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In 2012, the U.S. Geological Survey’s Hawaiian Volcano Observatory (HVO) installed an array of zenith-pointing ultraviolet spectrometers to track gas emissions from summit of Kīlauea (Businger et al., 2015; Elias et al., 2018). The instruments are arranged in an arc perpendicular to the dominant trade-wind direction approximately 2 kilometers (km) southwest of the actively degassing summit vents. When volcanic plumes emitted from these vents pass overhead during daytime hours, the spectrometers record the spectral radiance of ultraviolet scattered skylight passing vertically through these plumes at 11 distinct locations. The HVO performed updates to the original spectrometer array in 2024. An additional spectrometer was installed on the northern end of the fenceline to better capture plumes emitting from the southwest side of Kīlauea’s summit crater which became more active after sections of the southwest rim collapsed in 2018. Also, the automated spectral processing routines were switched from the correlation spectroscopy approach employed by FLYSPEC instruments (Elias et al., 2018; Horton et al, 2006) to a differential optical absorption spectroscopy (DOAS) retrieval (Platt and Stutz, 2008). A variable-wavelength fit window (Elias et al., 2018; Kern, 2025) was implemented to avoid strong absorption effects stemming from very high overhead SO2 concentrations and make the derived emission rates consistent with those measured by the HVO using vehicle-based Mobile DOAS traverses (Nadeau et al., 2023). Since switching to the DOAS analysis methodology in 2024, we refer to the spectrometer array as the DOAS Fenceline Array (DFence). The raw data contained in this release consist of measured spectral radiances. During daylight hours, each node along the fenceline independently records the spectrum of scattered skylight overhead. Each spectrometer’s exposure time is automatically adjusted depending on illumination conditions, and spectra are co-added for a total integration time of 10 seconds. The spectra are stored in an ASCII format (*.std), the details of which are described in the metadata. The purpose of these measurements is to determine the emission rate of sulfur dioxide from active vents at Kīlauea’s summit. The recorded spectra are analyzed using DOAS retrievals which target the characteristic absorption of SO2 between 306 and 335 nanometers (nm) and yield the overhead column density of SO2 at each station as a function of time. Integrating across the entire array yields the cross-sectional gas burden (e.g., in molecules/centimeter). Finally, multiplication with the wind speed yields the gas emission rate, e.g. in kilograms/second (kg/s) or metric tons per day (t/d). The wind speeds reported in this dataset stem from an anemometer located near the center of the array but are scaled by a factor of 1.2 to account for ground effects (Elias et al., 2018). The measured SO2 emission rates represent an important volcano monitoring parameter as they track the volume of magma reaching shallow depths in the volcano’s plumbing system and erupting at the surface (Kern et al., 2020; Lerner et al., 2021). The measurements are also used by the University of Hawaiʻi’s Vog Measurement and Prediction project (VMAP, Businger et al., 2015; Holland et al., 2020, http://weather.hawaii.edu/vmap/new/) to provide air quality forecasts for the Hawaiian Islands. Note that successful calculation of the emission rate depends on the entire plume being captured by the nearly 4-km long fenceline array. Analysis shows that this requires wind directions between about 35 and 85 degrees azimuth (winds out of the northeast) measured at the location of the anemometer. Note that this does not necessarily accurately reflect the direction that the plume is traveling overhead, as ground effects can skew the wind direction to higher values near the ground when compared to conditions several hundred meters higher. The array must not only capture the plume center but also detect either edge to ensure that the plume is fully accounted for. For this purpose, we report a plume completeness parameter with each emission rate measurement (see the metadata for a detailed description). The reporting period encompasses episodes of high lava fountaining at Kīlauea summit. These episodes are associated with prodigious gas emissions and plumes that can reach many kilometers above the active vents. In these conditions, the fenceline array is often overwhelmed as SO2 clouds drift over all nodes in the system, and we are therefore often not able to reliably track the emission rate during such episodes. While the spectral radiances measured by the individual DOAS nodes represent the raw data, we additionally include a few derived products in this release to demonstrate the utility of the measurements. FilteredDFenceEmissionRates.csv provides a table of derived SO2 emission rates and auxiliary data. Details of the data processing steps followed to produce this table are given in the metadata file (DFence.xml). We also include three figures depicting example time series of SO2 emission rates. Figure1.png shows the emission rate between December 23, 2024, and December 32, 2025, which includes 39 episodes of lava fountaining (indicated by the shaded regions) from Kīlauea summit vents occurring during the 2024 – present eruption. Figure2.png shows emission rates derived leading up to and during episode 25. Although DFence was unable to capture the highest emissions due to the gas plume spreading over the entire array, the existing data show that emission rates exceeded 2,000 kg/s during the intense lava fountaining period. Finally, Figure3.png shows an example of gas pistoning (Patrick et al., 2016) occurring in the morning hours of June 11, 2025, leading up to episode 25. Gas pistoning behavior often preceded lava fountaining episodes, with SO2 emission rates typically fluctuating between about 0 and several 10 kg/s on minute time scales. Also shown is real-time seismic amplitude measured at a location near the volcano’s summit (data available at https://doi.org/10.7914/SN/HV). SO2 emissions and seismicity show notable correlation, measured peaks in degassing lagging behind the seismic observations by about 5 minutes – the time it takes for the gas plume to drift from the point of emission to the fenceline array 2 km downwind. Figure4.png shows a map of the DFence network, with overhead SO2 column densities mapped to the color scale on the right. References Businger, S., Huff, R., Pattantyus, A., Horton, K.A., Sutton, A.J., Elias, T., Cherubini, T., 2015. Observing and Forecasting Vog Dispersion from Kilauea Volcano, Hawaii. Bull. Amer. Meteor. Soc. 96, 1667–1686. https://doi.org/10.1175/BAMS-D-14-00150.1 Elias, T., Kern, C., Horton, K.A., Sutton, A.J., Garbeil, H., 2018. Measuring SO2 Emission Rates at Kīlauea Volcano, Hawaii, Using an Array of Upward-Looking UV Spectrometers, 2014–2017. Front. Earth Sci. 6, 1–20. https://doi.org/10.3389/feart.2018.00214 Holland, L., Businger, S., Elias, T., Cherubini, T., 2020. Two Ensemble Approaches for Forecasting Sulfur Dioxide Emissions From Kīlauea Volcano. Weather Forecast 35, 1923–1937. https://doi.org/10.1175/WAF-D-19-0189.1 Horton, K.A., Williams-Jones, G., Garbeil, H., Elias, T., Sutton, A.J., Mouginis-Mark, P., Porter, J.N., Clegg, S., 2006. Real-time measurement of volcanic SO2 emissions: validation of a new UV correlation spectrometer (FLYSPEC). Bull. Volcanol. 68, 323–327. https://doi.org/10.1007/s00445-005-0014-9 Kern, C., Lerner, A.H., Elias, T., Nadeau, P.A., Holland, L., Kelly, P.J., Werner, C.A., Clor, L.E., Cappos, M., 2020. Quantifying gas emissions associated with the 2018 rift eruption of Kīlauea Volcano using ground-based DOAS measurements. Bull Volcanol 82. https://doi.org/10.1007/s00445-020-01390-8 Kern, C., 2025. Ultraviolet and visible remote sensing of volcanic gas emissions. J. Volcanol. Geotherm. Res. 468, 108423. https://doi.org/10.1016/j.jvolgeores.2025.108423 Lerner, A.H., Wallace, P.J., Shea, T., Mourey, A.J., Kelly, P.J., Nadeau, P.A., Elias, T., Kern, C., Clor, L.E., Gansecki, C., Lee, R.L., Moore, L.R., Werner, C.A., 2021. The petrologic and degassing behavior of sulfur and other magmatic volatiles from the 2018 eruption of Kīlauea, Hawaiʻi: melt concentrations, magma storage depths, and magma recycling. Bull Volcanol 83, 1–32. https://doi.org/10.1007/s00445-021-01459-y Nadeau, P., Kern, C., Cappos, M., Elias, T., Warren, S., Lerner, A., Sealing, C., Slagle, C., Moisseeva, N., Holland, L., Clor, L., Werner, C., 2023. Sulfur dioxide emission rates from Hawaiian volcanoes, 2018-2022. USGS Data Release. https://doi.org/10.5066/P9SNW2B7 Patrick, M.R., Orr, T., Sutton, A.J., Lev, E., Thelen, W., Fee, D., 2016. Shallowly driven fluctuations in lava lake outgassing (gas pistoning), Kilauea Volcano. Earth Planet Sci Lett 433, 326–338. https://doi.org/10.1016/j.epsl.2015.10.052 Platt, U., Stutz, J., 2008. Differential Optical Absorption Spectroscopy - Principles and Applications. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-75776-4