Abstract
We report measurements of the atmospheric plume emitted by Erebus volcano, Antarctica, renowned for its persistent lava lake. The observations were made in December 2005 both at source, with an infrared spectrometer sited on the crater rim, and up to 56 km downwind, using a Twin Otter aircraft; with the two different measurement platforms, plume ages were sampled ranging from <1 min to as long as 9 h. Three species (CO, carbonyl sulfide (OCS), and SO2) were measured from both air and ground. While CO and OCS were conserved in the plume, consistent with their long atmospheric lifetimes, the downwind measurements indicate a SO2/CO ratio about 20% of that observed at the crater rim, suggesting rapid chemical conversion of SO2. The aircraft measurements also identify volcanogenic H2SO4, HNO3 and, recognized for the first time in a volcanic plume, HO2NO2. We did not find NOx in the downwind plume despite previous detection of NO2 above the crater. This suggests that near‐source NOx was quickly oxidized to HNO3 and HO2NO2, and probably NO32−(aq), possibly in tandem with the conversion of SO2 to sulfate. These fast processes may have been facilitated by “cloud processing” in the dense plume immediately downwind from the crater. A further striking observation was O3 depletion of up to ∼35% in parts of the downwind plume. This is likely to be due to the presence of reactive halogens (BrO and ClO) formed through heterogeneous processes in the young plume. Our analysis adds to the growing evidence for the tropospheric reactivity of volcanic plumes and shows that Erebus volcano has a significant impact on Antarctic atmospheric chemistry, at least locally in the Southern Ross Sea area.
Highlights
[2] An important finding concerning the impact of global volcanism is the disproportionately high contribution of sulfate loading in the atmosphere due to sulfur emissions from nonexplosive, degassing volcanoes compared with other sulfur sources, including anthropogenic and oceanic emissions [e.g., Chin and Jacob, 1996; Graf et al, 1997; Stevenson et al, 2003]
Based on plume sampling at the crater, Zreda-Gostynska et al [1997] confirmed the volcano’s strong emission of many species including halogens and trace metals leading them to suggest Erebus might contribute up to 80% of the Cl deposited at South Pole
[6] The new measurements we report here were made both by tracking the plume downwind using an instrumented aircraft, and at the summit crater using a Fourier transform infrared (FTIR) spectrometer sited on the crater rim
Summary
[2] An important finding concerning the impact of global volcanism is the disproportionately high contribution of sulfate loading in the atmosphere due to sulfur emissions from nonexplosive, degassing volcanoes compared with other sulfur sources, including anthropogenic and oceanic emissions [e.g., Chin and Jacob, 1996; Graf et al, 1997; Stevenson et al, 2003]. Radke [1982] reported the results of several research flights carried out in mid-November 1980 He found that most of the plume aerosol mass was narrowly confined to particles with diameter of $100 nm, suggesting a single mechanism involved in aerosol production operating close to the crater. Specific aims included an assessment of the nitrogen and sulfur chemistry of the plume, with an emphasis on contrasting the gas phase composition of the very young plume (in the crater) with the aged plume drifting downwind
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