PM2.5 lives in two regimes indoors: chronic baseline (5-15 μg/m³ from infiltration, cooking residuals, accumulated dust) and acute events (wildfire smoke, cooking spikes, candles). The intervention strategy is the same shape for both: filter what is already there, prevent what you can prevent. The WHO 2021 PM2.5 24-hour guideline is 15 μg/m³; the WHO annual guideline is 5 μg/m³.
Filtration: HVAC + portable HEPA. Upgrade the HVAC filter to MERV-13 (the cheapest broad-spectrum win in most homes; ~$15-30 every 3 months). Add a portable HEPA in any high-occupancy room sized per CADR: room volume in cubic feet divided by desired air changes per hour, divided by 60, equals CADR in CFM. Most living rooms need 200-300 CADR; bedrooms 100-150. AHAM Verifide lists tested CADR values; do not trust unverified manufacturer claims.
Budget option: Corsi-Rosenthal box. A box fan and four MERV-13 furnace filters in a cube produces 600-800 CADR for ~$80 in materials. See DIY Corsi-Rosenthal. For wildfire-smoke events specifically, a CR box per occupied room outperforms most commercial units.
Source control. Exhausted range hood during all cooking, especially high-temperature frying (the biggest residential PM2.5 generator most users have). Avoid candles, incense, and oil burners. Damp-dust rather than dry-dust (dry-dusting just re-suspends what you are trying to remove). For homes with gas appliances, see reducing NO2; for outdoor-driven events, see wildfire smoke.
This is general guidance, not a substitute for professional assessment of your specific home. Major interventions (HVAC redesign, sealing a leaky envelope, mold remediation, electrical work for fans or venting) should be done with a certified professional. For chronic problems that don't respond to the steps here, see when to call a pro.
References
- WHO Global Air Quality Guidelines (2021) www.who.int
- AHAM Verifide - Directory of air cleaners ahamverifide.org
- ASHRAE - Standards and guidelines (MERV) www.ashrae.org
- EPA - Particulate matter (PM) pollution www.epa.gov
