Emissions head north

Arctic’s pollutants come from all regions of the Northern Hemisphere

When it comes to Arctic air, various regions of the Northern Hemisphere are equal opportunity polluters. Even some subtropical countries in southern Asia get into the act, a new study suggests.

Air pollution, especially that originating in large urban areas, can affect air quality thousands of miles away (SN: 9/8/07, p. 152). Although much of the world’s population is in temperate latitudes, atmospheric circulation often carries human-generated pollutants to the high Arctic, says Drew T. Shindell, an atmospheric chemist at ColumbiaUniversity. He and his colleagues recently used a suite of 17 computer models to estimate how weather patterns sweep pollution generated throughout the Northern Hemisphere to Arctic regions above 68°N. Those models included state-of-the-art simulations used in Britain, Europe and the United States, Shindell says.

The researchers scrutinized emissions coming from four regions: Europe and North Africa (considered as one region), East Asia, South Asia and North America. Altogether, these areas account for about 75 percent of the emissions generated by human activity in the Northern Hemisphere, Shindell says. In general, different levels of the Arctic atmosphere receive pollution from different sources, the researchers note in an upcoming Atmospheric Chemistry and Physics. Also, they say, each region’s relative contribution to Arctic pollution varies according to the season.

The results suggest that most of the high Arctic’s low-level air pollution — including its sulfate aerosols, black carbon soot and carbon monoxide — originate in Europe. Much of the low-altitude ozone in the region results from nitrogen oxides generated in North America, but significant amounts of those gases come from Europe and East Asia as well, Shindell says. Most of the sulfate aerosols and black carbon found at high altitudes — say, at heights of 5 to 8 kilometers — come from East Asia.

Short-lived, quick-reacting emissions often don’t survive their trip northward, but slow-to-react emissions such as carbon monoxide can waft all the way from southern Asia to the Arctic, traveling thousands of kilometers.

Most of the carbon soot that taints the snow in low-altitude regions of the Arctic comes from sources in Europe. The soot that darkens high-altitude portions of the Greenland ice sheet, however, comes from three sources: North America (40 percent), Europe (40 percent) and East Asia (20 percent).

In winter, a dome of high pressure prevents most pollution generated at low latitudes from sweeping into the Arctic at ground level, the models suggest. Because much of Europe lies within that dome, however, the continent’s contribution to Arctic pollution during that season is particularly high.

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