Air Quality Assessment

Indoor PM_2.5 Decision Tool

Step-by-step guidance to diagnose and resolve elevated indoor particulate matter

Input

Sources

Outdoor

HVAC

Action

Step 1

Enter indoor PM₂.₅ concentration

Use a sensor reading from inside the room or building

Current indoor PM₂.₅ reading

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.

Recheck indoor PM₂.₅ after removing source

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

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.

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.

PM₂.₅ after 1 hour with HVAC running

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.

PM₂.₅ after replacing filter and running HVAC

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.

Assessment trail

EPA PM₂.₅ standard: 10 µg/m³ (24-hr) · This tool provides decision support, not clinical advice