It was 12:30 p.m. Wednesday, and the red digital number blinking on the ozone analyzer was .095. Forty seconds later, the next reading flashed--.087.
That meant it was safe to go outside, said Jeff Song, an instrument specialist for the South Coast Air Quality Management District's monitoring station in Azusa. There was a good chance the reading would not hit .200, or 20 parts of ozone per billion parts of air.
"No Stage 1 smog alerts this afternoon--that's unusual for this time of year," he said, checking the tubes leading into the analyzer, a bulky, rectangular instrument in which air is sucked in by a tiny vacuum and tested for ozone levels 24 hours a day.
Song and his colleagues spend their days measuring and testing the air that is breathed--and seen--in Los Angeles County.
Recorded on Computers
Information from Azusa and 40 other stations in the county is sent via telephone lines to AQMD headquarters in El Monte, where it is recorded on computers and spit out in "contaminant reports" every hour.
Song, 27, spends most of each workday in a room filled with strip charts, electronic measuring devices and air samplers in a small square building on Loren Avenue in Azusa. There, and at stations in Walnut and Pomona, he watches over analyzers that measure amounts of ozone, carbon monoxide, nitrogen dioxide and sulfur dioxide in the air.
But it is atmospheric ozone, a pale blue gas composed of three oxygen atoms, that can cause lung damage and reduce resistance to infection, that concerns Song the most. Although ozone measured at the Azusa station exceeded state health standards on 173 days last year, the other gases have stayed far below the standard.
When the ozone reading reaches .200, it activates an alarm in the air district headquarters at El Monte, signaling a first-stage smog alert. A second-stage alert is sounded if the ozone reaches .350.
El Monte officials call Song to verify the results. If he confirms the machines' readings, AQMD broadcasts an alert from its radio room. Television stations, newspapers and school districts are notified by telephone.
Song works in what air district officials say is the smoggiest spot in the San Gabriel Valley, where stagnant air is surrounded by the hillsides and trapped by the inversion layer, an invisible roof of hot air pressing down upon cooler air.
Other smog hot spots are in Pomona, Glendora, San Bernardino, Fontana and Upland.
During a first-stage smog alert, people with special health problems are advised to follow precautions recommended by their doctors. Schools are asked to stop all strenuous activities for students, and public messages are broadcast encouraging ride-sharing and the curtailing of unnecessary driving.
In a second-stage alert, businesses are prohibited from burning combustible refuse. Often, Song said, a reading will come dangerously close to setting off a smog alert.
"It happened three weeks ago," he said. "The temperature was up in the 90s and my (ozone) strip chart looked like it was 35. So I called AQMD headquarters to check, but their computers, which are more refined than my chart, showed it was at 34. It was close."
One of Song's most important jobs is to make sure the analyzers are working correctly. "These are pretty reliable, but sometimes the paper gets stuck in the hole. Or the pen might break," he said.
At 3:45 a.m. each day, a known concentration of a certain gas is released into the analyzer, and if the instruments are working correctly, that value should appear on the charts at the appropriate time. The first thing Song does each morning is check the strip charts for accuracy.
Later in the day, he climbs the steep stairs to the roof of his small one-story, one-room station, where eight metal silo-shaped structures called PM-10 (particulate matter, less than 10 microns) and TSP (total suspended particulate) samplers are whirring.
The samplers run 24 hours for six days--their day off rotates--and collect airborne particles that are tested at AQMD headquarters. Song is responsible for starting the samplers' motors, changing the filters and cleaning the air ducts.
Song also records data from several weather instruments on the roof that measure the wind's velocity, direction and strength, as well as humidity and temperature. That information, too, is transmitted by telephone line to El Monte.
After he finishes in Azusa, he drives to the smaller stations at Pomona and Walnut, and repeats the process.