Smog's ozone spawns funky carpet smells. (Environment).

Chemicals in synthetic carpeting can react with a component of smog to generate unpleasant aromas. The resulting scents, which may persist for up to 3 years, are independent of the months-long release of chemicals that's come to be known as new-carpet smell.

To investigate a potential contributor to sick-building syndrome, environmental engineers at the University of California, Berkeley exposed squares of nylon or olefin carpeting to airborne ozone at a concentration of 100 parts per billion (ppb). Though high, that's not beyond what's present in some large cities. After 7 to 10 days, the researchers measured gases coming off the samples--which were either intact or with most of their upper pile sheared off so the team could check the effects of the backing. The researchers then extrapolated the results to what might occur under prolonged exposure to the lower ozone concentrations typical of many urban homes and offices.

William W. Nazaroff and Glenn C. Morrison, now at the University of Missouri in Rolla, detected a host of smelly aldehydes, such as 2-nonenal. Ranging in scent from grassy to solventlike, these aldehydes appear to stem from the oxidation of vegetable-derived oils used in carpet making, Morrison says. He likens the aldehydes' difficult-to-describe composite scent to "an unpleasant cucumber smell."

The new data suggest that even at indoor-ozone concentrations of just 2 ppb, there would be sufficient oxidation activity to produce enough of these aldehydes for a person to notice the smell, Morrison told Science News. And because the reactions responsible don't occur until they're triggered by ozone, the precursor molecules might not get used up for years if indoor pollutant concentrations remain low. At the beginning of ozone exposure, the reactions occurred in the carpet pile but later were almost exclusively in the backing. Not toxic at the air concentrations likely to occur, the smelly aldehydes may suggest poor air quality and thus account for lingering claims of sick-building syndrome, Morrison adds.

Although most indoor ozone comes from outdoor sources, shutting windows won't end the problem. Smoggy pollutants get through even tiny gaps in windows, Morrison notes, especially ones that haven't been weatherproofed. --J.R.