Wildfire Smoke Impacts on Indoor Air Quality Assessed Using Crowdsourced Data in California

Abstract

<p>Wildfires have become the dominant source of particulate matter (PM<sub>2.5</sub>, < 2.5 µm diameter) leading to unhealthy air quality index occurrences in the western United States. Since people mainly shelter indoors during wildfire smoke events, the infiltration of wildfire PM<sub>2.5 </sub>into indoor environments is a key determinant of human exposure, and is potentially controllable with appropriate awareness, infrastructure investment, and public education. Using time-resolved observations outside and inside over 1400 buildings from the crowdsourced PurpleAir sensor network in California, we found that infiltration ratios (indoor PM­<sub>2.5 </sub>of outdoor origin/outdoor PM<sub>2.5</sub>) were reduced on average from 0.4 during non-fire days to 0.2 during wildfire days. Even with reduced infiltration, mean indoor concentration of PM<sub>2.5 </sub>nearly tripled during wildfire events, with lower infiltration in newer buildings and those utilizing air conditioning or filtration. </p>

Outdoor and indoor fine particulate matter at skilled nursing facilities in the western United States during wildfire and non‐wildfire seasons

“…7 Another study used publicly available data from the PurpleAir sensor network to measure PM 2.5 infiltration among 1400 buildings in California. 39 In contrast with our results, the authors found that particle infiltration to the indoor environment decreased during wildfire events compared with days not impacted by wildfires. However, even with reduced particle infiltration, mean indoor PM 2.5 concentrations were still nearly three times higher on wildfire days than on non-wildfire days.…”

“…Reisen et al measured indoor and outdoor air quality for 1 week at 21 residences and found that age and ventilation due to penetration points played a significant role in the infiltration of ambient PM 7 . Another study used publicly available data from the PurpleAir sensor network to measure PM 2.5 infiltration among 1400 buildings in California 39 . In contrast with our results, the authors found that particle infiltration to the indoor environment decreased during wildfire events compared with days not impacted by wildfires.…”

“…Zhou et al used 21 µg/m 3 as a threshold for a wildfire day based on PM 2.5 concentrations that correspond to heavy smoke according to the National Oceanic and Atmospheric Administration's Hazard Mapping System 31 . Others have used the US EPA’s 24‐hour ambient PM 2.5 standard (35 µg/m 3 ) to classify a wildfire day, 39 or data‐driven approaches (98 th percentile of daily PM 2.5 concentration across western US counties) to classify a wildfire smoke wave 45 . Future work would benefit from a standardized method of classifying wildfire‐impacted days that can incorporate area‐specific information such as background (historical) PM 2.5 concentrations that help account for the widely varying geographic and land‐use characteristics of wildfire‐impacted areas.…”

“…31 Others have used the US EPA's 24-hour ambient PM 2.5 standard (35 µg/ m 3 ) to classify a wildfire day,39 or data-driven approaches (98 th percentile of daily PM 2.5 concentration across western US counties) to classify a wildfire smoke wave 45. Future work would benefit from a standardized method of classifying wildfire-impacted days that can incorporate area-specific information such as background (historical) PM 2.5 concentrations that help account for the widely varying TA B L E 4…”

Field measurements of indoor and community air quality in rural Beijing before, during, and after the COVID ‐19 lockdown

“…One approach to estimating infiltration of PM 2.5 of outdoor origin $$$ {F}_{inf} $$$ is to apply a physical model, which is based on several known quantities: air change rate, penetration coefficient of outdoor PM 2.5 , and deposition rate of indoor PM 2.5 . This approach has been widely used in the literature 24‐27 . However, these parameters are difficult to obtain for a large number of different households and communities in a large‐scale study like ours.…”