One of Scotland's coal-fired power stations has been labelled the dirtiest in Europe, belching pollution that damages public health and spreads acid rain.

An expert report for the European Commission outs Cockenzie in East Lothian as by far the worst emitter of nitrogen oxides (NOx). Longannet power station in Fife is also named as one of the biggest NOx polluters.

Industrial plants across the UK are responsible for much greater amounts of NOx pollution than any other country in Europe, emitting 100,000 tonnes a year more than their nearest equivalents in Spain, Germany and Poland.

NOx causes breathing problems, aggravates heart conditions and stunts the growth of crops. The Institute of Occupational Medicine has estimated that air pollution from traffic and industry kills more than 600 people a year in Scotland's central belt.

The new report was prepared by Entec consultants for the European Commission to assess emissions of NOx, sulphur dioxide and dust from large industrial plants in 27 European countries between 2004 and 2006.

On NOx pollution, Cockenzie power station comes out as the worst offender by a large margin. Per unit of energy input, it emits 50% more NOx than the next-worst plants in Middlesbrough, and nearly twice as much as the most polluting plants in Italy.

When just the total amounts of NOx are measured, Longannet comes tenth in the league of big polluters. It is behind five other plants in England, two in Poland and two in Spain.

Altogether, large industrial plants in the UK released 385,000 tonnes of NOx a year, compared to 287,000 tonnes in Spain, 271,000 in Germany and 266,000 in Poland. UK emissions also increased by more than 8% between 2004 and 2006.

"NOx emissions add to acid rain over Europe and create local air pollution problems. It's bad news for those with complaints like asthma or emphysema," said Dr Richard Dixon, director of the environmental group WWF Scotland.

According to Sepa, improvements were being made to the boilers at Longannet and Cockenzie which would reduce future NOx emissions. Longannet has also begun a project to install selective catalytic reduction.

Cockenzie, however, has been prevented by European law for operating for longer than 20,000 hours between January 1, 2008, and December 31, 2015. "This means that once the plant has used up its permissible hours," explained a Sepa spokeswoman, "it must cease operation or fit selective catalytic reduction to operate beyond the end of 2015."

ScottishPower pointed out that it was currently investing £35.5 million in technology at both plants to cut NOx emissions by 25%.

"ScottishPower carries out air quality modelling annually at Longannet and Cockenzie, using the latest new generation modelling software, to ensure that emissions don't adversely impact on local air quality. Both stations also comply with legislation on emission controls."

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