Atmos. Chem. Phys. Discuss., 12, 2517-2558, 2012
© Author(s) 2012. 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.
Microphysical simulations of sulfur burdens from stratospheric sulfur geoengineering
J. M. English1,*, O. B. Toon1, and M. J. Mills2
1Laboratory for Atmospheric and Space Physics, Department of Atmospheric and Oceanic Sciences, UCB 600, University of Colorado, Boulder, CO 80303, USA
2NCAR Earth System Laboratory, National Center for Atmospheric Research, 3450 Mitchell Lane, Boulder, CO 80301, 303-497-1425, USA
*now at: NCAR Climate and Global Dynamics Division, National Center for \newline Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, USA

Abstract. Recent microphysical studies suggest that geoengineering by continuous stratospheric injection of SO2 gas may be limited by the growth of the aerosols. We study the efficacy of SO2, H2SO4 and aerosol injections on aerosol mass and optical depth using a three-dimensional general circulation model with sulfur chemistry and sectional aerosol microphysics (WACCM/CARMA). We find increasing injection rates of SO2 in a narrow band around the equator to have limited efficacy while broadening the injecting zone as well as injecting particles instead of SO2 gas increases the sulfate burden for a given injection rate, in agreement with previous work. We find that injecting H2SO4 gas instead of SO2 does not discernibly alter sulfate size or mass, in contrast with a previous study using a plume model with a microphysical model. However, the physics and chemistry in aircraft plumes, which are smaller than climate model grid cells, need to be more carefully considered. We find equatorial injections increase aerosol optical depth in the Northern Hemisphere more than the Southern Hemisphere, potentially inducing regional climate changes. We also find significant perturbations to tropospheric aerosol for all injections studied, particularly in the upper troposphere and near the poles, where sulfate burden increases by up to 100 times. This enhanced burden could have implications for tropospheric radiative forcing and chemistry. These results highlight the need to mitigate greenhouse gas emissions through means other than geoengineering, and to further study geoengineering before it can be seriously considered as a climate intervention option.

Citation: English, J. M., Toon, O. B., and Mills, M. J.: Microphysical simulations of sulfur burdens from stratospheric sulfur geoengineering, Atmos. Chem. Phys. Discuss., 12, 2517-2558, doi:10.5194/acpd-12-2517-2012, 2012.
Search ACPD
Discussion Paper
    Final Revised Paper