Extraction of dust collected in HVAC filters for quantitative filter forensics
The analysis of dust collected on the filters installed in the heating, ventilation, and air-conditioning (HVAC) systems, filter forensics, is a useful approach to explore concentration, size distribution, and composition of indoor particles. The extraction of dust from filters represents one of the biggest challenges to obtain accurate results from filter forensics. Although vacuuming is one of the most common dust extraction techniques, it is unclear how efficient it is and whether it provides a representative sample in terms of particle size. In this article, we used a high-capacity vacuum sampler to extract dust from 20 filters artificially loaded with well-characterized test dust as well as from 41 filters naturally loaded in residential HVAC systems. After all extractions, we recovered 0.1–5.5 g and 0.02–11.4 g of dust from the artificially and naturally loaded filters, respectively. These ranges were equivalent to 11.3–52.2% and 1.8–72.9% recovery efficiency, the ratio of dust recovered to the dust loaded in the filters. Multiple extractions were found to be an effective strategy to add to the recovery to enable filter forensics for the detection of multiple analytes. The recovered samples were slightly over-representative of particles greater than 10 µm. Therefore, caution should be taken when applying filter forensics for studying contaminants associated with smaller particles.
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