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.

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