UK carbon monoxide emissions fell to 4.6 million tonnes in 1996, 6 per cent lower than in 1995 and 34 per cent lower than in 1989. Road transport accounted for 71 per cent of emissions in 1996, and emissions from this source have fallen by 34 per cent since 1989, mainly as a result of the introduction of catalytic converters in cars. Exceedences of the UK standard for carbon monoxide, of 10 ppm measured as a running 8 hour mean, were reported at one of these monitoring sites, Exeter Roadside, on one day in 1996.