Hi All
On 1 January 2015 I circulated to the geo-group a comment on the Stuart
coagulation paper pointing out that the words 'electrostatic' and
'charge' did not appear. I also pointed out that coagulation will be
higher in spray with the very wide range of drop sizes assumed by Stuart
than in the mono-disperse spray which we hope to produce.
Anand and Mayya do not mention electrostatic charge either. At the top
of the right column of page 754 they do mention polydispersity but only
in connection with the Stuart paper and do not say what spread of drop
sizes their model uses.
Alan Gadian tells me that, as the sea surface stays at near constant
temperature and the night time cooling of the air above it will be
increased even further by the loss of latent heat for evaporation spray,
there will extreme instability at the bottom of the marine boundary
layer. It would be useful to know if this could be even more unstable
than class A used in section 2 of Anand and Mayya.
I agree with the Poster's comment about wanting experimental validation
especially for a mono-disperse spray. However one obvious requirement
is missing.
Stephen
Emeritus Professor of Engineering Design. School of Engineering.
University of Edinburgh. Mayfield Road. Edinburgh EH9 3JL. Scotland
[email protected] Tel +44 (0)131 650 5704 Cell 07795 203 195
WWW.see.ed.ac.uk/~shs YouTube Jamie Taylor Power for Change
On 07/02/2015 01:14, Andrew Lockley wrote:
Poster's note : I personally look forward to seeing thesethe plume
models experimentally validated. Lack of dispersion validation is a
major issue for MCB.
Comment on "Reduced efficacy of marine cloud brightening
geoengineering due to in-plume aerosol coagulation: parameterization
and global implications" by Stuart et al. (2013)
S. Anand and Y. S. Mayya
Abstract.
We examine the parameterized model of Stuart et al. (2013) vis-??-vis a
diffusion-based model proposed by us earlier (Anand and Mayya, 2011)
to estimate the fraction of aerosol particles surviving coagulation in
a dispersing plume. While the Stuart et al. approach is based on the
solutions to the coagulation problem in an expanding plume model, the
diffusion-based approach solves the diffusion???coagulation equation for
a steady-state standing plume to arrive at the survival fraction
correlations. We discuss the differences in the functional forms of
the survival fraction expressions obtained in the two approaches and
compare the results for the case studies presented in Stuart et al.
(2013) involving different particle emission rates and atmospheric
stability categories. There appears to be a better agreement between
the two models at higher survival fractions as compared to lower
survival fractions; on the whole, the two models agree with each other
within a difference of 10%. The diffusion-based expression involves a
single exponent fit to a theoretically generated similarity variable
combining the parameters of the problem with inbuilt exponents and
hence avoids the multi-exponent parameterization exercise. It also
possesses a wider range of applicability in respect of the source and
atmospheric parameters as compared to that based on parameterization.
However, in the diffusion model, the choice of a representative value
for the coagulation coefficient is more prescriptive than rigorous,
which has been addressed in a more satisfactory manner by the
parameterization method. The present comparative exercise, although
limited in scope, confirms the importance of aerosol microphysical
processes envisaged by Stuart et al. for cloud brightening
applications. In a larger context, it seems to suggest that either of
the two forms of expressions might be suitable for incorporation into
global-/regional-scale air pollution models for predicting the
contribution of localized sources to the particle number loading in
the atmosphere.
Citation:
Anand, S. and Mayya, Y. S.: Comment on "Reduced efficacy of marine
cloud brightening geoengineering due to in-plume aerosol coagulation:
parameterization and global implications" by Stuart et al. (2013),
Atmos. Chem. Phys., 15, 753-756, doi:10.5194/acp-15-753-2015, 2015.
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