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. [ABSTRACT FROM AUTHOR]