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Weekday pollution winds way to desert.

Weekday pollution winds way to desert

Mother nature has her own natural periods--sunsets, lunar months, and the equinoxes. But the weekly cycle that guides our lives is an artificial one, dreamed up by humans. Atmospheric scientists are exploiting this unnatural cycle to study how Los Angeles pollution travels into the distant desert.

Warren H. White from Washington University in St. Louis and colleagues monitored summertime levels of methylchloroform (1,1,1-trichloroethane) in the air at four stations: one located inside the Los Angeles basin, one on a mountain pass near L.A., a third atop a Nevada mountain and a fourth about 20 kilometers from the mouth of the Grand Canyon in Arizona. Used by many industries as an electronics solvent, methylchloroform depletes the ozone layer and contributes to global warning. Because no natural source produces this chemical, scientists can use it to trace the path of human-made pollution.

In all four locations, White's groups found that methylchloroform levels followed a workweek cycle -- high for five days, then low for two -- suggesting that most emissions come from the workplace rather than the general activities of an urban population.

Though concentrations dropped in the L.A. region on Saturday and Sunday, similar lows in the levels measured at the Nevada and Arizona stations did not show up until Monday and Tuesday, the researchers report in the July GEOPHYSICAL RESEARCH LETTERS. That implies it takes one or two days for the pollution to rise out of the L.A. basin and travel the 400 km to the Arizona station. By studying details of the seven day cycle, researchers also hope to learn how much the polluted L.A. air mixes with clean air as it travels from the city, out to the desert.
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Title Annotation:how Los Angeles pollution travels to the desert
Publication:Science News
Date:Jul 28, 1990
Words:291
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