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- Tinted blood red by a thick cloud of smoke and pollution, the sun sets on the mountains above Mexico City, Monday, May 13, 2019. Mexico City's government has warned residents to remain indoors as forest and brush fires carpeted the metropolis in a smoky haze that has alarmed even many of those accustomed to living with air pollution. (AP Photo/Marco Ugarte)
- MEXICO CITY, MEXICO - MAY 16: Buildings covered by smog are seen on May 16, 2019 in Mexico City, Mexico. Mexico City's air pollution has been worsened as a consequence of high temperatures, lack of rain and fires located around the city's valley, where people have been advised to stay indoors, avoid using their vehicles and schools have been ordered to close. (Photo by Toya Sarno Jordan/Getty Images)
- MEXICO CITY, MEXICO - MAY 16: Buildings covered by smog are seen on May 16, 2019 in Mexico City, Mexico. Mexico City's air pollution has been worsened as a consequence of high temperatures, lack of rain and fires located around the city's valley, where people have been advised to stay indoors, avoid using their vehicles and schools have been ordered to close. (Photo by Toya Sarno Jordan/Getty Images)
- A view of Mexico City, on May 16, 2019. Third day of extraordinary environmental contingency in the megalopolis due to the high levels of 2.5 particles and ozone in the environment, this increase is attributed to forest fires around the city that have been aggravated by the drought and the high temperatures. Restrictions have been placed on the circulation of motor vehicles, in addition to the fact that classes have been suspended at all educational levels. (Photo by Carlos Ogaz/NurPhoto via Getty Images)
- Mexico City has low visibility due to air pollution on May 15, 2019. - Authorities in Mexico City and the metropolitan area study a contingency protocol for environmental pollution that has worsened due to dozens of forest fires, while issuing recommendations to its more than 20 million inhabitants to protect themselves. (Photo by ALFREDO ESTRELLA / AFP) (Photo credit should read ALFREDO ESTRELLA/AFP/Getty Images)
- MEXICO CITY, MEXICO - MAY 15: The sun sets in an area surrounded by smog on May 15, 2019 in Mexico City, Mexico. Mexico City's air pollution has been worsened as a consequence of high temperatures, lack of rain and fires located around the city's valley, where people have been advised to stay indoors, avoid using their vehicles and schools have been ordered to close on May 16. (Photo by Toya Sarno Jordan/Getty Images)
- View of vehicles in Mexico City on May 15, 2019. - Authorities in Mexico City and the metropolitan area study a contingency protocol for environmental pollution that has worsened due to dozens of forest fires, while issuing recommendations to its more than 20 million inhabitants to protect themselves. (Photo by ALFREDO ESTRELLA / AFP) (Photo credit should read ALFREDO ESTRELLA/AFP/Getty Images)
- MEXICO CITY, MEXICO - MAY 14: The sunset cuts through the haze as seen from the Latin American Tower during a day when city authorities activated a contingency plan due to bad air conditions on May 14, 2019 in Mexico City, Mexico. Mexico City has been experiencing severe air pollution over the last four days, the result of firess surrounding the city. Critics say the government's response to the problem has been inadequate. (Photo by Cristopher Rogel Blanquet/Getty Images)
- Smoke hangs over in Mexico City, Monday, May 13, 2019. Mexico City's government has warned residents to remain indoors as forest and brush fires carpeted the metropolis in a smoky haze that has alarmed even many of those accustomed to living with air pollution. (AP Photo/Marco Ugarte)
- CORRECTS DATE - Smoke and pollution hangs over in Mexico City's iconic Reforma Avenue and Chapultepec Castle, Tuesday, May 14, 2019. Mexico City has declared a pollution emergency over smoke from brushfires that has cast a pall over the city of 9 million. The measure is not accompanied by the usual driving restrictions because this time the pollution isn't coming from cars. The city's pollution alerts are usually triggered by high ozone levels. (AP Photo/Gerardo Carrillo)
- Air pollution hangs over Mexico City, Wednesday, June 6, 2018. Authorities have issued a smog alert for the capital after ozone levels rose. (AP Photo/Marco Ugarte)
- Buildings shrouded in smog, are pictured as Mexico's government ordered schools in and around Mexico City to be closed on Thursday due to elevated levels of pollution, in Mexico City, Mexico May 16, 2019. REUTERS/Henry Romero
- Buildings shrouded in smog, are pictured as Mexico's government ordered schools in and around Mexico City to be closed on Thursday due to elevated levels of pollution, in Mexico City, Mexico May 16, 2019. REUTERS/Henry Romero
- A building shrouded in smog is pictured as Mexico's government ordered schools in and around Mexico City to be closed on Thursday due to elevated levels of pollution, in Mexico City, Mexico May 16, 2019. REUTERS/Henry Romero
- A woman wears a surgical mask after the authorities declared an environmental emergency on Tuesday for metropolitan in Mexico City, Mexico May 15, 2019. REUTERS/Carlos Jasso
- A woman wears a surgical mask after the authorities declared an environmental emergency on Tuesday for metropolitan in Mexico City, Mexico May 15, 2019. REUTERS/Carlos Jasso
- A general view shows a building during high levels of pollution in Mexico City, Mexico, May 14, 2019. Picture taken through a glass window. REUTERS/Henry Romero
- A general view shows a Mexico flag against hazy backdrop of buildings in metropolitan Mexico City May 14, 2019 as Mexico authorities declared an environmental emergency on Tuesday for metropolitan Mexico City, as smoke from nearby wildfires pushed pollution to levels deemed potentially harmful to human health. Picture taken through a glass window. REUTERS/Henry Romero