Mexico City's Pollution: Understanding The Complex Factors Involved

Mexico City, once named the world's most polluted city, has seen substantial improvements in its air quality since the 1990s. However, it still faces challenges due to various factors that contribute to its air pollution problem. The city's unique geographical location, rapid urbanisation and industrialisation, proliferation of vehicles, and lack of stringent industry regulations have all played a role in its air quality issues. With over 20 million inhabitants, Mexico City grapples with the negative consequences of pollution on its citizens' health and the environment.

Population growth and industrialisation

Mexico City's population rapidly increased during the 20th century as industrialisation brought thousands of migrants from all over the world. This population boom occurred mainly because of migrants seeking better opportunities. The population in Mexico City increased from three million in 1950 to twenty million in 2015, 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.

The rapid and unexpected population growth, coupled with industrialisation, led to severe air quality issues. Industrial growth emitted over 11,000 tons of waste material into the atmosphere daily. The unchecked release of pollutants from manufacturing plants, power stations, and oil refineries contributed significantly to the air pollution crisis. The proliferation of vehicles, including older models with outdated emissions systems, further exacerbated the problem.

The unique geography of Mexico City, located in a basin surrounded by mountains, also plays a role in trapping air pollutants. The "bowl" effect hinders the natural dispersion of pollutants, causing them to linger longer. Additionally, the city's high altitude of 7,300 feet above sea level results in oxygen levels being 25% lower, further compounding the pollution issue.

To address the pollution caused by population growth and industrialisation, the Mexican government has implemented various measures. These include vehicular restrictions, incentives for purchasing cleaner vehicles, investments in public transport, the expansion of bicycle accessibility, and the closure or relocation of polluting factories. While these efforts have led to improvements, the ever-increasing number of cars and inefficient public transport systems continue to challenge the city's air quality.

In summary, the combination of rapid population growth and industrialisation in Mexico City has resulted in severe air quality issues. The unchecked release of pollutants from industrial activities and the proliferation of vehicles have contributed significantly to the problem. The unique geography of the city further exacerbates the issue. While government interventions have led to improvements, addressing the persistent vehicular emissions and inefficient public transport remains crucial in the quest for cleaner air in Mexico City.

Vehicle emissions

By the 1990s, the situation had worsened, with the United Nations declaring Mexico City the "most polluted city on the planet" in 1992. This prompted local governments to take action, implementing driving restrictions, incentivising the purchase of cleaner vehicles, and investing in public transport. These measures helped improve air quality, but the number of vehicles continued to grow, with a doubling of the vehicle fleet between 1992 and 2012. This growth in the number of cars, especially older models with outdated emissions systems, has led to an unchecked release of harmful pollutants.

The Mexican government has recognised the impact of vehicle emissions and has taken further action. In addition to the existing "Hoy No Circula" programme, which restricts driving on certain days of the week, the government reactivated the Mexican Atmospheric Environmental Contingency Plan (AECP) in 2016. This plan included further restrictions on vehicle use, limiting driving to two days a week, and reducing greenhouse gas emissions from factories. These measures have helped reduce air pollution, but it remains a significant issue, especially with the continued presence of older, more polluting vehicles on the roads.

To address the problem of vehicle emissions, Mexico City has also focused on expanding public transportation options and promoting active transport, such as cycling and walking. The government has invested significantly in public transport infrastructure and created incentives for the purchase of cleaner vehicles. These efforts aim to reduce the number of vehicles on the roads and encourage the use of more environmentally friendly modes of transportation. Additionally, the city has implemented vehicular restrictions and expanded bicycle accessibility to encourage a shift towards more sustainable transport options.

While vehicle emissions are a critical factor in Mexico City's air pollution, it is important to recognise that it is part of a multifaceted issue. Other factors, such as industrial emissions, wildfires, and deforestation, also contribute significantly to the city's poor air quality. Addressing vehicle emissions is a crucial step towards improving the health and well-being of the city's residents and achieving sustainable urban development.

Poorly regulated industry

The industrial areas surrounding and within Mexico City have been major contributors to its poor air quality. Chemicals from manufacturing plants and emissions from power stations have been released without restriction, severely damaging the environment. Compliance with regulations and modernisation remain challenges, despite the existence of some rules.

The unchecked release of pollutants is exacerbated by the geography of Mexico City, which is surrounded by mountains. This natural "bowl" effect prevents the dispersion of pollutants, causing them to linger. The topography of the city does not favour its industrialisation, and air pollutants are trapped.

The industrial growth of the 20th century, which brought thousands of migrants to the city, was responsible for emitting over 11,000 tons of waste material into the atmosphere every day. This rapid industrialisation and urbanisation, coupled with a substantial increase in population, led to severely poor air quality. The proliferation of vehicles, especially older models with outdated emissions systems, has further contributed to the problem.

The burning of organic matter, such as forest fires, firewood, and fuel burning, especially diesel, is also a significant source of pollution. In 2019, the Ministry of Environment and Natural Resources reported at least 66 fires in the capital and 130 in the State of Mexico, which borders Mexico City. The smoke and particles from these fires, coupled with above-average temperatures, low rainfall, drought, and higher solar radiation, created a perfect storm for worsening air quality.

Geography and climate

Mexico City is located 7,300 feet (2,225 metres) above sea level in a valley surrounded by mountains and volcanoes. This high altitude means that the city's oxygen levels are 25% lower than at sea level. The city's topography also means that it is geographically predisposed to trap pollutants, with the "bowl" effect hindering the natural dispersion of pollutants, causing them to linger for longer. This is exacerbated by the climate in Mexico, which is particularly hot and dry during the spring, creating the perfect conditions for ozone to form.

The unique geography and climate of Mexico City have contributed significantly to its air quality issues. The city's high altitude and mountainous surroundings trap air pollutants, leading to a build-up of smog and haze. This is particularly noticeable during the spring season, when high concentrations of ground-level ozone occur. Ozone is formed through the interaction of nitrogen oxides (NOx) with volatile organic compounds (VOCs), and the intense ultraviolet (UV) radiation from the sun accelerates this reaction.

The climate in Mexico City also influences the impact of wildfires on air quality. Wildfires, especially during dry spells, release massive amounts of smoke and ash, deteriorating air quality and exacerbating respiratory conditions. In 2019, the Ministry of Environment and Natural Resources reported at least 66 fires in the capital and 130 in the neighbouring State of Mexico. The smoke and particles generated by these fires were compounded by above-average temperatures, low rainfall, drought, high solar radiation, and a high-pressure system that prevented the dispersion of contaminants.

In addition to the immediate health risks, the environmental challenges posed by air pollution in Mexico City have far-reaching consequences. The city's poor air quality has been linked to increased healthcare costs and reduced workforce productivity, with workers losing an average of 7.5% of their working hours on days with very high PM contamination. The effects of air pollution are particularly pronounced for lower-income residents, with nearly 95% of households in low-income neighbourhoods reporting it as a problem.

Wildfires

The impact of wildfires on air quality in Mexico City is significant, as the burning of organic matter, such as forest fires, contributes to the concentration of particulate matter (PM2.5) in the air. In May 2019, levels of PM2.5 reached between 150 and 160 μg/m3, equivalent to Mexico City's inhabitants consuming nearly three and a half cigarettes worth of pollutants on those days.

To combat the pollution caused by wildfires and other sources, Mexico City has implemented various measures. These include vehicular restrictions, such as the "Hoy No Circula" program, which restricts driving on certain days of the week, and limiting factories' greenhouse gas emissions by up to 40%. The Mexican government has also prioritized the expansion of public transportation, green areas, and bicycle accessibility to reduce emissions and improve air quality.

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