Indoor vs outdoor concerns

As winter draws near, for many people it's time to wear masks, reduce the amount of time they spend outdoors and prepare for high levels of air pollution caused by coal-fired heating. However, the air we breathe indoors is often only slightly cleaner than that outside.

Levels of many indoor pollutants may be two to five times - on occasion more than 100 times - higher than outdoors, according to the US Environmental Protection Agency.

It is estimated that many people spend as much as 90 percent of their time indoors during long winters.