Penetration of ambient fine particles into the indoor environment

Several recent studies have indicated significant health risks associated with exposure to fine particles as measured outdoors. However, much of the exposure is believed to have occurred indoors. Consequently, there is considerable interest in the relationship between indoor and outdoor fine particles. This paper describes some results from a study in which the processes of particle removal from infiltrating air by building envelopes are simulated in a chamber. The chamber consists of two compartments, each having a volume of 19 m(3), Particles with aerodynamic diameters in the range of 0.05 to 5 mum are generated in one compartment and then transported through simulated leakage paths to the other compartment under the action of applied pressure differentials, The simulated leakage paths described in this paper consist of horizontal slits (0.508 mm high, 102 mm deep, and 433 mm wide) between aluminum plates. The penetration factor for each size particle is determined by simultaneously measuring the concentrations in the two compartments as a function of time, The penetration factor is obtained through a mathematical solution of the mass balance equations. The measured values of penetration are compared to predictions of a mathematical model describing deposition by the mechanisms of settling and diffusion. At applied pressures of 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 particles 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. Measured deposition rate constants for particles spanning the range 0.015 to 5 mum in diameter are shown.