Air Is Cleanest Since Monitoring Began in ’73 : Pollution: A county official says the weather and tighter regulations on industry were responsible for the good showing.

Air quality during 1990 was better in Ventura County than it has been since pollution monitoring began in 1973, officials at the county Air Pollution Control District said Wednesday.

The county violated federal health standards for ozone pollution on only 16 days in 1990, compared to 45 days in 1989 and a 10-year average of 51 days.

The county’s air failed the more stringent California health standards on 100 days in 1990, compared to an average of 130 days a year over the previous 10 years.

The South Coast Air Quality Management District, which combines Los Angeles, Orange, Riverside and San Bernardino counties to form the smoggiest air basin in the state and the nation, also enjoyed fewer air quality violations in 1990, officials said.

The South Coast district violated federal standards on 130 days in 1990 compared to 157 days in 1989. It failed state standards on 180 days in 1990 and on 211 days in 1989.

But officials in both districts said Wednesday that they cannot claim much of the credit for the surprisingly good air quality of 1990. Weather factors were primarily responsible, said Richard H. Baldwin, Ventura County’s air pollution control officer.

“With the cooler than normal temperatures and better than normal winds, we didn’t have the emissions sitting around to be cooked by the sunlight to form ozone,” Baldwin said.

District regulations on industry, which have reduced emissions that cause ozone by 25% over the last 10 years, also helped keep the ozone levels low in 1990, Baldwin said. Another factor, he added, was the effect of state regulations mandating reductions in motor vehicle tailpipe emissions.

The effects of the weather make dramatic changes from one year to the next, but results of emission reduction regulations show up over the long term, he said.

The result is a gradual improvement in air quality in Ventura County and statewide, despite population and industrial growth.

“In general, air quality throughout the state has remained the same or slightly improved in the face of significant growth,” said Bill Sessa, spokesman for the California Air Resources Board, which sets air quality policy for the state.

The exception to the statewide trend is the San Joaquin Valley, where growth has been so intense in the last 10 years that air quality is worsening despite regulations, Sessa said.

Ozone, a primary ingredient of photochemical smog, is formed when oxides of nitrogen react with hydrocarbons in sunlight. In Ventura County, the primary emission sources are motor vehicles and Southern California Edison power plants.

The state and federal standards for ozone are based on the level at which ozone affects health, said Dr. Michael Lipsett, public health medical officer at the state Department of Health Services in Berkeley.

According to federal standards, health is affected when the ozone concentration in the air reaches .12 parts per million. State standards put the health hazard at anything over .09 parts per million.

Ozone pollution causes the lungs to lose their elasticity, decreasing their ability to deliver oxygen to the blood.

“When you look at the inflammatory changes that take place in the lungs from exposure to ozone, they are very similar to the effects of early cigarette smoking,” Lipsett said.

Some tests show that ozone can also induce asthmatic episodes. The National Toxicology Program is also studying whether chronic ozone exposure can be linked to cancer, Lipsett said.