The N2O data are provisional estimates and are "very uncertain", said Mr Trippier. They were compiled for the Department of the Environment by Warren Spring Laboratory.
Nylon production was pinpointed as a major source of N2O only last year, when US scientists estimated that the global emission from this source was 700,000 tonnes per year (ENDS Report 194, pp 6-7). At the time ICI said that one of its plants on Teesside was emitting 90,000 tonnes of the gas per year. However, figures published by the company this month showed that its N2O release in 1991 was 77,250 tonnes. ICI says it is aiming to eliminate the emission by 1996.
It is not clear whether Warren Spring's estimates take into account suggestions in a recent study for the European Commission that cars equipped with catalytic converters emit larger quantities of N2O than "uncontrolled" vehicles (ENDS Report 205, pp 6-7 ). The figures also exclude emissions arising indirectly from fertiliser use which occur when nitrate-contaminated groundwater enters surface waters.
Although the N2O data appear insignificant when compared with the 630 million tonnes or so of carbon dioxide emitted annually in the UK, N2O has a global warming effect some 200 times larger than CO2 over a time-horizon of 100 years. According to Mr Trippier, Warren Spring's estimates suggest that the UK's emissions of N2O have a direct global warming effect equivalent to about 7% of that from its CO2 releases.