PNNL

Abstract

Increasingly large and frequent wildfires affect air quality even indoors, by emitting and 1 dispersing fine/ultrafine particulate matter known to pose health risks to residents. With this health 2 threat, we are working to help the building science community develop simplified tools that may 3 be used to estimate impacts to large numbers of homes based on high-level housing characteristics. 4 In addition to reviewing literature sources, we performed an experiment to evaluate interventions 5 to mitigate degraded indoor air quality. We instrumented one residence for one week during an 6 extreme wildfire event in the Pacific Northwest. Outdoor ambient concentrations of PM2.5 reached 7 historic levels, sustained at over 200 µg/m3 for multiple days. Outdoor and indoor PM2.5 were 8 monitored, and data regarding building characteristics, infiltration, and mechanical system operation 9 were gathered to be consistent with the type of information commonly known for residential energy 10 models. Two conditions were studied: a high-capture minimum efficiency rated value (MERV 13) 11 filter integrated into a central forced air (CFA) system, and a CFA with MERV 13 filtration operating 12 with a portable air cleaner (PAC). With intermittent CFA operation and no PAC, indoor corrected 13 concentrations of PM2.5 reached 280 µg/m3, and indoor/outdoor (I/O) ratios reached a mean of 0.55. 14 The measured I/O ratio was reduced to a mean of 0.22 when both intermittent CFA and PAC were in 15 operation. Data gathered from the test home were used in a modeling exercise to assess expected 16 I/O ratios from both interventions. The mean modeled I/O ratio for the CFA with MERV 13 filter 17 was 0.48, and 0.28 when the PAC was added. The model overpredicted the MERV 13 performance 18 and underpredicted the CFA with MERV 13 filter plus PAC, though both conditions were predicted 19 within 0.15 standard deviation. Results illustrate ways models can be used to estimate indoor PM2.5 20 concentrations in residences during extreme wildfire smoke events.