Mexico City declared an environmental alert on Tuesday, May 14th, as a blanket of smog enveloped the sprawling urban area of 20 million people for a fourth straight day, AFP has reported.
A series of wildfires on the city's outskirts have combined with stagnant weather conditions to cloak the capital in a grey cloud of air pollution, which passed the critical level of 150 points on the authorities' air quality index.
The city's environmental commission said in a statement, "The extraordinary environmental contingency plan has been activated for the Mexico valley metropolitan area due to particles" in the air.
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.
However, since the alert was only declared Tuesday morning, when many commuters were already on their way to work, the authorities said they would hold off on such measures for now.
Mayor Claudia Sheinbaum said they would decide whether to implement such emergency measures for Wednesday, May 15th, based on conditions later in the day.
Firefighters have been battling nearly two dozen wildfires on the outskirts of the capital. And with little wind, no rain and temperatures of around 30 degrees Celsius (86 Fahrenheit), weather conditions have allowed the resulting contamination to stagnate.
Mexico City is naturally prone to air pollution: it is surrounded by a ring of mountains that often traps smog over the capital, preventing it from dissipating.