Background Essay: Arctic Haze
There is often a haze in the Arctic skies—especially during the winter and early spring. Instead of the clear blue skies one might expect to see over the region, the air looks dirty. From the ground, the sky looks pale instead of blue; from the air, there is a reddish-brown layer of haze hovering above Earth's surface. This diminished visibility is due to the presence of fine particles in the atmosphere, which scatter sunlight and reduce the transparency of the air.
Some of the particulates in Alaska's atmosphere may be of natural origin, such as sand and sea salt, but most of the aerosols—tiny particles suspended in the air—are the result of human activities. For example, sulfates, a large component of the haze, are the result of the burning of fossil fuels such as coal and oil. However, the Arctic region is not a significant source of these aerosols; the pollution that causes the haze originates in industrialized areas outside of the Arctic.
Pollution produced in lower latitudes can travel thousands of miles to the Arctic via air currents. In particular, atmospheric circulation patterns (essentially convection currents), caused by the temperature difference between the north polar region and the tropics, bring air masses northward. As the warmer, less dense air near the equator rises and flows toward the Arctic, it picks up and transports pollutants within it; emissions produced in Europe could reach the Arctic in just a matter of days. However, when the warmer, polluted air flows over the cold air mass above the Arctic, it gets "trapped" because the atmosphere is stabilized. Especially during the winter, when there is little or no sunlight to warm the ground or air, the air temperature increases with height—there is a temperature inversion—which inhibits atmospheric movement. This stability also minimizes the formation of precipitation, which typically removes pollutants from the air. As a result, the particulates may be...
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