The relationship between indoor and outdoor airborne particles in the residential environment

The relationship between indoor and outdoor airborne particles was investig ated for 16 residential houses located in a suburban area of Brisbane, Aust ralia. The submicrometer particle numbers were measured using the Scanning Mobility Particle Sizer, the larger particle numbers using the Aerodynamic Particle Sizer and an approximation of PM2.5 was also measured using a Dust Trak. The measurements were conducted for normal and minimum ventilation co nditions using simultaneous and non-simultaneous measurement methods design ed for the purpose of the study. Comparison of the ratios of indoor to outd oor particle concentrations revealed that while temporary values of the rat io vary in a broad range from 0.2 to 2.5 for both lower and higher ventilat ion conditions, average values of the ratios were very close to one regardl ess of ventilation conditions and of particle size range. The ratios were i n the range from 0.78 to 1.07 for submicrometer particles, from 0.95 to 1.0 for supermicrometer particles and from 1.01 to 1.08 for PM2.5 fraction. Co mparison of the time series of indoor to outdoor particle concentrations sh ows a clear positive relationship existing for many houses under normal ven tilation conditions (estimated to be about and above 2h(-1)), but not under minimum ventilation conditions (estimated to be about and below 1h(-1)). T hese results suggest that for normal ventilation conditions, outdoor partic le concentrations could be used to predict instantaneous indoor particle co ncentrations but not for minimum ventilation, unless air exchange rate is k nown, thus allowing for estimation of the "delay constant". (C) 2001 Elsevi er Science Ltd. All rights reserved.