The National Research Council report also said based on a review of recent research, the committee found that deaths related to ozone exposure was more likely among individuals with pre-existing diseases and other factors that could increase their susceptibility.

However, premature deaths aren't limited to people who are within a few days of dying, the report said.

In addition, the committee examined research based on large population groups to find how changes in ozone air concentration could affect mortality, specifically to determine the existence of a threshold -- a concentration of ozone below which exposure poses no risk of death. The committee concluded that if a threshold exists, it is probably at a concentration below the current public health standard.

As people have individual susceptibilities to ozone exposure, not everyone may experience an altered risk of death if ozone air concentration also changes. Further research should explore how personal thresholds may vary and the extent to which they depend on a person's frailty, the committee said.

Copies of the report is available at http://www.nap.edu.