ozone depletion at polar sunrise sources and mechanism of reactive halogen species
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OZONE DEPLETION AT POLAR SUNRISE SOURCES AND MECHANISM OF REACTIVE HALOGEN SPECIES. EAS6410 Jide & Rita. General Information about ODEs. Discovery - PowerPoint PPT PresentationTRANSCRIPT
OZONE DEPLETION AT POLAR SUNRISEOZONE DEPLETION AT POLAR SUNRISESOURCES AND MECHANISM OF REACTIVE HALOGEN SOURCES AND MECHANISM OF REACTIVE HALOGEN
SPECIESSPECIES
EAS6410EAS6410
Jide & RitaJide & Rita
General Information about ODEsGeneral 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 Inverse correlation between Ozone and HalogenOzone 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]
Where does halogen comes fromWhere 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
Organohalogen in the airOrganohalogen in the air
Sources of Sea saltSources of Sea salt
• Airborne sea salt aerosol
• Arctic ocean sea ice
• Frost flower
Aerosol is not enoughAerosol 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
Why people care about thisWhy 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 IceSea 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 FlowerFrost Flower
Frost FlowerFrost 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 Chemical Mechanism Destroying OzoneOzone
• Cycle A
X +O3 XO +O2 (R1)Y + O3 YO +O2 (R2) XO + YO X + Y + O2 (R3)
Net reaction:
2O3 3O2
(XOx = XO, X)(YOx = YO, Y)
XOx, YOx
Chemical Mechanism Destroying Chemical Mechanism Destroying OzoneOzone
• 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)
XOx, HOx
Liberation From Sea SaltLiberation From Sea Salt
http://www.atmos.ucla.edu/%7ejochen/research/hox/hox.html
Processes that depletion Processes that depletion ozoneozone
Human InfluenceHuman 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 ProcessesDifferent Processes InvolvedInvolved
Open QuestionsOpen 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 youThank you
Questions?Questions?