Bronte Wells
Mexico City has long struggled with air pollution, which has been a concern for the city's population and health officials for decades. In 1992, the UN declared it the most polluted city in the world, and while it has improved since then, air pollution remains a significant issue. The city's high altitude, rapid industrialization, proliferation of vehicles, and population growth have all contributed to the problem. Various factors affect the air quality at different times of the year, with some months experiencing higher pollution levels than others.
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What You'll Learn
Population growth and industrialisation
Mexico City has long been notorious for its poor air quality, which has been a concern for its population and health officials for decades. The city's air pollution problem is largely attributable to its rapid population growth and industrialisation during the 20th century.
From 1950 to 2015, the population of Mexico City skyrocketed from three million to twenty million, with the metropolitan area of the valley of Mexico, or Greater Mexico City, growing from 3.1 million in the 1950s to 14 million in the 1980s. This population boom was driven by migrants seeking better opportunities, which in turn spurred industrialisation. As a result of this rapid and unexpected growth, the United Nations (UN) declared Mexico City the most polluted city in the world in 1992.
The industrialisation of Mexico City led to the emission of over 11,000 tons of waste material into the atmosphere daily. This was exacerbated by the proliferation of vehicles, with the number of cars and light-duty trucks per 1000 residents increasing from 124 in 1980 to 267 by 2010. The inefficient use of energy in industry and transportation has resulted in high carbon dioxide emissions, with Mexico ranking first in Latin America. The burning of fossil fuels in vehicles, power plants, and industrial processes has led to the release of harmful pollutants such as carbon monoxide, sulfur dioxide, nitrogen oxides, and ozone.
The geographical location of Mexico City also contributes to its poor air quality. The city's high altitude of 7382 feet above sea level results in oxygen levels that are 25% lower than at sea level. This reduces the efficiency of car engines, leading to increased emissions. Additionally, the city is located in a basin where warm air traps pollutants, preventing their dispersal.
To address the air pollution crisis, the Mexican government has implemented various measures. These include the "Hoy No Circula" program, which restricts vehicle usage based on emissions testing results, the removal of lead from gasoline, the reformulation of fuels, the closure or relocation of polluting factories, and the expansion of public transportation. As a result of these efforts, Mexico City's air quality has shown significant improvement, dropping to the 917th most polluted city in the world in 2021.
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Proliferation of vehicles
Mexico City's air pollution has been a concern for decades, with the United Nations declaring it the most polluted city in the world in 1992. One of the critical factors contributing to this problem is the proliferation of vehicles.
The number of automobiles in Mexico City has been increasing yearly. In 1980, there were 124 cars and light-duty trucks per 1000 residents, and by 2010, this number had risen to 267. The total number of registered vehicles in the city is approximately 5.5 million. This increase in vehicles has had a direct impact on air quality, as cars emit pollutants such as carbon monoxide and nitrogen oxides, which contribute to the formation of ozone, a harmful secondary pollutant.
The impact of the proliferation of vehicles is exacerbated by the city's high altitude of 7382 feet (or 7000 feet according to another source) above sea level, which results in oxygen levels being 25% lower than at sea level. This thin air exacerbates the harm caused by pollutants. Additionally, the city experiences an "ozone season" from February to June due to the prevalence of high-pressure systems, clear skies, weak wind, intense solar radiation, and the absence of humidity. During this period, pollutants accumulate, leading to even higher ozone concentrations.
To address the issue of vehicle emissions, Mexico City has implemented several measures. One example is the Hoy No Circula (HNC) program, introduced in 1989, which assigns colored stickers to vehicles based on their license plates and prohibits them from driving one day a week. The program has been successful in reducing emissions by 25% to 70%, depending on the pollutant. Additionally, the city has mandatory emissions testing, with hologram stickers assigned to the cleanest vehicles, exempting them from restrictions. The city has also expanded public transportation, including new rapid-transit bus lines and the largest bicycle-sharing initiative in North America.
However, despite these efforts, vehicle emissions remain a significant contributor to air pollution in Mexico City. A 2022 study found that older cars, while making up a small portion of the fleet, contribute a disproportionately large share of emissions. Taxis, for example, showed 2.2-3.1 times higher emissions across all pollutants compared to private vehicles. Furthermore, certain popular vehicle models certified to the latest national emission standards still showed emissions several times above the fleet average, indicating the need for stricter regulations and enforcement.
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Fuel and combustion
The burning of fossil fuels in vehicles, power plants, and industrial processes releases primary pollutants such as carbon monoxide and sulfur dioxide directly into the environment. Carbon monoxide is a toxic gas emitted primarily by vehicles, which can cause dizziness, brain dysfunction, and even death. In 2011, the limit for carbon monoxide established in the NOM for stations within Mexico City had not been exceeded, indicating some improvement in air quality. However, in May 2019, the government of Mexico City declared an extraordinary atmospheric environmental contingency due to harmful particle levels exceeding accepted standards. Sulfur dioxide is produced by the combustion of fossil fuels, and exposure to it is associated with increased respiratory symptoms, disease, and breathing difficulties.
To address these issues, the Mexican government has implemented several measures. In 1993, the government mandated the removal of lead-octane additives from gasoline and their replacement with MTBE and PEMEX, the state-run petroleum company. This, along with the implementation of catalytic converters in automobiles, helped reduce carbon monoxide levels. Additionally, the government has worked to reduce sulfur content in diesel transportation fuel and substitute fuel oil in industry and power plants with natural gas. In 2016, CRE enacted NOM-016-CRE-2016, allowing ethanol blends in gasoline outside metropolitan zones, and in 2017, they increased the allowable ethanol blends to 10%. While these measures have helped, air pollution remains a critical issue, with ozone and PM2.5 levels continuing to exceed safe limits and adversely impacting the health of residents.
Volatile Organic Compounds (VOCs) from vehicle emissions and combustion sources are a significant contributor to Mexico City's pollution. VOCs are precursors to ambient ozone and secondary organic aerosols (SOAs), and their levels directly impact ozone concentrations. As a result, higher VOC emissions lead to increased ozone and PM2.5 levels, exacerbating health problems. The city's altitude also plays a role in ozone formation, as ozone levels are VOC-limited. While the government has made efforts to improve air quality, the slow implementation of low-sulphur standards and the continued use of fuel ethers have hindered progress.
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Secondary pollutants
Mexico City's air pollution is a problem that has been of concern to its population and health officials for decades. In 1992, the United Nations named Mexico City "the most polluted city on the planet". This was due to a combination of factors, including the city's high altitude, which lowers its oxygen levels, and the proliferation of vehicles and rapid industrial growth.
The pollutants in Mexico City's atmosphere are classified as primary and secondary pollutants. Primary pollutants are those emitted directly into the environment, such as carbon monoxide and sulfur dioxide. Secondary pollutants, on the other hand, are created in the atmosphere due to chemical reactions. These include sulfate and ozone.
Ozone is a significant secondary pollutant and is formed primarily from photochemical reactions between organic compounds and nitrogen oxides. Ozone can affect the respiratory, cardiovascular, and central nervous systems. Exposure to ozone has been linked to early death and problems with reproductive health and development. In April and May 2016, ozone and suspended matter pollution in Mexico City reached levels detrimental to health. More recently, in 2022, the Environmental Commission of the Megalopolis issued five air quality alerts, with levels of small particles, known as PM10, reaching 581 points in one borough, on a scale where 100 is considered the highest acceptable level.
Another critical secondary pollutant is nitrogen dioxide, which is produced when primary pollutants react with sunlight. While not mentioned specifically in the context of Mexico City, sulfuric acid is another secondary pollutant that forms when sulfur dioxide, a primary pollutant, reacts with other chemicals in the atmosphere.
To combat air pollution, the Mexican government has implemented several measures, including requiring the reformulation of gasoline, closing or relocating polluting factories, and prohibiting drivers from using their cars one day a week. These measures have helped improve air quality, with ozone and other air pollutants ranking at about the same level as Los Angeles in 2012.
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Government policies to reduce pollution
Mexico City has been ranked as the most polluted city in the world. The pollution is mainly due to the city's high altitude, which causes its oxygen levels to be 25% lower, and carbon-based fuels that do not combust completely. Other factors include the proliferation of vehicles, rapid industrial growth, and a population boom. Recognising the severity of the situation, the Mexican government has implemented several policies and plans to reduce emission levels. Here are some of the key government policies and initiatives aimed at reducing pollution in Mexico City:
Vehicular Restrictions and Promotion of Public Transportation:
The Mexican government has implemented measures such as ""No-Drive Days" or "Hoy No Circula", which prohibit drivers from using their vehicles one day a week, including Saturdays. This policy was introduced in 1989 and aimed to reduce the number of vehicles on the road. However, it was later recognised that this policy was not as effective as hoped, as people started buying additional cars to drive on restricted days. As a result, the government has focused on expanding and improving public transportation options. This includes the Metrobus system, the introduction of hybrid and electric taxis, and the improvement of pedestrian areas.
Fuel Reformulation and Emission Control:
The government has mandated the reformulation of gasoline and diesel fuel to reduce pollutants. This includes removing lead from gasoline, implementing catalytic converters, and reducing the sulphur content in diesel. Additionally, the government has worked to improve fuel quality and introduced programs to identify high-emitting and non-compliant vehicles.
Closure or Relocation of Polluting Industries:
The Mexican government has taken steps to close or relocate polluting factories and industries, moving them away from populated areas.
Expansion of Green Areas and Reforestation:
Mexico City authorities have plans to increase green spaces and promote reforestation. This includes initiatives like the Green inspectors program and the strengthening of health programs to improve air quality and encourage sustainability.
Solid Waste Management:
The city has implemented improved collection and disposal methods for solid waste, including the potential use of landfill gas recovery to supply clean energy. Residents are also encouraged to follow new trash and recycling regulations.
Energy-Efficient Buildings and Renewable Power Supply:
Mexico City has launched initiatives to improve energy efficiency in public and private buildings, such as replacing lamps with better technology and installing photovoltaic panels.
Reduction of Agricultural Waste Burning:
The government is helping regulate the open burning of agricultural waste through fire prevention workshops, treatment of controlled burns, and the creation of buffer zones between agricultural and forest areas.
Air Quality Monitoring and Data Collection:
Mexico City has an extensive data collection system, including air quality monitoring stations that measure various pollutants. This information is crucial for designing and implementing effective air pollution control policies and alerting the public to high pollution events in advance.
These policies and initiatives have contributed to a significant improvement in Mexico City's air quality, with the city dropping to the 917th position in the ranking of polluted cities globally in 2021. However, there is still work to be done, as the concentration of airborne particles (PM2.5) exceeds the World Health Organization's guidelines.
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Frequently asked questions
In 1992, the United Nations named Mexico City "the most polluted city on the planet".
The high levels of pollution were caused by a combination of factors, including the proliferation of vehicles, rapid industrial growth, the burning of fossil fuels, and the population boom.
Primary pollutants such as carbon monoxide and sulfur dioxide, which are emitted directly into the environment, and secondary pollutants such as sulfate and ozone, which are created in the atmosphere due to chemical reactions.
The Mexican government has implemented several measures to reduce emission levels, including vehicular restrictions such as the "Hoy No Circula" policy, requiring emissions testing for vehicles, increasing green areas, and expanding public transportation and bicycle accessibility.
Yes, the air quality in Mexico City has significantly improved in recent years. According to IQAir, a company that tracks air quality worldwide, Mexico City dropped to the 917th most polluted city in the world in 2021, although its concentration of airborne particles still exceeds WHO guidelines.
