The Hazy Days of Alaska's Summer

More than 1 million acres of Alaska have gone up in smoke this summer, clouding the views of people from the foothills of the Brooks Range to the Kenai Peninsula.

While most of us wish for the smoke to blow some other way, Cathy Cahill seeks it out. Cahill is an atmospheric chemist at the Geophysical Institute who studies the smoke from wildfires. Studying something that floats in the air isn't easy. Cahill said smoke is made up of particles so small that 50 of them could line up side-by-side along the width of a human hair.

Though these specks fuzz our views, they also create beautiful sunsets. Smoke hides the mountains and paints the sunset red because it scatters light, Cahill said. Much of the sun's energy reaches Earth as radiation waves of visible light, in colors ranging from purple to red. We see the sun as yellow on clear days because more yellow light reaches our eyes than any other color. Smoke particles are just the right size to deflect some photons of light energy before they reach the eye. By bouncing away light that represents distant images, smoke particles blur the view. When the sun is low on the horizon, smoke particles team with other molecules in the atmosphere to deflect all colors except red and orange, creating memorable sunsets. The same colors can be caused by other particles floating in the air, such as volcanic ash and sulfur compounds belched by tiny creatures that live in the sea. In summer, the dominant particles in Alaska's air are those from fire smoke.

Cahill studies smoke to figure out its effects on people and the atmosphere, and because there may soon be more smoke in Alaska's air. Some scientists predict that an increase in forest fires will be a side effect of global warming.

Cahill recently went hunting for smoke at Little Poker Creek, north of Fairbanks. She was there for an experiment during which researchers burned more than 800 acres to study the effects of fire on the soil, air, and everything in between. Cahill and others involved in her study set up an instrument that sniffed the air in the middle of the area that burned. Pulled into a box by a vacuum, the smoke particles stuck to filter paper inside. By looking at the residue, Cahill hopes to find out the nature of fire smoke with an Alaska flavor. She wants to determine what kind of smoke is produced when black spruce burns, for example, because she knows the color and particle size of fire smoke will determine how it warms or cools the air.

In 1991, Cahill studied the black smoke from oil fires in Kuwait. She found that the oily smoke absorbed much of the sun's radiation over the Kuwait desert. This caused the ground to be cooler in the shadow of the smoke plume. Alaska's fire smoke, often a reddish brown, will probably have different effects on the climate of Alaska.