Arctic haze: From Russia, with soot: smoke from forest fires, agricultural burning blankets north.

Data gathered by aircraft flying over northern Alaska and the Arctic Ocean in April 2008 hint that much of the haze that blankets the region in spring, long thought to be associated with industrial emissions, in fact results from forest fires and agricultural burning in Asia.

The distinct layers of dirty air, often dubbed arctic haze, have been regularly observed at high latitudes of the Northern Hemisphere since the 1950s. But the sources of these plumes have never been well identified, says Charles A. Brock of NOAA's Earth System Research Laboratory in Boulder, Colo.

Many scientists have presumed that the plumes of haze include industrial emissions from Europe, Asia and North America that are carried to the high Arctic by weather systems, Brock notes. The new analyses, reported by Brock and his colleagues in the Jan. 28 Geophysical Research Letters, finds that the layers do include acetonitrile, benzene and carbon monoxide, consistent with industrial sources or fires. But there is little if any propane or tetrachloroethene, substances that would betray an industrial origin.

Using computer simulations to track smoky plumes back to their sources, the researchers found many had originated in forest fires raging in southern Siberia, and others came from agricultural burning in Kazakhstan.

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The new analyses "are an interesting way of looking at different emissions" that end up in the Arctic, says Rick Shetter of the University of North Dakota in Grand Forks. The smoky plumes are "all together quite a big input [of emissions]" to the region, he adds.