Abstract View
Characterizing Infiltration and Indoor Contribution of PM2.5 Based on Volunteer-generated Monitoring Data at Large Spatial and Temporal Scales
JIANZHAO BI, Lance Wallace, Jeremy A. Sarnat, Yang Liu, Emory University
Abstract Number: 594
Working Group: Aerosol Exposure
Abstract
Personal PM2.5 exposure may deviate from ambient levels due to differential infiltration and contribution of indoor sources. It is important to quantify infiltration factors (Finf) and the contribution of indoor sources. Research in this area has been historically limited in space and time due to the high labor and capital costs of deploying and maintaining collocated indoor/outdoor monitors. Recently, the growth of volunteer-generated PM2.5 data provides an unprecedented opportunity to characterize Finf and indoor contribution at large spatial and temporal scales. In this study, 94 volunteer-maintained PurpleAir indoor/outdoor PM2.5 monitor pairs with ~1.1 million hourly measurements were identified within 500 m from each other during a 20-month period (November 2018 to June 2020) in California. A data-driven method was developed based on local polynomial regression to estimate site-specific Finf with an assumption that indoor sources were negligible when outdoor levels were sufficiently high (the highest 20 outdoor measurements for each site). The estimated Finf had a mean of 0.25 (25th, 75th percentiles = [0.13, 0.32]) with a mean standard error of 0.05, the scale of which generally agreed with those reported in previous studies. A seasonal analysis (dry and wet seasons) showed no significant difference in Finf across seasons probably because the seasonal changes were mild in California. The Finf estimates were also similar for different building types (homes or buildings). By applying the Finf estimates, we found the indoor-generated PM2.5 contributed an average of 50% (25th, 75th percentiles = [35%, 65%]) of the total indoor levels. We further identified outdoor level thresholds for individual sites above which the indoor sources were not substantial for personal exposure assessment. This is the first time the indoor contribution for multiple sites monitored over thousands of hours were characterized at a large spatial scale.