Integrated O₂ line fluxes F_{O2(ν1 ← 0)} extracted from MUSE observations of empty sky fields, acquired with the nominal WFM asterism of laser guide-stars (62″ in radius), normalized to the pre-recoating flux level. Each symbol, color-coded as a function of the airmass of the observation, corresponds to a single exposure. The time lines of specific events affecting UT4 are all indicated. The yellow diamond corresponds to the exposure acquired with the telescope in parked position, and the four 22 Watt lasers propagating in the closed dome on 2017-08-15 (see Fig. 3).