Air Pollution in Fairbanks
The influence of a particular geographic setting and of certain weather conditions can make dispersion of pollutants especially difficult. An excellent example is provided by Alaska's second largest metropolitan area, Fairbanks, situated within a three-sided basin (Birch Hill to Chena Ridge) within a still larger three-sided basin (the Salcha Bluffs behind Eielson Air Force Base to Chena Ridge). These hills protect Fairbanks from strong winds on three sides. On the fourth side, the south, the Alaska Range and the Coast Range beyond it are distant but effective blockades against wind and storms.
As a result, Fairbanks has, at ground level, one of the lowest wind conditions in the world. The lack of wind allows the air over the city to remain relatively stagnant. A further effect of this highly sheltered location is that Fairbanks is typically clear-skyed (except for summer thundercloud; which often form within the valley).
Without the insulating effect of a cloud cover, heat from the earth's surface radiates directly into space, cooling the ground. When the ground cools sufficiently (as in winter or on a summer night), it cools the nearby, lower layers of air. Then the usual trend toward cooler air at higher altitudes becomes inverted: the air closest to the ground becomes colder than the air at higher altitudes. This temperature inversion is very stable because the cold air is heavier and tends to just sit, inert on the ground. Fairbanks' inversions are considered among the most extreme in the world, with temperatures sometimes increasing 16°F (9°C) with each 100 feet of altitude.
Since an inversion resists vertical mixing of air, any pollution put into the air tends to stay in the layer it enters. Strong winds can break up inversions by mixing up the air, as occurs at Delta or Healy where wind funnels through nearby mountain passes. However, in the highly sheltered Fairbanks basin strong winds are infrequent. Therefore pollutants tend to move away from their sources horizontally and quite slowly--especially near the ground. As a result pollution levels in Fairbanks are comparable with those in Los Angeles even though that city has a population more than 200 times greater.
There is no known way to change the low wind or the inversion layers such as occur at Fairbanks. Consequently, the only ways to reduce pollution are to limit pollution sources. Decreasing auto traffic, for example, or use of care in selecting sites for power plants or other industrial developments will help. The mine-mouth power plant at Healy, Alaska is an example of a site well chosen to avoid buildup of air pollution. The Delta, Alaska area can probably also dilute pollution far better than sites closer to Fairbanks.
