Using a Particle Sensor Network to Characterize Indoor and Outdoor Air Quality of Buildings in Areas Prone to Wildfires
Presented by: Heidi Vreeland, US EPA Office of Research and Development
Summary: When wildfire events increase outdoor particulate matter concentrations to unsafe levels, a common recommendation for mitigating smoke exposure is to spend time indoors. However, effectively reducing smoke exposure and maintaining clean air indoors depends on a variety of building characteristics and occupant behavioral factors. To gain insights into the indoor/outdoor relationships of PM2.5 across buildings, this study utilizes low-cost sensors (PurpleAir PA-II-SD) to characterize indoor and outdoor PM2.5 at public and commercial buildings in two locations impacted by wildfire events in recent years: Missoula, Montana and Hoopa, California. Sensors were stationed inside and outside of 18 buildings across Missoula during summer 2019 (July–Sept) to coincide with peak fire season, and 11 buildings across Hoopa during winter (Nov 2019 – Feb 2020) when woodstove heating dominates outdoor emissions. Prior to evaluating indoor reductions, criteria were developed to identify indoor-generated sources. Preliminary results suggest that indoor reductions ranged from 6% to 44% (26±11%) in Missoula, and 19% to 69% (51±16%) in Hoopa. The smaller reductions in Missoula are largely attributed to frequent door openings for ventilation during summer. In Missoula, indoor reductions were similar during smoke-impacted and typical (non-smoke) periods indicating that measurements taken outside of fire season are informative and may be useful for improving smoke preparedness. Although the only smoke events that occurred in Missoula during summer 2019 were moderate and associated with prescribed burns, this work provides valuable insights into the variance among indoor/outdoor PM2.5. This work also demonstrates the utility of low-cost sensor networks for residents and public health agencies to better understand where clean indoor spaces exist and, potentially, to offer guidance on reducing indoor concentrations before smoke events occur.