Understanding Air Pollution: Gases And Their Effects

Air pollution is a major concern, causing 6.7 million premature deaths worldwide. It is caused by the presence of dangerous substances in the atmosphere, including gases, solids, and liquid aerosols. These pollutants are released at rates that exceed the environment's capacity to dissipate or absorb them. While some air pollution is natural, such as gases from decomposing organic matter, human activities like transportation, industry, and heating are significant contributors. The gases that cause the most air pollution include nitrogen oxide (NOx), volatile organic compounds (VOCs), carbon dioxide (CO2), and sulfur oxide (SOx). These gases have harmful effects on human health and the environment, leading to respiratory issues, cancers, and climate change. Addressing air pollution requires a transition to cleaner fuels and industrial processes to reduce emissions and their impact on the planet.

Nitrogen oxide (NOx)

The combustion of fossil fuels, such as fuel oil, gasoline, and coal, is a significant source of NOx emissions. During combustion, nitrogen and oxygen react at high temperatures, forming NOx. This process occurs in car engines, power plants, and other combustion sources, releasing NOx into the atmosphere. Additionally, agricultural practices, such as the use of nitrogen-fixing plants and nitrogen fertilizers, contribute to NOx emissions. Nitrogen oxide released from forest soils is expected to be particularly high in states like Indiana, Illinois, Michigan, Kentucky, and Ohio.

NOx is also formed naturally through lightning strikes, which produce NOx at altitudes greater than 5 km. Scientists have estimated that each flash of lightning turns an average of 7 kg of nitrogen into reactive NOx. With approximately 1.4 billion lightning flashes per year, the total annual production of NOx by lightning is estimated to be 8.6 million tonnes.

The presence of NOx in the atmosphere can have detrimental effects on both human health and the environment. High concentrations of NOx contribute to the formation of smog, which can reduce visibility and cause respiratory issues in affected areas. Additionally, NOx plays a role in the creation of acid rain, which can harm ecosystems and damage infrastructure.

To mitigate the impact of NOx on air quality, efforts have been made to reduce emissions from industrial and transportation sources. While the COVID-19 pandemic led to a substantial decrease in air pollution in some regions, air pollution remains a pressing concern. By understanding the sources and effects of NOx, societies can implement measures to reduce NOx emissions and improve overall air quality, protecting the health and well-being of communities.

Sulphur oxide (SOx)

Gases are one of the many factors that contribute to air pollution. Sulphur oxide (SOx) is one such gas that is harmful to the environment and human health. SOx refers to Sulphur oxides, which include Sulphur dioxide (SO2) and Sulphur trioxide (SO3). Sulphur dioxide is a colourless gas with a sharp odour that is produced from the combustion of coal or oil. It is also emitted during industrial processes that use sulphur-containing raw materials and additives. Sulphur trioxide is derived from SO2 and is responsible for acid rain.

Sulphur oxides are easily soluble in water, forming sulphuric acid, a highly corrosive substance. SOx emissions have been a significant concern for environmental regulatory bodies worldwide, such as the UN and EU. These organizations have implemented regulations and directives to control and reduce SOx emissions, recognizing their detrimental impact on air quality.

The sources of SOx emissions can be both natural and anthropogenic. Volcanic activity is the most significant natural source of SOx on a global scale. However, human activities, particularly the combustion of sulphur-containing fuels like coal and fuel oil, are major contributors to the high levels of SOx in the atmosphere.

To address the issue of SOx pollution, regulations have been established to control the sulphur content of fuel oils. For example, Regulation 14 provides limit values and compliance guidelines to ensure that fuel oils used within specific areas do not exceed applicable limits for sulphur content. These measures aim to reduce the emission of SOx and its harmful effects on the environment and human health.

It is important to note that while coal usage is declining, and vehicle fuels are becoming more advanced, the emission of SOx gases into the atmosphere by industries remains very high. Therefore, continued efforts and adherence to regulations are necessary to mitigate the adverse effects of SOx on air quality and the environment.

Carbon monoxide (CO)

Breathing air with a high concentration of CO reduces the amount of oxygen transported in the bloodstream to critical organs like the heart and brain. At very high levels, which are more likely to occur indoors or in enclosed spaces, CO can cause dizziness, confusion, unconsciousness, and even death. While very high levels of CO are unlikely to occur outdoors, elevated outdoor CO levels can be particularly concerning for individuals with certain types of heart disease.

To address CO pollution, the Environmental Protection Agency (EPA) in the United States has established the Clean Air Act. Under this act, the EPA sets and reviews standards for CO concentrations in outdoor air. These standards assist state, tribal, and local agencies in maintaining safe CO levels.

CO is one of the six major gaseous criteria air pollutants of primary concern in urban areas, along with sulfur dioxide and nitrogen dioxide. These pollutants are released directly into the air from the burning of fossil fuels such as fuel oil, gasoline, and natural gas in power plants, automobiles, and other combustion sources. While natural processes can contribute to air pollution, it is important to note that only gases generated by human activities, such as industry and transportation, are subject to reduction and control measures.

Volatile organic compounds (VOC)

Volatile organic compounds (VOCs) are organic compounds that are found in the air in gaseous and vaporous forms. They are emitted from natural sources and human activities, such as industrial and commercial processes. VOCs include substances like hydrocarbons, alcohols, aldehydes, and organic acids. Many solvents, liquid fuels, and synthetic substances can also be VOCs.

VOCs are released into the air when solvents or liquid fuels evaporate, or when liquid or paste-like products dry out. This can happen during technical processes involving incomplete combustion, particularly in vehicle emissions, or as a by-product of industrial or commercial activities. For example, printing, surface cleaning, vehicle coating, dry cleaning, and the manufacture of footwear and pharmaceutical products.

The VOC Solvents Emissions Directive in the European Union aims to reduce industrial emissions of VOCs. It covers a range of solvent-using activities and sets emission limit values or requires compliance with a reduction scheme. Similarly, the Paints Directive limits the use of organic solvents in decorative paints, varnishes, and vehicle finishing products.

VOCs can also be found in indoor air, with sources including construction and interior decoration products, body care products, cleaning materials, tobacco smoke, and food preparation. The impact of indoor VOCs on health can be significant, especially in regions where people spend a lot of time indoors.

Overall, VOCs are a major contributor to air pollution, and their regulation and control are important to improve air quality and reduce potential health risks.

Radon (Rn)

Radon is a rare gas due to the short half-life of its isotopes and the scarcity of its source, radium. However, it can be found in the atmosphere in trace amounts near the ground as a result of seepage from soil and rocks, which contain minute quantities of radium. Radon can also be found in groundwater. The national average for radon in outdoor air is 14.8 becquerel/m³ (Bq/m³), or 0.4 picocuries per liter (pCi/L).

Radon is a significant health hazard and is considered the greatest cause of lung cancer among non-smokers in the United States. It can enter buildings through openings in floors or walls that are in contact with the ground and accumulate in poorly ventilated areas. The decay of radon produces radioactive "daughters," including polonium, bismuth, and lead isotopes, which can be ingested from well water or absorbed through dust particles and inhaled. High levels of radon have been found in homes built over geological formations containing uranium mineral deposits.

Radon compounds can be formed by the decay of radium in radium halides, and it has been oxidised by powerful oxidising agents such as fluorine to form radon difluoride (RnF2). It has a low volatility and decomposes back into its elements at temperatures above 250 °C (482 °F). The chemical behaviour of radon is similar to that of a metal fluoride, and it is believed to be ionic in nature.

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