SO FAR, AREA AIR-POLLUTION LEVELS FAR BELOW SMOGGY '03'S.

Byline: Amy Raisin Darvish Staff Writer

SANTA CLARITA - Despite the visible layer of smog that often hangs over the area, air quality so far this year in the Santa Clarita Valley is on par with pollution levels recorded in 2004, the cleanest year in nearly two decades, according to experts.

Credit cooler temperatures and an early start to the rainy season for the reduction in ozone and other pollutants this year, said Joe Cassmassi, senior meteorologist for the South Coast Air Quality Management District.

``This year and last, we had some favorable weather conditions,'' Cassmassi said late last week. ``We've seen the June gloom extend into later summer and other conditions that lend to better dispersion of the atmosphere.''

At this time two years ago, air quality in the valley was the worst in 10 years, largely because of fires burning in surrounding wilderness and several days of 100-plus temperatures.

This year, however, local air quality generally has been no worse than what regulators call ``moderate'' and identify as air quality in which ``unusually sensitive people should consider limiting prolonged outdoor exertion.''

During one period in late June and early July of 2003, air quality was unhealthy on nine days, with ozone and particulate levels that posed a health risk not only to unusually sensitive people, but to all children and adults active outdoors.

Ozone is an invisible, reactive, toxic chemical gas that, in the stratosphere, plays a vital role in shielding the Earth from radiation, but that, in the air down at levels where people live, causes health problems, especially for those with asthma and other respiratory ailments.

Particulates - solid or liquid particles of soot, dust, smoke, fumes and aerosols - enter and irritate the lungs, as well as the eyes and nasal passages. Unlike ozone, particulate pollution is visible and creates the smoggy ``blanket'' seen overhead.

The layer of smog that hangs above the Santa Clarita area is partially generated by local vehicles and the growing community, but mainly swept in on easterly ocean winds that pass over greater Los Angeles, Cassmassi said.

``There are three or four natural routes out of the (Los Angeles Basin), and the basin has 15 million people,'' he said. ``It comes up along the 405 and 5 freeways on the way to the desert.''

Cassmassi said temperatures are expected to rise this week, and the marine layer will decrease - a combination likely to produce more unhealthful air quality. And as temperatures heat up, fire danger rises.

``We've had a good year so far,'' Cassmassi said late last week. ``But fires are a major short-term impact. Wildfires, from a standpoint of public health, are bad news.''

Amy Raisin Darvish, [phone]

amy.raisin(at)dailynews.com

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Photo:

(color) The Magic Mountain tower at Six Flags California, Valencia, is barely visible across the Santa Clarita Valley on a summer day.

David Crane/Staff Photographer