1) Plumes from Piton de la Fournaise appear to be halogen-poor. Halogens in volcanic plumes are mostly found in the form of halides like HCl and HBr . Although no data on gas-phase HCl and HBr are available for the 2018 eruption, previous gas observations at Piton de la Fournaise indicate a low-HCl and low-HBr signature for gases emitted from this volcano 71,72 and hot-spot volcanoes in general 68 , with HBr/SO2 ratios typically being up to one order of magnitude lower than in subduction zone volcanic gases . In addition, we observed no enhancement of particle phase Cl -or Br -in submicron aerosols when Piton de la Fournaise entered volcanic activity (see Figure ). As HCl and HBr partially adsorb onto aerosols , the low concentrations of halogen ions in the particle phase also suggest halogen-poor plumes in the gas phase.