Ask the Expert

In our daily life we are exposed to a variety of air pollutants. We have a lot to learn about what they are, how much there are, to what extent they are harmful, and what we can do about it.

Airborne pollutants fall into two categories: Gases and particles. Outdoors the kinds of gases we’re breathing (in addition to air) include carbon monoxide, nitrous oxides (called “NOx”), and ozone. Particle pollutants not only include natural sources like wind-blown dust, but also result from human activities, especially combustion emissions from car engines, furnaces, fireplaces, barbecues, and cigarettes.

The good news for our health is that regulations of car, power plant, and industrial emissions over the last few decades have helped keep outdoor air much cleaner than it would be without those laws. But as population continues to increase we have more cars, houses, and energy demand than ever before. That means that even as we make everything cleaner, we could still see rises in overall pollution.

The bigger issue, however, is the air you breathe indoors because that’s where people, on average, spend about 90 percent of their time. Indoor spaces have unique kinds of air pollution, but there are virtually no regulations to limit them at all.

The stuff we breathe indoors can be worse than outdoors for some pollutants, like vaporized chemicals, which come from paint and furniture (these are called “volatile organic compounds” or VOCs), and biological particles, such as pet dander and molds. In some places if you measure carefully, you can even find small amounts of other nasty things in the indoor dust, such as lead. We used to have lead in our gasoline and particles containing it settled next to roadways. People still track that in on their shoes, leave it on the floor and then kick it back up into the air later.

Recently my students and I have been studying indoor mold levels to determine how much of it comes in from outdoors versus how much gets kicked up indoors when people walk over carpets. By taking measurements in carpeted public spaces and homes, we’ve found a strong correlation between foot traffic and mold levels. We’ve shown the carpet to be a major source by comparing walking on carpeting with walking on a clean tarp.  By having volunteers dressed in Tyvek suits walk around under the same conditions, we been able to determine that people and their clothes are not a major source.

One of the places we took measurements was in a hospital, where there are likely to be patients with poor immune systems and greater susceptibility to lung infections. If indeed further tests confirm that walking on carpets really kicks up molds into the indoor air, hospitals may want to rethink having carpets.

But regulation of indoor air is tricky. People are going to do what they want to do in their own homes (I’ve studied air quality in Bangladesh where people are so poor, they can’t afford to vent their indoor wood-burning stoves).

Even in public spaces, regulators would have to grapple with issues such as which spaces (perhaps other than hospitals) are vital to regulate, what levels of different pollutants are really unsafe and what regulations would actually be effective.

For example, we don’t really know everything we need to know about what can make particles harmful to people. Is it their size? Their shape? Their chemical composition? Maybe it’s how much of it you breathe.

Of course, people who want to improve their indoor air quality don’t need regulations to do so. I think about this especially because I have a young child. We have very little carpet at home. Our furniture is leathery rather than cloth because that holds less dust. We probably light our fireplace only once every 10 years or so. We’ve also used low-VOC paint for years.

Don’t pin all your hopes on home air filtering machines, however. Your furnace’s filter, if it is very efficient, can do some good for particles because so much of your home’s air circulates through it. But portable units typically don’t move enough air per minute through a filter to affect much more than the space immediately around them.  And the “ionic” and “oxidizer” air cleaners release ozone – a pollutant that is regulated outdoors due to its health effects.