Atmos. Chem. Phys. Discuss., 13, 16961-17019, 2013
www.atmos-chem-phys-discuss.net/13/16961/2013/
doi:10.5194/acpd-13-16961-2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
The direct and indirect radiative effects of biogenic secondary organic aerosol
C. E. Scott1, A. Rap1, D. V. Spracklen1, P. M. Forster1, K. S. Carslaw1, G. W. Mann1,2, K. J. Pringle1, N. Kivekäs3, M. Kulmala4, H. Lihavainen3, and P. Tunved5
1School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK
2National Centre for Atmospheric Science, University of Leeds, Leeds, LS2 9JT, UK
3Finnish Meteorological Institute, Erik Palmenin aukio 1, 00560 Helsinki, Finland
4Department of Physics, University of Helsinki, P.O. Box 64, 00014, Finland
5Department of Applied Environmental Research, Stockholm University, Svante Arrhenius Väg 8c, 10691 Stockholm, Sweden

Abstract. We use a global aerosol microphysics model in combination with an offline radiative transfer model to quantify the radiative effect of biogenic secondary organic aerosol (SOA) in the present day atmosphere. Through its role in particle growth and ageing, the presence of biogenic SOA increases the global annual mean concentration of cloud condensation nuclei (CCN; at 0.2% supersaturation) by 3.6–21.1%, depending upon the yield of SOA production, and the nature and treatment of concurrent primary carbonaceous emissions. This increase in CCN causes a rise in global annual mean cloud droplet number concentration (CDNC) of 1.9–5.2%, and a global mean first aerosol indirect effect (AIE) of between +0.01 W m−2 and −0.12 W m−2. The radiative impact of biogenic SOA is far greater when it also contributes to particle nucleation; using two organically-mediated mechanisms for new particle formation we simulate global annual mean AIEs of −0.22 W m−2 and −0.77 W m−2. The inclusion of biogenic SOA substantially improves the simulated seasonal cycle in the concentration of CCN sized particles observed at three forested sites. The best correlation is found when the organically-mediated nucleation mechanisms are applied, suggesting that the AIE of biogenic SOA could be as large as −0.77 W m−2. The radiative impact of SOA is sensitive to the presence of anthropogenic emissions. Lower background aerosol concentrations simulated with anthropogenic emissions from 1750 give rise to a greater fractional CCN increase and a more substantial indirect radiative effect from biogenic SOA. Consequently, the anthropogenic indirect radiative forcing between 1750 and the present day is sensitive to assumptions about the amount and role of biogenic SOA. We also calculate an annual global mean direct radiative effect (DRE) of between −0.08 W m−2 and −0.78 W m−2 in the present day, with uncertainty in the amount of SOA produced from the oxidation of biogenic volatile organic compounds (BVOCs) accounting for most of this range.

Citation: Scott, C. E., Rap, A., Spracklen, D. V., Forster, P. M., Carslaw, K. S., Mann, G. W., Pringle, K. J., Kivekäs, N., Kulmala, M., Lihavainen, H., and Tunved, P.: The direct and indirect radiative effects of biogenic secondary organic aerosol, Atmos. Chem. Phys. Discuss., 13, 16961-17019, doi:10.5194/acpd-13-16961-2013, 2013.
 
Search ACPD
Discussion Paper
    XML
    Citation
    Final Revised Paper
    Share