There appears to be much confusion on the sources of micro particulates. Wood burning produces large quantities of microparticulates smaller than 0.03 microns. In large measure there has been little actual measurements of particulates in residential areas. The following two charts are based on data supplied by the Bay Area Air Management District and published in the San Francisco Chronical, p A1 & A21, on 11/28/96.
Sources of PM-2.5 (pop up)

This chart was generated from the lower chart by Dr. Wayne Ott by assuming "construction" and "other" sources of PM-10 have zero PM-2.5 emissions. (W. Ott, 8/17/97) Dr. Ott has monitored PM-2.5 in residential for over two years.

Bare in mind that the figures are based on a yearly average. If one concentrated on the heating season, the contribution of Fireplaces and woodstoves would be even greater. Sources of PM-10 (pop up)