Throughout the 1990s, Mexico City was considered one of the most polluted cities in the world. Since then, Mexico has taken significant steps to combat air pollution, particularly in the capital and surrounding Valley of Mexico. A major refinery was relocated outside the valley. Limitations were put on the sulphur content of industrial fuel. Programmes like Hoy No Circula restricted vehicle use one day a week, stringent emissions inspections improved compliance and reduced corruption, and public transit was expanded. Now, diesel vehicles are in the process of being phased out.
Recent air quality data has moved Mexico City down the list of the worlds most polluted capital cities, reflecting that while the challenge remains, significant progress has been made through impactful, sustained policies.
Improving air quality remains a central focus for Mexico a strong funding partner of the United Nations Environment Programme (UNEP). A key part of that effort includes employing stringent air quality standards and keeping residents informed through regularly updated data.
On 7 September, the world will celebrate the International Day of Clean Air for blue skies, which is designed to showcase solutions to air pollution. Ahead of the commemoration, UNEP explored how Mexico City has managed to rein in air pollution with Sergio Zirath, Director General of Industry, Clean Energy and Air Quality Management in Mexicos Undersecretariat of Environmental Regulation.
UNEP: What is Mexicos biggest air pollution challenge?
Sergio Zirath (SZ): In the Valley of Mexico, the historical problem has been ground-level ozone. The metropolitan area of Mexico City is home to 22 million people living in a relatively small area, with approximately 5.5 million vehicles circulating nearly every day. This generates a large volume of emissions. In the warm and dry season, high temperatures, little cloud cover and low wind speeds create the perfect mix for large amounts of ozone to form and accumulate.
A new comprehensive air pollution management plan was introduced in Mexico City two years ago, which includes very strong actions. Whats concerning is that we can see significant reductions in emissions, particulate matter and gases like nitrogen oxides and sulphur dioxides, but were not seeing the same progress with ozone, even though were applying very restrictive measures.
Why is that the case?
SZ: This is because atmospheric chemistry is quite unpredictable. We saw it during the pandemic: in many parts of the world, despite restrictions on vehicle circulation and reduced industrial activity, ozone levels actually increased.
What is the Metropolitan Air Quality Index?
SZ: Mexico City was the nations first city to have an air quality index, which began in the 1980s. Over time, other Mexican cities began to implement their own air quality indices, with significant differences between them. In addition, there were cities where air monitoring was carried out, but the information was not made available to the public, or the data was summarized and published days later, which is not useful for protecting health during high-pollution events. In 2019, the Ministry of Environment and Natural Resources published an official Mexican standard that defines how to calculate and publish the air quality index, prioritizing health protection.
So, how does Mexico track air pollution today?
SZ: The model we use is known as NowCast. It has helped enormously in terms of health protection, because we can now warn people much sooner, telling them not to go outside, not to exercise outdoors and to avoid inhaling highly polluted air.
The model gives significant weight to the most recent hours. If pollution briefly spikes, we can reach extremely poor air quality levels within a 12-hour window, even though the 24-hour average air quality only appears as poor.
For an air quality index, using a 24-hour average creates a serious problem, because if you average an extremely high value with 23 very low ones, the result appears moderate. With this new indicator, people assume there is now more air pollution and demand greater action from the authorities to resolve the issue.
This is being addressed through the implementation of each state's air quality improvement programs, which establish short- and medium-term public policies to prevent and control pollution. However, solving air quality problems doesn't happen overnight: progress is gradual. It's not possible to change things as quickly as one would like.
How are you continuing to improve the index?
SZ: The communication of the index is passive. Even if theres a high-pollution event where you are, if you dont actively check the index, you wont know.
Thats why were working to develop an official Mexican standard for responding to episodes of high-pollution events what we call atmospheric environmental contingencies. The idea is that when certain concentrations of pollutants are reached, local and federal authorities will be required to take action.
Mexico City is also working on developing an app that monitors the location of each person on their mobile phone and notifies them when pollution could affect their health. This takes into account specific factors for each person, such as whether they are older adults, children or have comorbidities. This will further advance the protection of the population's health.
How does Mexicos work on air quality help it achieve its other environmental goals?
SZ: Air quality has essentially two links to climate change. The first is that the emission sources are usually the same, so actions targeting those sources can generate both direct results and co-benefits reducing both air pollutants and greenhouse gases.
The second link is the interaction between climate change and air quality deterioration. That is, with higher temperatures, well not only have greater emissions of volatile organic compounds think of solvents or fuels evaporating more readily but also increased generation of ozone.
So, higher temperatures mean more volatile organic compound emissions, more energy use because people turn on air conditioning and more photochemical reactions in the atmosphere, which leads to more ozone production.
The measures being implemented by Mexico City aim primarily at reducing ozone precursors. But in doing so, by targeting a wide range of sources, we are also addressing short-lived climate pollutants and other greenhouse gases.
Mexico is a regional leader for providing UNEP with voluntary funding. Why is supporting UNEP important to your country?
SZ: As an international organization and convening partner, UNEP helps us avoid repeating the mistakes of others and therefore progress much faster. Lessons learned both positive and negative are extremely valuable for advancing more quickly in the fight against pollution.
Mexico is one of UNEPs valued funding partners, whose contributions to UNEPs core fund, the Environment Fund, enable UNEP's global body of work. Learn how to support UNEP to invest in people and planet.
On 7 September the world will mark the International Day of Clean air for blue skies. The day promotes action to reduce air pollution, which leads to around8.1 millionpremature fatalities every year.
