墨西哥城的空气质量

What is the air quality index of Mexico City?

Mexico City is (often abbreviated as CDMX) the capital and largest city of Mexico and the most populous city in North America. In 2009 the population for the city itself was 8.8 million people but when looking at the entire metropolitan region, this number swells to 21.3million. At the beginning of 2021, Mexico City was experiencing a “Moderate” level of air quality with a US AQI reading of 74. This follows the classification by the World Health Organisation (WHO). The concentration of PM2.5 was 23.3 µg/m³ but the level of sulphur dioxide (SO₂) was 0 µg/m³.

What is the main source of air pollution in Mexico City?

Vehicles represent a major source of air pollution in Mexico City. The automotive fleet includes a large group of vehicles propelled by the combustion of hydrocarbons (fossil fuels) and include mopeds, cars and trucks.

The emissions from the exhausts of these vehicles contain carbon monoxide, hydrocarbons and nitrogen oxides that are released into the atmosphere in significant quantities; they are the components of "photochemical oxidising smog". For this reason, the most populated urban areas are those that suffer the most pollution of this type.

Another aggravating factor in the growing air pollution is the geographical location of the city. Because it is in a valley, when the intensity of the winds is reduced, the diffusion of pollutants in the atmosphere is minimal. For almost 7 months a year, the area maintains on average low-speed winds (less than 1.5 m/sec.), Altitude also plays a part in the high rate of pollution, since the low oxygen content causes deficiencies in the internal combustion processes of the engines. In Mexico City, a cubic meter of air contains 212 grams of oxygen, while at sea level it contains 275. The combustion efficiency of a well-tuned car is 92 per cent, and in the DF 69 per cent, due to the higher altitude.

What is the history of the pollution level in Mexico City?

Throughout 2019, Mexico City’s registered air quality was between 12.1 and 35.4 µg/m³. The highest level recorded was in May when the figure jumped to 34 µg/m³. Looking back over previous years, it is not seen to change by a noticeable amount. In 2017 the reading was 20.4 µg/m³ followed by 19.7 µg/m³ in 2018. The average figure for 2019 was 20.5 µg/m³, so not much different.

Is air pollution in Mexico City getting better or worse?

Back in the 1980s and 1990s lead, ozone, sulphur and carbon were so common that residents used to say that birds would fall from the sky because of it.

As the Mexican economy grew at that time, so did the number of vehicles on the road and emissions from factories increased at an alarming rate. It earned the accolade of the world’s most polluted city. A management programme was introduced which introduced reforms that would clean up the air. Levels of ozone were reported to be around 500 parts per billion (ppb), they are now at a more respectable level of between 120 and 150 ppb.

In 1986 natural gas was being introduced as a replacement for fuel oil in industry and in thermoelectric power generation. In 1989, both city and regional governments introduced a “Cars don’t circulate” (Hoy No Circula) which eliminated about one-fifth of the cars on rotating days between Monday to Friday from the city, depending on the last digit of their registration plates. Higher quality unleaded fuel was made readily available and stricter emissions were established through the broad use of catalytic converters.

In the 80s and 90s, Mexico City issued “red” alerts almost constantly whereas now, they maybe happen as rarely as three or four times per year.

What can be done to improve the air quality in Mexico City?

One way to protect the health of the population is through continuous monitoring and dissemination of the status of air quality. In Mexico City, the Atmospheric Monitoring System (SIMAT) is responsible for the permanent measurement of the main air pollutants.

SIMAT has more than 40 monitoring sites distributed in the metropolitan area, including demarcations of the Federal District and the metropolitan area of the State of Mexico. These sites are known as air quality monitoring stations, and most of them use continuous equipment to measure the criteria pollutants required by federal regulations such as sulphur dioxide, carbon monoxide, nitrogen dioxide, ozone and suspended particles. In some of them, continuous measurements of the main surface meteorological variables are also made, including ultraviolet solar radiation. In the rest, manual equipment is used to collect samples of suspended particles and atmospheric deposition.

Based on information gathered by these systems is the government able to act in a way to mitigate the impact of high levels of pollution. The ban on driving cars into the city is one such example.

It is estimated that there are some 4.7 million vehicles registered in Mexico City and 5.3 million in the entire metropolitan area. It is estimated that 80 per cent are for private use, 7 per cent correspond to public transport and 13 per cent to cargo transportation. On a brighter note though, it is thought that private cars represent only one-third of the total trips made by the inhabitants daily, while public transport accounts for the remaining two thirds.

It is recognised that cargo transportation (of which more than 700,000 units are registered) is essential for the country's economy but is highly polluting, as it causes problems of road traffic, increased noise and emissions of black carbon and fine particles.

The cars in general used in Mexico City are of poorer quality than their USA counterparts. It is estimated that they create 8 - 10 times more pollution than USA vehicles due to the strict rules and regulations there.

What are the effects of breathing Mexico City’s poor quality air?

Long-term exposure to air pollutants can not only imply effects such as watery eyes, cough or irritation in the throat, it is also associated with heart disease, cerebrovascular infarctions, lung diseases and cancer, in the case of adults, as well as acute respiratory diseases in minors, such as asthma.