This is the VOA Special English ENVIRONMENT REPORT.
Wildfires have been burning in forests in parts of the western United States this summer. American scientists are studying the effect of the wildfires on the environment. Some scientists have flown over the fires to measure the levels of the chemical element mercury in the smoke. The National Center for Atmospheric Research and the University of Washington are organizing the flights.
Scientists want to understand what causes mercury to form in Earth’s atmosphere. They also want to learn how much of the chemical falls on the land and water and enters the food supply. High levels of mercury are poisonous to people and animals.
During a wildfire, mercury stored in trees and on the ground is released and carried into the atmosphere. Mercury travels as a gas in the atmosphere for about a year before landing in water or on the ground. About six-thousand metric tons of mercury are in the atmosphere at any one time.
About half the mercury in the atmosphere comes from natural sources, such as oceans, soil and volcanoes. The other half comes from human activities. The Environmental Protection Agency estimates that American coal-burning factories release about thirty-seven metric tons of the chemical each year.
Mercury changes in the atmosphere through chemical processes. It returns to Earth’s surface in wet or dry particles.
Hans Friedli is a scientist with the National Center for Atmospheric Research in Boulder, Colorado. He says trees store mercury in their leaves or needles. It stays there until the trees burn.
The scientists carried out tests to find out how much mercury is released during a forest fire. For the experiment, researchers gathered trees from across the United States. They burned the trees at the Forest Service Fire Science Laboratory in Missoula, Montana. Scientific equipment immediately reported the presence of mercury when the trees were burned. All of the trees released nearly all the mercury they had stored.
The mercury studies developed from the scientists’ efforts to understand wildfires and how they spread. They want to provide information to help firefighters battle such fires in the future.
This VOA Special English ENVIRONMENT REPORT was written by George Grow.