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Atmospheric Composition

Volcanic SO2 gas emissions are oxidized to atmospheric sulfate particles that in turn directly affect the atmospheric transfer of solar and terrestrial radiation, causing a direct radiative forcing of climate change. This forcing, although natural, is as important as anthropogenic radiative forcing because volcanic sulfate particles have a longer lifetime than anthropogenic aerosols, and hence make a disproportionally larger contribution to the budget of sulfate radiative forcing. Furthermore, the forcing of volcanic sulfate aerosols is one of the least well-constrained aspects of the climate models, in part due to inadequate knowledge of the amount, the injection height, and the spatiotemporal variability of their precursor (i.e., SO2) emissions. Here, we propose to quantify the variation of volcanic sulfate direct radiative forcing since 1978 on both global and regional scales with unprecedented accuracy using a combination of EOS satellite data and the GEOS-Chem model.

Our approach involves four steps: (i) Apply the recently-developed iterative spectral fit (ISF) technique (Yang et al., 2009) to all OMI data (starting from Aug. 2004) to create a unique and improved volcanic SO2 inventory that includes simultaneous and accurate estimates of both SO2 amount and SO2 injection height from OMI, and extend this inventory by applying the ISF algorithm and other volcanic information from ground or sub-orbital reports to TOMS data back to 1978; (ii) Use AIRS and MLS SO2 retrievals, as well as MODIS fire products to provide supplementary information for the volcanic SO2 emission inventory derived from OMI and TOMS; (iii) Conduct GEOS-chem simulations with and without input of volcanic SO2 emissions to quantify the distribution of volcanic sulfate aerosols, from which their direct radiative forcing and impact on sulfate particle composition will be quantified; (iv) Estimate the uncertainties in our updated volcanic SO2 emission inventory and sulfate forcing calculations through selected case studies in which the model results will be compared with aerosol data from OMI, MODIS, MISR, and CALIOP.

The proposed project builds on the PI’s previous studies in which the (solid and aqueous) phase transition of sulfate particles was explicitly implemented in the GEOS-Chem model for accurate calculation of radiative forcing. It also benefits from the expertise provided by the Co-Is in volcanism (S. Carn) and in the satellite retrieval of SO2 amount and plume height (K. Yang). Through collaboration with our partners (P. Colarco and M. Chin) at NASA, the volcanic SO2 inventory developed in this project will be implemented (by the PI) into NASA's GEOS-5 system and will be delivered to users of NASA's GOCART model. Given the worldwide community of GEOS-Chem CTM, GEOS-5 system, and GOCART model users, we foresee that the results from this proposed project will have a broad scientific impact on modeling of upper-tropospheric heterogeneous chemistry in which aerosol phase and volcanic eruptions play an important role.

Project PI: Jun Wang/University of Nebraska - Lincoln

Department of Earth and Atmospheric Sciences University of Nebraska - Lincoln 303 Bessey Hall Lincoln, NE, 68588-0340

Phone: (402) 472-3597

Fax: (402) 472-4917

Email:  jwang7 @ unl. edu

http://eas.unl.edu/~jwang/

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Started: Sep 03, 2010

Last Activity: Feb 02, 2011

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