Abstract
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 part of the ICARTT 2004 campaign. Three different chemical mechanisms (CBIV, CB05, and SAPRC99) were used to test model responses to changes in NOx and VOC concentrations. 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.
Highlights
Since the 1970s, studies of particle sulfate (SO24−) formation and fate have played a key role in advancing the scientific understanding of diverse phenomena such as acid precipitation, tropospheric particle matter composition, and, more recently, in the role SO24− particles play in the direct and indirect forcings of the earth’s radiative budget
Comparison of base case model results and measurements demonstrates that all three chemical mechanisms capture the levels of boundary layer H2O2, SO24− and total nitrate (HNO3/NO−3 ) within 50 % for 20 July 2004 (Fig. 1). (All results presented in this work for July 20 are representative of similar results obtained for July 18 and 22, which are not shown for brevity.) These results are consistent with the model comparisons performed by Yu et al (2010) for the same dataset
CBIV and CB05 show volatile organic compounds (VOC) sensitivity to be dominant for the formation of sulfate
Summary
Since the 1970s, studies of particle sulfate (SO24−) formation and fate have played a key role in advancing the scientific understanding of diverse phenomena such as acid precipitation, tropospheric particle matter composition, and, more recently, in the role SO24− particles play in the direct and indirect forcings of the earth’s radiative budget. Formation of SO24− is chemically linked to primary emissions of sulfur dioxide (SO2) and to the abundance of atmospheric oxidants such as hydroxyl radical (OH), hydrogen peroxide (H2O2), ozone (O3), methylhydroperoxide (MHP), and peroxyacetic acid (PAA) (Seinfeld and Pandis, 1998). All of these oxidant species are formed via photochemical reactions which originate from emissions of nitrogen oxides (NOx) and volatile organic compounds (VOC). Changes in the amount of primary emitted NOx and VOC were introduced for each mechanism to understand the responses of sulfate formation processes to variations in SO2 oxidant concentrations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
