Volanoes, page-45

NOx, on the other hand, reacts with oxygen and water in the atmosphere to form nitric acid, which is completely miscible with water (i.e. there is no solubility limit). For SOx and NOx, this is why their residence time in the atmosphere is very short: days to weeks in the troposphere, at most a couple of years in the stratosphere. They combine with the first water they come across and fall as (acid) rain.