Ammonia levels in Mexico City's air have increased over the last decade

Ammonia (NH3), a precursor of particulate pollutants in the atmosphere, can affect air quality, climate, and biodiversity. It is a gas that forms part of acid rain and its presence in Mexico City is high. However, it is a little analyzed issue, warned Jennifer Murphy, a researcher at the University of Toronto.

While participating in the conference series "Current Panorama of Atmospheric Sciences and Climate Change", organized by the Institute of Atmospheric Sciences and Climate Change (ICAyCC), she considered that it is important to carry out more studies on local, regional, and global levels, as well as their long-term impacts.

Research carried out "by UNAM experts shows significant increases in the amount of ammonia in the last ten years in Mexico City...so we see that the CDMX is a place where these emissions are constantly increasing, which should be a target for review to investigate whether this is linked only to emissions or changes in particulate matter," she said.

The expert in active nitrogen studies shared some of the results of her research with ICAyCC students and researchers. She explained that atmospheric ammonia is a compound formed by one atom of nitrogen and three of hydrogen, which is generated especially in the tropics or near them due to agricultural activities by the application of nitrogen-rich fertilizers used for food production and on farms where chickens, pigs, or cattle are raised.

In her talk on the impact of ammonia on air quality and climate around the world, the doctor of chemistry pointed out that when talking about polluting emissions, in addition to oxygen dioxide or ozone, ammonia has also been reported as part of acid rain.

Studies carried out in the United States and Canada show that since 1990, its presence has increased dramatically; that is, there is more and more of it in the air. In the case of Mexico, the researcher showed the records of the country's capital from the Secretariat of the Environment of Mexico City, which reports on its website that in 2016 1.39 million tons of criteria pollutants were emitted (those that must be monitored), of which 47,717 tons was ammonia.

The campaign called Megacity Initiative: Local And Global Research Observations (MILAGRO), coordinated by the Massachusetts Institute of Technology and in which the UNAM's Center for Atmospheric Sciences participated, was carried out from March 1 to 30, 2006 in three main locations (the Mexican Petroleum Institute; the Technological University of Tecámac in the State of Mexico; and Rancho La Biznaga, in Hidalgo), through which emissions of the main greenhouse gases were reviewed, including ammonia and its nitrogenous derivatives.

"I have not done any work in Mexico, but I have reviewed ammonia measurements, especially those obtained by the MILAGRO project in 2006, where it was observed that there are large amounts of ammonia but not many of its derivatives such as nitrous oxide," commented the researcher.

In addition, she said, the study "Measurement report: Evolution and distribution of NH3 over Mexico City from ground-based and satellite infrared spectroscopic measurements" by Beatriz Herrera of the ICAyCC was recently published by the journal Atmospheric Chemistry and Physics of the European Geosciences Union.

In this study, atmospheric NH3 was measured over Mexico City using ground-based solar absorption spectroscopy from 2012 to 2020, revisiting total ammonia columns, and the data were compared to those from the Infrared Atmospheric Sounding Interferometer.

Most of the NH3 that was measured at the urban station came from nearby sources, while most of the NH3 that was found at the remote site probably came from the city and nearby areas.

Based on what can be seen from Beatriz's data and that others have given, it appears that the ammonia level is high in Mexico City and the MILAGRO data shows that the particles are not very sensitive to ammonia because they have an excess at the base and then lower levels such as nitrate sulfates. "Reducing ammonia is not the most efficient way to reduce particulate pollutants; it would be more efficient to reduce the presence of other gases that react with it," considered Murphy.

In Mexico City, there seems to be too much "and it is not what we would like to reduce environmental pollution, but there is justification for the acidification of water and acidification of the soil," added the Canadian specialist.

Regional climate change

Over the past ten years, the researcher and her team of experts have taken measurements of this gas in rural areas of the U.S. and Canada. These measurements show how ammonia affects the composition of the air in many different places.

Airborne and ground-based calculations from a 2017 study of winter fine particulate matter in Utah, USA, suggest that gas plays an important role in regulating the mass loading of these when attempting to improve air quality.

"Our measurements of ammonia eddy covariance flux over-fertilized corn fields in 2017 and 2018 show that management practices and environmental conditions can control the amount and even the direction of ammonia flux," said Murphy.

This phenomenon is not foreign to the poles, as in the Arctic atmosphere during the summer season, he and his team identified that migratory seabird colonies play an important role as a source of ammonia due to their feces.

This is important because the atmosphere at the poles is thought to be relatively clean. However, she found that this gas had a big effect on the number of cloud condensation nuclei and, ultimately, on regional climate change.

How is air quality measured?

To know the air quality in real-time, you can consult the web page www.aire.cdmx.gob.mx/ as well as the recommendations to take care of your health and the map where you can see the points with the highest pollution. Air quality is divided into categories ranging from good, acceptable, bad, very bad, extremely bad, and no data or maintenance.

What does poor air quality mean?

It refers to pollution indexes that are above adequate levels, which can be caused by natural or anthropogenic sources resulting from human activities. The higher the index value, the higher the concentration and health risk.

How does poor air quality affect us?

Poor air quality can affect our health in different ways, especially if we are exposed to it for long periods. The main damage is reflected in the respiratory system and affects people suffering from related diseases, such as asthma.