Air Quality

The Washington Department of Ecology records air quality at monitoring stations in Winthrop and Twisp. The data in the chart below shows the number of days per year (24-hour average) of a given Air Quality Index (AQI) category. Of the 245 records of air quality in the “Unhealthy for Sensitive Groups” or worse, all but six of these recordings were from July, August and September, during periods of wildfire.

Number of Days with Unhealthy Air Quality, 2005-2025

Data compilation and analysis by Julie Grialou. Graphics and photography by Benjamin Drummond.
Last updated April 2026.