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| Titel |
On the wintertime low bias of Northern Hemisphere carbon monoxide found in global model simulations |
| VerfasserIn |
O. Stein, M. G. Schultz, I. Bouarar, H. Clark, V. Huijnen, A. Gaudel, M. George, C. Clerbaux |
| 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. 17 ; Nr. 14, no. 17 (2014-09-09), S.9295-9316 |
| Datensatznummer |
250119015
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| Publikation (Nr.) |
 copernicus.org/acp-14-9295-2014.pdf |
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| Zusammenfassung |
| Despite the developments in the global modelling of chemistry and of the
parameterization of the physical processes, carbon monoxide (CO)
concentrations remain underestimated during Northern Hemisphere (NH) winter
by most state-of-the-art chemistry transport models. The consequential model
bias can in principle originate from either an underestimation of CO sources
or an overestimation of its sinks. We address both the role of surface
sources and sinks with a series of MOZART (Model for Ozone And Related Tracers) model sensitivity studies for the
year 2008 and compare our results to observational data from ground-based
stations, satellite observations, and vertical profiles from measurements on
passenger aircraft. In our base case simulation using MACCity
(Monitoring Atmospheric Composition and Climate project) anthropogenic
emissions, the near-surface CO mixing ratios are underestimated in the
Northern Hemisphere by more than 20 ppb from December to April, with the
largest bias of up to 75 ppb over Europe in January. An increase in global
biomass burning or biogenic emissions of CO or volatile organic compounds (VOCs)
is not able to reduce the annual course of the model bias and yields
concentrations over the Southern Hemisphere which are too high. Raising
global annual anthropogenic emissions with a simple scaling factor results
in overestimations of surface mixing ratios in most regions all year round.
Instead, our results indicate that anthropogenic CO and, possibly, VOC
emissions in the MACCity inventory are too low for the industrialized
countries only during winter and spring. Reasonable agreement with
observations can only be achieved if the CO emissions are adjusted
seasonally with regionally varying scaling factors. A part of the model bias
could also be eliminated by exchanging the original resistance-type dry
deposition scheme with a parameterization for CO uptake by oxidation from
soil bacteria and microbes, which reduces the boreal winter dry deposition
fluxes. The best match to surface observations, satellite retrievals, and
aircraft observations was achieved when the modified dry deposition scheme
was combined with increased wintertime road traffic emissions over Europe
and North America (factors up to 4.5 and 2, respectively). One reason for
the apparent underestimation of emissions may be an exaggerated downward
trend in the Representative Concentration Pathway (RCP) 8.5 scenario in
these regions between 2000 and 2010, as this scenario was used to
extrapolate the MACCity emissions from their base year 2000. This factor is
potentially amplified by a lack of knowledge about the seasonality of
emissions. A methane lifetime of 9.7 yr for our basic model and 9.8 yr for the
optimized simulation agrees well with current estimates of global OH, but we
cannot fully exclude a potential effect from errors in the geographical and
seasonal distribution of OH concentrations on the modelled CO. |
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