The end of February marks the beginning of the "ozone season" (temporada del ozono) in the Mexican capital. With the approach of spring, the temperatures soften, the sun shines, the wind is less strong ... and levels of pollution with ozone rise. During this period, the ozone levels are close to (or even exceed) the thresholds considered "a risk", practically every day from 13h to 18h. The southern zone of the city is the most affected because the peaks of El Ajusco block the particles carried by the wind.
Ozone is formed from hundreds of chemical reactions between nitrogen oxide and hydrocarbons, under the influence of solar energy. So there is no ozone production during the night. According to Mexico's Environment Ministry, 70% of pollutant emissions that produce ozone are caused by vehicles and homes.
Over the last thirty years, the number of vehicles in circulation in Mexico City has steadily increased from just under two million (1,869,000) in 1980 to nearly five and a half million (5,471 .000) in 2017. To these must be added the cars registered in the State of Mexico, Metro Area, (on which extends part of the megalopolis) which, for their part, have multiplied at an even more spectacular pace : from 318,000 to more than seven million over the same period *!
This situation worries the inhabitants so much so that a group of lawyers, led by a professor of the Autonomous Metropolitan University, Bernardo Bolaños, decided to file a complaint against the government of Claudia Sheinbaum. As summarized in an article published last week in El País, Professor Bolaños denounces the effects of the recent relaxation of pollution control standards for vehicles in circulation. Since last December, some 169,000 vehicles, previously dumped during the bi-annual verification checks, are again allowed to travel the city. Whatever the outcome of the current legal process, which promises to be more than random (it would indeed be necessary to be able to measure the specific impact of these 169,000 vehicles on the production of ozone, whereas this one is precisely a multifactorial phenomenon, as explained by the head of the Program for Air Quality of Mexico City), mobilization in the legal arena is a (good?) sign of the involvement of citizenship in the struggle for a healthier environment.