OZONE DEPLETION AT POLAR SUNRISEOZONE DEPLETION AT POLAR SUNRISESOURCES AND MECHANISM OF REACTIVE HALOGEN SOURCES AND MECHANISM OF REACTIVE HALOGEN

SPECIESSPECIES

EAS6410EAS6410Jide & 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 BXO + 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?