Assessing the effectiveness of HEPA filters at reducing PM2.5 levels in residential settings in Los Angeles, California

Abstract

This thesis assesses indoor fine particulate matter (PM2.5) levels in homes in Los Angeles County, California and identifies variables that might impact the effectiveness of High-Efficiency Particulate Air (HEPA) filters in reducing PM2.5 levels in residential settings. While research has confirmed that HEPA filters effectively reduce PM in controlled environments, additional research is needed to understand how well HEPA filters work in residential and commercial settings. For this study, twelve homes in Los Angeles County had either HEPA filters (n=6) or sham filters installed in their bedrooms and living rooms for six months. All twelve homes had indoor and outdoor air pollution sensors installed to monitor and report hourly PM2.5 levels. Results showed varying degrees of HEPA filter effectiveness in each home. One home experienced a reduction in the geometric mean PM2.5 from 6.99 (2.13) µg/m3 during the pre-filter period to 3.2 (2.2) µg/m3 during the filter period; four homes experienced reductions between 0.51 and 1.33 µg/m3; one home experienced a 0.09 µg/m3 increase. In homes with sham filters, all experienced increases in PM2.5 between 0.22 and 1.76 µg/m3. I identified temporal patterns in indoor and outdoor PM2.5 levels and investigated whether housing characteristics and behavior patterns influence the concentration of PM2.5 and the indoor/outdoor (I/O) ratio of particles. A relationship is seen between dramatic spikes in outdoor pollution during events such as the 4the of July and indoor PM2.5 levels. While this is a small study, results from this can be used to inform future study design and best practices for HEPA filter use.