I've sailed near the volcano on Montserrat several times, and have ended up with a coat of fine dust on the boat. And we experience it here at our home on Nevis
from time to time, depending on the wind
direction. The volcanic dust is irritating to the eyes, throat and lungs, but according to what I've read, not hazardous from a health
standpoint at typical exposure levels. The stuff is a nuisance, mostly. If it gets wet, it kind of sets up, like cement, and it's acidic as well. Hard on paint
. Montserrat's Soufriere Hills volcano can easily put out 500 tonn of sulfur dioxide in a 24 hour period. You can smell it when sailing downwind of the island (won't do that again!). I don't imagine CO2 is a significant part of it's emissions, if at all.