Air quality in Monterrey

What is the current level of air pollution in Monterrey?

Monterrey is the capital and largest city of the north eastern state of Nuevo León, Mexico. It is the second most productive city in Mexico and has the second largest metropolitan area. According to a census conducted in 2020, Monterrey had an estimated population of approximately 1.1 million within the city and over 4.6 million in the entire metropolitan area.

At the beginning of 2022, Monterrey was enjoying a period of “Good” quality air with a US AQI reading of 43. This United States Air Quality Index number is an internationally used set of metrics supported by the World Health Organisation (WHO) and is used to compare the air quality in different cities throughout the world using comparable standards. It is calculated by using the levels of the six most commonly found pollutants such as nitrogen dioxide, sulphur dioxide, ozone, carbon monoxide and both sizes of particulate matter, which are PM2.5 and PM10. If all six figures are not always available in which case, a level is calculated by using what data there is. In Monterrey only PM2.5 was recorded which was 10.5 µg/m³. This level of PM2.5 is slightly over the recommended safe level of 10 µg/m³ as suggested by the World Health Organisation (WHO) as being an acceptable level. Although no amount of air pollution is considered to be safe.

When air quality is classified as being “Good” doors and windows can safely be opened to allow a stream of fresh air to enter the building. All types of outdoor activities can be enjoyed without fear of breathing in polluted air.

Does the air quality vary throughout the year in Monterrey?

Air quality can be affected by many things, therefore it can and does change rapidly depending on the local conditions. Looking back at the 2020 figures published by IQAir.com, it can be seen that the months of June and August achieved the WHO target figure of being 10 µg/m³ or less. The respective figures were 9.1 and 9.5 µg/m³. The month of May saw air quality from the “Good” category with a figure of 11.1 µg/m³. The remaining nine months of the year saw air quality from the “Moderate” bracket with figures between 12.1 and 35.4 µg/m³. Overall, the month with the poorest air quality was December with a figure of 20.4 µg/m³.

Historically, records were first kept regarding air pollution in 2017 when a figure of 15.7 µg/m³ was recorded. It rose the following year to 17.2 µg/m³ and again in 2019 to 19.3 µg/m³. The latest reading for 2020 was 14.5 µg/m³ but this lower figure was almost expected because it would have been affected by the COVID-19 pandemic as many vehicles were no longer in daily use because the offices were closed and the staff encouraged to work from home, in an attempt to halt the spread of the virus. Many factories and non-essential production units were also required to close which removed their emissions from the atmosphere, albeit on a temporary basis. Worldwide, cities reported a much better quality of air due to the general lack of traffic pollution in city centres due to the pandemic.

What is the main source of air pollution in Monterrey?

Atmospheric pollutants come, in general, from four sources: stationary: industry; mobile (cars and trucks); area sources, that is, commercial activities and services; and natural sources, such as soil erosion, among others.

During the autumn of 2007 and the summer of 2008, different measurements were made in the atmosphere of two sites in the Monterrey metropolitan area, and from there it was inferred how the different sources contributed to the emission of particles smaller than 2.5 micrometres. As can be seen, during the autumn of 2007, vehicle emissions contributed 53 per cent of the total PM2.5, while during the summer of 2008 the proportion was lower, 37.38 per cent. However, in both cases vehicle emissions were the main source of PM2.5.

What can be done to improve air quality in Monterrey?

Improving the air quality of the Monterrey metropolitan area is an arduous task, it requires specific and permanent actions towards the different emission sources. This is the only way to generate, in the medium and long term, a reduction in air pollution levels. It is urgent to establish, in a coordinated manner, the necessary public policies between the three levels of government and that the necessary resources be allocated to execute them effectively. Likewise, it is necessary to create awareness in the population about the impact of human activity on the environment and to join organized civil society, as well as universities and research centres.

What are the different pollutants and where do they originate?

Among the most common air pollutants and their effects are: carbon monoxide (CO), generated mainly by the burning of fuel from vehicles and engines. Its inhalation reduces the amount of oxygen in the organs and tissues of the body, aggravates heart disease, causes chest pain, among other symptoms.

Ozone (O₃), a secondary pollutant formed by the chemical reaction of volatile organic compounds (VOCs) and nitrogen oxides (NOx) in the presence of sunlight, decreases lung function and causes respiratory symptoms, such as coughing and shortness of breath, triggers asthma and worsens other lung diseases.

Nitrogen dioxide (NO₂) is generated by the burning of fuel (from power companies, large industrial boilers and by vehicles) and the burning of wood, its inhalation aggravates lung diseases that cause symptoms of respiratory problems and increases susceptibility to respiratory infection. Also, by particulate matter (PM10 and PM2.5) that are formed through chemical reactions, from combustion (for example, burning coal, wood, diesel, gasoline), industrial processes, agriculture (ploughing, field burning), and during the construction of roads and in erosion processes and the extraction of stone material. Short-term exposures worsen heart or lung disease and cause breathing problems; and long-term exposures, heart or lung disease.

Another pollutant, sulphur dioxide (SO₂), comes from the ignition of fuels (especially coal with a high sulphur content), electrical companies and industrial refining processes, its inhalation aggravates asthma and makes breathing difficult. Air pollution is also constituted by acidification, which involves chemical reactions that involve air pollutants and create acidic compounds that damage vegetation and buildings.