REDUCTION POTENTIAL OF URBAN PM 2.5 MORTALITY RISK USING MODERN VENTILATION SYSTEMS IN BUILDINGS Short title: “Exposure reduction in modern buildings” Otto O. Hänninen 1* , Jari Palonen 2 , Jouni T. Tuomisto 1 , Tarja Yli-Tuomi 1 , Olli Seppänen 2 and Matti J. Jantunen 1 1 KTL, Centre for Environmental Health Risk Analysis, P.O.B. 95, FIN-70701 Kuopio, FINLAND 2 Helsinki University of Technology, Laboratory of Heating, Ventilating & Air Conditioning, FIN-02150 Espoo, FINLAND * E-mail: otto.hanninen@ktl.fi , fax: +358-17-201 184 Submitted for Indoor Air, October 7 th , 2004