TROPOMI/PlumeTraj SO2 fluxes consistent with partially degassed magma supplying the 2018 Kīlauea eruption

Volcanic sulfur dioxide (SO₂) emission measurements are a key element of volcano monitoring strategies and underpin our understanding of magmatic degassing impacts on air quality, aircraft, and climate. Volcanic SO₂ emission monitoring is usually performed with near-field ground-based measurements, but ever-improving satellite observations increasingly offers the capacity for volcanic emission monitoring from space. Here we examine the May-August 2018 eruption at Kīlauea, Hawai'i, which produced a voluminous low-altitude gas plume. We compare SO₂ emissions calculated with three approaches: ground-based networks, dissolved sulfur (S) contents and lava effusion rates, and new satellite-derived SO₂ data. The high emission rates of this eruption posed a major challenge for near-field ground-based measurements, and corrections were needed to account for attenuation of the SO₂ signal from the optically thick plumes. Our satellite-derived gas emissions use Sentinel-5 Precursor (S5P)/Tropospheric Monitoring Instrument (TROPOMI) observations and PlumeTraj back-trajectory analysis, deriving a total mass of 1.3 to 3.3 Mt of SO₂ compared to 10.2 Mt from ground-measured fluxes (Kern et al., 2020). Our measurements deal with uncertainties such as plume aging and SO₂ oxidation as well as cloud coverage which can underestimate results. The S contents also hold their own uncertainties partly due to when sampling was possible. We find agreement between satellite-derived fluxes and those that would be produced by magma which had previously lost at least 200-750 ppm (16-85%) of its initial S content during residence in the Halema'uma'u lava lake and reservoir. Our measurements allow an estimate of the efficiency of S loss from the Halema'uma'u lava lake prior to the 2018 eruption, and this implies a lava lake magma supply rate of 0.0019-0.0072 km³ per day for 2013-2018. The 2018 eruption produced a lava volume equivalent to 5 to 19 months of magma supply to Kīlauea during 3 months of eruption.