Quantitative filter forensics: Size distribution and particulate matter concentrations in residential buildings

Area of Science:

• Environmental Science
• Indoor Air Quality
• Particle Science

Background:

• Heating, Ventilation, and Air-Conditioning (HVAC) systems circulate indoor air, influencing particle exposure.
• Understanding particle size distribution and concentration is crucial for indoor air quality assessment.
• Filter forensics offers a novel approach to characterizing airborne particles within residential environments.

Purpose of the Study:

• To measure particle size distribution and total suspended particle (TSP) concentrations in residential indoor air using filter forensics.
• To evaluate the relationship between filter characteristics, HVAC system operation, and quantitative filter forensics (QFF) concentration estimates.
• To assess the utility of filter forensics for indoor air quality monitoring, particularly for smaller particles.

Main Methods:

• Deployment of four filters (MERV 8-14) in 21 Toronto residences over one year.
• Characterization of effective filtration volumes based on flow rate, runtime, and in-situ filter efficiency.
• Particle extraction from filters, laser diffraction for size distribution analysis, and quantitative filter forensics (QFF) for concentration estimation.

Main Results:

• Approximately 90% of particle volumetric distributions were greater than 10 µm, with Volume Median Diameters (VMD) ranging from 23.4 to 75.1 µm.
• Total suspended particle (TSP) concentrations varied widely (2.9–823.7 µg/m³), showing moderate correlation with filter loading and effective filtration volume.
• No strong correlation was found between PM10/PM2.5 concentrations and low-cost sensor data, suggesting limitations in current low-cost sensor evaluations.

Conclusions:

• Filter forensics is a viable method for assessing particle size distribution and TSP concentrations in homes.
• Integrating filter forensics with HVAC metadata provides more accurate QFF concentration estimates.
• Further research into QFF is recommended for evaluating smaller airborne particles and improving indoor air quality monitoring.