Penetration of ambient fine particles into the indoor environment

Several recent studies have indicated significant health risks associated w ith exposure to fine particles as measured outdoors. However, much of the e xposure is believed to have occurred indoors. Consequently, there is consid erable interest in the relationship between indoor and outdoor fine particl es. This paper describes some results from a study in which the processes o f particle removal from infiltrating air by building envelopes are simulate d in a chamber. The chamber consists of two compartments, each having a vol ume of 19 m(3), Particles with aerodynamic diameters in the range of 0.05 t o 5 mum are generated in one compartment and then transported through simul ated leakage paths to the other compartment under the action of applied pre ssure differentials, The simulated leakage paths described in this paper co nsist of horizontal slits (0.508 mm high, 102 mm deep, and 433 mm wide) bet ween aluminum plates. The penetration factor for each size particle is dete rmined by simultaneously measuring the concentrations in the two compartmen ts as a function of time, The penetration factor is obtained through a math ematical solution of the mass balance equations. The measured values of pen etration are compared to predictions of a mathematical model describing dep osition by the mechanisms of settling and diffusion. At applied pressures o f 2 Pa, only 2% of 2 mum particles and 0.1% of 5 mum particles pass through the 0.508 mm high slits, At a pressure of 5 Pa, 40% of 2 mum particles and <1% of 5 <mu>m particles pass through the slits. At 10 Pa, 85% of 2 mum pa rticles and <1% of 5 <mu>m particles pass through the slits, At 20 Pa, 90% of 2 mum particles and 9% of 5 mum particles pass through the slits. Measur ed deposition rate constants for particles spanning the range 0.015 to 5 mu m in diameter are shown.