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Smog alarm

Mexico City streets wore a deserted look on September 19 as the first pollution alert in almost three years was declared in the region. Hundreds and thousands of cars were ordered off the road after ozone levels reached more than 2.5 times the acceptable limits. The ban affected about 350,000 of the city's older-model vehicles. Residents who had bought newer, cleaner models were, however, allowed to ply their vehicles during the emergency.

Since the last such alert, declared in October 1999, the city has not revised the danger level of smog: 240 points on a scale in which 100 is considered acceptable. Environmentalists feel that the threshold should be lowered further.

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