When more aerosols are added to the air, like from ship exhaust, water molecules have more particles to collect around. (sciencedaily.com)
People are exposed to harmful aerosols from industrial sources, too, but fires produce more aerosol per amount of fuel burned. (sciencedaily.com)
What he really means, of course, is that additional volcanic activity, had it taken place, would have added more aerosols, thus slowing the overall dissipation, which would in turn have enhanced the cooling effect of said aerosols. (realclimate.org)