Air quality platform

Learn a little more about air pollutants

Air pollution, especially in large cities, has been associated with the worsening of respiratory, cardiovascular and neurological diseases, especially among children, the elderly, and those with chronic illnesses. Studies also show a correlation between exposure to certain pollutants and the occurrence of different types of cancer (WHO, 2000 and 2006; California Air Resources Board, 2011 and Brunekreef et al., 2012, Olmo et al., 2011, Miranda et al., 2012). The impacts of air-borne pollutants on ecosystems also deserve attention, since the their deposition can lead to acidification of rain water and dust, contaminating bodies of water, their biomes, soil, and plants, leading to reduced photosynthetic capacity (MassDEP, 2011). These are impacts that also bring about negative effects from the economic and social viewpoint. Suffice it to mention the increased vulnerability of the poor, the rising costs of healthcare systems on hospital admissions, and declining agricultural productivity, among other examples (op. cit. IEMA, 2014).

This harks to a general definition, which considers pollutants as any substance present in the air that, by the concentration thereof, may make the air unsuitable, harmful or injurious to health, causing inconvenience to public welfare, damage to materials, fauna and flora, or detrimental to the safety, usage and enjoyment of the property and the normal activities of the community (CETESB, 2014).

Since the variety of substances that can be found in the atmosphere is very large, it becomes difficult to establish a classification for them. To make this easier, pollutants are divided into two categories:

Primary pollutants: those emitted directly by emission sources.

Secondary pollutants: those formed in the atmosphere through chemical reactions between primary pollutants and the natural components of this medium.

Polluting substances can be classified in the following ways:

Halogenated Compounds Heavy metals Particulate Matter Photochemical Oxidants
HClHF chlorides
and others
Mixture of compounds in solid or liquid state O3
Sulfur Compounds Nitrogen Compounds Organic compounds Carbon monoxide
Reduced sulfur compounds:
(H2S, Thiols, carbon disulfide, etc.)
organic acids

Source: CETESB, 2014

Although the presence of all these pollutants is equally concerning, not all of them are monitored all the time and everywhere. The systematic measurement of air quality is restricted to a number of pollutants, defined in terms of their importance and the resources available for monitoring them. This means that a given group was chosen and universally adopted, serving as air quality indicator pollutants, both by the frequency of their occurrence and by the levels of human exposure and potential effects previously mentioned.

They are: Particulate matter (PM), Sulfur Dioxide (SO2), Carbon Monoxide (CO), photochemical oxidants such as Ozone (O3), hydrocarbons (HC) and nitrogen oxides (NOX).

Particulate matter (PM): can be classified as Total Suspended Particles (TSP), Inhalable particles (PM10), fine respirable particles (PM2.5) and Smoke:

Total Suspended Particles (TSP)
In simplified terms, TSPs can be defined as those whose aerodynamic diameter is less than 50 µm. A portion of these particles is inhalable and can cause serious health problems; another part may adversely affect the population’s quality of life, interfering with the aesthetic conditions of the environment and impairing the community’s normal activities.

Inhalable particles (PM10)
In simplified terms, they can be defined as those whose aerodynamic diameter is less than 10 µm. Depending on the size distribution in the range of 0 to 10 µm, they can be retained in upper respiratory system or penetrate deeply, reaching the pulmonary alveoli.

Fine Respirable Particles (PM2.5)
In simplified terms, these can be defined as those whose aerodynamic diameter is less than 2.5 µm, and come mainly from the burning of fossil fuels. Due to their small size, they penetrate deep into the respiratory system, reaching the pulmonary alveoli.

Smoke (FMC)
They are associated with the suspended particulate matter in the atmosphere, and like PM10 and PM2.5, they are strongly associated with combustion processes, mainly originating from motor vehicles. The method for determining smoke is based on the measurement of light reflectance falling on the dust (collected in a filter), which gives this parameter the characteristic of being directly related to the level of soot in the atmosphere.

Sulfur dioxide (SO2)
This is a toxic, colorless gas that can be emitted by sources such as volcanoes or natural anthropogenic sources, which can react with other compounds in the atmosphere forming smaller-diameter particulate matter. Anthropogenic emissions are caused by the burning of fossil fuels containing sulfur; power generation, vehicle usage, and home heating are the activities with the most significant emissions. Among health effects, we can mention the worsening of symptoms of asthma and other respiratory problems. Such oxides are precursors to the formation of secondary particulate matter; in the environment they can react with water in the atmosphere to form acid rain.

Carbon Monoxide (CO)
This is an odorless, colorless gas formed in the fuel burning process. Its main emission source is therefore in processes of combustion that occur under non-ideal conditions, where there is not enough oxygen to achieve the complete burning of the fuel. Most emissions in urban areas result from motor vehicles.
This gas has a high affinity with hemoglobin in the blood, replacing the oxygen and reducing the supply of oxygen to the brain, heart and the rest of the body during the breathing process. In low concentrations, it causes fatigue and chest pain, in high concentrations, it can lead to asphyxiation and death.

Tropospheric ozone (O3)
Secondary pollutant, i.e., it is not emitted directly, but formed from other pollutants, and highly oxidizing in the troposphere (lower layer of the atmosphere). Ozone is found naturally in the stratosphere (the layer situated between 15 and 50 km altitude), which has the positive function of absorbing solar radiation, preventing most of the ultraviolet rays from reaching the earth’s surface.
The formation of tropospheric ozone occurs through complex chemical reactions that occur between nitrogen dioxide and volatile organic compounds in the presence of solar radiation. These primary pollutants, whose main sources of emission are the burning of fossil fuels, the volatilization of fuels, livestock breeding and agriculture.
Among the health effects are worsening the symptoms of asthma, respiratory failure, as well as other pulmonary diseases (emphysema, bronchitis, etc.) and cardiovascular disease (arteriosclerosis). Long exposure time may result in reduced lung capacity, development of asthma, and shortened life expectancy. Besides the effects on human health, O3  is also considered a short-lived climatic agent, contributing to global warming.

Hydrocarbons (HC)
They are gases and fumes resulting from incomplete combustion and evaporation of fuel and other volatile organic products. Various hydrocarbons, such as benzene, are carcinogenic and mutagenic, and there is no environment concentration that is totally safe. The actively participate in the formation reactions of “photochemical smog.”

Nitrogen Oxide (NOx) and Nitrogen Dioxide (NO2)
Formed during combustion processes; therefore, in big cities, vehicles are most often primarily responsible for the emission of nitrogen oxides. NO, under the action of sunlight, turns into NO2  and plays a major role in the formation of photochemical oxidants such as tropospheric ozone.
Sources of (NO2) can be either natural (volcanoes, bacterial action, lightning) or anthropogenic (combustion processes in stationary and moving sources). Natural emissions are on a larger scale than man-made emissions; however, because of their distribution around the globe, they have less impact on the concentrations in urban centers.
High concentrations of (NO2) may have the effect of leading to an increase in hospital admissions due to respiratory and pulmonary problems, and worsening the responses of people who are sensitive to allergens. In the environment, it can lead to the formation of photochemical smog and acid rain. The particulate can also reduce visibility in the atmosphere.