Findings: Soot cut could prove harmful

February 28, 2003

Cutting emissions from diesel fuel could lead to an increase in other harmful pollutants, according to US researchers, writes Natasha Gilbert.

In a study published in the Journal of Geophysical Research , Daniel Jacob of the department of earth and planetary sciences at Harvard University and his team found that reducing atmospheric particles such as soot from diesel fuels would lead to higher concentrations of ground-level ozone unless restrictions also curb emissions from other fossil fuels.

Ozone pollution forms when ozone precursors (released from gasoline fumes and chemical solvents), volatile organic compounds and oxides of nitrogen react under strong ultraviolet radiation. Soot particles, which cause respiratory disease and contribute to global warming, shield the earth's surface by absorbing UV radiation and, according to Professor Jacob, therefore reduce ozone formation. "Scientists had not previously made this link," he said.

Ozone pollution, which can cause lung damage and impair plants' ability to produce and store food, often exceeds Europe's air-quality standard of 55 parts per billion. Although ozone naturally persists at 5ppb to 15ppb, the study estimates that curbing atmospheric particles without also reducing ozone precursors may increase surface ozone by 5ppb across northern Europe.

Despite a 50 per cent reduction in ozone precursors over Europe in the past ten years, Professor Jacob suggests that the necessity to control both soot emissions and surface ozone requires them to drop even further.

"One environmental problem should not compensate for another," he states.

David Fowler of the Centre for Ecology and Hydrology, Edinburgh University, said the Harvard researchers' findings gave an "amazing" insight into the secondary causes of current surface ozone levels. He pointed out, however, that the ozone pollution Europeans breathe was not solely from local sources. For the level to attenuate, North America would have to limit its contribution, he said.

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