When the outdoor air pollution is extremely poor, one may seek refuge in their home assuming that it will provide shelter from the ill effects of the smog outside. But half or more of what one experiences outside is probably penetrating into their home. Although outdoor air quality gets most of the attention, we must remember that we also experience outdoor pollution while we are indoors—where many people spend 90 per cent of their time.
To make matters worse, the source of air pollution is not limited to the outdoors. We must also contend with indoor air pollutants that can make the air inside even worse than outside.