OZONE DEPLETION AT POLAR SUNRISE SOURCES AND MECHANISM OF REACTIVE HALOGEN SPECIES EAS6410 Jide & Rita

General Information about ODEs Discovery Sampling at Alert and Barrow in support of haze investigations discovered severe ozone depletion events (ODEs) in the boundary layer over the Arctic Ocean at the time of polar sunrise in 1980’s Human efforts TOPSE POLARCAT ARCTOC

Inverse correlation between Ozone and Halogen Figure 2: Ozone and BrO concentrations during a low ozone event in spring 1996 in Ny Ålesund, Spitsbergen [Tuckermann et al. 1997] Figure 1:A comparison of daily mean ground level O 3 and filterable Br (f-Br) concentrations at Alert, Canada, in April 1986 [ Barrie et al. 1988]

Where does halogen comes from Degradation of organohalogen compounds of anthropogenic or natural origin Liberation from sea salt Sea salt containing by weight 55.7% Cl,0.19% Br and % I

Organohalogen in the air

Sources of Sea salt Airborne sea salt aerosol Arctic ocean sea ice Frost flower

Aerosol is not enough Lifetime of sea salt aerosol is about few days Typical concentration levels between ug/m 3  This can only account for up to few ppt of photolysable bromine. One order of magnitude too low

Why people care about this Bad ozone is not always bad Ozone and its photochemical derivative OH, which is the major oxidants for most reduced gases It shows how less we know about the atmosphere

Sea Ice Fresh sea ice surface is known to act as a huge reservoir of halogens, nearly a inexhaustible source The sea ice surface provides the reactive surface 1000 times compared to the sea salt aerosol  Transport limitations between the phase boundary and the atmosphere have to be taken into account

Frost Flower

What is frost flower Ice crystals which grow on frozen leads and polynyas What component Enhanced salinities and bromide ion concentration of about 3 times of that of bulk seawater

Chemical Mechanism Destroying Ozone Cycle A X +O 3 XO +O 2 (R1) Y + O 3 YO +O 2 (R2) XO + YO X + Y + O 2 (R3) Net reaction: 2O 3 3O 2 (XOx = XO, X) (YOx = YO, Y) XOx, YOx

Chemical Mechanism Destroying Ozone Cycle B XO + HO 2 HOX + O 2 (R4) HOX + hv X + OH (R5) OH + CO, O 3 or VOC HO 2 + products (R6) Net reaction incl. reaction (1): O3 O2 (HOx = OH, HO2) XOx, HOx

Liberation From Sea Salt

Processes that depletion ozone

Human Influence Arctic haze Arctic haze is mostly composed of particles of sulfuric acid and organic compounds formed in the air from the combination of naturally occurring chemicals and pollutant sulfur dioxide or hydrocarbon gases. This provide very acidic condition Acid sea salt Below pH=6.5 sea salt solution are very efficient bromine sources

Different Processes Involved

Open Questions What are the conditions (meteorology, tide, biology) necessary for a release of reactive halogens? What are the exact sources? Are salt pans a significant source of reactive halogen species on a global scale? What is the release mechanism of RHS on the salt pans? What are RHS levels in the free troposphere? What is the influence on ozone chemistry there? Does halogen chemistry have an impact not only in local regions but on a global level? What is the influence on global ozone levels and the resulting consequences for the oxidizing capacity and the global radiation budget?

Thank you Questions?