Federal air quality standards and exhaust pipe emissions controls have made a genuine difference to concentrations of carbon monoxide in the USA according to the National Academy of Sciences.

An academy panel of the private organization, which is chartered by Congress to advise the government about scientific matters, told the assembly that the regulation and industry response to it had been 'one of the greatest success stories in air pollution control, reducing the problem, once widespread, to a few difficult areas'.

In those places where pollution remains a problem, such as the southern California cities of Lynwood and Calexico, the panel pointed to severe atmospheric conditions as the main contributory factor.

However, the panel also noted that vehicle pollution drifting across the border from Mexico added to the problem, recommending that such areas increase vehicle inspections and maintenance to assure catalytic converters and oxygen sensors are operating properly.

Frank O'Donnell, executive director of the Clean Air Trust, an environmental advocacy group, said the story of carbon monoxide showed the success of enforcing tough regulations.