Measuring SO2 Emission Rates at Kīlauea Volcano, Hawaii, Using an Array of Upward-Looking UV Spectrometers, 2014–2017

Abstract

Retrieving accurate volcanic sulfur dioxide (SO 2) gas emission rates is important for a variety of purposes. It is an indicator of shallow subsurface magma, and thus may signal impending eruption or unrest. SO 2 emission rates are significant for accurately assessing climate impact, and providing context for assessing environmental, agricultural, and human health effects during volcanic eruptions. The U.S. Geological Survey Hawaiian Volcano Observatory uses an array of ten fixed, upward-looking ultraviolet spectrometer systems to measure SO 2 emission rates at 10-s sample intervals from the Kīlauea summit. We present Kīlauea SO 2 emission rates from the volcano's summit and middle East Rift Zone during 2014-2017 and discuss the major sources of error for these measurements. Due to the wide range of SO 2 emissions encountered at the summit vent, we used a variable wavelength spectral analysis range to accurately quantify both high and low SO 2 column densities. We compare measured emission rates from the fixed spectrometer array to independent road and helicopter-based traverse measurements and evaluate the magnitudes and sources of uncertainties for each method. To address the challenge of obtaining accurate plume speed measurements, we examine ground-based wind-speed, plume speed tracking via spectrometer, and SO 2 camera derived plume speeds. Our analysis shows that: (1) the summit array column densities calculated using a dual fit window, are within −6 to +22% of results obtained with a variety of other conventional and experimental retrieval methods; (2) emission rates calculated from the summit array located ∼3 km downwind provide the best, practical estimate of summit SO 2 release under normal trade wind conditions; (3) ground-based anemometer wind speeds are 22% less than plume speeds determined by cross-correlation of plume features; (4) our best estimate of average Kīlauea SO 2 release for 2014-2017 is 5100 t/d, which is comparable to the space-based OMI emissions of 5518 t/d; and (5) short-term variability of SO 2 emissions reflects Kīlauea lava lake dynamics.

The cascading origin of the 2018 Kīlauea eruption and implications for future forecasting

“…Sulfur dioxide emissions (Fig. 4e) were measured with an ultraviolet spectrometer used in vehicle-based traverses beneath the Puʻu ʻŌʻō gas plume 56,97,98 .…”

Spatial and Temporal Variations in SO2 and PM2.5 Levels Around Kīlauea Volcano, Hawai'i During 2007–2018

“…Kīlauea's 2018 eruption was the largest LERZ eruption in the last two centuries. SO 2 emissions reached a monthly average of 200 kt/day during June (Kern et al 2019), significantly exceeding emissions from Kīlauea during 2008-2017, which averaged 5-6 kt/day (Eguchi et al, 2011;Beirle et al, 2014;Carn et al, 2016;Elias et al, 2018). During the 2018 LERZ eruption, SO 2 mass concentrations exceeding the Hawai'i 24-h-mean threshold (366 µg/m 3 ) primarily occurred in the south of the island, at Volcano Observatory and in Pāhala and Ocean View (2.1, 5.3, and 4.2 % of the time during the 3-month long eruption, respectively).…”

“…At this time, emissions from both the ERZ and the summit were significant, with the two sources contributing variable amounts to the total degassing rate (Elias and Sutton, 2012). For the period 2009-2017, the dynamic activity at Kīlauea was reflected in variable emissions, with a longterm average of 5-6 kt/day based on satellite and ground-based measurements (Eguchi et al, 2011;Elias and Sutton, 2012;Carn et al, 2016;Elias et al, 2018) (Figure 2A). Lava was first observed in the Halema'uma'u summit crater in September 2008, with a permanent lava lake visible from February 2010 until May 2018 (Patrick et al, 2013;Neal et al, 2019).…”

Quantifying Light Dilution in Ultraviolet Spectroscopic Measurements of Volcanic SO2 Using Dual-Band Modeling

“…Multiplying a plume SO 2 cross-section by the wind velocity then produces an instantaneous flux. Observatories can also construct SO 2 cross-sections autonomously using zenith pointing spectrometer arrays (Elias et al, 2018) or permanent scanning stations (e.g., Edmonds et al, 2003). Scanning networks are more widespread, including the FLAME network on Sicilian active volcanoes (Salerno et al, 2009a), and the NOVAC network (Galle et al, 2010) which covers 37 volcanoes as of June 2018 (https://novaccommunity.org/).…”