We tend to think of air pollution as something outside — smog, ozone, or haze hanging in the air, especially in summer. But the truth is, the air inside homes, offices, and other buildings can be more polluted than the air outside. The air inside your home may be polluted by lead (in house dust), fire-retardants, radon, even volatile chemicals from fragrances used in conventional cleaners. Some pollutants are tracked into the home. Some arrive via a new mattress or furniture, carpet cleaners, or a coat of paint on the walls.