VALLEY CATCHES SOME FRESH AIR COOLER SUMMER HELPING KEEP SMOG AT BAY.

Byline: Kerry Cavanaugh Staff Writer

Los Angeles' cooler-than-average summer has produced a healthy side effect: Air quality has improved, with the basin exceeding national pollution standards on just 15 days compared with 44 smoggy days last year, officials said Tuesday.

And it's not just Southern California that's enjoying cleaner air. The rest of the state and much of the country have escaped serious smog thus far, though forecasters do expect to see pockets of high ozone levels through the rest of the summer.

``Weather's been a real factor,'' said Joe Cassmassi, senior meteorologist with the South Coast Air Quality Management District. ``Last year at this time, we'd had a real heavy-duty weather influence in the opposite direction.''

Indeed, in Southern California, the marine layer known as ``June gloom'' lasted well into July this year, followed by a period of cooler temperatures that has kept smog levels relatively low.

Last year, there were record-breaking high temperatures in July and early August, coupled with a strong inversion layer of warm air that acted as a lid, trapping pollutants close to the ground. Ground-level ozone, the main ingredient in smog, is formed when emissions - from cars, power plants, factories, paints and aerosols - are cooked in high heat and sunlight.

``It's wonderful. We're thrilled the air is cleaner and people are breathing easier,'' said Bonnie Holmes-Gen, assistant vice president for governmental relations at the American Lung Association of California.

``But it's mainly due to cooler weather and not so much an indication that smog has dramatically decreased from last year to this year.''

A look at the San Fernando Valley provides comparison. The average high temperature at Pierce College in July 2003 was 95 degrees. Last month, the high averaged 91 degrees at Van Nuys Airport - the closest monitoring station with readings available Tuesday.

As for smog, ozone exceeded short-term health exposure limits on 10 days in Reseda by this time last year. So far this summer, Reseda has recorded only one day over the limit.

Santa Clarita had a record smoggy season last year, with 25 days exceeding the short-term exposure limit. This year Santa Clarita has had just six days over the limit.

However, these comparisons are based on the former measurement for short-term exposure to ozone - 0.12 parts per million over a one-hour period.

The U.S. Environmental Protection Agency this year adopted a limit of 0.08 ppm over eight hours - a new standard designed to protect people from lung damage associated with breathing low levels of ozone over a longer period.

The South Coast region had 71 days over the new long-term exposure health standard by this time last year, compared with 52 days this year.

Reseda had 34 days over the new ozone limit this time last year and 14 days this year.

Santa Clarita had 46 unhealthy days this time last year and has had 29 days so far this year.

While Southern California residents enjoy a milder smog season, the new ozone standard is a reminder that the region still has plenty of pollution to cut.

``There are days when air quality is better because of meteorological conditions,'' said Holmes-Gen. ``There's still a tremendous amount of vehicle pollution and a long way to go to meet state and federal standards.''

Kerry Cavanaugh, [phone]

kcavanaugh(at)dailynews.com

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2 photos

Photo:

(1 -- 2 -- color) Air quality in the San Fernando Valley has noticeably improved over last year, as these pictures of Warner Center taken in July 2003, left, and August 2004 show.

Tina Burch/Staff Photographer