Abstract:
Background: This study addresses critical aspects of indoor air quality management with a focus on community congregate settings through a combination of laboratory and field studies. We aimed to 1) Develop a standardized laboratory protocol for characterizing and calibrating the performance of low-cost optical particle sensors, 2) Evaluate the real-world effectiveness of portable HEPA air cleaners (HEPA PACs) in reducing indoor particle levels in community congregate settings, while assessing usage patterns and factors influencing their efficacy, and 3) Understand the impact of filter dust loading on HEPA PAC’s long-term performance concerning wood smoke particles. Methods: For Aim 1, we developed a standardized laboratory experimental protocol to assess the performance of a low-cost optical particle sensors against a lab-grade aerodynamic particle sizer in a controlled environment. This involved utilizing standardized polydisperse testing aerosols and developing improved calibration algorithms based on particle sizes, physical characteristics, number concentration, and mass indices. The sensor-to-sensor reproducibility was also evaluated. For Aim 2, we assessed the real-world effectiveness of HEPA PACs in reducing particle concentrations in community congregate living settings. We deployed multiple HEPA PACs in three homeless shelters in King County, Washington, and utilized low-cost optical particle sensors to measure indoor and outdoor optical particle number concentration (OPNC). Additionally, we tracked HEPA PAC usage with power data loggers and modeled its relationship to indoor/outdoor ratios of total OPNC. Post-hoc surveys were implemented to identify the challenges in HEPA PAC utilization. For Aim 3, we conducted a laboratory study to assess how filter dust loading affects HEPA PAC’s long-term performance. We pre-loaded HEPA PAC filter combinations of pre-filter, charcoal filter, and HEPA filter with varying amounts of ISO 12103-1 A2 fine test dust, simulating 1 to 11 months of continuous use at max fan speed in typical US homes. Fresh woodsmoke was used to test filter performance. We examined the relationship between filter loading and airflow rate, pressure drop, power consumption, and clean air delivery rate (CADR).
Results: Results revealed discrepancies in particle size distribution between low-cost particle sensor original equipment manufacturer’s (OEM) calibration and reference aerodynamic particle sizer measurements. Calibration models demonstrated improved accuracies for number and mass concentrations, with limitations at lower concentrations and larger size bins. Additionally, evidence was found of HEPA PACs effectively reducing indoor particle concentrations, with usage patterns significantly influencing efficacy. Keeping HEPA PACs on was the main challenge to operate them in multi-zone congregate living settings. Laboratory investigations supported the use of HEPA PACs under max fan speed for up to 7 months without a significant decrease in CADR in typical US residential environment.
Conclusion: This study advances indoor air quality management through laboratory experimentations and field evaluations. Our findings refine low-cost optical particle sensor calibration, underscore the efficacy of HEPA portable air cleaners (PACs) in community settings, and highlight the importance of filter maintenance for sustained performance. Through evidence-based findings, this research contributes to ongoing efforts to improve public health outcomes and indoor air quality.