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Asked by megansaurus to Davie, Gemma, James P, James V, Nuala on 27 Jun 2012.
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James Verdon answered on 27 Jun 2012:
Hi megansaurus,
That depends. Pure water is neutral, so has a pH of 7. However, most rain will have a small amount of CO2 dissolved in it. This creates carbonic acid, so rainwater will usually be very very mildly acidic – say pH 6 to 6.5 or so. However, industrial pollution (and volcanic activity) can emit sulphuric gasses into the atmosphere. These react with rainwater to form sulphuric acid, which can make rainwater even more acidic. According to Wikipedia, some acid rain in really polluted areas has been as acidic as pH 2.4, which is really quite acidic!
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James Pope answered on 27 Jun 2012:
Hi megansaurus,
The most famous effect of acidic rain was that rain from factories and power stations in the UK was falling on the Scandinavian Forests and causing them to be badly damaged! The main reason for this acid rain was the sulphur that was released when coal was being burnt, and so an agreement was made internationally to reduce the sulphur being released from coal fired power stations. This did have one big impact though, the sulphur was also hiding the warming effect from the carbon dioxide being released and so we got a sudden increase in global warming, which can bee seen on temperature graphs of 1950-2000 really well!
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Gemma Purser answered on 27 Jun 2012:
The boys are right, gases like carbon dioxide, sulphur dioxide, nitrogen oxide and nitrogen dioxide all make rain water more acidic and these are all the gases that are released when fossil fuels are burnt.
Things like vinegar and lemon juice have a pH of 2.4 too, just to give you an idea of how acid it is!
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