Review of Sulfur Dioxide to Sulfate Aerosol Chemistry at Kilauea Volcano, Hawaii

Atmospheric sulfur dioxide chemistry and major processes responsible for sulfate formation are well documented in urban or industrial settings.  The atmosphere in the vicinity of Kīlauea Volcano on the island of Hawai‘i does not reflect previous investigations being far removed from both urban and industrial settings in a remote, tropical marine atmosphere.   Also, the high rate of sulfur dioxide emissions from Kīlauea Volcano create a unique scenario requiring a new look at potential conversion pathways to determine the dominant reactions.  Sulfur dioxide emissions from the volcano and the subsequent formation of sulfate aerosols have caused a public health hazard across the state of Hawai‘i since Kīlauea began erupting continuously in the 1980’s.  The University of Hawai‘i at Mānoa began to forecast the dispersion of emissions in 2010 to help mitigate impacts on public health.  Recent efforts to improve air quality forecasts have focused on improving the representation of the sulfur dioxide chemistry in the model and have resulted in a detailed investigation of all potential conversion reactions.  The goal being to determine the dominant reactions necessary to include in the numerical dispersion model and estimate their reaction rate based on chemical theory.  The dominant reactions are found to be between sulfur dioxide and the hydraxyl radical in clear air (0.01 to 5% h^-1) and hydrogen peroxide in cloudy envirnments (3-50% s^-1). Given high SO₂ emissions from the Halema‘uma‘u Crater vent, the oxidation of sulfur dioxide by these reactants is limited by their modest ambient concentrations.