North American fires pollute Europe and Greenland

Forest fires in North America in August 1998 which, it has already been revealed, caused elevated ozone levels over Europe, also produced large clouds of nitrogen dioxide (NO2), one of which was subsequently traced to over Greenland, and other, smaller one over the Atlantic Ocean, near to Europe, new research has revealed.

In July and August 1998, there were severe forest fires in Canada, especially in the Northwest Territories, with more than 1000 different fires burning a 10,000 square kilometre area in the worst week, 5-11 August. It was already known that an aerosol cloud resulting from these fires had been detected over Greenland, and carbon monoxide concentrations in Ireland were strongly affected, with a dense layer of pollutant gases over Europe, containing a substantial amount of ozone.

However, according to new research, the fires also produced 5.5 tonnes of oxides of nitrogen (NOx) per square kilometre burned, reaching a total of 46,000 tonnes in the first ten days of August. This corresponds to 12.5% of human-produced NOx in the whole of North America over the same time period.

By 8 August there was a forest fire plume covering large regions over the Atlantic Ocean, with a nitrogen dioxide maximum midway between North America and Europe. The following day, the plume was over Europe, with the NO2 reaching the Irish coast, and an NO2 maximum to the west of Greenland in the centre of a low-pressure system, although the researchers admit that there is a possibility that the NO2 could have come from another source. The high levels of ozone on the plume that had previously been observed would have resulted from photochemical processes on the NOx in the plume, say the researchers.

Although it had taken six days for the NOx to reach Europe – longer than the gas’ normal lifetime on the ground, it is thought to last for longer in the free troposphere.

The paper, Satellite detection of a continental-scale plume of nitrogen oxides from boreal forest fires, by researchers from the Technische Universität München and the University of Heidelberg in Germany, is published by the American Geophysical Union.

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