These GEM depletions also suggest that terrestrial volcanism does not only act as a source of mercury to the atmosphere through direct Hg degassing. It may also act as a sink for atmospheric mercury due to the simultaneous emission of aerosols that do not only scavenge GEM that was emitted from the volcanic vent but also GEM that was already present in the atmosphere. The source and sink effects may partly balance each other out, and both may have to be adequately estimated to determine the net impact of terrestrial volcanism on the atmospheric Hg reservoir.