Proximal ground-level assessment of sulfur dioxide gas and fine aerosol in the volcanic gas plume downwind from Kilauea volcano indicates high levels of both species. Fine aerosol and SO₂ data were collected in the Kau district, 37–74 km downwind from the eruption, and at a nonexposed control site in Hawi, Hawaii. Typical trade winds and effusive eruption occurred during sampling in August–September 2003. Ambient SO₂ concentrations, measured with diffusion tubes, ranged from 6 to 34 ppbv and correlated negatively with altitude. In contrast, fine aerosol (≤0.3 μm size) concentrations, measured with a cascade impactor, ranged from 0.61 to 11.82 μg/m³ and correlated positively with altitude. We attribute decrease of SO₂ with altitude to rapid oxidation as diurnal wind patterns blow the plume from oceanic terrain landward to more abundant oxidation sources. Aerosol increase with altitude likely reflects emission of H₂SO₄ from Kilauea, supplemented by oxidation of SO₂ in atmospheric hydrosols. Kau residents are exposed to volcanogenic pollutants at concentrations that warrant concern for adverse health effects.

Keywords: medical geology, Kilauea, volcanic risk, sulfur dioxide, degassing, health