Secondary pollution: what is it, types and examples

On the one hand, we know that primary pollution is the intrusion of substances or elements into a medium, capable of producing changes and modifications that are harmful to it or its environment. On the other hand, secondary pollutants are those that are not emitted directly, but are formed from the reaction or combination of primary pollutants .

Uniting these two concepts, we can determine that secondary pollution consists, therefore, in the modification or alteration that is harmful or dangerous for the environment produced from secondary pollutants. To understand this idea well, it will be necessary to go to some examples.

Here we talk about the main secondary pollutants with examples :

Sulfuric acid ( H2SO4 )

This secondary pollutant is formed from water vapor contained in the atmosphere and gases that contain sulfur such as:

• Hydrogen sulfide (SH 2 ): it is a pollutant of natural origin, produced by the putrefaction of organic matter in the absence of oxygen, although it can also be produced in an artificial way, as occurs in the paper industry and the refinery.
• Sulfur dioxide (SO 2 ) and sulfur trioxide (SO 3 ) : sometimes these gases are produced from hydrogen sulfide, although their origin is mainly industrial. These elements can be irritating and lead to damage to the eyes and alterations to the respiratory tract.

Methane (CH4)

It originates from decomposing organic matter, which can be found in landfills, or in agricultural and livestock activities. On the other hand, it also originates in the transit of vehicles, in oil refineries or in processes that use solvents. This gas is characterized by its bad smell and because it is highly flammable, in addition to promoting the greenhouse effect.

Ozone (O3)

Ozone exists in a natural way, however, it can also be produced artificially by the reaction of nitrogen oxides emitted into the atmosphere by heating systems and ultraviolet radiation. The result is ozone free radicals that have both toxic and harmful effects.

Depending on the origin, composition and types of pollutants we can find different types of secondary pollution :

Photochemical pollution

This type of pollution is produced from the reaction of atmospheric oxygen, hydrocarbons, nitrogen oxide and ultraviolet radiation from the sun. These elements, added to meteorological conditions of weak winds that make it difficult for the pollutants to disperse and favor their reaction, give rise to the so-called photochemical pollution or photochemical smog .

This type of pollution takes place in large cities of industrialized countries and has negative effects on the environment and human beings, being, in turn, a driver of other types of pollution, which we will see below.

Acidification of the medium

Also known as acid rain . It is produced due to the presence of polluting gases such as sulfur and nitrogen oxides, which are transported by rain and can reach the ground, affecting and impacting the entire earth’s surface. Some of the damages that acid rain produces are the acidification of terrestrial waters, with the consequent damage to aquatic fauna, significant damage to vegetation, due to nutrient deficiency and substrate acidification, surface deterioration of some materials, both natural and artificial.

Ozone layer destruction

Pollutants and the emission of different components into the atmosphere can cause ozone decomposition, through its reaction or by the absorption of ultraviolet rays. The main consequence of the destruction of the ozone layer is the greenhouse effect, which has multiple consequences, such as an increase in the temperature of the earth’s globe, the destruction of the poles, climatic and meteorological changes in different areas of the earth, the repercussion of these changes in the habitat of different species, the loss of biodiversity and a long etcetera.

Now that all the information on secondary pollution has been well explained, to broaden our understanding of the great global problem that exists, we want to end by talking about primary pollution.

Remember that the primary ones are emitted to the environment , while the secondary ones are produced or generated in it. These are the main primary pollutants :

• Carbon monoxide (CO)
• Sulfur oxide (SOx)
• Lead (Pb)
• Radioactive waste
• Chlorofluorocarbonatos (CFC)

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