For more than 20 years, events with almost complete loss of ozone have been observed in the Arctic in springtime. Reactive halogens play a major role in these ozone depletion events (ODE): the reaction of bromine atoms with ozone, followed by the self-reaction of bromine oxides (BrO) represents a catalytic loss mechanism for ozone in the polar boundary layer (PBL). However, the triggering of the so-called bromine explosion remains unclear. We used the chemical and microphysical model MISTRA in the lagrangian box-model mode to study the mechanisms leading to these observed depletions in the boundary layer. We will present model results where we used prescribed bromine or chlorine fluxes as responsible for ODEs. Our sensitivity study consisted in a set of four-day runs where we changed initial mixing ratios or fluxes (or both) of 19 different species (including halogens, NOx, NOy, DMS, H2O2, HCHO...) and compared the results with base runs. The sensitivity on temperature and humidity has also been examined. We investigated the importance of these compounds for the chemistry of the PBL and focused on species which influence the occurrence of an ODE using two thresholds: depletion from a typical background O3 mixing ratio of 40 ppb to 20 ppb (partial ODEs) and to 4 ppb (major ODEs), respectively. This study allows us to better understand which species are important in the process of depleting ozone. In addition to the sensitivity study, we are now examining the role that frost flowers play in the bromine explosion, using MISTRA in the lagrangian 1D mode. The considered column passes over a field of frost flowers, followed by an area of open lead. We assume CO3- and SO4-- ions to have precipitated. Due to brine rejection of the freezing sea water, the concentration of the sea salt on frost flowers is about three times higher than in sea water. We observed that all the bromide from sea salt aerosols is released to the gas phase. The 300m inversion layer is overshot due to strong increase in temperature over the open lead. Our results indicate that aerosols from frost flowers are probably not directly responsible for the bromine explosion and that additional cycles have to been taken into account.
DE: 0365 Troposphere: composition and chemistry
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005