Business drivers have larger, heavier vehicles that do fewer miles per gallon. They also drive faster and receive four times as many speeding tickets.
TNO, the Netherlands organisation for applied science, concluded that driver for driver, frequent users of company cars were responsible for five times as much global warming carbon dioxide gas and four times as much smog- forming nitrogen oxides as private motorists. The findings apply broadly to Britain, where the company car culture is as deeply rooted. Last year 52 per cent of all new UK car sales were to companies and business users.
The Dutch research was based on questioning 1,100 drivers who fell into four groups - those who only used their car for family travel, those who also used it to commute, people who used their own cars during their work and company car drivers.
The difference in pollution produced by the first and last groups is mainly because of the much higher mileage of company car drivers - an average 21,000 miles a year compared to only 5,000.
But even compared mile for mile, the company car drivers still produce 10 per cent more carbon dioxide and the same quantity of oxides of nitrogen (NOx) when they should be producing substantially less NOx. Overall, company cars are much newer than privately owned ones and more are fitted with the pollution-stripping catalytic converters which have been compulsory for new vehicles since 1993.
Tinus Pulles, of TNO, said the company cars' failure to produce less NOx despite having more catalytic converters could be explained by their larger cars and 'the fast, aggressive driving that is common practice for this group.' Company car drivers drove on motorways at an average of 127 kilometres per hour - the Dutch legal limit is 120. Private motorists drove at 115 kph.
In curbing car pollution 'human behaviour is the key issue,' said Mr Pulles. 'People or their employers buy heavier and more luxurious cars and drive them faster. At the same time, the desire for mobility increases.'
Graham Dymott, of the UK Society of Motor Manufacturers and Traders, pinned the blame on company car drivers' higher mileage. 'If you cover tens of thousands of miles a year in your work, it's not really practical to have a small, high economy car.'
Asthmatics and others with chest problems may suffer extra wheezing and chest tightness during periods of poor air quality like the one now affecting the South- east. They are advised to avoid vigorous exercise.
While ozone levels in the region are peaking at more than 90 parts per billion (ppb), today's forecast peak for ozone is 180 ppb in the Los Angeles basin.
The city's South Coast Air Quality Management District describes this level as 'unhealthful' but it is typical for the time of year. Last year's highest reading in southern California was 280 ppb; the peak for Britain this July has been 113.