... Venus . ... Have venusian volcanoes been caught in the act? Venusт?? atmosphere contains more than a million times as much sulfur dioxide as Earthт??s, where almost all of the toxic gas is generated by volcanic activity. ... Most of the sulfur dioxide on Venus is hidden below the planetт??s dense upper cloud deck because the gas is readily destroyed by sunlight. ... Results from a long-term study of Venus find evidence of a clear injection of sulfur dioxide into its upper atmosphere. ...