Are indoor gases sickening microcircuits?

Tiny electronic circuits are extremely vulnerable to corrosion and failure from the buildup of nitrate salts. To protect their sensitive switches from such deposits -- which can enter buildings with dust -- telephone companies typically install sophisticated dust filters. Yet switches continue to suffer from transient processing glitches and sometimes a catastrophic shorting out.

A trio of chemists now suggests a new reason for the salty circuits plaguing telephone companies -- and probably, unknowingly, consumers as well.

Although these salts can be a constituent of outdoor dust, they also can form after their parent gases slip unchallenged through dust filters, the researchers now find. Moreover, their new data show, under these circumstances, salt-forming acids can develop directly on vulnerable indoor surfaces -- including electronic circuitry. The group, led by Charles J. Weschler of Bell Communications Research in Red Bank, N.J., reports its findings in the November ENVIRONMENTAL SCIENCE & TECHNOLOGY.

For 14 months, the scientists monitored the air inside and outside a telephone switching facility in California for concentrations of ozone, nitric oxide (NO), and nitrogen dioxide ([NO.sub.2]) -- all major components of smog.

Depending on the time of day and season, indoor concentrations of these pollutants could be high, notes Weschler. Indoor ozone tended to fluctuate between 25 and 60 percent of outdoor concentrations. And indoor [NO.sub.2] typically ran 70 to 90 percent of outdoor concentrations.

Because the building lacked the usual indoor sources of these gases, such as photocopiers, laser printers, cigarette smoke, and gas ranges, Weschler's group believes the pollutants came from outdoors.

When present together, ozone and [NO.sub.2] formed the reactive nitrate radical. If the relative humidity was high enough -- and it typically was, in summer -- this radical could foster reactions between a kindred molecule and water on the surfaces of materials, Weschler's team found. The resulting nitric acid is corrosive and a source of nitrate salts. At the same humidity, [NO.sub.2] can also react directly with surfaces to form the weaker -- though still salt-producing -- nitrous acid.

Though [NO.sub.2] played a principal role in creating both nitrogen-salt-forming acids, barring its infiltration from outside may not prevent acid buildup, the data suggest. For one thing, [NO.sub.2] also forms indoors from ozone and NO.

Indeed, Weschler concludes, these pollutants -- and their effects on the health of building occupants and on possessions -- can only be predicted by graphing the "intricate dance" that each gas performs about the others.

That these reactions can occur indoors "has been largely unrecognized," observes atmospheric chemist Chet Spicer of Battelle Memorial Institute in Columbus, Ohio. Why? Few chemists "expected as much ozone to exist in buildings as shown here -- and that [ozone] really triggers these reactions."

Indeed, this "is not a deeply mined topic," observes Glen R. Cass of the California Institute of Technology in Pasadena. Moreover, the few related studies that he and others have performed monitored smog-gas interactions for only a few days. "It's been hard to tell from such experiments if what you're looking at is an anomaly or typical," Cass says.

But the take-home message for most consumers, Weschler believes, should be to

keep living areas moderately dry and to isolate vulnerable electronics -- especially computers -- from indoor NO and [NO.sub.2] sources, such as gas ranges.