Re: Is rain more acidic than snow?

Snow can become very acidic if it falls through polluted air much the same 
as rain can. The details are a little bit different. 

In both cases, the most important pollutants involved are sulfur dioxide, 
and oxides of nitrogen. In both cases, these gases react with oxygen (in 
the form of hydroxyl radicals or ozone) and water to produce strongly 
acidic substances with a high affinity for water -- sulfuric acid and 
nitric acid.

In rain or fog, these acids simply dissolve into the liquid droplets 
present; in snow, they cannot get to the interior of ice particles, but 
that does not stop them sticking onto the surfaces, and because snow 
consists of masses of tiny, fluffy ice crystals, there is quite a lot of 
surface area for the acid molecules to stick to.

I do not know much about the relative amounts of acids in acid snow and 
acid rain. I live in a city where it never snows, and there is not too much 
pollution anyway. I think that acid snow is on average less acidic than 
acid rain, but there is such a wide range of places and conditions where 
they fall that you could not really do a fair comparison. The pH of 
rainfall ranges from around 6 down to around 2; anything less than 5 is 
defined as "acid rain", because 5 is about the lowest you usually get in 
the absence of pollution.

As I understand it, the really big problem with acid snow that is a bit 
different to acid rain, is that most of the acid that is contained in snow 
that has fallen over the winter is released into various waterways all at 
once during the springtime thaw, causing a sudden increase in acidity of 
lakes and streams.