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OZONE DEPLETION AT POLAR SUNRISE SOURCES AND MECHANISM OF REACTIVE HALOGEN SPECIES

OZONE DEPLETION AT POLAR SUNRISE SOURCES AND MECHANISM OF REACTIVE HALOGEN SPECIES. EAS6410 Jide & Rita. General Information about ODEs. Discovery

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OZONE DEPLETION AT POLAR SUNRISE SOURCES AND MECHANISM OF REACTIVE HALOGEN SPECIES

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  1. OZONE DEPLETION AT POLAR SUNRISESOURCES AND MECHANISM OF REACTIVE HALOGEN SPECIES EAS6410 Jide & Rita

  2. 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

  3. 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 O3 and filterable Br (f-Br) concentrations at Alert, Canada, in April 1986 [ Barrie et al. 1988]

  4. 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 0.00002% I

  5. Organohalogen in the air

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

  7. Aerosol is not enough • Lifetime of sea salt aerosol is about few days • Typical concentration levels between 0.1-1 ug/m3 • This can only account for up to few ppt of photolysable bromine. One order of magnitude too low

  8. 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

  9. 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

  10. Frost Flower

  11. 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

  12. XOx, YOx Chemical Mechanism Destroying Ozone • Cycle A X +O3 XO +O2 (R1) Y + O3 YO +O2 (R2) XO + YO X + Y + O2 (R3) Net reaction: 2O33O2 (XOx = XO, X) (YOx = YO, Y)

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

  14. Liberation From Sea Salt http://www.atmos.ucla.edu/%7ejochen/research/hox/hox.html

  15. Processes that depletion ozone

  16. 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

  17. Different ProcessesInvolved

  18. 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?

  19. Thank youQuestions?

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