The injection of HCl into the stratosphere by large volcanic eruptions has long been considered to be of minor importance. This is due to the widespread assumption that any HCl will be efficiently taken up by hydrometeors in the cooling plume. However, this assumption does not account for the possibility that prior scavenging processes can act within the high temperature core of the eruption plume. The adsorption of HCl onto ash surfaces to form soluble -Cl salts is a hitherto unconstrained scavenging mechanism, and their fate within the atmosphere and environment is uncertain. Here, we investigate the capacity of volcanic glasses of tephrite, phonolite, dacite and rhyolite composition to adsorb HCl. The experiments are conducted in the presence of He-SO2-CO2 mixtures at temperatures of 200-800°C. Our experimental findings show that only the tephrite and phonolite glasses exhibit significant reactivity to HCl, which show optimal efficiency of uptake at 400-600°C. The primary reaction product formed during adsorption is halite (NaCl), in addition to minor quantities of Ca-, K-, Al- and Fe-bearing chlorides. Uptake of HCl by glass surfaces is sustained by the outward diffusion of Na+ and other Cl-reactive cations via exchange with H+. Simple mathematical models can be used to yield Na diffusion coefficients for the four experimental glasses, and suggest that a varying structural role for Na within the glass network governs the capacity for HCl retention. The uptake of HCl under experimental conditions is limited above 500°C by a Cl-induced dehydroxylation process, but the presence of H2O in the hydrous plume may sustain or even enhance adsorption. The present experimental data, combined with cooling gradients obtained from established plume evolution models, lead us to conclude that HCl adsorption within the eruption plume core can be a more significant scavenging mechanism in large explosive eruptions than previously considered. We additionally highlight the importance of magma composition in dictating volatile adsorption, and suggest that HCl adsorption by peralkaline ash may be highly effective as an HCl sink. The fate of adsorbed HCl is variable; some may be removed from the plume within pyroclastic flows, whereas any chloride-coated ash ejected into the stratosphere could promote the formation of reactive Cl species. Our study also suggests that HCl adsorption could emplace Fe- and Cl-bearing salts on ash surfaces within the plume cores of large explosive eruptions. The ocean fertilising potential of such eruptions could therefore be greater than than that inferred from ash from smaller, compositionally similar events.