Raging wildfires in western Canada have sent huge plumes of smoke spreading across North America in recent days, with pollution captured in images by NASA satellites, aircraft, and ground-based observatories.

An animation released by NASA on Friday showed smoke blanketing the Canadian provinces of British Columbia, Alberta, Saskatchewan, Manitoba, and the Northwest Territories and drifting into other parts of the Midwest, including Montana, Colorado, Kansas, and Wisconsin.

This map uses data from NASA to show the concentration and movement of black carbon, a type of aerosol pollution released by wildfires, over North America from July 17 to July 24.

As of Friday afternoon, there were 948 fires burning in Canada, with 387 of them considered out of control. Canadian Joint Forest Fire Centre The fast-spreading fire caused widespread damage in the popular alpine resort city of Jasper in Alberta and forced the evacuation of 25,000 people.

Massive fires in the Pacific Northwest and California are also polluting the air nearby. Air quality alerts and watches have been issued in Washington, Oregon, Idaho, Colorado, and Wyoming over the past week. Smoky skies have also been reported in North Dakota, South Dakota, and across the High Plains.

Oregon is experiencing the largest wildfire season in the US, fueled by lightning, high temperatures, and strong winds, with more than 35 out-of-control wildfires burning a combined total of nearly 1 million acres in the state.

In neighboring Idaho, fast-spreading fires forced the evacuation of the entire town of Juliaetta on Thursday, with more than 600 residents evacuated as the Gwen Fire and other wildfires burning in the area continued to grow.

Cities in Oregon, Montana, California, and Idaho topped the list of places with the worst air quality in the country on Friday. According to IQAir: For example, air pollution levels in Burns, Oregon, were listed as “hazardous,” while air quality in Stevensville, Montana, was listed as “very unhealthy,” according to a Swiss air quality monitoring company.

In California, the Park Fire has already burned more than 250 square miles in the Chico area since starting on Wednesday and remained uncontained as of Friday morning.

Firefighters are also battling the lightning-fought Gold Complex Fire in California’s Plumas National Forest, which has burned more than five square miles since July 22. As of Friday afternoon, the fire was only 11 percent contained, and winds are causing the blaze to spread quickly. According to the California Fire Department.

Smoke from wildfires that have spread eastward to New England and south to Mexico is having a variety of effects on human health.

In addition to black carbon, wildfires release carbon dioxide, carbon monoxide, a variety of chemicals, and tiny particles called particulate matter into the air. Together, these substances can irritate the eyes, nose, throat, and lungs and worsen the conditions of diabetes, heart disease, COPD, and chronic kidney disease.

Young children, older adults, pregnant women, and people with asthma or other existing respiratory conditions are at greatest risk from wildfire smoke.

Thunderstorms have played a role in igniting many wildfires in Canada and the western United States, with gusty winds, high temperatures, and more thunderstorms fanning the flames.

Summer wildfires are common in western Canada and the United States, but scientists say climate change is making them more dangerous by creating more favorable conditions for fires to start and spread. Rising temperatures also drier vegetation, making it more flammable.