The eastern United States is covered by a thick haze from the Chinchaga fire in western Canada.

The Chinchaga fire, also known as the Wisp fire, Chinchaga River fire and Fire 19, was a forest fire that burned in northern British Columbia and Alberta in the summer and early fall of 1950. With a final size of between 1,400,000 and 1,700,000 hectares, it is the single largest recorded fire in North American history. The authorities allowed the fire to burn freely, following local forest management policy considering the lack of settlements in the region. The Chinchaga fire produced large amounts of smoke, creating the "1950 Great Smoke Pall", observed across eastern North America and Europe. As the existence of the massive fire was not well-publicized, and the smoke was mostly in the upper atmosphere and could not be smelled, there was much speculation about the atmospheric haze and its provenance. The Chinchaga firestorm's "historic smoke pall" caused "observations of blue suns and moons in the United States and Europe". It was the biggest firestorm documented in North America, and created the world's largest smoke layer in the atmosphere.