Acid-driven multiphase chemistry of isoprene epoxydiols (IEPOX), key isoprene oxidation products, with inorganic sulfate aerosol yields substantial amounts of secondary organic aerosol (SOA) through the formation of organosulfur compounds. The extent and implications of inorganic-to-organic sulfate conversion, however, are unknown. In this article, we demonstrate that extensive consumption of inorganic sulfate occurs, which increases with the IEPOX-to-inorganic sulfate concentration ratio (IEPOX/Sulfinorg), as determined by laboratory measurements. Characterization of the total sulfur aerosol observed at Look Rock, Tennessee, from 2007 to 2016 shows that organosulfur mass fractions will likely continue to increase with ongoing declines in anthropogenic Sulfinorg, consistent with our laboratory findings. We further demonstrate that organosulfur compounds greatly modify critical aerosol properties, such as acidity, morphology, viscosity, and phase state. These new mechanistic insights demonstrate that changes in SO2 emissions, especially in isoprene-dominated environments, will significantly alter biogenic SOA physicochemical properties. Consequently, IEPOX/Sulfinorg will play an important role in understanding the historical climate and determining future impacts of biogenic SOA on the global climate and air quality.
Bibliographical noteFunding Information:
This work is also funded in part by the U.S. EPA Grant R835404, the National Science Foundation (NSF) Grants AGS-1703535, AGS-1703019, AGS-1554936, CHE-1404644, and CHE-1404573, and by the National Oceanic and Atmospheric Administration (NOAA) Climate Program Office’s AC4 program, Award Number NA13OAR4310064. The authors wish to thank the Camille and Henry Dreyfus Postdoctoral Fellowship Program in Environmental Chemistry for their financial support. The authors would like to thank the Michigan Center for Materials Characterization for use and help with the SEM and the Banaszak-Holl laboratory for the use and help with the AFM. The contents of this publication are solely the responsibility of the authors and do not necessarily represent the official views of the U.S. Environmental Protection Agency (U.S. EPA). Further, the U.S. EPA does not endorse the purchase of any commercial products or services mentioned in the publication. The U.S. EPA through its Office of Research and Development collaborated in the research described here. It has been subjected to Agency administrative review and approved for publication but may not necessarily reflect official Agency policy. The authors wish to thank the IMPROVE network. IMPROVE is a collaborative association of state, tribal, and federal agencies and international partners. U.S. EPA is the primary funding source, with contracting and research support from the National Park Service. The Air Quality Group at the University of California, Davis, is the central analytical laboratory, with ion analysis provided by the Research Triangle Institute and carbon analysis provided by Desert Research Institute.
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