Fine particles are very good insulation. For a volcano to spit out enough particles to cover our region, the amount of particle, collectively would probably come to about the size of an island, like Singapore. - and that was just fine particles that could float in the air.

During an eruption, it also split out larger earth particles, rocks, that would drop almost immediate to ground. Imagine that, it would take a volcano that probably half the size of peninsular malaysia to cause total blackout which could maintain for few years.

Which is unlikely to happen.