Mexico City's Air: What's Behind The Pollution?

Mexico City has long struggled with air pollution. In 1992, the United Nations named it the most polluted city on the planet, and in 1998, the most dangerous city for children. The city's air quality has improved since then, but it still exceeds the World Health Organization's guidelines for airborne particles. The pollution is caused by a combination of emissions from transport and industry, the burning of organic matter, and the city's topography, which traps pollution. High levels of ozone have recently led authorities to restrict vehicle use and order factories to limit greenhouse gas emissions.

Population growth and industrial activities

Mexico City's population grew from 3 million in 1950 to 20 million in 2015, with 14 million of those living in the metropolitan area in the 1980s. This population boom was largely due to migrants seeking better opportunities, and it triggered an era of industrialization. This industrial growth emitted over 11,000 tons of waste material into the atmosphere every day. As the economy boomed, so too did the proliferation of vehicles. There were 124 cars and light-duty trucks per 1,000 residents in 1980, and by 2010, this had increased to 267.

The sharp rise in emissions from transport and industry resulted in Mexico City being named the world's most polluted city. Lead, ozone, carbon, and sulphur were so prevalent in the atmosphere in the 1980s and 1990s that they were thought to be causing birds to fall out of the sky. The air quality was described as similar to that of India today, and it posed a huge threat to public health.

The Mexican government has since introduced measures to tackle the air pollution crisis, such as the Management Programme to Improve Air Quality (Proaire), which has helped to significantly reduce pollution levels. However, air pollution remains a problem in Mexico City, and it is still estimated that nearly 33,000 Mexicans die each year due to outdoor and indoor air pollution.

One of the main sources of indoor air pollution is the use of organic fuels for cooking and heating. Nearly half of the world's population cooks with solid fuels such as wood, crop residues, agricultural waste, and dried animal dung, and when used in simple cooking stoves, these fuels emit substantial amounts of toxic pollutants. In households with limited ventilation, exposure to these pollutants can be much higher than World Health Organization (WHO) guidelines and national standards.

To combat this, households can transition to cleaner fuels such as propane (LPG), which has been shown to reduce pollution and the risk of disease and death. Improved cookstoves with chimneys, such as the Eco-Stove, can also help to reduce exposure to toxic pollutants.

Topographical location and climate

Mexico City's location in a basin surrounded by mountains, coupled with its significant altitude, has contributed to the city's historical struggles with air pollution. This geographical configuration creates a “bowl-like" effect, trapping pollution and preventing its dispersion. The city's height further exacerbates this issue, as it already acts as a natural barrier to the free movement of air.

The basin in which Mexico City is located is part of the Valley of Mexico, which has experienced substantial population growth over the years. This rapid urbanisation and industrialisation have led to a sharp increase in emissions from transport and industrial activities, further contributing to the city's air pollution problem. The proliferation of vehicles, in particular, has been a significant source of pollution, with the number of cars and light-duty trucks per 1000 residents more than doubling between 1980 and 2010.

The combination of the city's topographical location and climate has created a unique set of challenges in managing air pollution. The high-pressure systems that are common in the region can prevent the dispersal of contaminants, leading to a build-up of pollutants in the atmosphere. Additionally, the city's altitude can also influence the formation and persistence of air pollutants.

Furthermore, the region's climate, characterised by above-average temperatures, low rainfall, and prolonged droughts, can exacerbate the impact of wildfires, which are a significant contributor to air pollution. The burning of organic matter, including forest fires, firewood, and fuel burning, particularly diesel, releases large amounts of smoke and particles into the atmosphere, further degrading air quality.

While the Mexican government has implemented various programmes to address air pollution, such as the Management Programme to Improve Air Quality (Proaire), the Cars Don't Circulate (Hoy No Circula) programme, and the activation of the ACEP during seasons of high air pollution, the success of these initiatives is closely tied to the federal government's commitment to providing the necessary financial and political support.

Wildfires

The topographical location of Mexico City exacerbates the impact of wildfires on air quality. The city sits in a basin surrounded by mountains, creating a bowl-like container that traps pollution. The city's high altitude of over 7,000 feet above sea level further contributes to this issue, as it already has lower oxygen levels.

To address the impact of wildfires and other sources of pollution on air quality, Mexico City has implemented various measures. These include driving restrictions, incentives for cleaner vehicles, investments in public transport, and the creation of bike lanes. While these efforts have helped, other factors, such as the increasing number of vehicles, continue to challenge the city's air quality.

Vehicle emissions

Mexico City's air pollution is caused by a combination of factors, including vehicle emissions, industrial activities, and geographical characteristics. Let's focus on vehicle emissions:

To address this issue, the city has implemented various measures over the years. In 1989, the "Cars Don't Circulate" (Hoy No Circula) programme was introduced, which restricts the use of a fifth of all vehicles on rotating days between Monday and Friday, depending on the last number on a vehicle's registration plate. This programme aimed to reduce the number of vehicles on the roads and, consequently, lower emissions. However, new rules and regulations that came into effect later may have contributed to loosening controls and allowing more vehicles on the roads, according to some sources.

Additionally, in 2017, a National Report on Air Quality was conducted, covering 20 air quality monitoring systems (SMCA) in 18 states across Mexico, including 177 monitoring stations in 71 cities and metropolitan areas. This report likely provided valuable data for policymakers to make informed decisions about reducing vehicle emissions.

Another critical aspect of addressing vehicle emissions is the verification process that vehicles must undergo before being allowed to transit in Mexico City. This process takes into account the number of pollutants emitted by each vehicle, and certain vehicles may be restricted from driving on particular days of the week. However, the specific details of this verification process and its effectiveness in reducing emissions are not immediately clear.

While vehicle emissions are a significant contributor to Mexico City's air pollution, it is important to recognize that the problem is multifaceted. Other factors, such as industrial activities, wildfires, and geographical characteristics, also play a role in the city's air quality issues. Therefore, a comprehensive approach that addresses multiple sources of pollution is necessary to improve the air quality in Mexico City sustainably.

Household air pollution

Mexico City's air pollution has been a concern for its population and health officials for decades. The city's air pollution is caused by a combination of factors, including industrial growth, a sharp increase in population, and the proliferation of vehicles. While the city has made significant improvements in reducing air pollution in recent years, it still faces challenges in addressing household air pollution.

The Mexican government has implemented policies to address air pollution, including requiring the reformulation of gasoline, closing or relocating polluting factories, and prohibiting drivers from using their cars one day a week. However, the impact of these policies on household air pollution may be limited. Deforestation and the expansion of livestock and agriculture have also contributed to the air pollution problem in Mexico City. Prioritizing public transport, electric transport, and active transport like cycling and walking can help reduce emissions from transportation, which is currently the main cause of air pollution in the city centre.

To effectively tackle household air pollution in Mexico City, a combination of improved ventilation in homes, the promotion of cleaner cooking fuels and technologies, and continued efforts to reduce emissions from transportation and industrial sources is necessary. Additionally, strengthening inspection and surveillance systems to prevent illegal changes in land use can help reduce deforestation and its associated air pollution impacts. By addressing household air pollution, Mexico City can further improve the air quality for its residents and protect their health, especially for vulnerable groups such as children, the elderly, and those with respiratory illnesses.

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