Depending on their origin, contaminants can be classified into natural and anthropogenic. The first comes from natural sources and the second is derived from human activities. If we live in a city it is common to identify air pollution and associate it with industrial and commercial activity and the use of vehicles; the poor visibility of distant places is an indicator of the deterioration of the quality of the air we breathe.
However, air pollution does not only originate from the above-mentioned sources or our homes. Natural phenomena that occur on the surface or in the interior of the Earth - such as volcanic eruptions, which generate emissions of gases, vapors, dust, and aerosols - also contribute. For this reason, pollutants are divided into natural and anthropogenic; the former comes from natural sources and the latter is derived from human activities.
The main pollutants that affect human health and ecosystems are called criteria pollutants. However, other compounds cause global effects, such as the destruction of the ozone layer, the greenhouse effect, and climate change. The effects on people depend on the type of pollutant, degree of exposure, nutritional and health status, and the genetic load of the individual.
The atmosphere is the gaseous layer that surrounds the Earth and any alteration on it has a great repercussion on living beings.
Composition and physical structure
The atmosphere is a mixture of transparent gases 640 kilometers thick, which has evolved to the current composition over millions of years, allowing life to develop.
The mixture of gases that make up the atmosphere is composed of approximately 78 percent nitrogen (N2) and 21 percent oxygen (O2), in almost constant percentage.
The remaining 1 percent is composed of trace gases, highlighting the greenhouse gases (GHG) - water vapor, carbon dioxide (CO2), methane (CH4), ozone (O3), among others - as well as volcanic particles, dust, and fumes. Despite this low percentage, these gases play a fundamental role in meteorological processes.
In the 5 kilometers closest to the earth's surface are the lower layers of the atmosphere, where half of its total mass is concentrated and where meteorological phenomena and chemical reactions that intervene in processes such as erosion and the hydrological cycle occur.
The chemical composition and temperature of the atmosphere vary depending on the altitude. The International Union of Geodesy and Geophysics adopted as structure four atmospheric layers: troposphere, stratosphere, mesosphere, and ionosphere.
Function and relevance
The Earth is the only planet we know with an atmosphere that allows the existence of water in its three states: liquid, solid, and gaseous. This is partly because the distance from the Earth to the Sun is appropriate and partly because the Earth has the ideal mass to have an adequate atmosphere in its composition, which allows life as we know it to exist.
The atmosphere maintains the temperature of the Earth, preventing sudden changes that would make the planet uninhabitable. Without the atmosphere, the Earth's temperature would reach more than 75°C during the day and more than 130°C below zero at night. Of the solar energy that reaches the planet a little more than 30 percent is reflected by the atmosphere or by the earth's surface. The rest of the solar energy is absorbed by the planet, allowing it to heat the air, water, and soil.
The atmosphere filters ultraviolet (UV) radiation through its different layers, just as sunglasses do, allowing the passage of some radiation and preventing the passage of others. The ozone layer, located in the stratosphere, absorbs part of the Sun's ultraviolet rays (UVB and UVC rays) protecting life on Earth.
What pollutes our air
Poor visibility of distant places as part of the landscape is an indicator of deteriorating air quality.
If we live in a city it is common to identify air pollution and associate it with industrial and commercial activity and the use of vehicles, which are characteristics of a city. However, air pollution does not only have its origin in industry, in our homes, or by the use of vehicles.
Natural phenomena that occur on the surface or in the interior of the Earth - such as volcanic eruptions, which produce emissions of gases, vapors, dust, and aerosols - also contribute to air pollution.
For this reason, air pollutants can be classified according to their origin as natural and anthropogenic. The former comes from natural sources and the latter are those derived from human activities.
It is of great importance to analyze the characteristics, properties, and origin of the most important contaminants according to their source since this is the most common criterion.
Type of contaminants
In the atmosphere several compounds contribute to air pollution, of which two main groups can be differentiated:
Primary pollutants. They are discharged directly into the atmosphere by some emission sources such as chimneys, and cars, among others. The atmospheric pollutants that integrate this group are:
Sulfur oxides (SOX). They are formed by the combustion of sulfur present in coal and oil. SOX forms aerosols with ambient humidity, increasing the corrosive power of the atmosphere, decreasing visibility, and causing acid rain.
Carbon monoxide (CO). It is the most abundant pollutant in the lower atmosphere. It is produced by the incomplete combustion of carbon compounds. It is an unstable gas that oxidizes generating carbon dioxide (CO2). About 70 percent of CO comes from vehicles.
Nitrogen oxides (NOX). They are produced in the combustion of fossil products, highlighting vehicles, coal, and wood burning. The production of fertilizers and explosives, tobacco, and boilers generate significant emissions of NOX. Nitrogen monoxide (NO) and nitrogen dioxide (NO2) require special attention. NO is oxidized to form NO2, while NO2 is a precursor to photochemical smog.
Particles. It is a respirable material present in the atmosphere in solid or liquid form (dust, ashes, soot, metal particles, cement, and pollen, among others). Their size can be divided into two main groups: those with an aerodynamic diameter equal to or less than 10 µm (PM10) and those with a smaller respirable fraction (PM2.5).
Hydrocarbons (HC). HC emissions are associated with the poor combustion of petroleum products. The most important sources of emissions are road transport, solvents, paints, landfills, and energy production. The most important are volatile organic compounds (VOC), dioxins, furans, polychlorinated biphenyls (PCB), and polycyclic aromatic hydrocarbons (PAH).
Secondary pollutants. They are the pollutants that originated in the air as a result of the transformation and chemical reactions that suffer the primary pollutants in the atmosphere. They can be considered:
Ozone (O3). As previously mentioned, O3 is part of the composition of the atmosphere, however at low altitudes (tropospheric O3) it is harmful due to its oxidizing, reactive, corrosive, and toxic character, so it reacts quickly generating secondary compounds.
Acid rain. It is the term that has been used to describe the process by which certain acids are formed in the atmosphere from pollutants and then precipitate into the earth. SO2 (sulfur dioxide) and NOX, cause acid rain. These substances in the presence of water, O2, and other chemical compounds form sulfuric acid (H2SO4) and nitric acid (HNO3) respectively, which precipitate the earth in liquid form when it rains or in dry form in the presence of snow or fog. The pH of normal rain is about 6, while acid rain has a pH lower than 5.
Photochemical contamination. It is made up of sunlight and substances that can be oxidized. Photochemical smog is a mixture of contaminants that are formed by reactions produced by sunlight when it strikes the primary contaminants.
Factors involved in air pollution
The quality of the air around us is the result of a combination of factors, which produce changes in its composition and can vary from one moment to another. These factors produce a local, regional, and global impact on air quality. In a local dimension, we can see how the source of emission affects only the immediate vicinity.
On a global scale, climate variations influence the movement of pollutants. For example, the predominant wind direction in Central America and northern South America is east to west, and in North America and southern South America is west to east.
Effects of air pollution
The problem of air pollution has become a constant in many industrial cities around the world, causing health problems to the population and ecosystems. Such is the case of the London smog of 1952, which caused nearly 4, 000 deaths, as well as the deterioration of European forests by acid rain in the fifties and sixties of the twentieth century.
The main pollutants affecting human health and ecosystems are called criteria pollutants. However, other compounds cause global effects such as the destruction of the ozone layer, the greenhouse effect, and climate change.
It is important to note that health effects depend on the type of contaminant, the degree of exposure, the nutritional and health status, and the genetic load of the individual.
Effects on ecosystems and buildings
The effects of air pollution are not only felt by us, but natural ecosystems, historical monuments, and buildings can also be damaged.
The effects of air pollution on ecosystems are a result of secondary pollutants such as acid rain. The fall of acid particles clogs and acidifies the tiny pores of leaves, hindering the process of photosynthesis, as well as degrading the soil, which affects the roots and nutrition of plants. Another effect is the reduction of fish by acidifying lakes, lagoons, rivers, and streams.
Buildings, statues, and sculptures are also affected by acid rain and dry sedimentation of acid particles by contributing to the corrosion of metals (such as bronze) and the deterioration of paint and stone (such as marble and limestone).
Actions to improve air quality
The World Health Organization (WHO) states that exposure to air pollutants is largely beyond personal control and requires action by public authorities at local, national, and international levels.
The WHO Air Quality Guidelines are an up-to-date consensus analysis of the health effects of pollution, which recommend air quality parameters to significantly reduce health risks. Derived from this, national authorities prepare the Mexican Official Standards (NOM) through the Ministry of Health, which set the maximum permissible values for those pollutants that represent a proven risk to human health. The limits are established using as reference the most sensitive groups of the population, such as children, older adults, and people with respiratory and cardiovascular diseases.
To evaluate compliance with the NOMs, it is necessary to have measurement and monitoring tools - atmospheric monitoring system, emissions inventory, and air quality index, among others - that allow the implementation of air quality improvement actions, which are integrated into the Management Program to Improve Air Quality (ProAire).
In Mexico, as in other countries, tools have been developed that allow the identification of the pollutants that are released into the atmosphere, the frequency, the amount in which it happens, as well as the main responsible parties.
Inventory of atmospheric pollutant emissions. They provide information about the number of pollutants released into the air. Currently, there is a national inventory of emissions (INEM), which contains information on the amount and type of pollutants that we generate, by source and state.
Atmospheric monitoring. It allows us to know the state of the air quality in the different zones in real-time, to inform the population promptly, and thus make decisions to protect health. The criteria to locate the monitoring stations are population density, distribution of emission sources, meteorology, and topography.
Most cities have had atmospheric monitoring stations since the 1990s. The stations do not always measure all parameters, as it depends on the type of pollutant generated in the area.
Air Quality Index. It is a non-dimensional value, calculated from information from the current legislation related to the different air pollutants modeled, to facilitate the population's understanding of the information related to air pollution at a local level.
In Mexico, in 1982, the Metropolitan Air Quality Index (Imeca) was implemented as a reference value to inform the population of large cities about the levels of air pollution that prevail in their area of residence or work.
Within the Imeca the concentrations of the criterion pollutants are transformed on a scale of 0 to 500 points. A color and a qualifier are assigned to the air pollutant criterion of greater magnitude that facilitates the population to understand the state of the air quality of the zone where it resides or carries out its activities.
The Atmospheric Environmental Contingency Programs are the main means by which the authorities inform the population about preventive measures to protect their health when the air quality does not comply with the limits established by the regulations. This set of measures is included in different phases that are activated according to the level of concentration reached by the air pollutants.
Management Programs to Improve Air Quality (ProAire). These are programs that establish diverse actions oriented to the control and/or diminution of atmospheric pollutants emitted by the accomplishment of the diverse human activities in a determined region and that, consequently, affect directly the health and the environment.
The ProAire has its antecedent in 1990 with the implementation of the Integral Program against Atmospheric Pollution in Mexico City. There are currently nine ProAires in force. Additionally, four states are developing their ProAire to implement it in their main urban areas.
Our contribution to improving air quality
Also on an individual level, we can contribute to improving the air quality of our location. Below is a list of measures that you can take or propose to your family to reduce the number of pollutant emissions that we emit into the atmosphere.
In your daily life
Avoid burning garbage, leaves, and other objects, as well as making fires in the woods or the city.
Properly closing containers of solvents, paints, and other chemicals that may have substances that evaporate into the atmosphere.
Take short baths to save gas. When you go on vacation, turn off the water heater, and do not leave it on the pilot light, because it continues to consume gas.
By saving electricity, reusing it, and in general changing your consumption habits in a more responsible way, you will reduce the amount of polluting emissions into the air that is generated as a result of its production.
Trying as much as possible to reduce the use of the car or sharing it with other people. Using public transportation or non-motorized transportation, such as bicycles and walking, are sustainable transportation alternatives.
Avoid overfilling the gas tank of the car. This avoids spills and therefore the evaporation of gasoline compounds.
Trying to keep the car in tune and taking it to the service periodically. It is very important to comply with the verification programs and keep the car clean and in good condition.
Make sure that the tires have the right air pressure. This will improve the vehicle's ride and help save gas.
Not driving at high speeds and avoiding sudden braking or starting, generates higher fuel consumption.
If you want to buy a car take into account the indicators of energy efficiency and vehicle emissions.