 |
| Titel |
Sources of uncertainties in modelling black carbon at the global scale |
| VerfasserIn |
E. Vignati, M. Karl, M. Krol, J. Wilson, P. Stier, F. Cavalli |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 10, no. 6 ; Nr. 10, no. 6 (2010-03-16), S.2595-2611 |
| Datensatznummer |
250008243
|
| Publikation (Nr.) |
 copernicus.org/acp-10-2595-2010.pdf |
|
|
|
|
|
| Zusammenfassung |
Our understanding of the global black carbon (BC) cycle is essentially
qualitative due to uncertainties in our knowledge of its properties. This
work investigates two source of uncertainties in modelling black carbon:
those due to the use of different schemes for BC ageing and its removal rate
in the global Transport-Chemistry model TM5 and those due to the
uncertainties in the definition and quantification of the observations, which
propagate through to both the emission inventories, and the measurements used
for the model evaluation.
The schemes for the atmospheric processing of black carbon that have been
tested with the model are (i) a simple approach considering BC as bulk
aerosol and a simple treatment of the removal with fixed 70% of in-cloud
black carbon concentrations scavenged by clouds and removed when rain is
present and (ii) a more complete description of microphysical ageing within
an aerosol dynamics model, where removal is coupled to the microphysical
properties of the aerosol, which results in a global average of 40% in-cloud
black carbon that is scavenged in clouds and subsequently removed by rain,
thus resulting in a longer atmospheric lifetime. This difference is reflected
in comparisons between both sets of modelled results and the measurements.
Close to the sources, both anthropogenic and vegetation fire source regions,
the model results do not differ significantly, indicating that the emissions
are the prevailing mechanism determining the concentrations and the choice of
the aerosol scheme does not influence the levels. In more remote areas such
as oceanic and polar regions the differences can be orders of magnitude, due
to the differences between the two schemes. The more complete description
reproduces the seasonal trend of the black carbon observations in those
areas, although not always the magnitude of the signal, while the more
simplified approach underestimates black carbon concentrations by orders of
magnitude.
The sensitivity to wet scavenging has been tested by varying in-cloud and
below-cloud removal. BC lifetime increases by 10% when large scale and
convective scale precipitation removal efficiency are reduced by 30%, while
the variation is very small when below-cloud scavenging is zero.
Since the emission inventories are representative of elemental carbon-like
substance, the model output should be compared to elemental carbon
measurements and if known, the ratio of black carbon to elemental carbon mass
should be taken into account when the model is compared with black carbon
observations. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|