World’s most polluted city fails to clean up its act


In one of the largest megacities in the world, is it possible to protect the planet and maintain economic growth? Mexico City has been facing this challenge for quite some time…

A UN study found Mexico City had the world’s dirtiest air in 1992 but have since been overtaken by Delhi and Beijing. Air pollution  in Mexico City is mainly caused fossil fuel combustion in motor vehicles  with 5.5 million cars used daily which has been a major social concern for the Mexican government and its citizens since the mid 1980s. The transport sector should be tackled first because it is responsible for all carbon monoxide emissions and 80% of nitrous oxides which are two of the main greenhouse gases in the atmosphere. Since 1988, the air quality standard of ozone has been violated for 80% of the year as well as being at twice the recommended level by the World Health Organisation along with other pollutants such as sulphur dioxide, dust and carbon monoxide. These gases trap radiation from the Sun which causes climate change as the average temperature increases. Mexico City is surrounded by a chain of mountains which is an unfortunate geographic location in terms of air pollution as it prevents the dispersal of pollutants, leaving a blanket of smog over the city as the pollution accumulates.


Scatter graphs showing that there has been little improvement to concentrations of carbon monoxide and nitrogen oxides Source


Policies were first driven by concerns for public health, rather than the environment. This is because many of the pollutants released have been linked to premature deaths in the elderly and infants and are responsible for causing respiratory conditions such as asthma, bronchitis and cardiovascular illness which leave thousands of people hospitalised each year. These effects on health create massive economic and social costs to society which could be avoided if there was investment in emissions reduction. By 2025, diesel cars will be banned from the city because they produce the most dangerous pollutants to human health. But what about the environment?

In order to address this pressing issue, Mexico City introduced ‘Hoy No Circula’ or ‘One Day Without a Car’ in 1989 . This policy is a license plate based driving restriction which uses the last digit of the license plate to ban vehicles from the road for one day a week . For example, a plate ending in 5 or 6 couldn’t be driven on Mondays. After being one of the first countries to implement a policy of this kind and many other countries following their example, Mexico City seemed to be a leading figure in air pollution policy. However, the programme was abandoned due to its inefficiency, but was reinstated including a driving ban for one Saturday a month based on the original license plate based system after Mexico City entered its worst environmental crisis in a decade on 15th March 2016. The city experienced two days of pollutant filled fog which forced the community to remain indoors and called for serious action. Scientists believed the upgraded policy would reduce vehicle emissions by 15% but this was not the case…


A map showing the area of Mexico City where the policy is implemented Source


The policy hit several roadblocks along the way with citizens finding ways to avoid it. Firstly, drivers began using taxis, as well as Uber and Lyft in recent years, on days they couldn’t use their car which didn’t reduce the number of vehicles on the road or emissions they released. Other strategies used were car pooling with family members and even purchasing extra vehicles! This did nothing to reduce emissions because the extra cars purchased were old, cheap  and high emitters. Other elements to the policy have been curbed by corruption where vehicle maintenance and clean air checks can be ‘passed’ in exchange for as little as $20.

Heavy traffic still persists despite Hoy No Circula   Source


Hoy No Circula was also introduced in the hope that citizens would turn to public transportation in a further attempt to reduce air pollution. Public transportation is widely available and inexpensive in Mexico City, so why didn’t people want to use it? Well there’s a general belief that public transport is slower and less convenient as well as a status belief associated with private car ownership. Dr Lucas Davis from the University of California, Berkley explains how “driving is a real status symbol in Mexico City, and once a family have raised enough money to buy a car, there’s a status associated with private vehicles that’s tough for people to break” that creates a cultural and socioeconomic barrier and public resistance against using public transport. Many residents are also concerned about safety public transport which needs to be addressed for use to increase. Public transport has seen significant government investment but the problem of corruption reared its ugly head again when the new subway was built in 2012. The subway has already been shut down due to structural faults caused by private payment authorisations for work that was never done. This is a significant loss to emissions reductions because the subway had the potential to transport 400,000 people a day . Several new bus transit lines have also opened recently as well as a bike sharing scheme that will be the largest in North America.


A graph showing that the number of registered vehicles in Mexico City has increased which can be attributed to continued economic growth Source


As an emerging economy, population growth and increasing private car ownership will make the problem worse before it gets better. Dr Davis has been studying air pollution levels in Mexico City and concluded that he “couldn’t find any evidence that the programme improved air quality” which shows that the current Hoy No Circula policy is simply not enough. An array of appropriate strategies need to be implemented and regularly evaluated with the focus on urgently reducing air pollution levels not only to benefit population health but to lower Mexico City’s significant contribution to climate change. The current policy has been banning vehicles for one day a week for more than 20 years and to still see no results really is a poor effort.




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