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Guide

How to Choose an Air Quality Monitor for Wildfire Smoke

Smoke season turns air quality monitoring into a daily decision: windows open or closed, purifier on high or off, safe to exercise or not. The monitor that helps has a PM2.5 sensor that reads smoke honestly, ideally one indoors and one out, and a way to compare them at a glance.

By the Akermin Editorial Team · 3 min read

For wildfire smoke, choose a PM2.5 monitor with a fan-driven laser sensor and a humidity sensor for correction, ideally one unit indoors and one outdoors or a reliable public outdoor reading nearby. The point is the indoor-outdoor comparison: when outdoor PM2.5 is high, keep windows closed and run a HEPA purifier until the indoor reading is under about 15 µg/m³; when outdoor air clears, ventilate to bring CO₂ down. Expect consumer sensors to over-read smoke by a third or more; the trend and the comparison are what you act on.

Why smoke is hard for sensors

Wildfire smoke particles are small (mostly under 1 µm), hygroscopic and optically different from the dust most sensors are calibrated on. Laser sensors scatter more light per microgram from smoke than from dust and report high. Public networks apply correction factors (the US EPA correction for PurpleAir sensors during smoke roughly halves the raw value). For household decisions this does not matter much: a reading of 150 that should be 90 still means keep the windows shut. See why particle sensors disagree.

What to buy

  • Indoor monitor: laser PM2.5 with humidity correction, a display showing µg/m³, and alerts. Plug-in so it runs continuously.
  • Outdoor reading: a public sensor within a kilometer or two, or your own weatherproof outdoor unit (IQAir AirVisual Outdoor, PurpleAir and similar). Valleys and hillsides can differ from the nearest public sensor by a factor of two.
  • CO₂ as well: during a sealed-windows week CO₂ climbs; a CO₂ sensor tells you when a brief airing is worth the smoke it lets in. See CO₂ vs PM2.5.
  • Portable unit: for checking the car, the office or the school.

Reading the bands

PM2.5 (µg/m³, 24 h) US AQI Meaning during a smoke event
0 to 12 Good Ventilate freely
12 to 35 Moderate Sensitive people limit exertion outdoors
35 to 55 Unhealthy for sensitive groups Windows closed; purifier on
55 to 150 Unhealthy Everyone limits outdoor exertion; seal a clean room
150 to 250 Very unhealthy Stay indoors; purifier on high; masks (N95) outdoors
Over 250 Hazardous Avoid outdoors; consider relocating vulnerable people

See how to interpret AQI.

Making a clean room

  1. Choose one room with few windows and a closable door.
  2. Run a HEPA purifier sized for at least the room’s volume (a clean-air delivery rate that gives 4 to 5 air changes per hour).
  3. Put the monitor in the room, away from the purifier outlet.
  4. Close windows and, if possible, tape or draft-strip gaps.
  5. Watch the reading fall; it should reach under 15 µg/m³ within an hour. If it does not, the purifier is undersized or the room leaks.
  6. Open the door and windows only when the outdoor reading drops below the indoor one.

See how to use a monitor with a purifier.

Other sources during smoke season

Cooking, candles and vacuuming add to already-high particle levels; postpone them or run the hood. A box-fan filter (a MERV-13 filter taped to a box fan) is an effective emergency purifier and the monitor will show it working. Monitors suited to this are compared in best air quality monitors and the selection process in how to choose a PM2.5 monitor.

IQAir AirVisual Air Quality Monitor Bundle, Swiss-Designed Indoor & Outdoor Sensors, Professional Grade Real-Time Air Quality Tracking

IQAir AirVisual Air Quality Monitor Bundle, Swiss-Designed Indoor & Outdoor

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GoveeLife Smart Air Quality Monitor with PM2.5 H5106, LED Display Wired

GoveeLife Smart Air Quality Monitor with PM2.5 H5106, LED Display

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Airthings 2960 View Plus - Battery Powered Radon & Air Quality Monitor (PM, CO2, VOC, Humidity, Temp, Pressure)

Airthings 2960 View Plus - Battery Powered Radon & Air

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Products shown because their documented specifications fit this guide. Price and availability are on Amazon and can change.

Frequently Asked Questions

Do consumer PM2.5 sensors read wildfire smoke accurately?

They tend to read high in smoke because smoke particles are small and hygroscopic. Public networks apply a correction of roughly 0.5 to 0.7 to raw PurpleAir-type readings during smoke events. The trend and the indoor-outdoor comparison remain reliable.

Do I need an outdoor monitor?

Not if a public sensor network gives a reading near you. If the nearest is kilometers away or you are in a valley, an outdoor unit on the balcony tells you exactly when to open or close windows.

What indoor PM2.5 should I aim for during a smoke event?

Under 12 to 15 µg/m³ in the room where you spend the most time. That usually needs windows closed and a HEPA purifier sized for the room running continuously.

Affiliate disclosure: Akermin earns a commission from qualifying Amazon purchases made through links on this page. Our editorial picks are based on documented specifications and owner feedback, not commissions.