Schneider T., Sundell J., Bischof W., Bohgard M., Cherrie JW,Clauser , Dreborg S., Kildeso J., Kaergaard SK, Lovik M., Pasanen P, Skyberg
Bibliographic info:
Indoor air. March 2003 , Vol 13 - 1, pp 38-48, 1 Tab. , 12 Ref.

The European interdisciplinary group of researchers have reviewed 70 papers and selected 8 studies for their final review. From most studies, no definite conclusions could have been drawn concerning the association between particles matter concentration and health outcomes.
So giving limit values or guidelines for particulate mass or number concentrations in non-industrial indoor environment is not an adequate scientific evidence.