Parameterization of black carbon aging in the OsloCTM2 and implications for regional transport to the Arctic 1CICERO – Center for International Climate and Environmental Research, Oslo, Norway
03 Aug 2012
2Department of Geosciences, University of Oslo, Oslo, Norway
Received: 24 Nov 2011 – Published in Atmos. Chem. Phys. Discuss.: 09 Dec 2011Abstract. A critical parameter for the atmospheric lifetime of black carbon (BC) aerosols,
and hence for the range over which the particles can be transported,
is the aging time, i.e. the time before the aerosols become available for
removal by wet deposition. This study compares two different
parameterizations of BC aging in the chemistry transport model OsloCTM2: (i)
A bulk parameterization (BULK) where aging is represented by a constant
transfer to hydrophilic mode and (ii) a microphysical module (M7) where aging
occurs through particle interaction and where the particle size distribution
is accounted for. We investigate the effect of including microphysics on the
distribution of BC globally and in the Arctic. We also focus on the impact on
estimated contributions to Arctic BC from selected emission source regions.
With more detailed microphysics (M7) there are regional and seasonal
variations in aging. The aging is slower during high-latitude winter, when
the production of sulfate is lower, than in lower latitudes and during
summer. High-latitude concentrations of BC are significantly increased during
winter compared to BULK. Furthermore, M7 improves the model performance at
Arctic surface stations, especially the accumulation of BC during winter. A
proper representation of vertical BC load is important because the climate
effects of the aerosols depend on their altitude in the atmosphere.
Comparisons with measured vertical profiles indicate that the model generally
overestimates the BC load, particularly at higher altitudes, and this
overestimation is exacerbated with M7 compared to BULK. Both
parameterizations show that north of 65° N emissions in Europe
contribute most to atmospheric BC concentration and to BC in snow and ice. M7
leads to a pronounced seasonal pattern in contributions and contributions
from Europe and Russia increase strongly during winter relative to BULK.
There is generally an increase in the amount of BC in snow and ice with M7
compared to BULK. However, in regions where the concentration of BC in snow
is strongly underestimated with BULK compared to measurements, this increase
with M7 is not sufficient to significantly improve the comparison.
Revised: 02 Apr 2012 – Accepted: 21 Jul 2012 – Published: 03 Aug 2012
Citation: Lund, M. T. and Berntsen, T.: Parameterization of black carbon aging in the OsloCTM2 and implications for regional transport to the Arctic, Atmos. Chem. Phys., 12, 6999-7014, doi:10.5194/acp-12-6999-2012, 2012.