The volcano injected some 15 billion tons of sulfur dioxide into the stratosphere. There it reacted with water to form a layer of aerosol particles, which are primarily sulfuric acid droplets. Winds have take those aerosol particles all around the world. The stratosphere lacks rain clouds as a mechanism to wash out pollutants fast. This heavy influx of aerosol pollutants will remain in the stratosphere for years until natural chemical reactions and atmospheric circulation can filter them out.
Fog develops when air having a relatively high humidity comes in contact with a colder surface, often the Earth's surface, and cools to the dew point. Additional cooling leads to condensation and the growth of low-level clouds.
