A dusky shroud hung high over Alaska and western Canada in early August, a plume of smoke, soot and other tiny particles tainting the lower stratosphere and thick enough for satellites to detect. But the particles suspended in the Alaskan and Canadian pall, called aerosols, didn’t emanate from one of the wildfires that often strike the region’s boreal forests during the long days of summer. Instead, space-based images traced the smoke to massive blazes that erupted in late July in central Russia, more than 9,000 kilometers to the west.
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