Increasing Isoprene Epoxydiol-to-Inorganic Sulfate Aerosol Ratio Results in Extensive Conversion of Inorganic Sulfate to Organosulfur Forms: Implications for Aerosol Physicochemical Properties
Riva, M., Y. Chen, Y. Zhang, Z. Lei, N. Olson, H. Boyer, S. Narayan, L. Yee, H. Green, T. Cui, Z. Zhang, K. Baumann, M. Fort, E. Edgerton, S. Budisulistiorini, C. Rose, I. Ribeiro, R. e Oliveira, E. dos Santos, C. Machado, S. Szopa, Y. Zhao, E. Alves, S. de Sá, W. Hu, E. Knipping, S. Shaw, S. Duvoisin Junior, R. de Souza, B. Palm, J. Jimenez, M. Glasius, A. Goldstein, H. Pye, A. Gold, B. Turpin, W. Vizuete, S. Martin, J. Thornton, C. Dutcher, A. Ault, AND J. Surratt. Increasing Isoprene Epoxydiol-to-Inorganic Sulfate Aerosol Ratio Results in Extensive Conversion of Inorganic Sulfate to Organosulfur Forms: Implications for Aerosol Physicochemical Properties. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 53(15):8682-8694, (2019). https://doi.org/10.1021/acs.est.9b01019
For locations such as the southeastern US and Amazon, inorganic particulate sulfate is converted to organosulfur via multiphase chemistry involving isoprene. The resulting organosulfur is a significant contributor to ambient particulate sulfur (~15% in the Great Smoky Mountains) as well as organic aerosol. As sulfur emissions are reduced, an increasing fraction of particulate sulfur is expected to be in the form of organosulfur. This has implications for aerosol properties that influence endpoints such as visibility and climate as well as for monitoring strategies that are based on assuming inorganic sulfate only.
Acid-driven multiphase chemistry of isoprene epoxydiols (IEPOX), a key isoprene oxidation product, with inorganic sulfate aerosol yields substantial amounts of secondary organic aerosol (SOA) through the formation of organosulfur. The extent and implications of inorganic-to-organic sulfate conversion, however, are unknown. Herein, we reveal that extensive consumption of inorganic sulfate occurs, which increases with the IEPOX-to-inorganic sulfate ratio (IEPOX:SO4), as determined by laboratory and field measurements. We further demonstrate that organosulfur greatly modifies critical aerosol properties, such as acidity, morphology, viscosity, and phase state. These new mechanistic insights reveal that changes in SO2 emissions will influence IEPOX:SO4, significantly altering aerosol physicochemical properties. Consequently, IEPOX:SO4 - will play a central role in understanding historical climate and determining future impacts of biogenic SOA on global climate and air quality.