Volcanic gas emissions and their impact on ambient air character at Kilauea Volcano, Hawaii

Abstract

Currently, gas emissions from Kilauea occur from the summit caldera, along the middle East Rift Zone (ERZ), and where lava enters the ocean. We estimate that the current ERZ eruption of Kilauea releases between 400 metric tonnes of SO2 per day, during eruptive pauses, to as much as 1850 metric tonnes per day during actively erupting periods, along with lesser amounts of other chemically and radiatively active species including H2S, HCl, and HF. In order to characterize gas emissions from Kilauea in a meaningful way for assessing environmental impact we made a series of replicate grab-sample measurements of ambient air and precipitation at the summit of Kilauea, along its ERZ, and at coastal sites where lava enters the ocean. The grab-sampling data combined with SO2 emission rates, and continuous air quality and meteorological monitoring at the summit of Kilauea show that the effects of these emissions on ambient air character are a complex function of chemical reactivity, source geometry and effusivity, and local meteorology. For all the measurement sites, ambient concentrations of the emitted gases decrease rapidly, even at short distances from point sources. Prevailing tradewinds typically carry the gases and aerosols released to the southwest, where they are further distributed by the regional wind regime. Episodes of kona, or low speed variable winds sometimes disrupt this pattern, however, and allow the gases and their oxidation products to collect at the summit and eastern side of the island. Summit solfatara areas of Kilauea are distinguished by moderate to high ambient SO2, high H2S at one location, and low H2S at all others, and negligible HC1 concentrations, as measured 1 m from degassing point-sources. Summit solfatara rain water has high sulfate and low chloride ioa concentrations, and low pH. The middle ERZ degassing areas show moderate to high SO2 at 100 m away from degassing lava, and low H2S concentrations. Moderate HC1 was found in ambient air. Rain water near the middle ERZ degassing areas have high sulfate, high chloride and low pH. Coastal entry areas are characterized by high HC1 in the gas plume and significant rain-out of this HCl as indicated by low rain water pH, and high rain water chloride. Sulfate in the coastal-entry rainwater is also high. Ambient SO2 and 112S are moderate to high near the coastal entry locations. Ambient air in the lower ERZ thermal and non-thermal areas shows essentially no influence from the on-going eruption, as evidenced by the absence of SO2, H2S, HC1, and the moderate rain water pH with low sulfate concentration. When the current eruption ceases, ERZ and summit gas emissions will be greatly reduced.