Review of sulfur dioxide to sulfate aerosol chemistry at Kīlauea Volcano, Hawai'i

Sulfur dioxide emissions from the Kīlauea Volcano on the island of Hawai'i and the subsequent formation of sulfate aerosols have caused a public health hazard across the state of Hawai'i since the volcano began erupting continuously in 1983. The University of Hawai'i at Mānoa began to forecast the trajectory and dispersion of emissions in 2010 to help mitigate the hazards to public health. In this paper a comprehensive review of potential conversion reactions is presented with the goal of more accurately representing the sulfur dioxide chemistry in the dispersion model.

Atmospheric sulfur dioxide chemistry and major process responsible for sulfate formation are well documented in urban and industrial settings. The atmosphere in the vicinity of Kīlauea Volcano on the island of Hawai'i differs from that in previous investigations by virtue of being far removed from both urban and industrial settings in a remote, tropical marine atmosphere. Additionally, the combination of the high rate of sulfur dioxide emissions and trace gases and metals from Kīlauea Volcano creates a unique circumstance that requires a new look at potential conversion pathways to determine the dominant reactions.

The theoretical analysis suggests that the dominant reaction in clear air will be between sulfur dioxide and the hydroxyl radical (0.01-5% h^-1) and the dominant reaction in cloudy air involves hydrogen peroxide (3-50% s^-1). Moreover, given the high SO₂ emissions from the Halema'uma'u Crater vent, the oxidation of sulfur dioxide by these reactants is limited by their rate of production.