Dense Smoke from Wildland Fires in Ontario

A rash of large wildland fires raged in western Ontario in mid-July 2026, sending thick smoke plumes streaming across several Canadian provinces and more than a dozen American states from the Great Lakes region to the Mid-Atlantic Coast. Tens of millions of people were advised to stay indoors, as air quality in several major population centers ranked among the worst in the world for July 15-16. In some places, smoke was lingering near the ground because of a heat dome that moved east and was causing extreme high temperatures across the Midwest and Northeast.

The Visible Infrared Imaging Radiometer Suite (VIIRS) instrument on the NOAA-20 platform acquired corrected reflectance imagery of the long and widespread smoke plumes on July 16, 2026. Red dots indicate thermal anomalies detected by VIIRS; these typically indicated the presence of active or recently burning fires.

In this wider view from NOAA-20 VIIRS—which includes seams from the edges of several orbital swaths—we see tan, aerosol laden clouds stretching well out into the North Atlantic. On the upper left, partly covered by the Worldview dashboard, we can also see the wildfire in Canada's Northwest Territories, including blazes near Great Bear Lake that are still sending plumes across northern territories and provinces.

The third image shows a level 3 ultraviolet aerosol index, a provisional product from the NASA-funded Tropospheric Emissions: Monitoring of Pollution (TEMPO) instrument. The data indicate the level to which particles in the air (aerosols) reflect and prevent sunlight from traveling through the atmosphere. At ground level, such dense aerosol concentrations are harmful to human health, especially for people with lung conditions.

Aerosols scatter and absorb incoming sunlight, reducing visibility. For an observer on the ground, an aerosol index of less than 0.1 is “clean” air characteristic of clear blue skies, bright sun, and maximum visibility. At an aerosol index level greater than 4.0—which is the case in much of this scene—aerosols have become so dense that the Sun is obscured.

This image pair compares the aerosol index from the July 2026 wildfire smoke event with a wildfire smoke event that blanketed eastern states and provinces in June 2023. These data (OMPS_NPP_NMMIEAI_L2) come from the Ozone Mapping and Profiler Suite (OMPS) on the Suomi National Polar orbiting Partnership (Suomi NPP) satellite. Researchers from NASA's Langley Research Center provided a research summary of the 2023 event.

For updates and the latest alerts on fire-related air quality in the U.S., visit AirNow, a partnership of the U.S. Environmental Protection Agency, the National Oceanic and Atmospheric Administration (NOAA), the National Park Service, the Centers for Disease Control, NASA, and tribal, state, and local air quality agencies.