AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Direct Measurements of Particle Decay Rates for Fine and Ultrafine Particles in 74 Residences in Edmonton, Canada
LANCE WALLACE, Jill Kearney, Morgan MacNeill, Warren Kindzierski, Marie-Eve Heroux, Amanda Wheeler, US EPA (retired)
Abstract Number: 149 Working Group: Indoor Aerosols
Abstract Particle deposition rates are a fundamental determinant of indoor particle concentrations. However, these rates are not well known due in part to the difficulty of untangling the concurrent effects of infiltration, exfiltration, filtration by furnace fans and portable or in-duct air cleaners, and (for ultrafine particles (UFP) in particular) coagulation. Previous studies in multiple homes generally have been unable to determine deposition rates for individual homes, and have only provided an average rate for all homes in the study. In this large-scale study in Edmonton, Canada, a new method of separating indoor-generated from outdoor-infiltrated particles was developed.
Indoor and outdoor fine particles (FP) and UFP were measured for 7 consecutive days in both summer and winter in 50 residences per season. Continuous 1-minute average measurements were made by DustTraks (Model 8520, TSI, Inc., Shoreview, MN) equipped with 2.5 micrometer inlets and P-Traks (TSI, Model 8525). Air exchange rates were determined using the perfluorotracer (PFT) method. A censoring algorithm was developed to identify and remove peaks due to indoor sources. The remaining indoor concentrations were assumed to be due to infiltration of outdoor particles. The daily average infiltration factor could thus be determined. The product of this factor with the outdoor concentration provided the time-resolved estimate of the background concentration to which the indoor concentration was trending. For “well-behaved” (R$^2>90%) indoor peaks, background-corrected decay rates could be determined. Subtraction of the air exchange rates provided an estimate of the deposition rates. About 400 (300) decay rates for UFP (FP) were determined in 60 (58) homes. On average, deposition and filtration accounted for about 75% of the total decay rates, the remainder being due to air exchange. These decay and deposition rate estimates for individual homes will allow a better estimate of distributions of rates across homes for modeling total indoor exposures.