Mexico City has faced repeated air quality emergencies during the first two months of 2026, with multiple environmental contingencies activated due to high ozone and particle pollution. But why is this happening, and what are the authorities doing to combat this perennial problem?
Back-to-Back Pollution Emergencies
The year started badly. On January 1, authorities declared the first environmental contingency of 2026. According to authorities, this was mainly caused by fireworks used during New Year celebrations and emissions from high volumes of traffic, which released large amounts of pollutants into the air.
Just one week later, on January 8, a second contingency was activated. This time, it was due to high ozone concentrations. A monitoring station in Cuajimalpa recorded 160 parts per billion (ppb) of ozone at 4:00 p.m., well above the 90 ppb standard that triggers emergency measures.
By mid-February, the pollution problem had not gone away. On February 13 and 14, another Phase I contingency remained in effect, with ozone reaching 156 ppb in Atizapán. As of February 16, the air quality index remained rated “MALO” (bad) in several parts of the city, with PM2.5 particles as the primary concern.
Pollution and Weather
The primary reason for this bad air is not that people are polluting more than usual. Rather, weather conditions have trapped pollution close to the ground.
A high-pressure system has been sitting over central Mexico. This creates atmospheric stability, which means weak winds and poor ventilation. Normally, wind helps scatter pollutants. Without it, emissions just build up.
Additionally, temperatures have been unusually warm for winter. On January 8, it reached 25 degrees Celsius. Sunlight triggers chemical reactions that form ozone from vehicle exhaust and industrial emissions. More sun means more ozone.
The dry season makes everything worse. Without rain to wash pollutants out of the air, they just keep accumulating day after day.
Geography Traps Pollution in the Valley
Mexico City’s location is a fundamental part of the problem. The city sits in a basin at more than 2,200 meters above sea level, surrounded by mountains and volcanoes. This geography acts like a bowl. Pollutants get released into the air but cannot easily escape because the surrounding walls block wind from flowing through.
During winter and early spring, temperature inversions make this even worse. Normally, the air gets cooler as you go higher. But during an inversion, a layer of warm air sits on top of cooler air near the ground. This warm layer acts like a lid, trapping pollutants underneath. These inversions can last for days, causing pollution levels to climb steadily.
The ‘Hoy No Circula’ Program
When a Phase I environmental contingency is declared, the main tool the government uses is the ‘Doble Hoy No Circula’ program. This restricts vehicle use to reduce emissions.
On a normal day, Mexico City implements a ‘Hoy No Circula’ program that bans the use of vehicles based on their license plate numbers and verification stickers. However, during a contingency, the restrictions tighten, effectively doubling the number of vehicles forced off the road.
For example, on February 16, the restrictions applied to:
All vehicles with verification hologram 2
Vehicles with hologram 1 whose last digit is 1, 3, 5, 6, 7, or 9
Vehicles with hologram 0 or 00 that have yellow stickers and plates ending in 5 or 6
The restrictions run from 5:00 a.m. to 10:00 p.m. Some vehicles are exempt, including electric and hybrid vehicles, vehicles with ecological plates, and emergency vehicles.
When contingencies fall on weekends, the restrictions follow a set rotation of sticker colors so that over time, all vehicle types share the burden equally.
Does the Program Work?
Experts who study this issue say the ‘Hoy No Circula’ program has limits. It was created 37 years ago when Mexico City had roughly 1.5 million vehicles on the road. Currently, the metropolitan area has approximately 6.5 million vehicles, plus more than 700,000 motorcycles that are not covered by the program.
In 2025, the worst year on record for environmental contingencies since tracking began in 1993. There were 12 days when Phase I was activated due to ozone. The first two months of 2026 suggest this year could be similar.
Researchers at the UNAM Atmospheric Sciences Institute note that although vehicle emissions have become cleaner over the decades, the number of vehicles continues to increase. Additionally, many public transport operators are not effectively regulated.