The Americas

Mexico City declares pollution alert, restricts auto usage

  • A woman combs though trash, looking for recyclable items, as a cloud of air pollution obscures the Mexico City skyline, Saturday, May 21, 2016. Mexican authorities have issued a new smog alert for the capital after ozone levels rose to almost twice acceptable limits. It's the fifth time this year that Mexico City has seen such an alert, which triggers additional restrictions on automobile usage. On Saturday 40 percent of vehicles have been barred from the streets of the capital and the surrounding suburbs. (AP Photo/Marco Ugarte)

    A woman combs though trash, looking for recyclable items, as a cloud of air pollution obscures the Mexico City skyline, Saturday, May 21, 2016. Mexican authorities have issued a new smog alert for the capital after ozone levels rose to almost twice acceptable limits. It's the fifth time this year that Mexico City has seen such an alert, which triggers additional restrictions on automobile usage. On Saturday 40 percent of vehicles have been barred from the streets of the capital and the surrounding suburbs. (AP Photo/Marco Ugarte)  (The Associated Press)

  • People make use of a pedestrian bridge as a cloud of air pollution obscures a portion of the Mexico City skyline, Saturday, May 21, 2016. Mexican authorities have issued a new smog alert for the capital after ozone levels rose to almost twice acceptable limits. It's the fifth time this year that Mexico City has seen such an alert, which triggers additional restrictions on automobile usage. On Saturday 40 percent of vehicles have been barred from the streets of the capital and the surrounding suburbs. (AP Photo/Marco Ugarte)

    People make use of a pedestrian bridge as a cloud of air pollution obscures a portion of the Mexico City skyline, Saturday, May 21, 2016. Mexican authorities have issued a new smog alert for the capital after ozone levels rose to almost twice acceptable limits. It's the fifth time this year that Mexico City has seen such an alert, which triggers additional restrictions on automobile usage. On Saturday 40 percent of vehicles have been barred from the streets of the capital and the surrounding suburbs. (AP Photo/Marco Ugarte)  (The Associated Press)

  • A man repairs his car to comply with air-emissions standards, in Mexico City, Saturday, May 21, 2016. Mexican authorities have issued a new smog alert for the capital after ozone levels rose to almost twice acceptable limits. It's the fifth time this year that Mexico City has seen such an alert, which triggers additional restrictions on automobile usage. On Saturday 40 percent of vehicles have been barred from the streets of the capital and the surrounding suburbs. (AP Photo/Marco Ugarte)

    A man repairs his car to comply with air-emissions standards, in Mexico City, Saturday, May 21, 2016. Mexican authorities have issued a new smog alert for the capital after ozone levels rose to almost twice acceptable limits. It's the fifth time this year that Mexico City has seen such an alert, which triggers additional restrictions on automobile usage. On Saturday 40 percent of vehicles have been barred from the streets of the capital and the surrounding suburbs. (AP Photo/Marco Ugarte)  (The Associated Press)

Mexican authorities have issued a new smog alert for the capital after ozone levels rose to almost twice acceptable limits.

It's the fifth time this year that Mexico City has seen such an alert, which triggers additional restrictions on automobile usage.

On Saturday, 40 percent of vehicles were barred from the streets of the capital and the surrounding suburbs.

In March, Mexico City issued its first pollution alert in over a decade.

Under a rule in effect through June, one-fifth of the city's vehicles normally must stay at home on a weekday, with the day determined by license plate numbers.

The pollution spike is due to seasonal weather patterns and the increasing number of cars in the city.