Acid rain cuts greenhouse gases in pollution paradox

Acid rain caused by industrial pollution could actually help reduce the greenhouse gas emissions of agriculture, say scientists.

Research led by the Open University's Dr Vincent Gauci suggests that sulphur-based acid rain from atmospheric pollution could cut the methane emissions associated with cultivating rice by almost a quarter.

Tonne for tonne, methane is more than 20 times more potent than carbon dioxide in terms of global warming.

Dr Gauci's findings suggest that, ironically, the high levels of pollution associated with China's rapid industrialisation may actually be going some small way towards mitigating its soaring CO2 output.

"Acid rain is one of several pollution problems in Asia that need solving in the coming decades but we need to appreciate the potential consequences of that clean up, one of which could be an increase in methane emissions as the effect of the acid rain wears off," said Dr Gauci.

"The reduction in pollution happens during a stage of the lifecycle when the rice plant is producing grain. This period is normally associated with around half of all methane emissions from rice and we found that simulated acid rain pollution reduced this emission by 24 per cent." said Dr Gauci.

The project , funded by the Natural Environment Research Council, used rice soils and grain from Portuguese paddies which have a similar chemical properties to Asian rice soils prior to their pollution.

To simulate acid rain experienced in polluted parts of China, the researchers added frequent small doses of sulphate.

"We need to do further research but it looks like there could be a combination of processes at work. One line of investigation we'd like to confirm is that the sulfate component of acid rain may actually boost rice yields," said Dr Gauci.

"This might, paradoxically, have the effect of reducing a source of food for the methane producing micro-organisms that live in the soil."

"There is also likely to be competition between these micro-organisms and sulphate-reducing bacteria. Normally in these conditions sulphate-reducers win which results in less methane."

This is not the first occasion where pollution has been shown to have a silver lining which goes some way towards offsetting its overall negative impacts.

Reducing smog in western Europe, for example, has improved air quality but potentially hastened warming, as the clouds of smog provided shading from the sun's rays.

Sam Bond


acid rain | air quality | agriculture


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