In 2021, western Washington experienced a relatively mild wildfire smoke season with only a few summer days with smoke impacts at most monitoring sites. Only three Puget Sound communities recorded a 98th percentile PM_2.5 concentration over Washington's healthy air goal of 20 μg/m³: Darrington, Marysville, and South Tacoma. Exceedances of Washington's health air goal were primarily observed during brief episodes of cold and stagnant weather in the winter months. During such conditions, residential wood combustion is a leading source of PM_2.5 in these communities. 

In 2020, greater than 99% of the Puget Sound population was exposed to impaired air quality. An extensive and severe wildfire smoke episode in late summer caused unhealthy air quality across the state, with many areas reaching the very unhealthy and hazardous ranges of PM_2.5 for several days. All but one monitoring site in the Puget Sound watershed (Neah Bay) recorded 98th percentile PM_2.5 concentrations above Washington's healthy air goal of 20 μg/m³. During this smoke event, many monitoring sites set records for their highest concentrations ever recorded. Outside of the wildfire season, PM_2.5 concentrations were relatively low.

After two consecutive years of prolonged wildfire smoke impacts in 2017 and 2018, calendar year 2019 was marked by a mild wildfire season with very few smoke-impacted days. The exceedances of Washington's healthy air goal of 20 μg/m³ were primarily observed during brief episodes of cold and stagnant weather in the winter months. These episodes occurred with moderate frequency relative to other years. Residential wood combustion is a dominant source of PM_2.5 during cold, stagnant weather.