Wildfire Smoke and Air Quality: A Pacific Northwest Guide for September and Beyond

After weeks of dense smoke that blanketed communities from the Cascades to the Snake River Plain, air quality across much of the Pacific Northwest has shown improvement heading into mid-September — but fire managers and health officials warn that the smoke season is far from over.

Where Things Stand Now

Conditions have varied significantly by location in recent days. Seattle reported an Air Quality Index (AQI) reading of 25 — squarely in the "Good" category — in the first week of September, benefiting from westerly flow that pushed smoke east of the Cascades. However, communities closer to active fires in eastern Oregon, eastern Washington, and Idaho have continued to experience periods of unhealthy air quality.

In early September, multiple fires ignited west of Salem, Oregon, generating localized light to medium density smoke over the Willamette Valley. A large smoke plume was also observed spreading across west-central Idaho from fires that ignited near that time, according to the National Weather Service smoke observation network.

Understanding the AQI Scale

The Air Quality Index is the standard measure for communicating daily air quality to the public. During wildfire smoke events, the key pollutant is PM2.5 — fine particulate matter smaller than 2.5 microns that can penetrate deep into the lungs and bloodstream.

0-50 (Good): No health concerns
51-100 (Moderate): Sensitive groups should limit prolonged outdoor exertion
101-150 (Unhealthy for Sensitive Groups): People with heart or lung disease, the elderly, and children should reduce prolonged outdoor activity
151-200 (Unhealthy): Everyone should reduce prolonged or heavy outdoor exertion
201-300 (Very Unhealthy): Avoid outdoor activity if possible
301+ (Hazardous): Remain indoors with windows and doors closed

When Smoke Is Present: Protective Actions

Health departments across Oregon, Washington, and Idaho recommend the following during smoke events:

Keep windows and doors closed and use HVAC systems set to recirculate indoor air
Use a portable air cleaner with a HEPA filter in the room where you spend the most time
If you must go outside, wear a properly fitted N95 or P100 respirator — cloth masks and surgical masks do not filter PM2.5 effectively
Avoid vigorous outdoor exercise when AQI exceeds 100
Check on neighbors, the elderly, and anyone with respiratory conditions
Keep pets indoors during heavy smoke events

Ongoing Smoke Threat Through Fall

With 58 large fires still active nationally and fire danger forecast to remain elevated across the Pacific Northwest through December, health officials caution that smoke events are likely to recur. The pattern of brief wet spells followed by rapid return to dry conditions — cited in the NIFC seasonal outlook — means that new ignitions and associated smoke remain a real possibility well into autumn.

Oregonians, Washingtonians, and Idahoans with chronic respiratory conditions such as asthma, COPD, or heart disease should work with their healthcare providers now to have action plans in place for the next smoke event.

Monitoring Resources