Northwest Wildfires Impact Air Quality Across North America
Wildfires continue to burn across large portions of the Pacific Northwest; you can see our earlier posts about these fires throughout the previous week. Persistent drought across the west has fostered conditions that are ideal for wildfire growth. However, the impact of these fires is being felt much further to the east as the smoke gets lofted upward into the general westward circulation of the atmosphere. Take a look at the last several days of aerosol optical depth (AOD) values retrieved from VIIRS aboard NOAA-21 as displayed on NASA’s Worldview. This animation depicts nearly two weeks of fire activity in the northwest creating smoke which then advects to the east. By the time the animation ends on the 9th, the smoke is stretching all the way to New England.
The VIIRS view gives us the most spatially detailed view of the AOD. This quantity is determined by comparing calculated shortwave reflectance values to those directly observed by the satellite. Since this depends on shortwave, these values can only be determined during daytime conditions, and, of course, the observations are only available when skies are clear. With a satellite like NOAA-21 hosting the VIIRS images seen above, we can only get one view a day. A geostationary satellite, of course, has reduced spatial resolution but much better temporal resolution. Here’s an animation of the AOD as calculated by the CSPP Geo package and displayed in CSPP Geosphere from GOES-18 (Goes West) data. Here, we’ve overlaid the AOD values on top of the true color imagery, so that we can see the gaps between the clouds filled in with the aerosol observations.
Note that the highest concentrations of AOD surround some grey-ish looking clouds. If we strip the AOD off of the animation and instead just have the true color instead, it’s a little more apparent what’s actually happening there: the smoke is actually so thick that the algorithm doesn’t recognize it as smoke and instead masks out those regions as clouds instead.
Ground-based observing networks help comfirm the presence of higher-than-normal aerosol concentration across the United States and Canada. Here’s a map from PurpleAir showing the PM2.5 values as of the morning of 10 August 2026. While the highest concentrations are found in the Pacific Northwest (consistent with our satellite observations), high levels are found pretty much throughout the contiguous United States.
And, as a bonus, this blog post was constructed in part while the author was flying east out of Madison. Here’s a photograph he took while crossing the eastern shore of Lake Michigan somewhere around Muskegon. You can see the milky color of the smoke stretching out to the horizon, the otherwise clear skies over the lake, and the beginning of a lake breeze front that is limiting the development of cumulus convection close to shore while uninhibited cumuli develop further inland.
