A fissure eruption occurred in Kīlauea Volcano’s Lower East Rift Zone (LERZ) from April to September 2018. During this event, volcanic gases were emitted from three active areas on the volcano. The most intense degassing occurred at the active fissures in the LERZ, thus causing parts of Hawaiʻi Island’s Puna district to be exposed to life-threatening sulfur dioxide (SO2) concentrations. At the same time, gas emissions from the volcano’s summit and East Rift Zone (ERZ) slowly declined from their decade-long averages as magma drained from the volcano’s shallow plumbing system. Throughout the eruption, the USGS used a Mobile Differential Optical Absorption Spectrometer (Mobile DOAS) to record ultraviolet (280 – 420 nm) spectra of downwelling scattered solar radiation passing through volcanic gases overhead. Mounted on a vehicle or carried by a hiking geologist, the instrument was passed beneath volcanic plumes emitted from each of the three active areas throughout the 2018 eruption. The recorded spectra were later used to retrieve SO2 vertical column densities in transects perpendicular to the plume propagation direction. SO2 emission rates could then be calculated from these, thereby tracking the volcano’s gas output as the eruption progressed. The resulting gas emission rates are published in the Bulletin of Volcanology (https://doi.org/10.1007/s00445-020-01390-8). All recorded spectra were stamped with GPS time and location. Each spectrum is saved in a separate ASCII file which includes 2048 radiances recorded across the spectral window of the spectrometer along with relevant metadata associated with each acquisition