The hazard is in chronic exposure, even at low concentrations.

Chronic exposure to the sun can cause cataracts and skin cancer.

But the annual standard, which affects chronic exposure, remains at its original 1997 level.

Most health research suggests that chronic long-term exposure is usually the way people get sick from pollution.

But he said that there was no standard definition of what constituted "chronic" exposure.

There is no thought being given to regulate chronic exposure to ozone over a period of a year or more, according to an agency spokesman.

Chronic exposure may lead to weight loss, anemia, and possible liver damage.

"Which is consistent with acute rather than chronic exposure."

Chronic, high-level exposure have shown to reduce fertility in males.