Air pollution in Mexico City has been of concern to the city's population and health officials for decades. In the 20th century, Mexico City's population rapidly increased as industrialization brought thousands of migrants from all over the world. Such a rapid and unexpected growth led to the UN declaring Mexico City as the most polluted city in the world in 1992. This was partly due to Mexico City's high altitude (7382 ft above sea level) and pollution getting trapped by the surrounding mountains. Carbon-based fuels also do not combust completely. Other factors include the proliferation of vehicles, rapid industrial growth, and the population boom. The Mexican government has several active plans to reduce emission levels which require citizen participation, vehicular restrictions, increase of green areas, and expanded bicycle accessibility.
Air pollution causes about one in seventeen (5.9%) of all deaths in the country (2014). It is the eighth-largest cause of death, after factors such as diet, overweight, high blood pressure, alcohol and drugs, smoking and lack of exercise.
The air pollution of the Mexico City Metropolitan Area, contained within the Valley of Mexico, is measured by the Índice Metropolitano de la Calidad del Aire (Metropolitan Index of Air Quality).
History
In 1992, the United Nations named Mexico City "the most polluted city on the planet" and "the most dangerous city for children" six years later. From 1950 to 2015, the population in Mexico City increased from three million to twenty million. This population boom occurred mainly because of migrants that were looking for better opportunities, and as a consequence, the industrialization era began. This industrial growth was responsible for emitting over 11,000 tons of waste material into the atmosphere every day. As a result, the economy boomed as did the proliferation of vehicles. In 1980, there were 124 cars and light-duty trucks per 1000 residents. By 2010, there were 267. Population growth, increasing motorization and industrial activities, a constrained basin and intense solar radiation combined to cause intense air-quality problems of both primary and secondary pollutants. The automatic air-quality monitoring network, established in the late 1980s, revealed high concentrations of all criteria pollutants: lead, carbon monoxide, nitrogen dioxide, sulfur dioxide, ozone and particulate matter (PM). Ozone exceeded the air quality standards more than 90 percent of days and peaked above 300 parts per billion (about three times the standard) 40–50 days a year, among the worst in the world.
In 1990 the Mexican government decided to implement some air quality management programs to reduce emissions. Some of the programs included removal of lead from gasoline and the implementation of catalytic converters in automobiles, reduction of sulfur content in diesel transportation fuel, substitution of fuel oil in industry and power plants with natural gas, reformulation of liquified petroleum gas used for heating and cooking.
In 1993 the government mandated the replacement of lead-octane additives with MTBE and PEMEX, the state-run petroleum company, replacing underground storage tanks at all of its petrol stations.
In 2012 ozone and other air pollutants ranked at about the same level as Los Angeles. This improvement in air quality was achieved through the Mexican government's requirement that gasoline be reformulated, that polluting factories be closed or moved, and that drivers be prohibited from using their car one day per week. More recently there has been an expansion of public transport. Air pollution has been a major issue in Mexico City for decades.
Alongside a doubling of the vehicle fleet in Mexico City from 1992 to 2012, and the slow implementation of low-sulfur standards, the use of fuel ethers contributed greatly to an 86% decrease in CO, a 53% decrease in ozone, and a 32% decrease in particulate matter in that 20-year span.
Air pollutants
Ozone: Ozone can affect people's health by creating a sore throat, increase breathing difficulty, damage airways, and worsening lung diseases such as asthma or chronic bronchitis. Carbon monoxide: Carbon monoxide is a gas that is mostly emitted by vehicles. Inhaling carbon monoxide can cause heart and brain damage, even leading to death. Sulfur dioxide: Sulfur dioxide is produced by combustion of fossil fuels.Inhaling sulfur dioxide may cause health problems for people with diseases in the lung, making it more difficult for people with asthma to breathe and even leading to death if exposed longer. Particulates: There are two types of particles, Coarse Particles and ultrafine particles. Coarse particles (PM10) can decrease respiratory functionality. Ultrafine Particles (PM2.5), tend to penetrate into the gas exchange regions of the lung (alveolus), and very small particles may pass through the lungs to affect other organs.
Effects of air pollution on human health
Air pollution causes millions of deaths around the world, as it affects people's health by causing diseases. Individuals who are most at risk of suffering of these effects are children, people with previous respiratory diseases, and senior citizens. Around 15% of global child deaths are caused to air pollution (2024). Air pollution has the following effects on human health. Ischemic heart disease: problems in the heart caused by a lack of blood due to obstructed vessels. Chronic obstructive pulmonary disease: respiratory disease that diminishes airflow and generates thick mucus in the lungs (sputum) Breast cancer: uncontrolled growth of malignant cells in the breast. Places with more air pollution showed an 8% increase of breast cancer appearing. Lung cancer: uncontrolled growth of malignant cells in the lungs. Pneumonia: infection in the lungs caused by problems in the alveoli. Cataract (provoked by household air pollution): dull section in the lens of the eye that impairs vision. Dementia: dementia is the loss of intellectual abilities in a human being (such as memory loss). Locations with higher air pollution make people with dementia lose their intellectual abilities at a higher pace. Fertility: fertility is an organism's (in this case human) ability to reproduce. Air pollution can decrease semen quality, fertility, and create reproductive problems. Over the years, Mexico City's air pollution has negatively affected the population of the city. From 1995 to 2015, the lower quality of air has affected 24 million people living in the Metropolitan Area of the city. Also, PM 2.5 levels cause around 6,700 premature deaths each year in Mexico City. Additionally, early stages of Alzheimer have been found in young children.
Mexico City's air quality index In April–May 2016, ozone and suspended matter pollution in Mexico City reached levels that were detrimental to health, though the criteria to signal a pollution alert was lower in 2016 than in the 1980s. The city's population continues to grow and spread out, increasing automobiles usage in the city each year.
Mexico City previously used IMECA (Índice Metropolitano de la Calidad del Aire / Metropolitan Index of Air Quality), but transitioned to IAIS in 2020. IAIS (Índice Aire y Salud / Air and Health Index) is the tool used to measure air quality in Mexico City. A total of 34 monitors, located all around Mexico City measure the levels for the 6 main pollutants that are found in the atmosphere of the city. The measured pollutants are: O3, PM10, PM2.5, CO, NO2, SO2.
Indicators for each pollutant allow to assess the air quality with respect to specific pollution events. Indicators of the maximum hourly concentrations or for every 8 hours are used to evaluate the quality of the air based on health protection standards.
Five main categories for the quality of air based on IAIS
Good — Air quality is good and can enjoy outdoor activities. It can be identified with the color green. Fair — It has a moderate level of risk; people can do outdoor activities but can affect people with cardiac or lung diseases, as well as elderly people. It can be identified with the color yellow. Bad — It has a high level of risk; people should reduce vigorous outdoor activities. People become more prone to respiratory problems (children, elderly people, and may lead people with respiratory and lung diseases to a premature death. It can be identified with the color orange. Really bad — Associated with a really high level of risk; healthy people will start to show symptoms of a lower lung capacity. Higher risk of premature death for people with cardiac or lung diseases, as well as worsening symptoms for children and elderly people. It can be identified with the color red. Extremely Bad— Associated with an extremely high level of risk. Increase of severe respiratory symptoms for the general population. Serious negative effects for people of risk (children, elderly people, and people who suffer from cardiac or lung diseases). Higher risks of premature death for people who suffer from lung and cardiac diseases. It can be identified with the color purple.
Concentration of pollutants during the last decade
PM10: According to the NOM, the annual limit for PM10 was 50 μg/m3 before 2014 and 40 μg/m3 from 2015 to present day. In Mexico City, the annual concentration of PM10 has been above the limit for the last 10 years. The highest concentration occurred in November 2019, when the PM10 levels were found to be over 110 μg/m3. Failure to comply with this NOM indicates that it is necessary to carry out actions to reduce the concentration of particulate material in the ambient air, given that it is not observed that there is a tendency to decrease in the concentrations registered for this pollutant criterion in recent years.
PM2.5: The values have exceeded the regulated limits (15 μg / m3 before and during 2014 and 12 μg/m3 as of 2015 ) since 2011. In May 2019, the level of PM2.5 reached levels between 150 and 160 μg / m3. This concentrations were reached due to burning of organic matter such as forest fires, firewood, fuel burning, especially diesel and some industrial processes. This concentrations amounts to the equivalent of Mexico City's inhabitants (of all ages) smoking nearly three-and-a-half cigarettes those days.
Ozone (O3): The limits for ozone according to the NOM were 0.11 parts per million before 2014 and 0.095 ppm from 2015 to present times. Over the past two decades, ozone levels gradually fell below government limits as authorities moved factories out of the capital and tightened regulations on fuel and cars. In 2015, 37% of the total days showed poor air quality due to O3, 2016 brought a small improvement to 35% of the days. And again in 2017, 35% of the days were recorded as "bad" due to O3 levels. At times during the past two years, ozone concentration levels in the city reached such extreme levels that officials issued environmental risk alerts, urging people to stay indoors.
Sulfur dioxide (SO2): The NOM has three different limits to be met for concentrations of SO2: 8 hours (moving average), 24 hours (daily average) and annual average of the hourly data. 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 guideline value recommended by the World Health Organization, which is 0.008 ppm. From 2015 to 2017, the % of days with regular amounts of SO2 are minimal (above 5%).