Geography's Impact On Mexico City's Air Pollution

Mexico City has long been notorious for its poor air quality. In 1992, the United Nations named it the most polluted city on the planet. While the situation has improved significantly since then, air pollution remains a major issue. Geography plays a crucial role in this regard. Mexico City is located in a basin surrounded by mountains, creating a bowl effect that prevents the dispersion of pollutants. This unique geographical structure, coupled with rapid urbanisation, a growing population, and industrial activities, has led to the entrapment of air pollutants, severely impacting the city's air quality and the health of its residents.

The basin geography of Mexico City traps pollutants

Mexico City has long struggled with air pollution. The city's air quality issues reached a peak in the 1980s and 1990s, with ground-level ozone, carbon monoxide, sulphur dioxide, nitrogen dioxide, and airborne particles all at record levels. These pollutants are largely the result of human activities, such as the burning of fossil fuels in power plants and vehicle emissions.

Mexico City's geography plays a significant role in trapping these pollutants. The city is located in a basin surrounded by mountains, creating a "'bowl' effect" that hinders the natural dispersion of pollutants. This unique geographical structure allows pollutants like carbon monoxide to linger longer than they would in a more open area. The basin geography, combined with the city's high altitude, which causes oxygen levels to be lower, exacerbates the pollution problem.

The basin effect traps emissions from the dense vehicle population in Mexico City. There are about eight million cars travelling in the city every day, contributing to smog and releasing primary pollutants such as carbon monoxide, nitrogen oxide, sulphur oxides, and particulate matter. The topography of the city did not favour its industrialisation, as the basin traps pollutants from factories, power plants, and oil refineries.

The geographical location of Mexico City, nestled in a basin surrounded by mountains, is a significant factor in its air pollution issues. The basin effect hinders the dispersion of pollutants, leading to their accumulation and prolonged presence in the city's atmosphere. This unique geography, coupled with rapid urbanisation and industrialisation, has resulted in the city's notorious air quality issues.

To address the air pollution crisis, Mexican officials introduced the Management Programme to Improve Air Quality (Proaire) in 1996. This programme successfully reduced air pollution levels, bringing down the city's rating on the Metropolitan Air Quality Index (Imeca) from dangerously high levels in the 1980s to more manageable averages today. Other initiatives, such as the "Cars Don't Circulate" programme, which restricts vehicle use, and community-driven campaigns for tree-planting and car-free days, have also contributed to improving air quality in Mexico City.

The city's high altitude lowers oxygen levels

Mexico City's high altitude of 7382 feet above sea level has a significant impact on the city's air quality. The thin air at this altitude contains less oxygen, with levels approximately 25% lower than at sea level. This has a twofold effect on pollution in the city. Firstly, the low oxygen levels mean carbon-based fuels do not combust completely, leading to the release of harmful, unburnt fuel into the atmosphere. Secondly, the resulting low oxygen environment encourages the use of supplemental oxygen machines, which further contributes to air pollution.

The high altitude also affects the dispersal of pollutants. Mexico City is surrounded by mountains, creating a "bowl" effect that traps pollutants and prevents their natural dispersion. This unique geographical structure allows carbon monoxide and other pollutants to linger, leading to the city's notorious smog and haze. The topography of the city, situated in a basin, further exacerbates this issue, as air pollutants are naturally trapped in low-lying areas.

The combination of high altitude, mountainous surroundings, and basin geography creates a perfect storm for air pollution in Mexico City. The natural geographical features of the region have contributed significantly to the city's historical struggle with poor air quality. While great improvements have been made in recent years, with the city dropping to 917th place in global air pollution rankings, the geographical challenges remain.

To combat these challenges, the Mexican government has implemented various measures. Reformulating gasoline, closing or relocating polluting factories, and enforcing car-free days have all contributed to significant reductions in carbon monoxide, ozone, and particulate matter. Additionally, the expansion of public transportation and increased use of fuel ethers have helped improve air quality. These efforts demonstrate the recognition of the role that geographical factors play in air pollution and the commitment to mitigating their impact.

The proliferation of vehicles

Mexico City's air pollution problem is partly caused by the proliferation of vehicles. The city's population boom, from 3 million in 1950 to 20 million in 2015, was driven by industrialization, which brought thousands of migrants from around the world. This led to a sharp rise in emissions from the transport sector, with the number of cars and light-duty trucks per 1,000 residents increasing from 124 in 1980 to 267 in 2010.

The densely populated capital now has more than 8 million cars traveling within it every day, contributing to the city's smog problem. The number of vehicles in the city increases yearly, and the expansion of the city means automobile trips are lengthening. These cars emit greenhouse gases and air pollutants such as carbon monoxide, nitrogen oxide, sulfur dioxide, and particulate matter. In addition, the use of liquefied petroleum gas (LPG) in metropolitan areas is an ongoing issue.

To combat this, the Mexican government has implemented several measures. These include requiring the reformulation of gasoline, closing or moving polluting factories, and prohibiting drivers from using their cars one day a week. The government has also expanded public transportation and increased bicycle accessibility. In 1989, the city introduced the "Cars Don't Circulate" (Hoy No Circula) program, which restricts the use of a fifth of all vehicles on weekdays, depending on the registration plate.

While these measures have helped to reduce air pollution, Mexico City still faces challenges. Traffic congestion remains a problem, and the persistence of PM2.5 and PM10 particles, which are difficult to control, continues to impact air quality. The basin geography of the city also plays a role, with the surrounding mountains preventing pollutants from escaping.

Industrial emissions

The burning of fossil fuels in power plants and industrial facilities has released harmful chemicals and gases into the atmosphere. Fossil fuels, such as coal, oil, and natural gas, are the primary sources of energy in Mexican factories. When these fuels are burned, they emit primary pollutants such as carbon monoxide, nitrogen oxide, sulfur oxides, and particulate matter (dust, ashes, etc.). These pollutants can irritate the eyes and throats of residents and contribute to global warming. Furthermore, when exposed to sunlight, primary pollutants can undergo photochemical reactions, forming secondary pollutants like nitrogen dioxide, sulfuric acid, and ozone.

The industrial growth and proliferation of vehicles during the 20th century, driven by rapid population growth and urbanisation, led to a significant increase in emissions. The number of cars per resident increased, and the use of toxic fuel and inefficient energy use in transportation contributed to the problem. The dense population of the capital, with its numerous industrial plants, resulted in a thick smog that enveloped the city. The geographical location of the city, surrounded by mountains, further hindered the escape of pollutants.

To address the issue of industrial emissions, the Mexican government has implemented measures such as requiring the reformulation of gasoline, closing or relocating polluting factories, and restricting vehicle use through programmes like "Cars Don't Circulate" (Hoy No Circula). These efforts have led to significant improvements in air quality, with decreases in carbon monoxide, ozone, and particulate matter levels. However, Mexico City still faces challenges in reducing emissions and improving air quality, and community initiatives and international collaborations are crucial in this endeavour.

The use of fossil fuels

Mexico City's air pollution has been a major concern for its population and health officials for decades. The city's topography, located in a basin, traps air pollutants. The burning of fossil fuels in vehicles, power plants, and industrial processes has been a significant contributor to the city's poor air quality.

During the 20th century, Mexico City underwent rapid industrialization and urbanization, with its population increasing substantially. This led to a proliferation of vehicles and industrial growth, which emitted large amounts of pollutants into the atmosphere. The burning of fossil fuels in power plants and vehicles releases harmful pollutants such as carbon monoxide, nitrogen dioxide, and sulphur dioxide. In the 1980s, the number of cars per resident was relatively low, but these vehicles were of poor quality and used highly toxic fuel.

The incomplete combustion of carbon-based fuels, a common issue at high altitudes, further exacerbated the problem. Mexico City's altitude of 7382 feet above sea level resulted in oxygen levels that were 25% lower, impacting the combustion of carbon-based fuels. The combination of these factors led to severe air pollution, with ground-level ozone, carbon monoxide, sulphur dioxide, nitrogen dioxide, and airborne particles reaching record levels in the 1980s and 1990s.

To address the air pollution crisis, the Mexican government implemented various measures. They mandated the reformulation of gasoline, closed or relocated polluting factories, and introduced a no-drive day for residents. These initiatives, along with the expansion of public transportation and the implementation of low-sulphur standards, contributed to significant improvements in air quality. By 2021, Mexico City's ranking had dropped to 917th in the list of the world's most polluted cities, a remarkable improvement from its previous position as the most polluted city.

Frequently asked questions