Mexico City declares air pollution alert

Mexico City declared an environmental alert Tuesday as a blanket of smog enveloped the sprawling urban area of 20 million people for a fourth straight day. A series of wildfires on the city's outskirts have combined with stagnant weather conditions to cloak the capital in a gray cloud of air pollution, which passed the critical level of 150 points on the authorities' air quality index.
"The extraordinary environmental contingency plan has been activated for the Mexico valley metropolitan area due to particles" in the air, the city's environmental commission said in a statement. Authorities called on residents to avoid physical activity outdoors, instructed schools to keep children inside at recess and urged the elderly and those with respiratory illnesses to remain inside. The city usually orders 20 percent of its estimated 9.6 million cars off the road under such alerts, as well as restricting the activities of polluting industries.