A pollutant is any chemical substance or form of energy (such as sound, heat, light or radioactivity) that is introduced into a medium (in this case the air) and changes the natural properties of said medium, which may cause adverse effects on health or environment.
According to the origin of the pollutants, the following are distinguished:
- Natural pollutants. Pollutants produced by natural processes but that alter the composition of the air. For example, the gases emitted by a volcanic eruption.
- Artificial pollutants. Produced by human activities such as the burning of fossil fuels in industries, cities, transportation vehicles, etc., or the emission of CFCs.
Air pollutants can be of several types:
- Chemical substances. Within chemical substances, they are divided into two groups:
- Primary pollutants. Substances that are emitted directly into the atmosphere.
- Solid and liquid particles.
- Sulfur compounds, such as sulfur dioxide (SO2), sulfur trioxide (SO3), and hydrogen sulfide (H2S).
- Organic compounds, such as methane.
- Nitrogen oxides.
- Carbon oxides, such as carbon monoxide (CO) and carbon dioxide (CO2).
- Halogenated compounds and derivatives. They are substances that have chlorine and fluorine. For example, chlorine (Cl2), hydrogen chloride (HCl) and hydrogen fluoride (HF), and among the derivatives, chlorofluorocarbons (CFCs).
- Heavy metals.
- Secondary pollutants. Primary pollutants can participate in chemical reactions in the atmosphere and form other new pollutants. For example, SO3, NO3, H2SO4 , HNO3 , O3 (tropospheric ozone) and PAN (peroxyacyl nitrates).
- Forms of energy. There can be several types of pollution by forms of energy:
- Ionizing radiation. Electromagnetic particles or waves such as alpha, beta, gamma radiation and X-rays. They can ionize atoms or molecules on which they act, altering the chemical balance of their structure.
- Non-ionizing radiation. They do not cause ionization of the atoms on which they act. For example, ultraviolet and microwave radiation.
- Noise. Due to its importance in our environment, we will dedicate a section to noise pollution.