When you hear the term "air pollution," what do you picture? A factory smokestack, perhaps? Or the tailpipe of a truck belching out black fumes and causing you to cover your mouth? While such things no doubt qualify, we should be more concerned about the air we breathe when we're indoors, according to the U.S. EPA.
In its report "The Inside Story: A Guide to Indoor Air Quality," the agency states that things like furniture, carpet, insulation, and cleaning products in homes and other buildings can expose us to high levels of pollutants. While any one source of pollution may not amount to much in isolation, the cumulative effect of all these sources can be considerable—especially given that most people spend the majority of their time indoors.
So how can we improve the quality of the air we breathe inside? Houseplants like Boston ferns and spider plants have long been championed for their air-cleaning abilities (for example, see this graphic from Good magazine), although there is controversy about their efficacy. The EPA recommends air cleaners for certain types of pollutants.
Most mileage can be gotten from eliminating the sources of pollution. Limit your exposure to paints, varnishes, and non-green cleaning supplies (you can make your own cleaners with simple ingredients like vinegar, baking soda, and borax). Avoid air fresheners, vinyl shower curtains, and paraffin candles. Steer clear of traditional dry cleaners, which use a chemical that's bad for both you and the environment.
Consider replacing furniture or flooring made of pressed wood or plywood, much of which offgasses formaldehyde (not all of it, though; the largest U.S. manufacturer of plywood furniture, Columbia Forest Products, uses formaldehyde-free technology). When shopping for furnishings, look for the Greenguard Environmental Institute's low-toxicity product certification, or consider secondhand items that have pretty much finished their offgassing.
Finally, simply opening a window to increase ventilation helps a great deal. And don't forget to get outside!