Atmos. Chem. Phys. Discuss., 11, 12441-12486, 2011
© Author(s) 2011. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Microphysical simulations of new particle formation in the upper troposphere and lower stratosphere
J. M. English1, O. B. Toon1, M. J. Mills2, and F. Yu3
1Laboratory for Atmospheric and Space Physics, Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, CO, USA
2NCAR Earth System Laboratory, National Center for Atmospheric Research, Boulder, CO, USA
3Atmospheric Sciences Research Center, State University of New York, Albany, NY, USA

Abstract. Using a three-dimensional general circulation model with sulfur chemistry and sectional aerosol microphysics (WACCM/CARMA), we studied aerosol formation and microphysics in the tropical upper troposphere and lower stratosphere (UTLS) based on three nucleation schemes (two binary homogeneous schemes and an ion-mediated scheme). Simulations suggest that ion-mediated nucleation rates in the UTLS are 25% higher than binary rates, but that the rates predicted by the two binary schemes vary by two orders of magnitude. However, it is found that coagulation, not nucleation, controls number concentration at sizes greater than approximately 10 nm. Therefore, based on this study, atmospherically relevant processes in the UTLS are not sensitive to the choice of nucleation schemes. The dominance of coagulation over other microphysical processes is consistent with other recent work using microphysical models. Simulations using all three nucleation schemes compare reasonably well to observations of size distributions, number concentration across latitude, and vertical profiles of particle mixing ratio in the UTLS. Interestingly, we find we need to include Van der Waals forces in our coagulation scheme to match the UTLS aerosol concentrations. We conclude that this model can accurately represent sulfate microphysical processes in the UTLS, and that the properties of particles at atmospherically relevant sizes are not sensitive to the details of the nucleation scheme. We also suggest that micrometeorites, which are not included in this model, dominate the aerosol properties in the upper stratosphere above about 30 km.

Citation: English, J. M., Toon, O. B., Mills, M. J., and Yu, F.: Microphysical simulations of new particle formation in the upper troposphere and lower stratosphere, Atmos. Chem. Phys. Discuss., 11, 12441-12486, doi:10.5194/acpd-11-12441-2011, 2011.
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