Smogs are something nasty. But despite all the headlines, talk and anxiety, we seem unable or unwilling to do much about them. It is almost as if we were fated to have spells of bad air quality, along with rainy bank holidays and late spring frosts.
True, the weather is largely to blame. Both winter and summer smogs require the kind of still, high pressure air that presently lingers over Britain. Wind is our great atmospheric cleaner, which is why these breezy islands enjoy cleaner air than continental Europe does most of the time.
But smog's sine qua non is pollution, especially from all kinds of road traffic - the single most important contributor - and power stations. Industrial and domestic use of solvents, the chemical and petrochemical industries, and home heating also make major contributions. When the air is still these pollutants build up.
The smogs became worse through the Seventies and Eighties as traffic grew, but none the less passed almost unnoticed. The reason they attract so much attention now is growing public awareness, and the fact that Government does far more monitoring of air quality and puts the information rapidly into the public domain.
The public, journalists and Friends of the Earth can find out about air quality all around the country on teletext or by dialling the Department of the Environment's free telephone number. The Met Office and the National Environmental Technology Centre (which monitors air quality for the Government) produce regular, fairly reliable pollution forecasts.
So now we know about smogs - but what do we do about them? There is no evidence that during smogs drivers use their cars less. For its part the Government produces only the most restrained of warnings, advising drivers to use their cars ''responsibly''.
Friends of the Earth argues that this week, when it was clear there was going to be a smog, the Government should have cut the motorway speed limit to 50 mph, ordered councils to close some streets in the centres of towns and cities and shut large car parks, thereby forcing many drivers on to public transport. At the same time there should have been loud and clear public warnings.
That kind of action might have prevented the World Health Organisation's recommended levels for ozone pollution being breached across much of Britain, says the Friends' air pollution campaigner, Roger Higman. The inconvenience, time and expense placed on motorists would be justified by reducing the health risk and discomfort for the millions who suffer from air pollution.
An experiment in Germany last year shows what can be achieved by this sort of temporary action. During four days in June the towns of Heilbronn and Neckarsulum, north of Stuttgart, were closed to all cars except those fitted with pollution-removing catalytic converters or the lowest-emission diesel engines.
Levels of traffic and oxides of nitrogen, one of the most important smog constituents, both fell by 40 per cent while use of public transport increased by 50 per cent. Concentrations of benzene, a carcinogenic air pollutant, fell from four to two millionths of a gram per cubic metre.
There are several cities where vehicles are severely curbed during smogs, notably Athens, which has also just tried a large traffic exclusion experiment. But these places experience pollution levels double those found during British smogs, and neither the Government nor the public here yet has an appetite for draconian action.
The costs of UK smogs, in terms of extra deaths, hospital admissions and general discomfort, do not seem to justify such curbs. That view may change, however, as a result of new health studies and increasingly "green", health-conscious attitudes.
Smogs are, by their very nature, transient. Friends of the Earth and the Government agree that the general level of air pollution throughout the year should be reduced. That would have the effect of making smogs less frequent and severe while improving overall air quality.
Since the Seventies, the biggest clean air initiatives in Britain have been part of European Union directives - tougher exhaust standards for diesel vehicles and compulsory catalytic converters fitted to all new cars since 1993. It will be more than a decade, however, until all cars have these fume-cleaning devices.
These and other policies, mostly required to comply with European air pollution treaties, are gradually bringing down the levels of most key smog constituents.
But the rising volume of traffic in Britain threatens to undermine the gains produced by higher standards for individual vehicles. Last year lorry traffic jumped by 7 per cent to reach its highest level ever. Over the past 15 years freight moved by heavy goods vehicles has grown by 39 per cent.
The Government has slashed the roads programme and road fuel is being ever more heavily taxed, raising its price by way over the inflation rate. Ministers attend high-profile crackdowns on polluting vehicles and push a few million pounds into encouraging cycle routes.
In real terms, however, petrol remains much cheaper than it was in the early Eighties and a genuine revolution in transport policy is still awaited. A number of sticks and carrots that would cut motoring show no sign of being grasped for years to come: motorway tolls, road pricing in cities, increased subsidies for public transport fares.
Take one example which has been advocated by pressure groups and political opponents for years - cutting vehicle excise duty (the tax disc) for older cars which have catalytic converters fitted. With a "cat" costing more than £100, £20 to £40 off the annual duty could persuade many motorists to make a lasting commitment to improving air quality.
Ministers must sense that public attitudes towards the private car are deeply ambiguous - tainted by hypocrisy but, above all, in a state of flux and ready to be led. Much more than air quality is involved; people have seen heavy traffic despoil city centres and new roads gobble up countryside within their lifetimes.
Yet the politicians lack the courage and imagination necessary to take advantage of this shifting mood.