The Hawaii Kilauea volcano has been active for over 20 years. The volcano produces a plume of SO2 and volcanic smog (vog) which affects the Hawaiian Islands in various ways. The figure below is a MODIS image showing the location of the Puu Oo vent on the eastern side of the island. Due to the trade wind inversion, the volcano plume is confined below the trade wind inversion with a lid at ~2km height. In the atmosphere, the volcanic plume is typically blown down wind (towards the WSW) from the island of Hawaii and has been measured as far away as Johnston Islands (~1000 mi. away) still strongly acidic (Clarke and Porter, 1997). When cold fronts approach the islands, SE and SW Kona winds can blow the volcano plume northward affecting the entire Hawaii island chain. Numerical dispersion modeling studies have been carried out and are consistent with the discussion presented here (Baerman et al., 2002).
The geological structure of the Kilauea volcano is such than when the lava rises from the earth, it reaches the surface at the Puu Oo vent first (see Figure below). Next it flows down to the ocean in lava tubes which are just below the surface. When the lava enters the ocean it creates a steam plume of hydrochloric acid (see USGS discussion http://pubs.usgs.gov/fs/fs169-97/ ).
When the lava reaches the surface at the Puu Oo vent, the majority of the SO2 is vented to the atmosphere at this site. Based on optical absorption measurements, SO2 emissions are roughly 1,000 tons a day from the Kilauea vent (Jeff Sutton, US Geological Survey, personal communication) but can go up to 32,000 tons per day on occasion. In the atmosphere the SO2 is converted to sulfuric acid aerosols. These aerosols exist in the accumulation mode (Porter and Clarke, 1997) between 0.1-0.4 μm diameters. Typical concentrations of sulfate in the volcano have been found to be near 12 μg/m3 ( Porter and Clarke, 1997). The Hawaii volcano aerosol, unlike city pollution, is composed of mostly sulfuric acid with very little neutralization by ammonium. The fact that the vog aerosols are small means that they penetrate deep into the lung when breathed. This along with their strongly acidic nature may be the cause of many respiratory problems in Hawaii. The health effects of these acidic aerosols are poorly known and the current National health standards do not account for the acidity of the aerosol.
The time required for the SO2 to be converted to H2SO4 accumulation mode aerosols is somewhat uncertain. Porter et al. (2002) drove under the volcano plume making lidar and sun photometer measurements (see figures below). Using these measurements, fluxes of sulfuric acid aerosols and SO2 gas (from Jeff Sutton) were calculated. Using these values, an SO2 half life of 6 hours (plus/minus 4 hr). In this case there were no clouds so a different value might occur under cloudy conditions. Furthermore it was necessary to assume the plume at the Puu Oo vent was only SO2 which may be questionable. Further studies with flux measurements at two or more locations are needed to better tie down the conversion rate of SO2 from the Hawaii volcano plume.
Image showing lidar measurements of the volcano plume while driving under the volcano plume. The bottom figure shows the plume along with sun photometer measurements made on the road while passing under the plume (Porter et al., 2002).