As the Pittsburgh region enters its smog season, expect to hear many more warnings from the state Department of Environmental Protection that airborne pollution has reached unhealthy levels.

Sean Nolan, a DEP meteorologist, said there will likely be a threefold jump in the number of Air Quality Index alerts this summer in southwestern Pennsylvania not because air quality is worsening but because federal health standards for smog and soot are tighter.

Mr. Nolan said the health standards were tightened because recent scientific studies show that lower levels of smog than previously thought are unhealthy for such at-risk groups as older adults and children, as well as people with heart or lung disease.

As a result, the department estimates that the average number of alerts it issues for unhealthy ground-level ozone, the primary component of smog, will increase from 7.2 days a year to 22 days this summer.

In addition, when new, tighter federal soot standards are issued later this summer, the number of soot alerts is expected to jump from an average of 13.2 days to 25 days.

On days when DEP air quality alerts are issued, individuals are urged to alter their activities by not exercising outdoors, mowing grass or fueling vehicles during the middle of the day.

The DEP made its predictions yesterday as it began forecasting ozone levels for the season and at the beginning of national Air Quality Awareness Week.

Pittsburgh is not in attainment of federal health standards for smog or soot, and levels of fine airborne particles in Allegheny County are among the highest in the nation, due to a combination of local emissions and coal-burning power plant emissions in the Ohio River Valley to the west that are transported into the region on prevailing winds.

Mr. Nolan said planned emissions controls that will reduce power plant emissions of nitrogen oxides and sulfur dioxides should result in future improvements in the region's air quality.