ASK THE METEOROLOGIST
“Has there ever been acid snow and is it possible?”
Acid precipitation can occur in any form of precipitation: rain, snow, sleet, etc. Acid precipitation forms from acidic gases (sulfur dioxide and sulfuric acid) released into the atmosphere from natural and non-natural sources such as volcanoes and wildfires to burning of coal and automobiles. These gases are carried by the wind and oxidized to nitric acid and sulfuric acid then dissolves and falls in the form of acid precipitation. Since snow is mostly frozen water is not as efficient at collecting these acid gases as liquid water and thus snow tends to be less acidic than rain.
In Oregon rain is only mildly acidic with rain typically having pH values of 5.2-5.4 while areas in the Northeast and southern California have rain with pH values of 4.2 to 4.8. Natural rain water tends to be about 5.7 and neutral pH which has no acidity or basicity is 7. Most of the acid rain in the Pacific Northwest is from natural sources, mostly volcanic in fact while in the Northeast acid precipitation comes from mostly non-natural sources.