Global cloud condensation nuclei influenced by carbonaceous combustion aerosol D. V. Spracklen1, K. S. Carslaw1, U. Pöschl2, A. Rap1, and P. M. Forster1 1Institute for Climate and Atmospheric Science, School of Earth and Environment, University of Leeds, Leeds, UK 2Biogeochemistry Department, Max Planck Institute for Chemistry, Mainz, Germany
Abstract. Black carbon in carbonaceous combustion aerosol warms the climate by
absorbing solar radiation, meaning reductions in black carbon
emissions are often perceived as an attractive global warming
mitigation option. However, carbonaceous combustion aerosol can also
act as cloud condensation nuclei (CCN)
so they also cool the climate by increasing cloud albedo. The
net radiative effect of carbonaceous combustion aerosol is uncertain
because their contribution to CCN has not been
evaluated on the global scale. By combining extensive observations of
CCN concentrations with the GLOMAP global aerosol model,
we find that the model is biased low (normalised mean bias = −77 %) unless
carbonaceous combustion aerosol act as CCN.
We show that carbonaceous combustion aerosol accounts for more than
half (52–64 %) of global CCN with the range due to uncertainty in
the emitted size distribution of carbonaceous combustion particles.
The model predicts
that wildfire and pollution (fossil fuel and biofuel) carbonaceous
combustion aerosol causes a global mean cloud albedo aerosol indirect effect of
−0.34 W m−2, with stronger cooling if we assume smaller particle emission size.
We calculate that carbonaceous combustion aerosol from
pollution sources cause a global mean aerosol indirect effect of
−0.23 W m−2. The small size of carbonaceous combustion
particles from fossil fuel sources means that whilst pollution sources account for
only one-third of the emitted mass they cause
two-thirds of the cloud albedo aerosol indirect effect that is due to
carbonaceous combustion aerosol. This cooling effect must be
accounted for, along with other cloud effects not studied here, to ensure that black carbon emissions controls that
reduce the high number concentrations of fossil fuel particles
have the desired net effect on climate.
Citation: Spracklen, D. V., Carslaw, K. S., Pöschl, U., Rap, A., and Forster, P. M.: Global cloud condensation nuclei influenced by carbonaceous combustion aerosol, Atmos. Chem. Phys., 11, 9067-9087, doi:10.5194/acp-11-9067-2011, 2011.