Smog: It Isn’t Good, but It’s Better : Environment: Data for the January through October period shows a wide reduction in days when the federal standard for ozone was exceeded.

Although it went out in a pall of wildfire smoke, the just-concluded smog season was the best since monitoring began in the 1950s, according to officials of the South Coast Air Quality Management District.

Air quality was hardly good, but it was the least unhealthful in decades, according to data from monitoring stations in Burbank, Reseda, Santa Clarita, Lancaster and 30 other locations.

In Burbank, the federal health standard for ozone, a lung-irritating gas that is the main component of smog, was exceeded on 17 days from January through October--well below the annual average of 49 days for 1988-92.

In Reseda, there were 32 days in which ozone levels topped the federal standard. This was more than the 1992 total of 25 days, but well under the five-year average of 49 days a year.

Santa Clarita had 44 days above the ozone standard, compared to a five-year average of 75 days. In Lancaster, the smog standard was violated on 14 days, compared to an average of 22 days.

Air quality officials attributed the improvement to favorable weather patterns, the economic slump and pollution-control regulations, but said they do not know precisely what each contributed.

“We saw a dramatic drop in the number of smog episodes this summer, with weather a major contributor,” AQMD Executive Officer James M. Lents said. “But there’s also been a long-term downtrend in pollution, showing that the region’s pollution-control efforts have worked.”

Even so, the ozone standard was violated at least somewhere in the four-county air basin on 122 days--by far the worst total in the country. Air district officials, who regulate stationary sources of pollution in Los Angeles, Orange, Riverside and San Bernardino counties, say it will be at least 2010 before the area meets the federal standard of 12 parts of ozone per 100 million parts of air.

When suspended miles above the Earth, ozone is part of the planet’s safety net, filtering out damaging ultraviolet rays. But at ground level, it can damage the lungs and cause coughing, headache and fatigue.

An invisible gas, ozone forms when fumes from auto exhaust, gasoline, paint, glues and chemicals mix in sunlight with nitrogen oxides, which are combustion byproducts. Because strong sunshine is a key to ozone buildup, high levels usually occur from April through October.

Many of the air district’s 34 monitoring stations recorded near-record low numbers in days of violations. Peak ozone concentrations also dropped, indicating that the worst days weren’t as bad as in the past.

During the year, there were 24 first-stage smog episodes----when ozone concentrations hit 20 parts per 100 million, vigorous outdoor activity is discouraged and people with heart or lung conditions are advised to stay indoors. That was a reduction from 41 first-stage alerts in 1992 and 47 in 1991. The more serious Stage II episode level has not been reached anywhere in the basin since 1988.

None of this year’s first-stage alerts included Burbank, which had eight of the episodes last year and four in 1991. There were three first-stage episodes in Santa Clarita--down from four in 1992 and eight in 1991. Neither Reseda nor Lancaster had any this year nor in the prior two years.

Air quality officials cautioned that the end of the ozone season brings the start of “winter smog”--when carbon monoxide becomes the area’s worst pollutant.

The South Coast air basin also violates health standards for carbon monoxide, but not as frequently as for ozone.

A colorless gas emitted mainly by vehicle exhaust, carbon monoxide reduces the blood’s ability to carry oxygen.

Peak levels occur during late fall and winter mornings when cold air hangs close to the ground, creating an inversion that traps emissions from rush-hour traffic.

To reduce carbon monoxide emissions, service stations in California from November through February are required to sell gasoline with a higher oxygen content.

Breathing (Somewhat) Easier

Ozone levels have decreased in the San Fernando, Santa Clarita and Antelope valleys. Number of days of violations of federal ozone standard*,1988-1993.

1993 1992 1991 1990 1989 1988 Burbank 17 47 55 40 40 64 Reseda 32 25 53 41 54 71 Santa Clarita 44 71 6 62 71 107 Lancaster 14 25 8 7 27 44 Los Angeles 8 23 23 32 34 24 Pasadena 53 71 70 69 80 119

* Number of days ozone concentration exceeded federal health standard of 12 parts per 100 million. Data recorded at monitoring stations in San Fernando, Santa Clarita and Antelope Valleys, and at two other stations included for comparison. Ozone, an invisible gas, is a lung irritant and and the main component of smog. Source: South Coast Air Quality Management Destrict