If adopted and enforced by ministers, it could seriously restrict the amount of traffic - particularly diesel vehicles - allowed in towns and cities. The meeting - which follows a week of soaring smog levels all over Britain - is set to mark the start of a long, hot summer for Environment Secretary John Gummer.
Particulates - tiny specks emitted in black smoke from burning fuel - have largely passed unremarked in the furore over last week's smog. Concern has centred on ozone, nitrogen dioxide and sulphur dioxide, all of which have exceeded health limits.
But experts agree that particulates pose a far more deadly danger. Estimates, based on US studies, suggest that they kill 10,000 Britons every year from respiratory and cardiovascular diseases
Emissions of black smoke from vehicles rose by 85 per cent between 1982 and 1992, and increasing sales of diesel cars - often marketed as "green" vehicles - have made matters worse.
Members of the Expert Panel said privately last week that they expect to set a tough standard on Friday and its chairman, Professor Anthony Seaton, said, earlier this year, that the recommendation "may cause a storm".
The standard may allow as little as 50 micrograms of the smallest, (and deadliest) particulates for every cubic metre of air, and the scientists are anxious to keep the level low, because research shows that there is a 1 per cent increase in deaths for every extra 10 micrograms of the pollution in the air.
Nobody knows the extent of the pollution across the country because the Government has not monitored it properly. But measurements suggest that it commonly ranges between 100 and 150 micrograms per cubic metre in urban areas.
Fiona Weir, air pollution campaigner for Friends of the Earth, said last week: "I have no doubt that a tough standard will require cuts in traffic in British towns and cities. But it is essential. We are talking about a pollutant that kills, and kills in large numbers."
Hospitals yesterday reported a slight increase in people attending casualty suffering from asthma attacks. Smog levels were the highest in East Anglia with 116 parts per billion; surveys says air quality becomes poor at 90 ppb.
nAn experiment to reduce congestion and pollution by cutting the 70 mph motorway speed limit will begin this month, Transport Secretary Dr Brian Mawhinney said yesterday. A section of the M25 around London, one of Britain's most congested stretches of motorway, will be used in the pilot project.
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