Global monitoring of volcanic SO degassing with unprecedented resolution from TROPOMI onboard Sentinel-5 Precursor.

Over the last four decades, space-based nadir observations of sulfur dioxide (SO) proved to be a key data source for assessing the environmental impacts of volcanic emissions, for monitoring volcanic activity and early signs of eruptions, and ultimately mitigating related hazards on local populations and aviation. Despite its importance, a detailed picture of global SO daily degassing is difficult to produce, notably for lower-tropospheric plumes, due largely to the limited spatial resolution and coverage or lack of sensitivity and selectivity to SO of current (and previous) nadir sensors. We report here the first volcanic SO measurements from the hyperspectral TROPOspheric Monitoring Instrument (TROPOMI) launched in October 2017 onboard the ESA's Sentinel-5 Precursor platform. Using the operational processing algorithm, we explore the benefit of improved spatial resolution to the monitoring of global volcanic degassing. We find that TROPOMI surpasses any space nadir sensor in its ability to detect weak degassing signals and captures day-to-day changes in SO emissions. The detection limit of TROPOMI to SO emissions is a factor of 4 better than the heritage Aura/Ozone Monitoring Instrument (OMI). Here we show that TROPOMI SO daily observations carry a wealth of information on volcanic activity. Provided with adequate wind speed data, temporally resolved SO fluxes can be obtained at hourly time steps or shorter. We anticipate that TROPOMI SO data will help to monitor global volcanic daily degassing and better understand volcanic processes and impacts.