The operation of the Tekran 2537A is based on mercury amalgamation on a gold trap and subsequent thermal desorption 24 . To allow for continuous observations, two different gold traps (here trap "A" and trap "B") are alternated. As trap "A" was operating at full efficiency during the volcanic episode on the 29 th of April 2018, we assigned a relative uncertainty of 10% (coverage factor k = 2) to all trap-A-based observations. Trap B, however, was operating with reduced efficiency, leading to several observations being rejected by our strict QA/QC procedures . In addition, we assign a larger relative uncertainty of 20% (k = 2) to all trap-B-based observations, even if flagged "valid".