L.A. Region on Track to Repeat Clean Air Record

This year’s smog season in the Los Angeles region, which began in May and ends Oct. 31, is expected to equal last year’s, the cleanest in 40 years of record-keeping.

Favorable weather played a key role in the anticipated rerun of last year’s dramatic improvement over the recent past, officials at the South Coast Air Quality Management District said. Relatively weak air inversions have also contributed to milder than usual bouts with smog throughout the state, according to the California Air Resources Board.

The air in Los Angeles, Orange, Riverside and San Bernardino counties is still by far the most polluted in the United States. But “the fact that 1991 mirrors 1990 is very encouraging,” said Joe Cassmassi, AQMD senior meteorologist. “We’re seeing air quality continuing to move in the right direction.”

The area violated federal standards for ozone, the main component of smog, on 107 days through the end of September, as compared to 117 days at that point last year, Cassmassi said. In both years, the AQMD called 39 Stage 1 smog alerts--which means air is unhealthful for everyone--by October.

During the same period in 1989, the region had 138 ozone violations, with 52 Stage 1 alerts; and in 1988, 148 violations and 68 Stage 1 alerts.

In both 1991 and 1990, smog alerts also were less widespread and of shorter duration than previously.

The numbers are bound to climb at least slightly this month. Indeed, under stifling heat and an inversion layer, Glendora and Norco, near Corona, reached the Stage 1 level Wednesday, Cassmassi said.

Air is considered unhealthful when ozone exceeds the federal standard of .12 parts per million. A Stage 1 alert is called when ozone reaches .2 parts per million.

The chemical is a powerful lung irritant, to which children, people with respiratory disorders, the elderly and athletes are especially vulnerable. Researchers are turning up increasing evidence that ozone can impede lung development and inflict permanent lung damage.

Ozone results when pollutants from cars, businesses and consumer products mix and bake in the sun. Stagnant air, which peaks from May to October, traps the ozone close to the ground, keeping it from dilution in the upper atmosphere.

But this year, cool weather in May, June and July combined with a strong on-shore wind flow to create a higher ceiling for the inversion layer, Cassmassi said. That gave the pollutants more clean air with which to blend. More smog has developed since temperatures warmed in August, with more traditional summer air flows.

Last year’s smog season also was marked by lower than normal temperatures, though the cool days were more evenly dispersed throughout the summer.

Similar conditions prevailed throughout the state this year, with upper atmosphere temperatures averaging as much as about 35 degrees Fahrenheit below normal, according to ARB spokesman Bill Sessa. Inversions were weaker and smog was less severe from San Diego through the San Joaquin Valley to Sacramento, he said, although specific figures were not available.

Los Angeles-area environmentalists said the lower smog levels should not affect the pace of new rules governing emissions being passed by the AQMD and the ARB. “We are nowhere near the job getting done,” said Tom Soto, president of the Coalition for Clean Air. “Simply because we’ve had two years’ worth of cool weather patterns doesn’t mean that we’re necessarily on the path to improved air quality.”

Cassmassi said regulations can be credited with long-term gains in air quality. In 1981, for example, the region experienced 94 Stage 1 episode days. “We’re reducing Stage 1 alerts by about four per year,” he said.