Soiled air

soil produces almost 70 per cent more of the polluting oxides of nitrogen (no^x) than previously believed, claims a new study based on satellite data. Led by Lyatt Jaegl of the University of Washington in the us, the research shows soil accounts for a surprising 22 per cent of the 40 million tonnes of no^x emitted annually all over the world (Faraday Discussions: Atmospheric Chemistry, 2005, Vol 130) .

The emissions from the soil are attributable to naturally occurring bacteria and extensive fertiliser use in agriculture. "Agricultural activities are likely to increase in the future, bringing more fertiliser use. As a result, there could also be even greater soil emissions of nitrogen oxides," says Jaegl. Besides soil, the other sources of no^x are fossil fuel combustion, which accounts for 64 per cent of the emissions and forest fires, which contribute 14 per cent.

The research was based on data gathered by the European Space Agency's European Remote Sensing ii satellite. This is for the first time that a satellite has been used to quantify no^x emissions from soil. Earlier, such remote data has been collected only to measure no^x emissions from fossil fuel combustion and forest fires.

The observations show fuel combustion dominates emissions at northern mid-latitudes, while fires are a significant source in the tropics. "Soil emissions peak in northern mid latitudes (North America and Europe) during summer due to heavy fertiliser use and in equatorial Africa at the beginning of the rainy season (due to bacterial activity)," Jaegl said.

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