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| Titel |
Heterogeneous uptake of HO2 by aerosols: Quantifying the chemical indirect effect of aerosols on climate |
| VerfasserIn |
H. Macintyre, M. Evans, K. Carslaw, C. Johnson |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250021436
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| Zusammenfassung |
| Aerosols can impact the global atmosphere in various ways. One of these is by providing a
surface on which reactions between adsorbed gas-phase components may occur. These
reactions perturb chemical processing in the atmosphere, leading to changes in the
concentrations of climate-relevant species, such as methane (CH4) and carbon dioxide
(CO2). This can be regarded as a chemical indirect effect of aerosols on climate.
Quantifying the impact of this effect is one of the current challenges facing climate
science.
Heterogeneous chemistry has been included in models for well over a decade. Much of
the focus on reactive uptake is on nitrogen species, such as N2O5, NO2, and NO. HO2 is also
taken up by aerosol. The rate of uptake of gas-phase species to aerosol is usually represented
in models by the parameter gamma (γ), which is defined as ‘the probability that a molecule
impacting the surface of the aerosol undergoes a reaction’. The first modelling studies to
include uptake of HO2 used a gamma HO2 value of 0.2, a value based on recommendations
from a review.
Recently, more lab data for uptake of HO2 has become available, including uptake
information for different aerosol types, and some information on how uptake varies with
temperature and humidity. This new lab data has been used to create a more detailed
parameterisation for uptake of HO2 by aerosol.
The GEOS-Chem chemistry transport model has been used to investigate the impact of
the new parameterisation for uptake of HO2. The global mean gamma for HO2 is found to be
0.03, much smaller than assumed previously. Large regional changes in atmospheric oxidants
are associated with this reduced uptake. Subsequent impacts on lifetimes of relevant climate
gases are discussed. |
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