Estimation of bias with the single-zone assumption in measurement of residential air exchange using the perfluorocarbon tracer gas method.
Residential air exchange rates (AERs) are vital in understanding the temporal and spatial drivers of indoor air quality (IAQ). Several methods to quantify AERs have been used in IAQ research, often with the assumption that the home is a single, well-mixed air zone. Since 2005, Health Canada has conducted IAQ studies across Canada in which AERs were measured using the perfluorocarbon tracer (PFT) gas method. Emitters and detectors of a single PFT gas were placed on the main floor to estimate a single-zone AER (AER(1z)). In three of these studies, a second set of emitters and detectors were deployed in the basement or second floor in approximately 10% of homes for a two-zone AER estimate (AER(2z)). In total, 287 daily pairs of AER(2z) and AER(1z) estimates were made from 35 homes across three cities. In 87% of the cases, AER(2z) was higher than AER(1z). Overall, the AER(1z) estimates underestimated AER(2z) by approximately 16% (IQR: 5-32%). This underestimate occurred in all cities and seasons and varied in magnitude seasonally, between homes, and daily, indicating that when measuring residential air exchange using a single PFT gas, the assumption of a single well-mixed air zone very likely results in an under prediction of the AER.


CONCLUSIONS
The results of this study suggest that the long-standing assumption that a home represents a single well-mixed air zone may result in a substantial negative bias in air exchange estimates. Indoor air quality professionals should take this finding into consideration when developing study designs or making decisions related to the recommendation and installation of residential ventilation systems.
Air Health Science Division, Health Canada, Ottawa, ON, Canada.
K
K
Van Ryswyk
Consultant, Santa Rosa, CA, USA.
L
L
Wallace
Consultant, Ottawa, ON, Canada.
D
D
Fugler
Air Health Science Division, Health Canada, Ottawa, ON, Canada.
M
M
MacNeill
Air Health Science Division, Health Canada, Ottawa, ON, Canada.|Present address: World Health Organization, European Centre for Environment and Health, Bonn, Germany.
M È
MÈ
Héroux
Department of Process Engineering and Applied Science, Dalhousie University, Halifax, NS, Canada.
M D
MD
Gibson
Community Health and Epidemiology, Faculty of Medicine, Dalhousie University, Halifax, NS, Canada.
J R
JR
Guernsey
School of Public Health, University of Alberta, Edmonton, AB, Canada.
W
W
Kindzierski
Air Health Science Division, Health Canada, Ottawa, ON, Canada.|School of Natural Sciences, Edith Cowan University, Joondalup, WA, Australia.
A J
AJ
Wheeler
D000392:Air Movements; D016902:Air Pollution, Indoor / Q000032:analysis* / Q000706:statistics & numerical data; D015982:Bias; D002170:Canada; D005466:Fluorocarbons / Q000032:analysis*; D006798:Housing; D006801:Humans; D014691:Ventilation
D005466:Fluorocarbons
Air exchange; Indoor air; Mass balance equation; Perfluorocarbon; Residential; Tracer gas