It has been an exceptionally smoky summer in the United States, as wildfires burning in the western United States and Canada have sent plumes of smoke over much of the continent.

For a sense of just how smoky it is, consider these two satellite-derived images of smoke cover, produced by the National Oceanic and Atmospheric Administration (NOAA). First, here’s the fire and smoke situation across North America as of March 21 this year. The red dots are the locations of wildfires, while the grayish splotches show the smoke they produce.


NOAA Hazard Mapping System Fire and Smoke, March 21. (National Oceanic and Atmospheric Administration)

There was fire activity in the Plains around this time but nothing too serious. The smoke from these fires was primarily a local issue, with little drift across large distances.

Compare the image above with the one below, which shows the fire and smoke situation this past Saturday.


NOAA Hazard Mapping System Fire and Smoke, Aug. 18. (National Oceanic and Atmospheric Administratio)

In this image, much of the continent is blanketed in a thick layer of smoke from massive fires in British Columbia, California and Ontario. The plume triggered air quality warnings from western Canada to the American Midwest, and created hazy skies as far east as Maine.

NOAA generates new images daily, so I’ve compiled the past 100 or so into a GIF going back to the beginning of May. It shows the ebb and flow of atmosphere smoke as North American wildfires ignite and die out. You can see the amount of smoke increase dramatically in the past few weeks.


Atmospheric smoke from May through August, via NOAA's Hazard Mapping System. (NOAA/Washington Post)

The agency cautions that there’s room for error in its measurements. Its analysts' “ability to detect fires and smoke can be compromised by many factors, including cloud cover, tree canopy, terrain, the size of the fire or smoke plume, the time of the day, etc.”

Public health experts treat wildfire smoke as a pollutant, similar in many ways to ozone or automobile emissions. Breathing it can be hazardous to your health, particularly for sensitive groups like children, the elderly and those with lung or heart disease.

Research has shown that even low levels of outdoor air pollution can cause notable deficits in cognitive performance and worker productivity. A 2014 study found that small particle pollution concentrations of just 20 micrograms per cubic meter — well below Environmental Protection Agency guidelines for 24-hour exposure — caused significant drops in the productivity of indoor agricultural workers, resulting in reduced pay for the workers affected.

Atmospheric smoke can cause air pollutant levels to surge well beyond those numbers. In parts of Idaho, for instance, current small particle pollutant concentrations are coming in at more than 100 micrograms per cubic meter.

So far 2018′s wildfire season has been a busy one, with a total year-to-date acreage burned well above the 10-year average. If that trend continues, expect more smoky skies heading into fall.