Ronald Reagan was right. Well, nearly. One of the former US president's most ridiculed statements was that acid rain came from trees. Up to half the acidity in rainfall over the US in summer does indeed come from volatile compounds given off by plants – just not the compounds Reagan was thinking of.
Formic acid is produced when we burn fossil fuels and biomass, and when plant compounds called terpenoids are oxidised by sunlight. It contributes to acid rain in remote regions, but more of it ends up in the atmosphere than we could trace back to a source. Until now.
New satellite data shows more than 100 million tonnes of formic acid is produced naturally each year – far more than thought and 10 times the total from all known sources.
Once, researchers thought ants might be a missing source. But Trissevgeni Stavrakou of the Belgian Institute for Space Aeronomy in Brussels found the highest densities above tropical and northern boreal forests during the spring growing season. Lab studies and modelling pin the blame on terpenoids.
A posthumous laureate for Reagan? Sadly not. He thought most air pollution was due to oxides of nitrogen.
http://www.newscientist.com/
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