Forest fires and residential wood-burning are significant sources of fine particle (PM2.5)
air pollution. As PM2.5 exposure is associated with adverse health effects, populations
need to be provided with exposure reduction strategies during smoke episodes that are
practical, effective, and evidence-based. Public health recommendations typically include
remaining indoors and use of air cleaners, yet little information is available on the
effectiveness of these measures. Specific objectives of this study were to measure indoor
infiltration of outdoor P M2.5 from forest fires/residential wood smoke, to determine
effectiveness of High Efficiency Particulate Air (HEPA) filter air cleaners in reducing
indoor PM2.5 and to investigate determinants of infiltration and air cleaner effectiveness
in homes.
Winter sampling at 21 homes was conducted in 2004 in a northern Canadian community
affected by residential wood-burning. Summer (2004-5) sampling at 17 homes was
conducted in southern British Columbian communities impacted by vegetation fire
smoke. Indoor and outdoor 1-minute PM2.5 averages and a 48-hour outdoor PM2.5 filter
sample were collected at each home. A portable HEPA filter air cleaner was operated
indoors with the filter removed for one of two sampling days. Infiltration (Finf) was
calculated for each home using a recursive model (Switzer & Ott, 1992; Allen et al.,
2003). Housing characteristics data were used in multivariable modeling of infiltration
and air cleaner efficiency (ACE).
Valid samples were obtained from 19 homes in winter and 13 homes in summer. Mean
Finf ± SD values of 0.27 ±0.18 and 0.61 ± 0.27 were found for winter and summer
respectively, for days when the filter was removed, with lower values of 0.10 ± 0.08 and
0.19 ± 0.20 on corresponding days with filters in place. Mean ± SD ACE, calculated as
[Finf without filter - Finf with filter]/ Finf without filter, in winter and summer were 55 ±
38% and 65 ± 35% respectively. Infiltration was predicted by the number of windows in
a home and the season (p<0.001) while no significant predictors of ACE were identified.
Remaining indoors combined with air cleaner use was concluded to effectively reduce
PM2.5 exposure during forest fire and residential wood burning episodes.Medicine, Faculty ofPopulation and Public Health (SPPH), School ofGraduat