Atmos. Chem. Phys. Discuss., 12, 8169-8182, 2012
www.atmos-chem-phys-discuss.net/12/8169/2012/
doi:10.5194/acpd-12-8169-2012
© Author(s) 2012. This work is distributed
under the Creative Commons Attribution 3.0 License.
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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.
Sensitivities of sulfate aerosol formation and oxidation pathways on the chemical mechanism employed in simulations
A. F. Stein1 and R. D. Saylor2
1Earth Resources and Technology (ERT) on assignment to the Air Resources Laboratory (ARL), NOAA, Silver Spring, MD, USA
2Air Resources Laboratory (ARL), NOAA, Atmospheric Turbulence and Diffusion Division, Oak Ridge, TN, USA

Abstract. The processes of aerosol sulfate formation are vital components in the scientific understanding of perturbations of earth's radiative balance via aerosol direct and indirect effects. In this work, an analysis of the influence of changes in oxidant levels and sulfur dioxide oxidation pathways was performed to study the underlying pathways for sulfate formation. Sensitivities of this constituent were calculated from a series of photochemical model simulations with varying rates of NOx and VOC emissions to produce variations in oxidant abundances using a photochemical model (CMAQ) that covers the Eastern US for the ICARTT 2004 campaign. Three different chemical mechanisms (CBIV, CB05, and SAPRC99) were used to test model responses to changes in NOx and VOC levels. Comparison of modeled results and measurements demonstrates that the simulations with all three chemical mechanisms capture the levels of sulfate reasonably well. However, the three mechanisms are shown to have significantly different responses in sulfate formation when the emissions of NOx and/or VOC are altered, reflecting different photochemical regimes under which the formation of sulfate occurs. Also, an analysis of the oxidation pathways that contribute to sulfur dioxide conversion to sulfate reveals substantial differences in the importance of the various pathways among the three chemical mechanisms. These findings suggest that estimations of the influence that future changes in primary emissions or other changes which perturb SO2 oxidants have on sulfate abundances, and on its direct and indirect radiative forcing effects, may be dependent on the chemical mechanism employed in the model analysis.

Citation: Stein, A. F. and Saylor, R. D.: Sensitivities of sulfate aerosol formation and oxidation pathways on the chemical mechanism employed in simulations, Atmos. Chem. Phys. Discuss., 12, 8169-8182, doi:10.5194/acpd-12-8169-2012, 2012.
 
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