But remember that the percentages of the different gases change constantly, and probably especially during eruptions when it is impossible to measure. The height to which volcanic ejecta soars depends on the strength of the eruption. In eruptions such as occur in Hawaii, lava and gases flow easily out of the ground, and the gases don't rise more than a few thousand feet into the sky. In explosive eruptions, like that of Mt. St. Helens in 1980, gases are forcefully thrust and bouyantly rise to heights of 60,000 to 150,000 ft. These eruption clouds are threats to aircraft and place so much SO2 into the upper atmosphere that the climate becomes cooler for a few years aferwards.
Winds carry such high volcanic material completely around the Earth within a few weeks.