In a statement, the agency explained that the decision was based on the persistent high concentration of ozone recorded at most of the stations in the city’s air quality monitoring system.

According to the statement, a concentration of 160 ppb was recorded at the Cuajimalpa station at 4:00 p.m. local time on Thursday; the following hour, it rose to 157 ppb at the Atizapan station, and by 6:00 p.m., five stations were above the standard level (90 ppb).

When activating the contingency plan, authorities reported the previous day that a high-pressure system was affecting the central part of the country, generating atmospheric stability with low humidity and ventilation.

This was compounded by a maximum temperature of 25 degrees Celsius, atypical for this time of year. This created unfavorable conditions for the dispersion of ozone and its precursors.

As part of the contingency measures, the agency asked the public to stay informed about air quality and heed recommendations to avoid exposure to pollution peaks between 1:00 p.m. and 7:00 p.m. local time, especially the most vulnerable individuals.

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