Fox News Weather Center

Mexico City authorities order cars off the road one day per week to combat dangerous smog

Mexico City officials ordered all cars to idle one day per week, following a smog alert and dangerous air quality during the middle of March.

The Environmental Commission of the Megalopolis of Mexico City (CAMe) announced the new measures to modify the program of environmental contingencies and launched a new initiative called "One day without car" to limit the volume of vehicles on the roads.

The objective of this program is to protect the health of the population during the dry and hot season and prevent high concentrations of ozone in the atmosphere.

From April 5 until June 30, all vehicles will participate in the program "One day without car." Previously, a hologram permit would allow exemptions from travel restrictions. Likewise, authorities have decided to eliminate the pre contingency, which previously only required restrictions to go into effect at air quality indices over 200, which are considered a "purple alert" or very unhealthy. Now, Phase 1 will be enabled when the air quality index reaches 150, which is considered a "red alert" or unhealthy. Phase 2 will begin when levels reach 200, according to the statement from CAMe.

An estimated 20 million people, owning roughly 10 million vehicles, live in Mexico City's metropolitan area, the Wall Street Journal reported in a recent article.

According to AccuWeather Senior Meteorologist Jason Nicholls, the geography of Mexico City plays a major role in the smog issues.

"The city is surrounded on three sides by mountains," Nicholls said. "The mountains act as a natural barrier to prevent smog from clearing the valley. Think of the city like being in a bowl."

"Other cities where geography helps play a role in air pollution problems are Beijing and New Delhi, both of which have notorious air pollution or smog problems," Nicholls added.

"Another problem for Mexico City is large areas of high pressure can routinely sit over central Mexico for long periods, leading to very little air flow and air stagnation," Nicholls said, adding that under high pressure temperature inversions, where air temperature increases with attitude rather than decreases, can form. Temperature inversions can act like a "lid" over the city resulting in hardly any wind.

"This along with the mountains really limits the ability of the pollutants to vacate the city," Nicholls added.

Mexico's ozone season, when levels can rise to dangerous levels, extends from late February to June. High solar radiation, stagnant air and low moisture levels in the atmosphere are forecast by Mexico's authorities, and all of these factors can combine to increase the episodes and duration of smog in the city. Due to the growing concerns, the President of the Republic of Mexico, Enrique Peña Nieto, instructed the Secretariat of Environment and Natural Resources (SEMARNAT) to adopt emergency measures to protect the health of the population and improve the air quality of the megalopolis.

The Executive Coordinator of the CAMe, Martin Gutiérrez Lacayo, accompanied by the secretaries of environment the State of Mexico, Hidalgo, Morelos, Puebla and Mexico City, said in a recent press conference, that it eliminated the pre contingency. Gutiérrez Lacayo explained that from now on Phase 1 will be activated when the air quality index exceeds 150, while Phase 2 will apply when the air quality index exceeds 200.

Air pollution hangs over Mexico City, Wednesday, March 16, 2016. Authorities have banned more than 1 million cars from the roads and offered free subway and bus rides to coax people from their vehicles as Mexico City's first air pollution alert in 11 years stretched into a third day. (AP Photo/Eduardo Verdugo)

Pollution alerts require new vehicle restrictions measures

Because vehicles contribute 88 percent of the ozone present in the Valley of Mexico, Gutiérrez Lacayo said the "One day without car" program will be temporarily modified. From April 5 until June 30, all vehicles, regardless of the number of hologram, that is 0, 00, 1 or 2, will cease to circulate in accordance with the color of decal and termination plate that corresponds, including restrictions for Saturday.

He clarified that motorcycles and federal transportation are included in this measure. Hybrid and electric transport vehicles operated with natural gas and LPG are exempt from the mandate, as well as vehicles that provide urban services, health, funeral, emergency, civil protection, public safety, accredited school transportation, hazardous waste and those that carry name plates to transport people with disabilities.

A further measure is the regulation of federal sources of pollutants in the Valley of Mexico. In Phase 1 the reduction of pollutant emissions will be between 30 and 40 percent, while Phase 2 will reach up to 60 percent of the industry. Moreover, 50 percent of the activity will be suspended at service stations, gasoline and LP gas carburetion.

"Recently high pressure has been dominating central Mexico, likely leading to air stagnation, but a cold front looks to push through this weekend which may help mix smog out of the city for a time," Nicholls said. "Not sure it clears smog completely out of the city but there can be some improvement in air quality this weekend into Monday."

However, smog levels can worsen again later next week, Nicholls warned.

Gutiérrez Lacayo said that the adoption of these measures is to prevent dangerous levels such as those recorded between March 15 and 17, 2016, when the air quality index exceeded 203.

Playlist used for trending content.