Mexico City's Air Pollution: Causes And Concerns

Mexico City has long been infamous for its poor air quality. In 1992, the United Nations declared it the world's most polluted city. Since then, the city has seen a significant improvement in its air quality, dropping to the 917th most polluted city in the world in 2021. However, Mexico City still faces air pollution issues, with its concentration of airborne particles exceeding the World Health Organization's (WHO) guidelines. The causes of air pollution in Mexico City are multifaceted and complex, ranging from rapid urbanisation and industrialisation to vehicle emissions and wildfires. The unique geographical location of the city, surrounded by mountains, also contributes to the trapping of pollutants. This combination of factors has resulted in severe health issues for its residents, including respiratory problems, skin issues, and long-term conditions such as asthma and cognitive decline.

Industrialisation and urbanisation

Mexico City has long been infamous for its poor air quality, which reached its peak in the 1980s and 1990s. During this period, the metropolis was a byword for thick smog and hazy skylines. The air was so toxic that birds were found dead from falling out of the sky. The United Nations declared Mexico City the world's most polluted city in 1992.

The primary cause of this air pollution was the combination of industrialisation and urbanisation. The population of Greater Mexico City grew exponentially from 3.1 million in the 1950s to 14 million in the 1980s. This rapid urbanisation led to a surge in human activities, such as the use of private vehicles and the establishment of factories, power plants, and oil refineries. The topography of the city, nestled in a basin surrounded by mountains, further exacerbated the problem by trapping air pollutants. The increase in industrial and human activities resulted in high levels of ground-level ozone, carbon monoxide, sulphur dioxide, nitrogen dioxide, and airborne particles, all significant contributors to air pollution.

The Mexican government recognised the severity of the air pollution crisis and implemented various policies to address the issue. The ""Hoy No Circula" program, for example, restricted vehicles from circulating on certain days based on their license plate numbers. The government also introduced emissions testing for all vehicles, with verification assigned based on performance. Additionally, Mexico's ProAire policies, introduced in 1990, played a crucial role in reducing pollution levels. These policies included the introduction of catalytic converters, the elimination of lead from gasoline, the relocation of high-polluting facilities outside the metropolitan area, and the improvement of vehicle fuel and emissions standards. As a result of these efforts, pollution levels in Mexico City have significantly decreased, with a 57% reduction attributed to the ProAire policies alone.

Despite the improvements, air pollution remains a significant concern in Mexico City. The city still struggles with high levels of PM2.5, fine particulate matter that can penetrate deep into the lungs and cause various health issues such as coughing, respiratory infections, and heart problems. The unique geographical location of the city, surrounded by mountains, continues to trap pollutants and hinder their natural dispersion. Additionally, the ever-increasing number of cars, especially older models with outdated emissions systems, contributes to the unchecked release of harmful pollutants.

To further combat air pollution, Mexico City has implemented additional measures such as investing in public transport, including the Metrobus rapid transit system, promoting the use of cleaner fuels like LPG, and encouraging the adoption of improved cookstoves in rural areas. These efforts have led to a notable decline in pollution levels, with Mexico City dropping to the 917th most polluted city in the world in 2021. However, there is still work to be done to ensure that the air quality in Mexico City meets the guidelines set by the World Health Organization (WHO) and to mitigate the health, economic, and quality-of-life impacts of air pollution on its residents.

Poorly-regulated industry

Mexico City's air pollution crisis has multiple causes, and while the city has improved its air quality in recent years, it still faces challenges. One significant contributor to the poor air quality in the past was the presence of poorly-regulated industries and manufacturing plants.

During the late 20th century, Mexico City underwent rapid industrialisation and urbanisation, with the population increasing from 3.1 million in the 1950s to 14 million in the 1980s. This rapid growth, coupled with a lack of stringent environmental regulations, resulted in severe air pollution. The city's unique geography, nestled in a basin surrounded by mountains, further exacerbated the issue as the basin traps air pollutants, hindering their natural dispersion.

The industrial areas within and surrounding Mexico City played a significant role in the city's air quality issues. Chemicals from manufacturing plants and emissions from power stations were released unchecked, posing severe environmental and health hazards. The topography of the city did not favour its industrialisation, and the pollutants were trapped, leading to even worse air quality. The situation was so severe that in 1992, the United Nations declared Mexico City the most polluted city globally, with pollution levels so high that birds were found dead from the toxic air.

To address the air pollution crisis, the Mexican government implemented various policies and initiatives. The ""Hoy No Circula" program, for example, restricted vehicles from circulating on certain days based on their license plate numbers. The government also introduced emissions testing for all vehicles, with underperforming vehicles being issued a verification. Additionally, the Comprehensive Program Against Air Pollution (PICCA), established in 1990, required new vehicles to have catalytic converters and introduced unleaded gasoline and vehicle emissions standards. These policies, along with others, contributed to a significant reduction in air pollution in Mexico City, with a 57% decrease in pollution levels since the introduction of the ProAire policies in 1990.

While great strides have been made, Mexico City still faces challenges in regulating its industries and ensuring compliance with environmental standards. The collaboration between the city's health and environmental officials and Harvard researchers aims to evaluate the health and economic benefits of the implemented policies and further improve air quality in the city.

Geography and topography

Mexico City is located in a valley surrounded by mountains. This unique geography creates a "bowl" effect that traps pollutants, preventing their natural dispersion. The topography of the city does not favour industrialisation, as the air pollutants from cars, factories, and power plants are trapped in the basin. This has led to severely poor air quality, with ground-level ozone, carbon monoxide, sulphur dioxide, nitrogen dioxide, and airborne particles reaching record levels in the 1980s and 1990s. The city's location at 7,300 feet above sea level also contributes to the challenge of reducing air pollution.

The "bowl" effect, caused by the surrounding mountains, hinders the dispersal of pollutants, causing them to linger longer than they would in more open areas. This geographical predisposition to trap pollution has resulted in Mexico City's notorious association with thick smog and hazy skylines. The city's topography, combined with rapid urbanisation and industrialisation, has led to a significant decline in air quality.

Mexico City's status as a valley surrounded by mountains has been specifically identified as a contributing factor to its poor air quality. The basin-like shape of the valley traps air pollutants, creating a situation where harmful emissions from vehicles, industries, and power plants accumulate rather than dissipate. This has resulted in the city frequently experiencing high levels of ground-level ozone, carbon monoxide, and other harmful pollutants.

The geographical layout of Mexico City, with its mountain enclosure, has significantly hindered the natural dispersion of pollutants. The trapped emissions from various sources have led to a concentrated build-up of harmful substances, impacting the health and well-being of residents. This unique geographical challenge has been a critical factor in Mexico City's historical struggle with air pollution.

The implementation of various policies, such as the ""Hoy No Circula" program, emissions testing for vehicles, and the introduction of cleaner fuels, has helped to mitigate the effects of the city's geography on air pollution. These measures have contributed to a notable reduction in pollution levels, with a 57% decrease reported since the introduction of the ProAire policies in 1990. However, the geographical constraints continue to pose a challenge, and further efforts are needed to overcome them.

Vehicle emissions

Mexico City has long suffered from poor air quality, and vehicle emissions have been a significant contributor to this issue. The problem of vehicle emissions is multifaceted and is caused by a combination of factors.

One major factor is the sheer number of cars on the roads. In the 1980s, there were about 124 cars per 1000 residents, and while this number may not seem particularly high, the cars themselves were of poor quality and ran on very toxic fuel. This, combined with a lack of efficient public transport systems, has led to an unchecked release of harmful pollutants from vehicles. The number of vehicles in Mexico City has continued to increase, with a doubling of the number of cars in the two decades since 1992, exacerbating the problem of vehicle emissions.

The unique geography of Mexico City also plays a role in trapping vehicle emissions and other pollutants. The city is located in a basin or "bowl" surrounded by mountains, which hinders the natural dispersion of pollutants, causing them to linger longer than they would in more open areas. This topography, combined with the high volume of traffic, has led to thick layers of smog that have become synonymous with the city.

To combat vehicle emissions and improve air quality, the government has implemented a range of policies and initiatives. The "Hoy No Circula" program, for example, restricts certain vehicles from being on the road on particular days based on their license plate numbers. While this program has had some impact, it has also been circumvented by residents who simply purchase second cars or take taxis on the days their primary vehicles are restricted. Other policies include emissions testing and verification for all vehicles, the introduction of catalytic converters and unleaded gasoline, and incentives for the purchase of cleaner vehicles.

The government has also invested significantly in public transport, including the Metrobus rapid transit system, which uses a fleet of clean, fuel-efficient buses, and the development of Latin America's largest bike-sharing program. These initiatives have helped to reduce vehicle emissions and improve air quality in Mexico City, with pollution levels dropping by 57% since the introduction of the 1990 ProAire policies. However, there is still work to be done, as air pollution continues to be a major health and quality-of-life issue for the city's residents.

Wildfires

Mexico's national forest commission reported 168 active wildfires burning over a quarter of a million acres in 2024, impacting air quality not just in Mexico but also in the southern United States. This fire season was fuelled by hot and dry conditions, with 82% of the country experiencing unusual dryness and nearly 70% under drought conditions. The combination of wildfires, agricultural burns, and persistent winds from the south sent smoke and haze over the Gulf Coast, from Texas to Florida, affecting visibility and air quality.

While wildfires are a natural occurrence, their frequency and intensity have been influenced by human activities and climate change. The dry spell and drought conditions in Mexico have provided favourable conditions for wildfires to spread, impacting the air quality in Mexico City and surrounding regions.

To address the air pollution caused by wildfires, Mexico City officials have implemented measures such as declaring environmental contingencies, advising residents to stay indoors, and temporarily closing schools. These actions aim to protect public health and reduce the immediate impact of wildfire smoke on the city's air quality.

Additionally, long-term strategies, such as improving forest management practices, implementing controlled burns, and enhancing wildfire prevention and suppression efforts, can help mitigate the impact of wildfires on air quality in Mexico City and surrounding areas. By proactively addressing the root causes of wildfires, Mexico can reduce their frequency and intensity, thereby minimising their contribution to air pollution.

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