This Is What You Breathe In The Polluted Air

Previously, I had talked a bit about the types of pollutants. This time I want to discuss, specifically, the chemical composition of air pollution.

The air is a mixture of different gases, the clean dry air in Earth's atmosphere is made up of the following elements: Nitrogen 78%, Oxygen 20.94%, Argon 0.9340%, Carbon Dioxide 0.0310%, Neon 0.0018, Helium 0.0005%, Methane 0.0002%, krypton 0.0001%, Sulfur Dioxide 0.0001%, and trace compounds. However, the compositional percentages of clean air are altered when pollutants enter the mixture, consequently, their concentrations vary giving higher levels for polluting and harmful substances to the environment and human life. Air pollution is composed of gases, particles, and ions; the dust, smoke, trash, and gaseous residues are the origin of these molecules due to the capacity to remain in the air or changing their physical state to gaseous and pollute the air. The pollution may have different chemical compositions according to its type; the molecules comprised in air pollution are:

• Main elements: Carbon Monoxide (CO), Nitrogen Dioxide (NO2), Carbon Dioxide (CO2), Air Toxics (phenol, polycyclic aromatic hydrocarbons, acrolein, aldehydes, formaldehyde, among others), Iron (Fe), Calcium (Ca), Potassium (K), Silicon (Si), Aluminum (Al), Oxides of Nitrogen and Sulfur (NOx and SOx), Ozone (O3), Sulfur Dioxide (SO2), Magnesium (Mg) and Sodium (Na)

• Minority elements: Lead (Pb), Barium (Ba), Cadmium (Cd), Arsenic (As), Zinc (Zn), Copper (Cu), Nickel (Ni), Cobalt (Co), Manganese (Mn), Chromium ( Cr), vanadium (V), titanium (Ti), organic acids (CH3COO-, HCOO-, CH2(COO)22-, (C2O4)2-) and trace anions (F-, NO2-, Br-, and PO43-).

• Water-soluble ions and carbon components: Organic carbon (OC), Element carbon (EC), Chloride (Cl-), Fluoride (F-), Ammonium (NH4 +), Sulfate (SO4-), and Nitrate (NO3-)

Their concentrations vary depending on how polluted the air is, this changes according to the place and region where air samples for analysis are taken. Particulate matter (PM) comprises many compounds included in these lists, these are classified according to their size, includes Iron (Fe), Silicon (Si), Sulfur Dioxide (SO2), Magnesium (Mg), Lead (Pb), Barium (Ba), and several more; being considered the most dangerous air pollutant. Next, in image 1, we observe an episode of air pollution in a city, flooded by it, the inhabitants and nature breathe polluted air day and night, inhaling the chemicals mentioned above and many more.

Image 1: The mixture of highly concentrated pollutants manifests as a dense layer of suspended material over the city.

Emissions of CO contribute to the formation of CO2 and ozone, greenhouse gases as CO2 and methane warm the atmosphere; some toxic air pollutants accumulate in the food chain after depositing to soils and surface waters. Wildlife and livestock are also be harmed with sufficient exposure. Oxides of nitrogen react with volatile organic compounds to form ozone and react with ammonia and other compounds to form particle pollution resulting in associated public health and environmental effect, mercury methylation. Its most important emission sources have been identified as urban dust, soil dust, construction dust, steel dust, vehicle engine emissions, and power plant dust. The concentrations of air pollutants vary throughout the year with the seasons, these changes are influenced by temperature; cooler temperatures allow particulate matter to remain suspended in the air for longer. The classification of air pollutants, based on the sources producing pollution, is distributed in four types, as follows:

• Major sources include the emission of pollutants from power stations, refineries, petrochemicals, the chemical and fertilizer industries, metallurgical, other industrial plants, and municipal incineration.

• Indoor area sources include domestic cleaning activities, dry cleaners, printing shops, and petrol stations.

• Mobile sources include automobiles, cars, railways, airways, and other types of vehicles.

• Natural sources include physical disasters such as forest fires, volcanic erosion, dust storms, and agricultural burning.

These are the most significant sources of pollutants in the air, so it is necessary to intervene in these areas and processes, by changing them for others that are more compatible with the environment and health. Next, Table 1 shows the types of air pollutants and their relationship with the particle diameter (PM diameter) or in other words, with their size.

Table 2: Types of air pollutants according to diameter.

Usually, smaller compounds tend to be easier to enter through the lungs into the body; while larger compounds tend to obstruct the airways and ducts of the respiratory system. When breathed in, pollutants invade the respiratory system, spread through the respiratory tract to the systemic circulation, causing systemic inflammation and the production of inflammatory cytokines (messenger molecules); they can, also, pass through the nasal passage, leading to spread in the brain and causing neuronal death, these pollutant compounds are stored in cells causing communication and response pathways to be triggered. The main disease mechanism due to air pollution is oxidative stress and inflammation, although the mechanisms may vary depending on the molecule, others include genotoxic, asphyxiating, lethargic, hypertensive, apoptotic, carcinogenic, teratogenic, etc. In another article, the percentage composition of polluted air will be explained in more detail. These compounds have great potential for damaging health and their production should be avoided in all areas of society. That is why the governments and institutions in charge should establish policies for safe processes within the limits, creating strategies to reduce their emissions, in addition to cleaning and capture methods; each person should contribute their grain of sand to achieve the objective of eliminating environmental pollution with environmental awareness.

References

• Manisalidis, Ioannis et al. “Environmental and Health Impacts of Air Pollution: A Review.” Frontiers in public health vol. 8 14. 20 Feb. 2020, doi:10.3389/fpubh.2020.00014.

• Zhang, Guiqin & Ding, Chun & Jiang, Xiaojing & Pan, Guang & Wei, Xiaofeng & Sun, Youmin. (2020). Chemical Compositions and Sources Contribution of Atmospheric Particles at a Typical Steel Industrial Urban Site. Scientific Reports. 10. 7654. 10.1038/s41598-020-64519-x.

• Elizanne P. S. JustoMaria Fernanda C. QuijanoKarmel BeringuiTatiana D. Saint’PierreAdriana Gioda.  Assessment of Atmospheric PM10 Pollution Levels and Chemical Composition in Urban Areas near the 2016 Olympic Game Arenas. J. Braz. Chem. Soc. 31 (5) • May 2020 • https://doi.org/10.21577/0103-5053.20190270. 

• EPA. Criteria Pollutant Trends Show Clean Air Progress. United States Environmental Protection Agency. Status and Trends Through 2020.