Ozone: indoors may offer little protection.

Ozone: Indoors may offer little protection

Premature cracking of rubber -- from seals and gaskets to microscope eye-pieces -- plagued Bell Communications Research Inc. (Bellcore) facilities in Red Bank, N.J. A rubber band, once stretched, could break in a week. The rubber casing on an appliance power-cord, when bent, would start cracking within months. Bellcore chemists eventually identified the culprit: smog ozone sucked indoors through ventilation. "That surprised us," says Charles J. Weschler, a senior scientist there, because most air pollution researchers have assumed indoor levels of smog ozone stand next to negligible.

Weschler's new data, reported last week at the American Chemical Society's fall national meeting in Miami Beach, show that indoor concentrations of this respiratory irritant can exceed 70 percent of outdoor levels.

For 150 days last summer, Weschler and his colleagues collected continuous ozone measurements both in and outside three Bellcore buildings differing only in the amount of outdoor air flushed through each hour. In one building used primarily for offices, air was replaced completely every 100 minutes. In the two that housed research labs, indoor air was exchanged with fresh outdoor air four to eight times per hour. The higher the air-exchange rate, the greater the indoor ozone level, according to Weschler's data.

Indoor sources, such as photocopiers and laser printers for computers, contributed little ozone, he found. However, even small, brief changes in outdoor ozone levels prompted indoor levels to rise and fall in lockstep.

Because most people spend the bulk of their time inside, the new findings indicate they may inhale more ozone indoors than out, Weschler says. And mechanically ventilated buildings aren't the only ones posing a risk: Homes with open windows can exceed five air exchanges per hour. That's worrisome, Weschler says, because more than half of U.S. residents live in areas that don't meet the national air-quality standard for ozone of 120 parts per billion. Though many technologies, such as activated charcoal, can filter ozone from indoor air, Weschler says "people won't use them if they don't realize indoor levels can be high."

While nobody thought indoor levels were zero, "most of us had believed they were not very significant," says William F. McDonnell, an Environmental Protection Agency ozone toxicologist in Research Triangle Park, N.C. It now appears indoor ozone could add greatly to a person's lifetime cumulative dose, he adds, noting that researchers have observed adverse lung changes in chronically exposed animals.

Michael D. Lebowitz, an ozone epidemiologist at the University of Arizona in Tucson, doubts indoor exposures will frequently exceed those outdoors. He reasons that people tend to be more active outdoors, and notes that exercise increases the breathing rate -- including ozone inhalation. But Lebowitz says Weschler's data do suggest that certain people may face a special risk during acute smog episodes: children exercising strenuously in homes and schools that lack air conditioning, and laborers who work up a sweat in well-ventilated buildings.