The impact of outdoor air particles on indoor concentrations was considered. Equilibrium mass balance models indicate that this is a function of the penetration P through the building envelope, the air exchange rate a, and the particle decay rate k. EPA's PTEAM Study provided an estimate for k of 0.39 h(-1) for fine particles and 1.01 h(-1) for coarse particles. Two studies suggest that P = 1 for PM(10). Using these results, the fraction of outdoor air PM(2.5) and PM(10) particles found indoors at a given air exchange rate can be calculated. The protective effect of reducing air exchange rates during periods of high outdoor particle pollution can thus be quantified.
那么，阻隔效率能有多少啊亲？One goal of the study was to estimate the contribution of outdoor PM2.5 to indoor concentrations. This depends on the infiltration factor F-inf, the fraction of outdoor PM2.5 remaining airborne after penetrating indoors. After confirming with our measurements the findings of previous studies that sulfur has few indoor sources, we estimated an average F-inf for each house based on indoor/outdoor sulfur ratios. These estimates ranged from 0.26 to 0.87, with a median value of 0.55. Since these estimates apply only to particles of size similar to that of sulfur particles (0.06-0.5 mu m diameter), and since larger particles (0.5-2.5 mu m) have lower penetration rates and higher deposition rates, these estimates are likely to be higher than the true infiltration factors for PM2.5 as a whole. In summer when air conditioners were in use, the sulfur-based infiltration factor was at its lowest (averaging 0.50) for most homes, whereas the average F-inf for the other three seasons was 0.62-0.63, Using the daily estimated infiltration factor for each house,we calculated the contribution of outdoor PM2.5 to indoor air concentrations.
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