Tecnobosque

Indoor Wildfire Smoke PM2.5 Calculator

WILDFIRE SMOKE · SINGLE-ZONE MODEL

Indoor Smoke PM2.5 Calculator

Estimate how outdoor wildfire smoke, building leakage and an air cleaner can change indoor fine-particle concentration over time. The model exposes every assumption instead of hiding it behind a single score.

Dynamic concentrationCADR + infiltrationMetric or imperial
Planning model—not an indoor-air measurement.Actual concentrations depend on changing weather, openings, HVAC operation, filter loading, mixing and indoor particle sources. Use a calibrated monitor and official guidance for real decisions.

Define the room and smoke event

Room geometry

Calculated volume: 1,440 ft³ · 40.8 m³

Particle conditions
Air cleaning and time

MODELLED AFTER 4 HOURS

10.5µg/m³ indoor PM2.5
Approaching a lower steady concentration
Modelled indoor PM2.5 concentration over timeA line chart of the calculated indoor concentration.15000 h4 houtdoor
Steady-state estimate10.5 µg/m³
Reduction vs no cleaner87.7%
Cleaner contribution5.00 ACH
System time constant10.5 min
Indoor / outdoor ratio0.07
Total removal rate5.70 h⁻¹

TRANSPARENT CALCULATION

A one-zone particle mass balance.

The room is treated as perfectly mixed, while outdoor concentration and all rates remain constant for the selected period.

dCin/dt = PλCout + S/V − (λ + k + CADR/V)CinC(t) = Css + [C(0) − Css]e−Kt
P

Penetration

Fraction of particles carried through the building envelope with infiltrating air.

λ

Infiltration

Outdoor-air exchange rate in air changes per hour.

k

Deposition

First-order particle loss to surfaces and other non-cleaner removal.

CADR/V

Clean-air ACH

Air cleaner delivery rate divided by the modelled room volume.

USE THE RANGE, NOT FALSE PRECISION

The uncertain inputs matter more than the decimals.

Air infiltration and particle penetration are rarely known without measurement. Test plausible low and high values and compare scenarios. A closed room is not a sealed room, and CADR at a label’s test setting may differ from operation in the home.

Before relying on the estimate

  • Confirm the cleaner’s smoke or particle CADR—not only its fan airflow.
  • Use the actual room dimensions and operating speed.
  • Set indoor source to zero only when cooking, candles and other sources are absent.
  • Compare the result with an indoor monitor whenever possible.

Sources and limitations

The calculation is a simplified single-zone, well-mixed mass-balance model. It does not model multiple rooms, duct leakage, intermittent door opening, filter loading, resuspension, changing outdoor smoke or size-resolved particles.

EPA: Indoor Air Quality Model for Particulate Matter · EPA: Create a clean room · EPA: Guide to air cleaners · NIST: IAQ measurements and simulation

Quick answers

Is this the same as the CADR calculator?

No. The CADR calculator sizes a cleaner. This model combines a chosen CADR with infiltration and particle losses to estimate concentration over time.

Does the result say the room is safe?

No. It is a scenario estimate, not a measurement, diagnosis, exposure limit or emergency instruction.

Why can indoor PM2.5 rise with a cleaner running?

If the starting indoor level is below the modelled equilibrium, continued outdoor entry or an indoor source can raise it even while the cleaner removes particles.