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| Titel |
Quantifying the processes contributing to the anomalous methane growth rate after the eruption of Mt. Pinatubo |
| VerfasserIn |
N. Bândă, M. Krol, M. van Weele, T. van Noije, T. Röckmann |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250070600
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| Zusammenfassung |
| The evolution of methane in the past two decades is not entirely understood. Its growth rate
showed particularly large fluctuations after the eruption of Mount Pinatubo in June 1991.
Being able to quantify the processes that determined these fluctuations can help us gain a
better understanding of the methane budget.
Methane concentrations are determined by methane emissions and methane lifetime. Its
lifetime is determined by OH concentrations, which are affected by UV radiation levels and
by non-linear tropospheric chemistry. OH is produced by ozone photolysis and
photolysis frequencies are determined by the amount of UV radiation reaching
the troposphere. OH reacts with other chemical species, such as NOX, CO and
NMVOC, and thus its concentration is also driven by the concentrations of these
species.
The Pinatubo eruption injected about 18.5 Mt of SO2 in the stratosphere, and triggered
different photochemical effects, including feedbacks between climate and atmospheric
photochemistry. These processes had both positive and negative impacts on the methane
growth rate, affecting methane emissions and methane lifetime. SO2 and sulfate
aerosols formed from SO2, as well as stratospheric ozone depletion observed after the
eruption, determined changes in tropospheric UV levels, thus in OH and methane
lifetime. The temperature decrease in the years after the eruption led to changes in
chemical reaction rates, in water vapour, as well as in natural emissions of methane and
NMVOCs.
We represent the globally yearly averaged state of the troposphere in a column chemistry
model, which accounts for non-linear CH4-NOX-CO-NMVOC-O3 photochemistry. The
effect of atmospheric perturbations on photolysis frequencies is calculated with the radiation
transfer model TUV, and then used in the chemistry model.
We model the transient response of methane and methane growth rate using the observed
atmospheric changes after the eruption of Pinatubo. Using this setup, we try to quantify the
different processes described above and find which of them contributed significantly to the
observed methane growth rate in the following years. |
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