MODELING THE CHEMISTRY OZONE, HALOGEN COMPOUNDS, AND HYDROCARBONS IN THE ARCTIC TROPOSPHERE DURING SPRING

The box model MoccaIce has been developed to stud!: the chemistry of t he arctic boundary layer. It treats chemical reactions in the gas phas e and in the aerosol as well as exchange between the 2 phases. Photoly sis rates vary according to the solar declination during polar sunrise . Apart from the standard tropospheric chemistry of ozone, hydrocarbon s, and nitrogen species, the reaction mechanism includes sulfur and th e halogens Cl, Br, and I. Modeling an ozone depletion event, we found that iodine species contribute to the chemical destruction of ozone si gnificantly if IO mixing ratios are about 1 pmol/mol. The reactions of BrO with BrO and IO are the main pathways of the ozone destruction cy cle. Hydrocarbon concentrations decrease during ozone depletion events due to reaction with halogen atoms. The rate of ozone destruction dep ends on whether the addition of Br to C2H4 and C2H2 yields inert produ cts or intermediates from which Br can be regenerated. Bromine and HCH O are positively correlated. The model produces HCHO during ozone depl etion events, though not as much as reported from field observations. Alter the destruction of ozone has been competed, the halogen species are converted to halides and subsequently scavenged by aerosol particl es.