A new study of 95 urban areas in the U.S. found a direct corrolation between increases in smog and increases in the number of deaths according to a report in today's 'Journal of the American Medical Association.'

The study specifically tried rule out other causes such as pollution or heat and concentrated on the effects of smog.

'The concern is that exposure is ubiquitous and the number of people affected is large. You take a small risk and spread it out over huge numbers of people, and you end up with a fairly large impact,' said Arden Pope, an air quality researcher at Bringham Young University in Provo, Utah.

There is pressure from environmentalists and other groups to lower the 'acceptable' smog level in major urban areas. As of now, the Environmental Protection Agency says that at least 450 counties in the nation don't meet the government's goal on smog levels. Over 160 million people live in those counties.

Smog is linked to damage to human airways and effects conditions like asthma or bronchitas. It also may increase the chance of getting pneumonia or other respitory ailments.