Tracing Outdoor/Indoor Penetration of PM2.5,PM1.0 by 210Po/210Pb

Abstract

Alpha activities of 210Po were determined in low-volume, 24-hour samples of 2 particulate matter (PM) size fractions indoors and outdoors in 3 localities in the centre of Prague during the winter periods of 2002-2003. High values of ventilation rates (0.34 0.12h 1) and penetration of outdoor aerosols into the indoor environment, which favours particles smaller than 1 m size, allows the application of a simplified equation of the indoor/outdoor (I/O) relationship. The slope of linear regression of indoors against outdoors for both mass concentrations and alpha activities as well as the I/O penetration factors C_mass, and Calpha, respectively were determined. While the C_mass ranged from 0.46 to 0.64, appropriate Calpha ranged from 0.57 to 0.95 being always greater and reflecting size selective particle penetration through the building envelope. Personal activities indoors had little effect on particle deposition indoors, which is in agreement with the finding that the majority (70%) of PM_2.5 indoors is formed by PM_1.0. For all 3 localities it was shown that outdoor PM concentrations determined indoor ones while probably the particle removal during infiltration through the building envelope is the most important aerosol loss mechanism.