One-zone indoor particle model
Indoor PM2.5 & Air Cleaner Calculator
Estimate steady-state indoor PM2.5 for a single well-mixed room using outdoor concentration, room volume, infiltration, particle penetration, deposition, purifier CADR, and an optional continuing indoor source.
Plan indoor PM2.5 with a one-zone mass-balance model
Estimate a well-mixed room's steady-state concentration from outdoor particles, infiltration, purifier clean air, deposition, and a continuing indoor source.
Estimated steady-state indoor PM2.5
- Reduction vs. outdoors
- 90.9%
- Room volume
- 50 m³
- Purifier clean-air rate
- 5 ACH
- Total removal rate
- 5.5 /h
- Time to target
- 23.1 min
This is a one-zone planning estimate, not a measurement or medical recommendation. It assumes a well-mixed room. Defaults are 0.5 infiltration ACH, penetration factor 1, and zero deposition and indoor source; every assumption can be changed above.
How the indoor PM2.5 planning model works
- Outdoor particle inflow equals penetration factor × infiltration ACH × outdoor PM2.5; an optional indoor source is divided by room volume.
- Total particle removal equals infiltration ACH + deposition rate + purifier clean-air ACH, where purifier ACH is CADR divided by room volume.
- Steady-state PM2.5 equals total particle inflow divided by total removal rate. The estimate assumes one well-mixed zone and constant inputs.
- Target time uses exponential approach to the calculated steady state. A target at or below steady state is correctly reported as unreachable for that scenario.
Air quality tools for the decision in front of you
Start with the number or question you already have. Every tool leads to a concrete calculation, comparison, or action plan instead of another generic article.
Air purifier size calculator
Calculate smoke CADR, air changes per hour, and purifier count for a room.
PM NowCast calculator
Turn the latest 12 hourly PM2.5 or PM10 readings into an EPA-weighted NowCast and AQI.
PurpleAir EPA correction calculator
Correct a PurpleAir CF=1 PM2.5 reading for humidity, including extreme-smoke conditions.
Trust Signals
Treat the result as a planning scenario, then verify with a monitor
Review policy
August 8, 2026. We update supporting pages when calculator logic, live data behavior, or source framing changes.
Primary sources
AQI uses EPA / AirNow breakpoint logic. Cigarette-equivalent framing follows Berkeley Earth’s PM2.5 interpretation.
Live data layer
City pages use EPA AirNow where supported, with cached fallbacks and planning baselines if the API fails or coverage is unavailable.
Indoor PM2.5 model questions
What should I use for infiltration ACH?
Use a measured estimate when available. The default 0.5 ACH is only a planning assumption and can differ substantially with building tightness, doors, windows, wind, and mechanical ventilation.
Can I add multiple purifier CADR values?
For a simple one-room planning estimate, add the smoke CADR of purifiers operating together in that room.
Why can a target be unreachable?
A continuing outdoor or indoor particle source creates a nonzero steady-state concentration. The model cannot cross below that equilibrium without changing infiltration, source strength, deposition, or clean-air delivery.
Is this an indoor air measurement or medical recommendation?
No. It is a single-zone mass-balance estimate. Use an indoor monitor to verify actual conditions and follow public-health advice for health decisions.