PM2.5 in Puget Sound: From PSCAA, 1999

"During the winter season, indoor burning emissions increase, accounting for approximately 63% of the Region's overall PM2.5 emissions. Exceedences of PM air quality standards are more likely to occur in the winter when weather conditions are cold and still. These weather conditions (inversions) cause pollution to be trapped close to the ground. Air quality can quickly deteriorate under these conditions, increasing the chance of an exceedence. Given the large percentage of emissions contributions from indoor burning during the winter season, it significantly contributes to the levels of pollution throughout the region. In addition, the levels of emissions currently generated by indoor burning are likely to contribute to the exceedences of the Health Committee's daily standard and reduce the probability that the Region will effectively move towards meeting the Health Committee's annual goal.

Geographically, indoor burning emissions are higher in residential areas, lower in urban and industrial areas. The problem is exacerbated in valleys where there are a high percentage of residential units because PM might remain for extended periods of time during episodes of air stagnation." (PSCAA, 1999).