El sistema de monitoreo de la calidad del aire IMECA es la herramienta que utilizan las autoridades mexicanas para medir la calidad del aire. Un total de ocho estaciones del sistema, ubicadas por toda la ciudad, miden los niveles de los seis principales contaminantes que se encuentran en la atmósfera. Los contaminantes medidos son: O₃, PM10, PM2.5, CO, NO₂ y SO₂. Además, las estaciones cuentan con una torre meteorológica equipada con sensores que miden la temperatura ambiente, la velocidad y dirección del viento, la precipitación, la radiación solar, la humedad relativa y la presión barométrica.

Los indicadores para cada contaminante permiten evaluar el estado de la calidad del aire con respecto a eventos específicos de contaminación. Se utilizan indicadores de las concentraciones máximas por hora y promedios móviles diarios para evaluar el comportamiento de las concentraciones presentadas por los que son considerados contaminantes y su relación con los estándares de protección de la salud.

Pollutants

PM10: According to the Mexican Official Standard (NOM), the annual limit for PM10 was 50 μg/m³ before 2014 and 40 μg/m³ from 2015 to date. In Mexico City, the annual concentration of PM10 has been above the limit for the last 10 years. The highest concentration was recorded in November 2019, when PM10 levels exceeded 110 μg/m³. Failure to comply with this NOM indicates the need to carry out actions to reduce the concentration of particulate matter in the ambient air, given that a decreasing trend is not observed in the recorded concentrations of this pollutant in recent years.

PM2.5: Values ​​have exceeded regulated limits (15 μg/m³ until 2014 and 12 μg/m³ from 2015) since 2011. In May 2019, PM2.5 levels reached between 150 and 160 μg/m³. These concentrations were due to the burning of organic matter, such as firewood, fuels (especially diesel), as well as some industrial processes. This level of pollution is equivalent to the inhabitants of Mexico City (of all ages) smoking almost three and a half cigarettes during those days.[8]​.

Ozone (O₃): The limits for ozone according to the NOM were 0.11 parts per million (ppm) until 2014 and 0.095 ppm from 2015 to date. Over the past two decades, ozone levels gradually fell below government limits as authorities relocated factories away from the capital and tightened regulations on fuel and automobiles. In 2015, 37% of days showed poor air quality due to ozone; in 2016 there was a slight improvement with 35% of the days; and in 2017 again 35% of days were recorded as “bad” for ozone levels. During recent years, ozone concentrations in the city reached such extreme levels that authorities issued alerts for environmental risk, urging the population to stay indoors.[9]​.

Sulfur dioxide (SO₂): The NOM establishes three different limits that must be met for SO₂ concentrations: 8 hours (moving average), 24 hours (daily average), and annual hourly average. During the last 10 years, concentrations below the three limits were recorded. However, in all stations the concentrations of this pollutant as a daily average are above the reference value recommended by the World Health Organization, which is 0.008 ppm. From 2015 to 2017, the percentage of days with regular amounts of SO₂ is minimal (above 5%).

Nitrogen dioxide (NO2): The NOM defines that the maximum allowable limit is 0.210 ppm as an average per hour. To comply with the standard, the established limit must not be exceeded more than once a year. At all monitoring stations where this NOM was evaluated, concentrations below the limit were recorded during 2015 to 2017. However, this NOM has not been updated since 1993 and the World Health Organization recommends as a guide that the hourly average limit for NO2 be set at 0.106 ppm. In each of the years, more than 90% of the days had good air quality.

Carbon monoxide (CO): The NOM establishes that the maximum permissible limit for CO is 11 ppm as an 8-hour moving average. To comply with the standard, the established limit must not be exceeded more than once a year. Since 2011, the limit established in the NOM for CO has not been exceeded in the stations located within Mexico City. Good air quality due to carbon monoxide predominates in all monitoring stations where it was possible to evaluate this pollutant.

On May 16, 2019, the Mexico City government declared an extraordinary atmospheric environmental contingency, indicating that the level of harmful particles in the air had exceeded accepted standards (160 ppm for PM2.5). Hours later, the same government would announce another environmental contingency due to ozone, making it necessary to reduce the number of vehicles circulating through the city. The Head of Government of Mexico City, Claudia Sheinbaum, stated that the main cause of the pollution levels was a series of fires that affected regions near the capital over the weekend. Schools remained closed for two days and authorities recommended citizens stay home until levels decreased.[10]​.

In an effort to reduce pollution, in 1989 the Mexican government implemented the Hoy No Circula program, which prohibits drivers from using their vehicles on a weekday. In 2008, this measure was expanded to include Saturdays. The use of public transport and bicycle sharing systems is also promoted.

To address the city's pollution levels, the local authority and the Metropolitan Environmental Commission (CEM) jointly implemented two action programs: the Comprehensive Program against Atmospheric Pollution (PICCA), launched in 1990, and ProAire, launched in 1995. The objective of both is to improve the air quality of the metropolitan area of ​​the Valley of Mexico.[11]​.

In 2023, Mexico City joined the Breathe Cities initiative to share air quality data, reduce carbon emissions, and share potential air quality solutions. Mexico City was the third city to join Breathe Cities, which has a total of 14 cities.[12]​.

El sistema de monitoreo de la calidad del aire IMECA es la herramienta que utilizan las autoridades mexicanas para medir la calidad del aire. Un total de ocho estaciones del sistema, ubicadas por toda la ciudad, miden los niveles de los seis principales contaminantes que se encuentran en la atmósfera. Los contaminantes medidos son: O₃, PM10, PM2.5, CO, NO₂ y SO₂. Además, las estaciones cuentan con una torre meteorológica equipada con sensores que miden la temperatura ambiente, la velocidad y dirección del viento, la precipitación, la radiación solar, la humedad relativa y la presión barométrica.

Los indicadores para cada contaminante permiten evaluar el estado de la calidad del aire con respecto a eventos específicos de contaminación. Se utilizan indicadores de las concentraciones máximas por hora y promedios móviles diarios para evaluar el comportamiento de las concentraciones presentadas por los que son considerados contaminantes y su relación con los estándares de protección de la salud.

Pollutants

PM10: According to the Mexican Official Standard (NOM), the annual limit for PM10 was 50 μg/m³ before 2014 and 40 μg/m³ from 2015 to date. In Mexico City, the annual concentration of PM10 has been above the limit for the last 10 years. The highest concentration was recorded in November 2019, when PM10 levels exceeded 110 μg/m³. Failure to comply with this NOM indicates the need to carry out actions to reduce the concentration of particulate matter in the ambient air, given that a decreasing trend is not observed in the recorded concentrations of this pollutant in recent years.

PM2.5: Values ​​have exceeded regulated limits (15 μg/m³ until 2014 and 12 μg/m³ from 2015) since 2011. In May 2019, PM2.5 levels reached between 150 and 160 μg/m³. These concentrations were due to the burning of organic matter, such as firewood, fuels (especially diesel), as well as some industrial processes. This level of pollution is equivalent to the inhabitants of Mexico City (of all ages) smoking almost three and a half cigarettes during those days.[8]​.

Ozone (O₃): The limits for ozone according to the NOM were 0.11 parts per million (ppm) until 2014 and 0.095 ppm from 2015 to date. Over the past two decades, ozone levels gradually fell below government limits as authorities relocated factories away from the capital and tightened regulations on fuel and automobiles. In 2015, 37% of days showed poor air quality due to ozone; in 2016 there was a slight improvement with 35% of the days; and in 2017 again 35% of days were recorded as “bad” for ozone levels. During recent years, ozone concentrations in the city reached such extreme levels that authorities issued alerts for environmental risk, urging the population to stay indoors.[9]​.

Sulfur dioxide (SO₂): The NOM establishes three different limits that must be met for SO₂ concentrations: 8 hours (moving average), 24 hours (daily average), and annual hourly average. During the last 10 years, concentrations below the three limits were recorded. However, in all stations the concentrations of this pollutant as a daily average are above the reference value recommended by the World Health Organization, which is 0.008 ppm. From 2015 to 2017, the percentage of days with regular amounts of SO₂ is minimal (above 5%).

Nitrogen dioxide (NO2): The NOM defines that the maximum allowable limit is 0.210 ppm as an average per hour. To comply with the standard, the established limit must not be exceeded more than once a year. At all monitoring stations where this NOM was evaluated, concentrations below the limit were recorded during 2015 to 2017. However, this NOM has not been updated since 1993 and the World Health Organization recommends as a guide that the hourly average limit for NO2 be set at 0.106 ppm. In each of the years, more than 90% of the days had good air quality.

Carbon monoxide (CO): The NOM establishes that the maximum permissible limit for CO is 11 ppm as an 8-hour moving average. To comply with the standard, the established limit must not be exceeded more than once a year. Since 2011, the limit established in the NOM for CO has not been exceeded in the stations located within Mexico City. Good air quality due to carbon monoxide predominates in all monitoring stations where it was possible to evaluate this pollutant.

On May 16, 2019, the Mexico City government declared an extraordinary atmospheric environmental contingency, indicating that the level of harmful particles in the air had exceeded accepted standards (160 ppm for PM2.5). Hours later, the same government would announce another environmental contingency due to ozone, making it necessary to reduce the number of vehicles circulating through the city. The Head of Government of Mexico City, Claudia Sheinbaum, stated that the main cause of the pollution levels was a series of fires that affected regions near the capital over the weekend. Schools remained closed for two days and authorities recommended citizens stay home until levels decreased.[10]​.

In an effort to reduce pollution, in 1989 the Mexican government implemented the Hoy No Circula program, which prohibits drivers from using their vehicles on a weekday. In 2008, this measure was expanded to include Saturdays. The use of public transport and bicycle sharing systems is also promoted.

To address the city's pollution levels, the local authority and the Metropolitan Environmental Commission (CEM) jointly implemented two action programs: the Comprehensive Program against Atmospheric Pollution (PICCA), launched in 1990, and ProAire, launched in 1995. The objective of both is to improve the air quality of the metropolitan area of ​​the Valley of Mexico.[11]​.

In 2023, Mexico City joined the Breathe Cities initiative to share air quality data, reduce carbon emissions, and share potential air quality solutions. Mexico City was the third city to join Breathe Cities, which has a total of 14 cities.[12]​.