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Those of us who curse the weekend rain apparently have only ourselves to blame. Randall Cerveny and Robert Balling, Jr., climatologists at Arizona State University, suggest that pollution may cause heavier rainstorms on the weekends, while it may weaken weekend hurricanes. Levels of ozone and carbon monoxide on the East Coast, Cerveny and Balling discovered, follow a seven-day cycle, peaking on Thursdays and Fridays, with lows from Sunday to Tuesday. When Cerveny and Balling looked at ocean rainfall records from Florida to Canada, they saw a peak in weekend rainfall, with 22 percent more rain on Saturdays than on Mondays. Hurricanes turned out to be less fierce on weekends than during the week, slower by about ten miles an hour. The seven-day cycles suggest that pollution from car exhaust and industry could be driving these weekly weather patterns. "The weekly cycle is man-made," says Cerveny. "It has no counterpart in nature." Heat-absorbing pollutant particles could warm surrounding air, driving it upward to create more clouds and rain. Pollutants could also increase rainfall at the edges of a hurricane, preventing heat from concentrating in the center and thus weakening the storm. "These are some of the biggest storms on the planet," says Cerveny. "And the idea that we're affecting them is a little bit frightening."

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