Background and rationale: The motivation for this research is that wildfires have been increasing in frequency and severity in recent years. Wildfire smoke is associated with numerous adverse health outcomes. Public health guidance during wildfire events has included recommendations to stay indoors, close doors and windows, and use portable air cleaners (PACs) to clean the smoke that infiltrates the indoor environment. Studies support the effectiveness of PACs in reducing indoor fine particulate matter, (PM2.5=fine particles 2.5 micrometers in diameter or smaller), one of the main components of concern in wildfire smoke.

Evidence of whether PAC use is associated with health benefits is mixed. In addition, commercially-available PACs can be expensive and hard to access. An affordable alternative that gained attention during the COVID-19 pandemic is a Do-It-Yourself (DIY) PAC, made from a box fan and high efficiency filter(s). Laboratory studies have shown DIY PACs to have excellent clean air delivery rates (CADR, a measure of effectiveness) with respect to fine particulate matter. However, their evidence in real-world settings is limited. Researchers have acknowledged that behaviors, such as turning on/off the fans, could have major impacts on efficacy.

The current study aims to examine the effect of PACs on indoor air quality and health during wildfire smoke exposure. The investigators will conduct this research in an agricultural community in central California that has experienced wildfire smoke exposure and routinely experiences dust. According to local partners, most residents of this county do not already own PACs. One risk of planning a Randomized Control Trial (RCT) of wildfire smoke exposure is that wildfire smoke will not occur. For this reason, the investigators selected a community with historically elevated levels of particle pollution (PM2.5, PM10, dust) in the fall and winter months as the study site. If wildfire smoke exposure does not occur during the study period, the efficacy of the DIY PACs on indoor air quality and health will be tested during periods of dust/high particle pollution exposure (anticipated October 2023).

Up to 120 recruited and consented study participants will be randomly divided into 2 groups. One group will use an effective DIY air cleaner (intervention); the other group will use a sham DIY air cleaner (control). All groups will have the same basic exposure to ambient air pollution.

Qualified participants will agree to have air quality sensors and door monitors placed in their home (bedroom and main exterior door). Air quality will be measured continuously during the study period. Other study activities will occur intermittently, during 5 visits by study staff to the participant's home. These activities will include completing 2 symptom and demographic questionnaires, collecting air and dust samples from inside the homes and collecting biological samples at 3 visits (capillary blood (by fingerstick) and nasal epithelial lining fluid). Blood and nasal fluid collected will be assessed for markers of inflammation and immune system activation. The investigators hypothesize that subjects in the intervention group will have reduced concentrations of measured air pollutants in their indoor air samples and lower levels of markers of inflammation compared to those in the control group. The investigators further hypothesize that symptoms, particularly related to respiratory inflammation, will differ between intervention (air filtration) and control (sham filtration) groups. Baseline measurements and post-intervention period measurements will be compared for intra-individual change and differences between study groups.