The Atmospherical Monitoring System of the Valley of Mexico reported bad air quality in the area.
"The maximum value is 144 IMECA points of ozone," reported the System on its Twitter account.
The IMECA is the main indicator of pollution in urban areas and works also as an indicator of possible health risks for their inhabitants.
The levels are revised every hour. There are five levels:
Good: From 0 to 50 IMECA points.
Regular: From 51 to 100, meaning an acceptable air quality.
Bad: When the index goes between 101 and 150, causing ill effects on some sensitive people.
Very bad: From 150 to 200. Most people will experiment ill effects in this situation.
Extremely bad: More than 201. The population in general will seriously resent this situation.