Sofas can pollute the air. They are not as dirty as, say, steel mill smokestacks. But they may emit formaldehyde into the atmosphere of homes and offices, if upholstered with urea-formaldehyde foam.
Some plywood, used in walls and ceilings, leaks the same substance. Wood stoves add a rustic glow - and nitrogen dioxide - to a home's atmosphere. Stone walls can be a source of radon, a form of natural radiation.
Indoor air pollution is a problem that so far has received little attention in this country. But it could be one of the most important environmental issues of the next decade, scientists say.
After all, Americans spend between 65 and 90 percent of their time indoors. And recent studies indicate that many hazardous air pollutants are more prevalent inside than out.
''Our largest exposure (to these pollutants) may come from the indoor environment, not outdoors,'' says Demetrios Moschandreas, chemical research director at the Illinois Institute of Technology.
All of this doesn't mean your home or office is a glowing, dangerous place. Many indoor pollutants are typically present at relatively low levels. But scientists are not sure what constitutes a safe amount of indoor pollution. They don't know how certain behavior patterns, such as leaning all day over a hot gas stove, increase vulnerability to dirty air indoors. And complaints about indoor air pollution are definitely on the rise - the Consumer Products Safety Council (CPSC) has received 3,000 in the last several years.
Ever since the environmental ethic took hold in the United States in the early 1970s, air pollution has been attacked as if it were mainly a product of smokestacks and tailpipes, and could be left behind by shutting the door. The Clean Air Act, for instance, empowers the Environmental Protection Agency (EPA) to set standards for ''ambient air,'' a phrase that regulators interpret to mean ''the atmosphere outdoors.''
Over the last five years, the US has spent about $52 billion on its largely successful fight to cleanse outdoor air, according to EPA figures. During the same period, $5 million to $7 million was spent on indoor air pollution, with almost every penny going for research.
''US society has in some sense ignored indoor air quality,'' says Ken Sexton, director of a California state indoor-air-quality group.
That is changing. The discovery of acute problems, such as dangerous, crumbling asbestos in schools, has brought new visibility to the indoor-air-pollution issue.
Environmentalists are becoming concerned about the increasing indoor use of synthetic building materials and dirty kerosene heaters and wood stoves. As homes and offices batten down to save energy, experts say, their ventilation is reduced, causing air quality to deteriorate.
Among the indoor pollutants getting attention:
Toxic chemicals. These dangerous substances - such as benzene and chloroform - may be more common and more concentrated indoors than out, according to recent studies by the CPSC and the EPA.
''The culprit here may be those things you keep under the sink and in the basement, such as cleaners and paint removers,'' says Dr. Sexton.
Formaldehyde. This toxic chemical is of particular concern to scientists, since it can leak from such commonplace items as urea-formaldehyde sofa foam and glue used in some types of plywood. The CPSC has tried to ban urea-formaldehyde foam, but the sanction was overturned by the courts in 1982.
Asbestos. A chalky, dangerous mineral, asbestos was a common component in roofing shingles, floor tiles, and pipe insulation installed before 1978.
Combustion byproducts. Gas stoves, wood stoves, and kerosene heaters produce nitrogen dioxide and carbon monoxide, which can build up to dangerous levels if not vented away.
Radon. This is a radioactive gas given off by earth, stone, and concrete building materials. It is the largest source of natural radiation, and is particularly prevalent in regions with much uranium and radium in the soil.
It's not clear what approach might be taken to cleaning up indoor air. Outdoors, the atmosphere is in essence public property; indoors, it's private.
EPA, says spokesman Chris Rice, ''can't have more than 10 or 15 people working on indoor air pollution.''
A congressional aide says that the ''EPA is not taking this seriously,'' and that Congress had to force it to begin a three-year study of the problem last year.