Input
Sources
Outdoor
HVAC
Action
Step 1
Enter indoor PM₂.₅ concentration
Use a sensor reading from inside the room or building
µg/m³
EPA standard: 10 µg/m³ (24-hr average)
✓
PM₂.₅ within guideline
Indoor PM₂.₅ of µg/m³ is at or below the 10 µg/m³ EPA standard. No action required at this time.
Step 3
Are there identifiable indoor PM₂.₅ sources?
Check for active sources of particulates
Common indoor sources: cooking, candles, incense, tobacco smoke, cleaning products, printers, fireplaces, dusty activities (vacuuming, construction), or pets.
Step 4
Remove or eliminate the indoor source
Take action, then recheck PM₂.₅ after 15–30 minutes
Actions: extinguish candles / incense, stop cooking, move the activity outdoors, improve local exhaust ventilation, or wait for levels to settle before rechecking.
µg/m³
Step 5
Check outdoor Air Quality Index (AQI)
Look up your local AQI to decide on ventilation strategy
Check the current outdoor AQI at AirNow.gov, then enter the AQI value below.
AQI guide: 0–50 = Good · 51–100 = Moderate · 101–150 = Unhealthy for Sensitive Groups · 151+ = Unhealthy
AQI guide: 0–50 = Good · 51–100 = Moderate · 101–150 = Unhealthy for Sensitive Groups · 151+ = Unhealthy
Indoor PM₂.₅
—µg/m³
Outdoor AQI
AQI
Step 7
Open windows — increase natural ventilation
Outdoor air is cleaner; ventilate the space
Outdoor AQI is (≤ 50 — Good), while indoor PM₂.₅ is µg/m³. Opening windows will dilute indoor particulates.
Recheck after 30–60 minutes. If levels remain elevated, consider running an air purifier as well.
Recheck after 30–60 minutes. If levels remain elevated, consider running an air purifier as well.
Recommended action
Open windows and doors on multiple sides of the building to create cross-ventilation. Run bathroom/kitchen exhaust fans if available.
Step 6
Is the HVAC system currently operating?
Outdoor air is worse — keep building closed; use HVAC
Outdoor AQI () is above 50. Do not open windows. Rely on the HVAC system to filter recirculated air.
Step 9
Turn on the HVAC system
Allow 1 hour for recirculation, then recheck
Switch on the HVAC in recirculation / indoor air mode (not fresh air intake) to avoid drawing in outdoor pollutants. Ensure all windows remain closed.
µg/m³
Step 8
Check the HVAC filter condition
A clogged filter reduces PM₂.₅ capture efficiency significantly
Inspect the filter for visible grey/brown discolouration, blockage, or deformation. Filters should typically be replaced every 1–3 months depending on usage and air quality.
Step 11
Replace the HVAC filter
Use MERV-13 or higher rated filter where possible
Install a new filter, then run the HVAC for at least 1 hour before rechecking. MERV-13 filters capture ≥90% of PM₂.₅-range particles.
µg/m³
Step 10
Deploy additional air purifier(s)
Supplement HVAC with portable HEPA filtration
⚡
Air purifier recommended
Place a HEPA air purifier in the most-occupied area. Size it for the room volume (check CADR rating). Run on medium-high speed until PM₂.₅ drops below 10 µg/m³.
If levels remain persistently high despite HVAC + purifier, investigate structural infiltration pathways or consult an indoor air quality specialist.
If levels remain persistently high despite HVAC + purifier, investigate structural infiltration pathways or consult an indoor air quality specialist.
Assessment trail