Breathing Smoke: How Air Quality Is Monitored During Wildfires and What AQI Numbers Mean for You

As wildfires become more frequent and severe across the Pacific Northwest, air quality has emerged as one of the most immediate public health concerns of fire season. Smoke from even distant fires can blanket communities in harmful particulate matter within hours, and knowing how to interpret air quality data can be the difference between a safe day outdoors and a dangerous one.

How Air Quality Is Monitored

Air quality monitoring in the PNW is a multi-agency effort. The U.S. EPA's AirNow network anchors the system with permanent regulatory-grade monitoring stations that measure fine particulate matter (PM2.5), ozone, and other pollutants. Oregon DEQ and Washington DOE operate their own networks of monitoring stations, supplemented by lower-cost PurpleAir sensors that provide dense, near-real-time data particularly useful during fast-moving smoke events.

During active fire incidents, mobile air quality monitoring units can be deployed to areas downwind of fires that lack permanent monitoring coverage. Satellite-based smoke detection and transport modeling — including NOAA's Hazard Mapping System and the Blue Sky smoke forecast — help predict where smoke will move before ground-level impacts are confirmed.

Understanding the AQI Scale

The Air Quality Index (AQI) translates complex pollutant measurements into a single number on a 0–500 scale. For wildfire smoke, PM2.5 is the key driver. Here's what each category means:

0–50 (Green — Good): Air quality poses little or no risk. Normal outdoor activity is fine.
51–100 (Yellow — Moderate): Acceptable for most, but unusually sensitive individuals may experience minor symptoms.
101–150 (Orange — Unhealthy for Sensitive Groups): People with heart or lung disease, older adults, and children should reduce prolonged outdoor exertion.
151–200 (Red — Unhealthy): Everyone may begin to experience health effects. Sensitive groups should avoid outdoor exertion.
201–300 (Purple — Very Unhealthy): Health alert. Serious effects for the entire population. Stay indoors if possible.
301–500 (Maroon — Hazardous): Emergency conditions. The entire population is at risk of serious effects.

PM2.5: The Invisible Threat

Fine particulate matter — particles 2.5 microns or smaller in diameter — is the primary health concern in wildfire smoke. These particles are small enough to bypass the nose and throat and penetrate deep into the lungs. Long-term or high-concentration exposure is linked to heart attacks, stroke, aggravated asthma, and reduced lung development in children.

A single day of exposure at Hazardous AQI levels is roughly equivalent to smoking multiple cigarettes, according to air quality researchers. Vulnerable populations — including pregnant women, children, the elderly, and those with pre-existing respiratory or cardiovascular conditions — face the greatest risk.

How to Protect Yourself

When AQI exceeds 100, health officials recommend:

Staying indoors with windows and doors closed
Running HVAC systems with a MERV-13 or higher filter, or using HEPA air purifiers
Using N95 or KN95 masks if you must be outside (cloth masks do not filter PM2.5)
Checking AirNow.gov or your state DEQ app before outdoor activities
Having clean air shelters identified in your community

Where to Check Air Quality