‘Clean’ Smog Season Credited to Weather : Environment: Air quality in August, usually the worst month for pollution, violated federal health standards only three days.

The air during the 1990 smog season will probably be the cleanest since the Ventura County Air Pollution Control District began monitoring air quality in 1973, district officials said.

The county’s air in August, which is usually the smoggiest month of the year, violated federal health standards on only three days, all in Simi Valley, the county’s smoggiest city. In July, county air was unhealthful on only two days, twice in Simi Valley and once in Ojai.

Overall, the county’s air has violated the federal standards on only nine days so far this year. Simi Valley accounted for eight of the days, with the county’s coastline escaping smog violation days completely.

The summer smog season lasts from May to October. Typically, low clouds and warm inversion layers trap pollutants near the ground, and there are 40 to 60 smoggy days in the county, said Herman Ragsdale, air quality specialist at the Air Pollution Control District’s data center. About 80% of the smoggy days, which are defined in terms of ozone levels, usually occur before September. Preliminary figures for 1989 show that there were 16 smog violation days in July and two in August.

“But even if we have a typical September and October, we will still have the cleanest year,” Ragsdale said. “We would not expect more than about 15 smoggy days in September and October, and that would still put us at half the norm.”

However, late September and October typically bring warm Santa Ana winds that blow pollutants in from the Simi and San Fernando valleys, district meteorologist Kent Field said.

“But this is not a typical year,” Field said.

Field said new Air Pollution Control District regulations have reduced emissions in recent years but deserve only a small part of the credit for the unusually clean air.

“We haven’t seen a drastic reduction in emissions,” he said. “No, this air is due to the weather.”

Unusual weather patterns this summer have brought light winds and weak, dry inversion layers that do not trap pollutants, he said. That has allowed the pollutants that cause ozone to disperse into the air, he said.

Field said he could not predict if the weather patterns that have kept ozone levels to a minimum will hold through September and October.

The same exceptionally low smog levels have prevailed in the sprawling South Coast Air Quality Management District, which includes Los Angeles, Orange, Riverside and San Bernardino counties, district reports show.

The AQMD does not measure smog in terms of unhealthful days. Instead, it measures federal health standard violations at 26 monitoring stations in the area. Thus, many stations might have violations on a given day. The South Coast District recorded 1,798 ozone violations from May through July. There were 3,283 such violations in all of 1989 and 3,416 in 1988.

Ozone, a primary ingredient of smog, is formed when nitrogen oxide reacts with hydrocarbons in sunlight. Motor vehicles in Ventura County account for more than half the nitrogen oxide in the air, and Southern California Edison’s power plants and the oil industry produce about 40%.

Motor vehicles produce more than 40% of hydrocarbons and are the largest single source. But engines used by the oil industry for pumping as well as industrial and agriculture solvents combine to produce 55% of hydrocarbons in Ventura County’s air.

Air Pollution Control District regulations have forced a 25% to 30% decrease in emissions over the past 10 years that has steadily improved air quality, district officials said.

Richard Baldwin, the county’s top air pollution control official, said emission levels are expected to continue to decrease gradually until the county meets federal clean air standards sometime in 10 to 20 years. The federal government sets the health standard at .12 parts per million of ozone.

State guidelines, which are stricter, say that any ozone concentration above .09 parts per million is unhealthful. A first-stage smog alert is called when ozone concentrations hit .20.

Ozone is an irritant that attacks the respiratory system and can cause lung tissue damage, according to the American Lung Assn.

Baldwin warned that the clean-air summer of 1990 could change drastically with weather conditions.

“If we had a horrible heat wave, we could still have poor air quality. The only difference is that it would have been worse without the emission reductions,” he said.

Ventura County has never had second- or third-stage smog alerts, which are more severe than first-stage alerts, but it did have three days of first-stage alerts in April. It was the first time in eight years the county had had a smog alert.

In that unusual episode, winds pushed polluted air over the ocean. A low inversion layer trapped the air mass and the sun baked it for four days. When the hot Santa Ana winds cooled, other winds kicked in and blew the pollution back over Ventura, causing a dim gray film to settle over the coast.

The dirty air mass later moved east into Simi Valley, where it backed up against hills that surround the valley and caused smog alerts there.