Factors influencing variability in the infiltration of PM 2.5 mass and its components M. MacNeill a, * , L. Wallace b , J. Kearney a , R.W. Allen c , K. Van Ryswyk a , S. Judek a , X. Xu d , A. Wheeler a a Air Health Science Division, Health Canada, 269 Laurier Ave West Street, Ottawa, ON K1A 0k9, Canada b Santa Rosa, CA, USA c Faculty of Health Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada d Department of Civil and Environmental Engineering, University of Windsor, 333 Essex Hall, Windsor, ON N9B 3P4, Canada highlights < This is one of the few papers to describe and model F inf and F pex on a daily basis. < F inf and F pex can be lower and less seasonally variable where heating and cooling systems are used. < Air cleaners and electrostatic precipitators may provide a mechanism of reducing exposures. < Ambient and Non-ambient contributions can be quantified using F inf and F pex . article info Article history: Received 5 April 2012 Received in revised form 5 June 2012 Accepted 4 July 2012 Keywords: Infiltration factor (F inf ) Ambient personal exposure factor (F pex ) PM 2.5 Ultrafine particles (UFPs) Black carbon (BC) Ambient Non-ambient Indoor air pollution Windsor, Ontario abstract The infiltration of particles into homes can vary seasonally, between homes in a community and between communities. However, few studies have examined the day to day variability across multiple homes. We used continuous data collected from a 2-year (2005e2006) personal exposure study conducted in Windsor, ON to estimate daily infiltration factors (F inf ) for fine particulate matter (PM 2.5 ), Black Carbon (BC), and ultrafine particles (UFP) as well as the ambient personal exposure factor (F pex ) for PM 2.5 . In addition, the daily ambient and non-ambient generated components of indoor and personal concen- trations were estimated. Median daily F inf estimates ranged from 0.26 to 0.36 across seasons for PM 2.5 ; from 0.28 to 0.59 for BC; and from 0.15 to 0.26 for UFP. Median daily F pex estimates ranged from 0.24 to 0.31 across seasons. Daily PM 2.5 and UFP F inf and F pex estimates were higher in summer than winter, although BC showed the opposite trend. Predictors of daily infiltration were typically related to window-opening behaviours, air conditioning, meteorological variables, and home age. In addition, use of electrostatic precipitators and stand alone air cleaners was associated with significantly reduced infiltration factors, indicating that these devices may provide a cost effective mechanism of reducing human exposures to particles of ambient origin. The majority of indoor PM 2.5 (median 57e73%) and indoor BC (median 90e100%) was of ambient origin across seasons, while both personal PM 2.5 and indoor UFPs had significant non-ambient contri- butions (median 60e65%). Factors that were found to increase non-ambient particle concentrations were typically related to cooking, candle use, supplemental heating, cleaning, and number of people in the home. Factors that were found to decrease non-ambient particle concentrations were open windows, and air cleaner use. This work has several implications to both epidemiologic studies and risk management. A better understanding of the factors influencing F inf and F pex can improve exposure assessment and contribute to reduced exposure misclassification in epidemiologic studies. Furthermore, by increasing our knowledge of non-ambient and ambient exposures, risk associated with PM exposure can be managed more effectively. Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved. 1. Introduction Over the past two decades there has been a growing body of epidemiological research demonstrating a relationship between exposure to particulate air pollution and adverse health effects * Corresponding author. Tel.: þ1 613 948 8233; fax: þ1 613 948 8482. E-mail address: Morgan.MacNeill@hc-sc.gc.ca (M. MacNeill). Contents lists available at SciVerse ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ e see front matter Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.atmosenv.2012.07.005 Atmospheric Environment 61 (2012) 518e532