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| Titel |
Factors controlling variability in the oxidative capacity of the troposphere since the Last Glacial Maximum |
| VerfasserIn |
L. T. Murray, L. J. Mickley, J. O. Kaplan, E. D. Sofen, M. Pfeiffer, B. Alexander |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 7 ; Nr. 14, no. 7 (2014-04-09), S.3589-3622 |
| Datensatznummer |
250118577
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| Publikation (Nr.) |
 copernicus.org/acp-14-3589-2014.pdf |
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| Zusammenfassung |
| The oxidative capacity of past atmospheres is highly uncertain. We present
here a new climate–biosphere–chemistry modeling framework to determine
oxidant levels in the present and past troposphere. We use the
GEOS-Chem chemical transport model driven by meteorological fields
from the NASA Goddard Institute of Space Studies (GISS) ModelE, with land
cover and fire emissions from dynamic global vegetation models. We present
time-slice simulations for the present day, late preindustrial era (AD 1770),
and the Last Glacial Maximum (LGM, 19–23 ka), and we test the sensitivity
of model results to uncertainty in lightning and fire emissions. We find that
most preindustrial and paleo climate simulations yield reduced oxidant levels
relative to the present day. Contrary to prior studies, tropospheric mean OH
in our ensemble shows little change at the LGM relative to the preindustrial
era (0.5 ± 12 %), despite large reductions in methane concentrations.
We find a simple linear relationship between tropospheric mean ozone
photolysis rates, water vapor, and total emissions of NOx and
reactive carbon that explains 72 % of the variability in global mean OH in
11 different simulations across the last glacial–interglacial time interval
and the industrial era. Key parameters controlling the tropospheric oxidative
capacity over glacial–interglacial periods include overhead stratospheric
ozone, tropospheric water vapor, and lightning NOx emissions.
Variability in global mean OH since the LGM is insensitive to fire emissions.
Our simulations are broadly consistent with ice-core records of
Δ17O in sulfate and nitrate at the LGM, and CO, HCHO, and
H2O2 in the preindustrial era. Our results imply that the
glacial–interglacial changes in atmospheric methane observed in ice cores
are predominantly driven by changes in its sources as opposed to its sink
with OH. |
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