The goal of this clinical trial is to compare indoor air quality and health in people exposed to air pollution, including possible exposure to wildfire smoke. The study will test the effect of using a do-it-yourself (DIY) air cleaner when air pollution is present to answer the following questions:

• Do health outcomes differ between participants who use a DIY PAC and those who use a sham air cleaner?
• How effective is the DIY air cleaner in reducing indoor concentrations of fine particles (PM2.5), and volatile organic compounds found in wildfire smoke? OR How effective is the DIY air cleaner in reducing indoor concentrations of fine and coarse particles (i.e., PM 10)?
• What are barriers to use of a DIY air cleaner and what factors facilitate its use?

Participants will be asked to do the following:

• Participate in 5 home visits from study staff between July - October 2023
• Have an air quality sensor placed in the participant's bedroom for the whole study period
• Have a small sensor attached to the main door of the participant's house to record when the door is open or closed (important for air quality inside)
• Allow researchers to take air and dust samples in the participant's bedroom
• Run a DIY air cleaner in the participant's bedroom for at least 6 nights while the participant sleeps
• Complete 2 interviews
• Allow study staff to collect 3 fingerstick blood samples
• Allow study staff to collect 3 samples of fluid from inside the nose
• Use the study air cleaner in the participant's bedroom during the study period

The investigators will measure air quality in participating homes and measure health outcomes for participants. The investigators will compare outcomes of participants who use a DIY air cleaner with filters that work well to those of participants who use a DIY air cleaner with a placebo filter (one that does not work well to remove the air pollutants of concern). The goal of the study is to see if using the effective air cleaner leads to better health outcomes and indoor air quality.

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.

Inclusion Criteria:

• Age 18 years or older
• Has access to telephone and/or the internet for study communication
• Is a resident of Tulare County, California
• Is proficient in English or Spanish for study communication

Exclusion Criteria:

• Anyone in the household smokes (tobacco, vape, or other) inside the home
• Plans to move before November 2023
• Regularly travels or sleeps away from home (e.g., once a week or more)
• Already owns and uses a portable air cleaner
• Lives in a multi-unit home with a shared central HVAC system
• Has a bleeding disorder, such as hemophilia (taking a blood thinning medication does not exclude)
• Takes any of the following anti-inflammatory medications regularly: abatacept (Orencia), adalimumab(Humira), anakinra (Kineret), anifrolumab (Saphnelo), apremilast (Otezla), azathioprine (Imuran),certolizumab pegol (Cimzia), etanercept (Enbrel), golimumab (Simponi Aria), hydroxychloroquine(Plaquenil), infliximab (Remicade), ixekizumab (Taltz), leflunomide (Arava), methotrexate(Rheumatrex, Trexall), prednisone (Deltasone), sulfasalazine (Azulfidine), rituximab (Rituxan,MabThera), sarilumab (Kevzara), tocilizumab (Actemra)

The control air filtration device will have a filter that looks like the intervention filter but is much less effective. A cover "shroud" will be placed over the air filtration device so that differences in components will not be noticeable to participants.