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| Titel |
Preindustrial to present-day changes in tropospheric hydroxyl radical and methane lifetime from the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) |
| VerfasserIn |
V. Naik, A. Voulgarakis, A. M. Fiore, L. W. Horowitz, J.-F. Lamarque, M. Lin, M. J. Prather, P. J. Young, D. Bergmann, P. J. Cameron-Smith, I. Cionni, W. J. Collins, S. B. Dalsøren, R. Doherty, V. Eyring, G. Faluvegi, G. A. Folberth, B. Josse, Y. H. Lee, I. A. MacKenzie, T. Nagashima, T. P. C. Noije, D. A. Plummer, M. Righi, S. T. Rumbold, R. Skeie, D. T. Shindell  , D. S. Stevenson, S. Strode, K. Sudo, S. Szopa, G. Zeng |
| 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 ; 13, no. 10 ; Nr. 13, no. 10 (2013-05-27), S.5277-5298 |
| Datensatznummer |
250018671
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| Publikation (Nr.) |
 copernicus.org/acp-13-5277-2013.pdf |
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| Zusammenfassung |
| We have analysed time-slice simulations from 17 global models, participating
in the Atmospheric Chemistry and Climate Model Intercomparison Project
(ACCMIP), to explore changes in present-day (2000) hydroxyl radical (OH)
concentration and methane (CH4) lifetime relative to preindustrial times
(1850) and to 1980. A comparison of modeled and observation-derived methane
and methyl chloroform lifetimes suggests that the present-day global
multi-model mean OH concentration is overestimated by 5 to 10% but is
within the range of uncertainties. The models consistently simulate higher OH
concentrations in the Northern Hemisphere (NH) compared with the Southern
Hemisphere (SH) for the present-day (2000; inter-hemispheric ratios of 1.13
to 1.42), in contrast to observation-based approaches which generally
indicate higher OH in the SH although uncertainties are large. Evaluation of
simulated carbon monoxide (CO) concentrations, the primary sink for OH,
against ground-based and satellite observations suggests low biases in the NH
that may contribute to the high north–south OH asymmetry in the models. The
models vary widely in their regional distribution of present-day OH
concentrations (up to 34%). Despite large regional changes, the
multi-model global mean (mass-weighted) OH concentration changes little over
the past 150 yr, due to concurrent increases in factors that enhance OH
(humidity, tropospheric ozone, nitrogen oxide (NOx) emissions,
and UV radiation due to decreases in stratospheric ozone), compensated by
increases in OH sinks (methane abundance, carbon monoxide and non-methane
volatile organic carbon (NMVOC) emissions). The large inter-model diversity
in the sign and magnitude of preindustrial to present-day OH changes (ranging
from a decrease of 12.7% to an increase of 14.6%) indicate that
uncertainty remains in our understanding of the long-term trends in OH and
methane lifetime. We show that this diversity is largely explained by the
different ratio of the change in global mean tropospheric CO and
NOx burdens (ΔCO/ΔNOx,
approximately represents changes in OH sinks versus changes in OH sources) in
the models, pointing to a need for better constraints on natural precursor
emissions and on the chemical mechanisms in the current generation of
chemistry-climate models. For the 1980 to 2000 period, we find that climate
warming and a slight increase in mean OH (3.5 ± 2.2%) leads to a
4.3 ± 1.9% decrease in the methane lifetime. Analysing sensitivity
simulations performed by 10 models, we find that preindustrial to present-day
climate change decreased the methane lifetime by about four months, representing
a negative feedback on the climate system. Further, we analysed attribution
experiments performed by a subset of models relative to 2000 conditions with
only one precursor at a time set to 1860 levels. We find that global mean OH
increased by 46.4 ± 12.2% in response to preindustrial to present-day
anthropogenic NOx emission increases, and decreased by
17.3 ± 2.3%, 7.6 ± 1.5%, and 3.1 ± 3.0% due
to methane burden, and anthropogenic CO, and NMVOC emissions increases,
respectively. |
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