MEASUREMENT OF AIR EXCHANGE-RATE OF STATIONARY VEHICLES AND ESTIMATION OF IN-VEHICLE EXPOSURE

The air exchange rates or air changes per hour (ACH) were measured und er 4 conditions in 3 stationary automobiles, The ACH ranged between 1. 0 and 3.0 h(-1) with windows closed and no mechanical ventilation, bet ween 1.8 and 3.7 h(-1) for windows closed with fan set on recirculatio n, between 13.3 and 26.1 h(-1) for window open with no mechanical vent ilation, and between 36.2 and 47.5 h(-1) for windows closed with the f an set on fresh air ACHs for windows closed with no ventilation were h igher for the older automobile than for the newer automobiles. With th e windows closed and fan turned off, ACH was not influenced by wind sp eed (p > 0.05). When the window was open, ACH appeared to be greatly a ffected by wind speed (R-2 = 0.86). These measurements are relevant to understanding exposures inside automobiles to sources such as dry-cle aned clothes, cigarettes and airbags. Therefore, to understand the in- vehicle exposure to these internal sources, perchloroethylene (PCE) em itted from dry-cleaned clothes and environmental tobacco smoke (ETS) i nside a vehicle were modeled for simulated driving cycles, Airbag depl oyment was also modeled for estimating exposure level to alkaline part iculate and carbon monoxide (CO). Average exposure to PCE inside a veh icle for 30 minute period was high (similar to 780 mu g/m(3)); however ; this is only 6% of the two-week exposure that is influenced by the s torage of dry cleaned clothing at home. On the other hand the exposure levels of respirable suspended particulate (RSP) and formaldehyde due to ETS could reach 2.1 mg/m(3) and 0.11 ppm, respectively, when a per son smokes inside a driving car even with the window open. In modeling the in-vehicle concentrations following airbag deployment, the averag e CO level over 20 minutes would not appear to present problem (less t han 28 ppm). The peak concentration of respirable particulate would ha ve exceeded 140 mg/m(3). Since most of the particle mass is composed o f alkaline material, these high levels might be expected to cause harm ful effects on susceptible people, such as asthmatics. In all modeled cases, ACH would significantly affect build-up and dilution of polluta nts originating from internal sources. Frequent stopping in congested urban traffic can greatly increase short-term exposures.