Asked by: Alex Round, London
Acid snow is produced in exactly the same way as acid rain. It all starts when sulphur dioxide and nitrogen oxides are emitted into the atmosphere, typically by power stations burning fossil fuels. Inside clouds, these molecules react with tiny droplets of water to form sulphuric and nitric acids. The water eventually falls as drops of acid rain, or, if it is cold enough, ice crystals form and fall as acid snow. Acid snow can be particularly damaging since it can accumulate on the ground, before abruptly releasing a large quantity of acidic water into the environment when it melts.