Clean air is in the eyes--or is it the lungs?--of the beholder.
Air quality officials announced this month that during the six-month smog season that ended Nov. 1, the Los Angeles Basin had the cleanest air they have ever recorded. There were fewer smog alerts in 1990 than in any year since records for Southern California were first kept in 1955.
Many people in the San Gabriel Valley say they can see and feel the improvement. But they also say the San Gabriel Valley is a long way from breathing clean, healthy air. And experts agree.
The San Gabriel Valley still reports more smog alerts at its four air quality stations than any other part of the basin. That makes it the nation's smoggiest region.
Also, while controls on auto and industrial emissions have helped clean the air, a significant part of the most recent improvement is believed to be caused by favorable weather conditions that may not last, said officials at the South Coast Air Quality Management District.
Researchers suggest that San Gabriel Valley residents continue to lose lung capacity from living in the ozone-laden air. And one city, Glendora, still has to bridle under its designation as "America's Smoggiest City."
But first, the good news:
The San Gabriel Valley's four air monitors--in Azusa, Glendora, Pasadena and Pomona--reported a total of 60 smog alert days during the 1990 "smog season," compared to 94 in 1989. As recently as 1982, the four monitors recorded 170 smog alert days.
Air quality officials declare first-stage smog alerts when ozone, the area's principal pollutant, reaches .20 parts per million. Second-stage smog alerts are declared when ozone reaches .35 parts per million.
During the 1990 smog season--for the fourth year in a row--no second-stage alerts were declared in the San Gabriel Valley.
AQMD officials called the improvements "mind-boggling" and "dramatic."
In the San Gabriel Valley itself, most people judge the smog by looking toward the San Gabriel Mountains. And by this measure, as well, many have seen improvement.
"There is no question I go out from my house more days and say, 'Aren't the mountains beautiful!' " said Glendora Mayor Bob Kuhn. "I used to go out and say, 'Where are the mountains?' "
The improvement can also be seen on the pages of the Glendora Unified School District's "Smog Book." The district has an ozone meter and logs days on which schools are notified to curtail students' exercise. The book shows 43 such alerts in 1986, compared to nine in 1989 and just two this year.
AQMD officials say the air has improved substantially over the last decade, in large part because of greater controls on car exhausts and industrial emissions. "When you compare it with the past, it's like night and day," said Joe Cassmassi, senior meteorologist with the AQMD. "There's really been a dramatic improvement."
In this year's improvement, favorable weather conditions also played an important part, they said.
Ozone forms in the air when hydrocarbons and nitrogen oxides emitted by cars and industry are exposed to sunlight. High pressure holds the pollution close to the ground and prevents it from blowing away.
But more low-pressure systems penetrated the Los Angeles Basin in the last year, cleaning the air, said Joe Cassmassi, AQMD senior meteorologist.
"Most of the days of improvement are based on weather conditions," Cassmassi said.
Weighing the impact of weather against emission controls is difficult, he said. Researchers have estimated that this year, an average of four smog-alert days were eliminated at each smog station by pollution controls, and the rest by helpful weather, Cassmassi said.
Experts say the elements will not always be so accommodating.
Researchers added that although they are encouraged by the lower ozone levels, residents' health is still suffering because of air pollution.
There were still 180 days this year when ozone levels at least one reporting station in the Los Angeles area exceeded the state's more stringent clean air standard of .09 parts per million of ozone, the AQMD reported.
"Certainly it's good news that we have had fewer alerts and lower levels of pollution," said Roger Detels, a professor of epidemiology at UCLA's School of Public Health. "But we should continue to be concerned about levels of air pollution."
Detels and a UCLA research group will soon publish the latest chapter in a study that has documented the decreased lung function of people who live in polluted areas.
The researchers compared residents of Glendora and Long Beach with Lancaster, a control area with relatively cleaner air.
"Young people tend to have an increase in lung function until the age of about 25," Detels said. "But in the polluted areas kids did not have as large an increase as in the control area. And after 25 years of age they had a greater decline in lung function."