|How Big Cities' Bad Air Pollutes the Sierras|
early every afternoon, winds from the ocean blow pollution through three major
passes in the coastal ranges -- the Carquinez Strait, Altamount Pass, and
Pacheco Pass -- into the Central Valley and up against the Sierra. The streams
of air carrying Bay Area emissions mix with locally generated pollution from
automobile traffic, small engine exhaust, industry, and agriculture in the
Valley and are diverted both north and south.
The Valley's geography is like a giant bathtub -- with a lid on top in the form of inverted layers of cool and warm air that cannot mix. This inversion layer traps both local and transported dirty air, sometimes for weeks or even months. Organized wind patterns in the summer help create an eddy or swirl-like pattern that circulates around the Valley "tub."
Winds move south in the daytime, transporting pollution toward Fresno
and Bakersfield. At night, the process reverses, taking it back north.
The next day, the cycle begins again and continues until weather
patterns change. This collection of trapped pollutants rises up into the
Sierra on a daily basis-giving large areas of the mountains some of the
worst air quality in the nation.
Next - The largest emitters of air pollution...
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