Possible changes in atmospheric chemistry caused by increased boreal and arctic fluxes of methane in a future climate
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Lansø, Anne Sofie 1, Forfatter
Walløe Hansen, Aksel 2, Vejleder
Geels , Camilla3, Vejleder
1Det Naturvidenskabelige Fakultet, Københavns Universitet, København, Danmark, diskurs:7010              
2Niels Bohr Institutet, Det Naturvidenskabelige Fakultet, Københavns Universitet, København, Danmark, diskurs:7023              
3Department of Environmental Science Aarhus University, Aarhus, Danmark , diskurs:18              
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 Abstract: In the future, a possibility exists of carbon being released to the atmosphere in the form of methane from the boreal and Arctic region as the permafrost degrade.
Methane affects the background concentration of ozone in the troposphere,and high concentrations of ozone near the surface are harmful for humans. When the background ozone concentration rises, the baseline upon which ozone in polluted regions is resting will increase. With a higher ozone baseline, elevated ozone events hazardous for humans can occur more often, and thus background levels have a significant influence on health related consequences of ozone. The possible connection between natural fluxes of methane and ozone is therefore interesting to examine.
A sensitivity study consisting of computational modeling will constitute the basis of this research. The model setup involves three models. The coupled atmospheric and ocean global circulation model ECHAM5/MPI-OM is generating present day and future meteorological conditions. These are used as input in the dynamic vegetation model LPJ-WHyMe, which produces the natural fluxes of methane from the boreal and Arctic region. Both the natural methane fluxes and the meteorological data are employed by the chemical transport model DEHM from which the atmospheric chemistry is analyzed. The sensitivity study comprises of three changeable parameters that will be altered between present day conditions (year 2000) and future conditions (2100). The three changeable parameters are: natural boreal methane fluxes, climate conditions and anthropogenic emissions.
A connection between an increase in natural methane fluxes from the boreal area and the surface concentration of ozone is obtained, and the relation is determined by the seasonal variation in the methane fluxes. Increases in the yearly methane fluxes on 57 Mt(CH4)yr -1 and 141 Mt(CH4)yr -1 enhances the regional ozone concentrations with 0.5-1.0 ppb and 1.0-1.5 ppb, respectively. The change in a future climate gives large regional concentration differences of ozone, primarily,as a consequence of the temperature increase. Over oceans the surface ozone concentration is reduced due to increased humidity, while in continental regions local concentations with increases up to 25 ppb are perceived. Overall the future anthropogenic emissions are reduced, which decrease the surface concentration of ozone,in the model domain, with an average of 3.5 ppb.
The signal in the surface concentration of ozone obtained solely from the increase in natural methane fluxes is conservative due to the chosen model setup. If DEHM had been designed with dynamical lateral boundary conditions, interhemispheric transport of methane could have been accounted for. With interhemispheric transport taken into consideration, the signal in ozone from the natural fluxes could have been enhanced with 0.5-1.5 ppb.
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 Type: Speciale
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 Datoer: 2011-11-01
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 Publiceringsinfo: København : Københavns Universitet
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 Type: Speciale
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