Abstract

Increased wildland fire activity is producing extreme fine particulate matter (PM2.5) concentrations impacting millions of people every year, especially in the western United States (US). Recommendations for limiting exposure to PM2.5 and associated adverse health outcomes focus on staying inside, closing windows and doors, and increasing filtration; however, relatively little is known about indoor air quality (IAQ) during major smoke events. Indoor and outdoor hourly PM2.5 (µg m–3) measurements from the publicly available PurpleAir sensor (PAS) network were analyzed for 42 sites (26 residential, 6 school, 10 commercial) across the western US during a September 2020 period of heavy wildfire smoke influence. The fraction of ambient PM2.5 that penetrates indoors and remains airborne (Fin), as well as the ratio (I/O) and correlation coefficient (R2) of indoor to outdoor PM2.5 concentrations, were lower in residential compared to commercial and school buildings. Interventions to improve IAQ were highly influential in PM2.5 infiltration in residential case studies, with multiple, continuously run filter units associated with lower Fin, I/O, and R2. A low-cost PM2.5 filtration method consisting of a Minimum Efficiency Rating Value-13 (MERV-13) filter attached to a box fan is evaluated as an alternative for improving IAQ during wildland fire smoke events. The MERV-13 fan filter unit proved highly effective at reducing indoor PM2.5 and particles 0.3–1.0 µm measured by PAS and a particle counter, respectively, when recirculating air in a single room. Low-cost filtration methods can have significant benefit for filtering submicron smoke particles and may reduce exposure to PM2.5 during wildfire smoke events.

Highlights

  • Publisher: Taiwan Association for Aerosol Research ISSN: 1680-8584 print ISSN: 2071-1409 onlineCopyright: The Author(s)

  • Corrected (Eq (2)) hourly average concentrations of indoor and outdoor PM2.5 measured by PurpleAir sensor (PAS), at 42 western United States (US) locations were used to evaluate PM2.5 infiltration by building type

  • The low median Fin (0.21) in residential buildings was more similar to median Fin of summer homes with high-efficiency particulate air (HEPA) filtration (0.19) than without (0.61) (Barn et al, 2008)

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Summary

Introduction

Publisher: Taiwan Association for Aerosol Research ISSN: 1680-8584 print ISSN: 2071-1409 onlineCopyright: The Author(s). The area burned by wildland fires in the United States (US) increased substantially over the past two decades (Jaffe et al, 2020), exceeding 3 million hectares burned in 6 of the past 10 years (National Interagency Fire Center, 2020). This is part of a larger US trend of increasing frequency and area burned, as well as fire season length, since the 1980s (Abatzoglou and Williams, 2016; Westerling, 2016). Health impacts from exposure to smoke include cardiovascular and respiratory mortality and morbidity, adverse reproductive, developmental, and neurodegenerative diseases, as well as eye irritation, wheezing, and coughing (Reid et al, 2016; Thurston et al, 2017; Cascio, 2018).

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