 |
| Titel |
Modelling marine emissions and atmospheric distributions of halocarbons and dimethyl sulfide: the influence of prescribed water concentration vs. prescribed emissions |
| VerfasserIn |
S. T. Lennartz, G. Krysztofiak, C. A. Marandino, B.-M. Sinnhuber, S. Tegtmeier, F. Ziska, R. Hossaini, K. Krüger, S. A. Montzka, E. Atlas, D. E. Oram, T. Keber, H. Bönisch, B. Quack |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 20 ; Nr. 15, no. 20 (2015-10-22), S.11753-11772 |
| Datensatznummer |
250120115
|
| Publikation (Nr.) |
 copernicus.org/acp-15-11753-2015.pdf |
|
|
|
|
|
| Zusammenfassung |
| Marine-produced short-lived trace gases such as dibromomethane
(CH2Br2), bromoform (CHBr3), methyliodide (CH3I) and
dimethyl sulfide (DMS) significantly impact tropospheric and stratospheric
chemistry. Describing their marine emissions in atmospheric chemistry models
as accurately as possible is necessary to quantify their impact on ozone
depletion and Earth's radiative budget. So far, marine emissions of
trace gases have mainly been prescribed from emission climatologies, thus
lacking the interaction between the actual state of the atmosphere and the
ocean. Here we present simulations with the chemistry climate model EMAC (ECHAM5/MESSy
Atmospheric Chemistry)
with online calculation of emissions based on surface water concentrations,
in contrast to directly prescribed emissions. Considering the actual state
of the model atmosphere results in a concentration gradient consistent with
model real-time conditions at the ocean surface and in the atmosphere, which
determine the direction and magnitude of the computed flux. This method has
a number of conceptual and practical benefits, as the modelled emission can
respond consistently to changes in sea surface temperature, surface wind
speed, sea ice cover and especially atmospheric mixing ratio. This online
calculation could enhance, dampen or even invert the fluxes (i.e. deposition
instead of emissions) of very short-lived substances (VSLS). We show that
differences between prescribing emissions and prescribing concentrations
(−28 % for CH2Br2 to +11 % for CHBr3) result mainly
from consideration of the actual, time-varying state of the atmosphere. The
absolute magnitude of the differences depends mainly on the surface ocean
saturation of each particular gas. Comparison to observations from aircraft,
ships and ground stations reveals that computing the air–sea flux
interactively leads in most of the cases to more accurate atmospheric mixing
ratios in the model compared to the computation from prescribed emissions.
Calculating emissions online also enables effective testing of different
air–sea transfer velocity (k) parameterizations, which was performed here for
eight different parameterizations. The testing of these different k values is
of special interest for DMS, as recently published parameterizations derived
by direct flux measurements using eddy covariance measurements suggest
decreasing k values at high wind speeds or a linear relationship with wind
speed. Implementing these parameterizations reduces discrepancies in
modelled DMS atmospheric mixing ratios and observations by a factor of 1.5
compared to parameterizations with a quadratic or cubic relationship to wind
speed. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|