Mexico's Pollution Problem: An Unusual Crisis

Mexico's air pollution has been a leading environmental, economic, and health risk for decades. The country's industrialisation, poor rural communities, and geographical location have contributed to air quality issues. In 1992, Mexico City was declared the world's most polluted city by the United Nations, with birds seen falling out of the sky dead due to the poor air quality. While air pollution in Mexico has improved since then, it still faces challenges. Mexico's PM2.5 levels in 2023 averaged over 20 µg/m³, exceeding the World Health Organization's recommended limit. The country's economic losses due to air pollution topped USD 8 billion in 2020, and it continues to pose significant risks to public health and the environment.

Mexico City's basin location and high altitude trap pollution

Mexico City's location in a basin surrounded by mountains, coupled with its high altitude, contributes to the trapping of air pollution in the city. The basin-like topography, often described as bowl-shaped, creates a unique atmospheric dynamic where warmer air traps colder air, preventing the dispersal of pollutants. This phenomenon, known as temperature inversion, allows pollution from human activities to accumulate over several days. The high altitude of Mexico City, approximately 7,400 feet (2,240-2,255 meters) above sea level, further exacerbates the problem by influencing oxygen levels and combustion processes.

The combination of geographical factors and human activities has led to acute air pollution issues in Mexico City. The metropolitan area, with a population of over 15 million people, has a significant number of motor vehicles, estimated at 1.5 million, and a substantial industrial presence, accounting for around 21% of the country's industrial activity. The proliferation of older, poorly made vehicles, along with the use of toxic fuel, has contributed to the high levels of ground-level ozone, carbon monoxide, sulphur dioxide, nitrogen dioxide, and airborne particles.

In addition to vehicle emissions, non-regulated factories, power plants, and oil refineries have historically played a significant role in polluting the air in Mexico City. The incomplete combustion of carbon-based fuels and the burning of other organic fuels for cooking and heating further exacerbate the problem. The loss of natural forests, due to agricultural expansion and land use changes, has also impacted air quality. Wildfires, influenced by environmental conditions like above-average temperatures, low rainfall, and drought, have been identified as another unusual cause of pollution in the city.

The unique geographical characteristics of Mexico City's basin location and high altitude have undoubtedly played a role in trapping pollution and contributing to the city's historical air quality issues. However, it is essential to recognize the significant impact of human activities, including industrialization, urbanization, and vehicle emissions, on the overall pollution levels in the area. Addressing these issues will require a combination of effective environmental policies, emission reduction strategies, and a shift towards more sustainable practices.

Industrial growth, population increases, and vehicle emissions

Mexico City has long been notorious for its poor air quality, having been named the world's most polluted city in 1992. While the city has since dropped to 917th place in global city air pollution rankings, it still faces significant pollution challenges. Industrial growth, population increases, and vehicle emissions are key factors in this.

During the 20th century, Mexico City underwent rapid industrialization, attracting thousands of migrants from across the globe. This industrialization and urbanization led to a substantial increase in the population of the metropolitan area, which grew from 3.1 million in the 1950s to 14 million in the 1980s. The population continues to grow, and as the city spreads out, automobile trips lengthen, and the number of vehicles in the city increases annually. In 1980, there were 124 cars and light-duty trucks per 1000 residents, and by 2010, this number had risen to 267. More than 3.5 million vehicles are registered in the country, 30% of which are over 20 years old.

The proliferation of vehicles, combined with poor-quality cars running on highly toxic fuel, has contributed significantly to air pollution in Mexico City. The burning of fossil fuels in vehicles emits ground-level ozone, carbon monoxide, nitrogen dioxide, sulphur dioxide, and airborne particles—all major air pollutants. In addition, industrial activities, power plants, and oil refineries have been significant sources of pollution, with unregulated and highly polluting operations in the past.

Mexico's energy sector, particularly the burning of fossil fuels, is responsible for the majority of greenhouse gas emissions. The country has made efforts to reduce emissions, but the trajectory of CO2 emissions remains higher than required to mitigate the worst effects of climate change. Vehicle emissions in Mexico have been historically higher than in the United States, attributed partly to outdated vehicle technologies.

To address these issues, the Mexican government has implemented various measures. These include removing lead from gasoline, implementing catalytic converters, reducing sulphur content in diesel fuel, substituting fuel oil with natural gas, and expanding public transportation. While these efforts have led to improvements, air pollution remains a critical issue, with about one in seventeen deaths in the country attributed to poor air quality.

Forest fires and other environmental conditions

Mexico has a total area of 1,967,183 square kilometres, with a forest area of 141.7 million hectares. The forest fire season usually occurs between January and July, with March and April being the major fire months due to the dry season. In 2020, the Mexican National Forestry Commission (CONAFOR) registered 5,583 wildfires across Mexico, affecting 310,000 hectares of grassland and 23,000 hectares of forest.

Human activities cause 97% of wildfires in Mexico, with agricultural and cattle activities causing 54% of fires. In tropical zones, the main cause of fires is the practice of slash-and-burn agriculture. In temperate forests, burns to improve grass conditions for cattle are the primary cause. Across Mexico and Central America, almost half of the fires are due to agricultural activities. Many are also linked to poverty and a lack of forestry culture. Fires are set to clear areas logged of valuable timber trees to generate pasture for cattle, and they are frequently reset yearly to improve the palatability of young grass to cows or to eliminate crop parasites.

Forest fires in Mexico have contributed to the country's air pollution problem. In 2019, wildfires were an unusual cause of pollution, with at least 66 fires reported in the capital and 130 in the State of Mexico. The smoke and particles generated by the fires, combined with other environmental conditions, worsened the situation. These included above-average temperatures, low rainfall, prolonged drought, higher solar radiation, and a high-pressure system that prevented the dispersion of contaminants.

The topographical location of Mexico City also plays a role in trapping air pollutants. The city is located in a basin surrounded by mountains, which creates a bowl-like effect. Additionally, the city's high altitude (7,382 feet above sea level) causes its oxygen levels to be 25% lower, impacting the combustion of carbon-based fuels.

Cooking with biomass fuels and poor ventilation

Mexico City was once the world's most polluted city, but it has since dropped to 917th place as of 2021. This improvement is largely due to the Mexican government's active plans to reduce emission levels, which include citizen participation, vehicular restrictions, increasing green areas, and expanding bicycle accessibility. However, air pollution remains a significant issue, with the city's concentration of airborne particles (PM 2.5) still exceeding World Health Organization (WHO) guidelines.

One contributing factor to Mexico's air pollution is the use of biomass fuels for cooking and heating, which is a significant source of indoor air pollution. Biomass fuels, such as wood, charcoal, dung, and crop residues, are commonly used in developing countries for cooking, heating, and lighting. In Mexico, the use of biomass fuels and simple cooking stoves can emit substantial amounts of toxic pollutants, particularly in households with limited ventilation. This is exacerbated by the poor design of stoves that lack flues or hoods to remove smoke from the living area, leading to increased exposure to pollutants for household members, especially women and children.

The adverse health effects of indoor air pollution from biomass fuel combustion are well-documented. Long-term exposure to biomass fuel smoke has been linked to an increased risk of respiratory infections, including pneumonia, tuberculosis, and chronic obstructive pulmonary disease (COPD). It is also associated with low birth weight, cataracts, cardiovascular events, and all-cause mortality in both adults and children. The impact of household air pollution is significant, contributing to an estimated 3.2 million deaths per year globally, including over 237,000 deaths among children under the age of five.

To address this issue, the WHO has issued guidelines for indoor air quality, recommending against the use of unprocessed coal and kerosene. Advanced biomass stoves with chimneys and blowers can significantly reduce pollutant concentrations, but their high cost remains a barrier for low-income households. Transitioning to cleaner fuels, such as liquefied petroleum gas (LPG), natural gas, or electricity, is another solution, but the success of these initiatives depends on making these alternatives cheaper and more accessible to low-income communities.

Health and economic impacts of air pollution

Mexico City was once labelled the world's most polluted city by the United Nations in 1992. Its location in a basin surrounded by mountains, coupled with its high altitude, makes it a place where pollution is trapped. The city's industrialisation and urbanisation, coupled with a rapid increase in population, led to severely poor air quality.

Health Impacts

The health impacts of air pollution in Mexico City are significant. A survey of 2000 households in lower-income neighbourhoods found that nearly 95% considered air pollution a "problem" or a "big problem". The concentration of airborne particles (PM 2.5) exceeds the guidelines of the World Health Organization (WHO), and people exposed to this level of pollution can suffer from coughing, shortness of breath, bronchitis, respiratory infections, and heart problems. In addition, the city's unique topography can trap air pollutants, leading to even higher levels of contamination. The frequent activity of the nearby volcano Popocatepetl has also been linked to increased pollution levels.

The social and economic factors that influence the perception of air quality are complex and involve socioeconomic status, demographic factors, social networks, and access to infrastructure. However, it is clear that air pollution disproportionately affects the poor, who are more likely to work in informal jobs without access to paid sick leave. As a result, they may be exposed to higher levels of pollution and are at a greater risk of developing respiratory and other pollution-related illnesses.

A study found that 15.5% of respondents had a respiratory illness or lived with someone who had a respiratory illness. These respondents were more likely to be aware of the IMECA index, which measures the level of pollution and the associated health risks in Mexico City. The index categorises air quality as "good", "fair", or "poor", with "poor" air quality posing health risks to sensitive groups, including people with breathing or heart problems, children, and the elderly.

Economic Impacts

The economic impacts of air pollution in Mexico City are also significant. On days with very high PM contamination, the city's roughly 3.5 million workers lose an average of 7.5% of their working hours. This has serious implications for informal workers, who tend to work more on days with high pollution levels and have less ability to make up for lost hours.

Mitigation Efforts

Recognising the severity of air pollution, the Mexican government has implemented various plans to reduce emission levels. These plans include citizen participation, vehicular restrictions, the expansion of green areas, and improved bicycle accessibility. The ProAire program, for example, aims to minimise unnecessary emissions by amending bus routes and introducing newer, more efficient buses. Additionally, the activation of the ACEP during the spring season has become necessary due to the seasonal high levels of air pollution from climate change.

Despite these efforts, current environmental policies lack sufficient financial and political backing from the federal government, highlighting the need for a more unified approach to tackling this national issue.

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