Inorganic and organic sulfate formation in multiphase processes in aqueous aerosols

It is well known that atmospheric modeling of sulfate formation in the atmosphere is lacking due to a large extent because of a lack of experimental data on several important parameters including pH, light and saturation effects. To address these uncertainties, the focus on understanding several new aspects of sulfur oxide chemistry in the atmosphere. In particular, sulfur oxidation and organosulfur formation in micron-sized aqueous aerosols will be investigated in laboratory studies, and we will use numerical modeling to analyze the data and evaluate the environmental importance of each reaction pathway. The results of these studies will be used to develop strategies for more accurately representing sulfate and organosulfate formation in large-scale atmospheric models. Gaps persist in the modeling of sulfate formation in the atmosphere, particularly during haze episodes, largely due to the need for more experimental data over a range of several important parameters including pH, ionic strength and different oxidants. Recent enhancements in rates of reactions in aerosols compared to bulk solutions suggest that these reactions need to be measured in aqueous aerosols. Furthermore, past studies have focused on inorganic sulfur oxidation chemistry in the absence of any organic compounds, however, given the importance and presence of organic compounds in the atmosphere, it is imperative to understand the role that organic compounds play in multiphase sulfur oxide chemistry. To address these uncertainties, the focus of the proposed studies will be to further understand and to quantify and compare directly sulfur oxide chemistry, including sulfate and organosulfur compound formation, within micron-sized aqueous aerosols. We are using a collaborative approach to (a) experimentally compare reaction rates for different mechanisms for sulfate formation in individual aqueous aerosols using Aerosol Optical Tweezers (AOT)-based techniques in the Grassian laboratory at UC San Diego (b) use the McNeill Group numerical model of multiphase atmospheric chemistry, GAMMA, in a “lab-to-environment” approach, to extract kinetics and mechanisms from the data and evaluate the relative importance of the studied mechanisms among other cloud and aerosol phase S(IV)S(VI) conversion pathways. Based on these studies, updated parameterizations of sulfate and organosulfate formation will be developed for use in large-scale atmospheric models. Measurements of the rate and extent of sulfate formation in several different processes relevant to atmospheric chemistry will be done in a series of experiments on single micron-sized aqueous aerosols. Several mechanisms for organosulfur and inorganic sulfate formation in aqueous aerosols will be investigated that include:

• Sulfur dioxide oxidation through different oxidation pathways in aqueous aerosols. 

• Competition between inorganic sulfate and organosulfur formation pathways in aqueous aerosols. 

• Multiphase chemistry containing inclusions of reactive solids within aqueous aerosols.