The Mexico City Environmental Commission (CAMe) announced Phase 1 emergency environmental measures Thursday afternoon, triggering vehicle restrictions within the greater metropolitan area that will remain in effect on Friday.

A Phase 1 air quality alert is in effect for the Valley of México after a heavy concentration of ozone was detected, and as of 10:00 a.m. on Friday, authorities announced the alert would remain in place throughout the day until 10 p.m.

The Phase 1 order affects all 16 Mexico City boroughs and 12 municipalities in the neighboring state of Mexico. The alert dramatically reduces the number of vehicles allowed to circulate in the Mexico City metropolitan area, cuts in half the number of LP gas delivery trucks on the road, prohibits certain cargo deliveries in the morning (from 6 a.m. through 10 a.m.) and cautions the public from engaging in outdoor activities.

In a Thursday night press release, CAMe reported that ozone measurements had topped out at 167 parts per billion (ppb) at 3 p.m., necessitating the Phase 1 alert which is declared any time ozone surpasses 100 ppb.

The CAMe report indicated that its meteorological models revealed a high-pressure system above the Valley of México accompanied by intense solar radiation, atmospheric stability and lack of wind, all of which contributed to the ozone concentration.

A thermal inversion was also detected, further complicating the situation. Such inversions play a major role in air quality, especially during the winter when these inversions are the strongest. 

Pollutants from vehicles, wood burning and industrial emissions become trapped near the ground, contributing to poor air quality. The lack of wind allows the pollutants to remain trapped above the valley.

Those considered most at risk from ozone exposure are children, people with asthma and other lung diseases, older adults, and adults who are active or work outside.

The CAMe will issue an updated bulletin on air quality at 3:00 p.m. on Friday, which can be consulted via the agency’s X account.

With reports from Infobae