Approximately 99% of the atmosphere is made up of nitrogen and oxygen, while the other fraction comprises gases such as carbon (IV) oxide and argon. However, when new compounds are introduced into the atmosphere, or the concentrations of these gases change in a manner that is harmful to the environment and living things on the Earth’s surface, air pollution is said to have occurred. Like land and water pollution, the quantity of a chemical in the air facilitates its categorization as either being harmless or a pollutant (the United States Environmental Protection Agency, 2020).
Sources of Air Pollution
There are two types of air pollution; outdoor pollution also referred to as ambient air pollution, and indoor pollution, which is generated by the household consumption of fuel. There are different types and forms of indoor air pollution, and they constitute combustion (fireplaces, wood stoves, and tobacco smoke), construction materials, household products, soil gas, and off-gassing from water. Soil gas is regarded as the primary source of indoor radon, a gas that is associated with significant health problems as it affects the respiratory and nervous systems (the United States Environmental Protection Agency, 2020). On the other hand, outdoor air pollution is a combination of a variety of pollutants from natural and human-made sources. It can be categorized into primary and secondary pollutants.
These are defined as pollutants that enter the atmosphere directly, and they include (International Agency for Research on Cancer, 2016):
- Volatile Organic Compounds (VOCs) – VOCs comprise volatile hydrocarbons and their organic molecules that are released into the atmosphere. They might have anthropogenic or biogenic sources. Some of the VOCs are emitted from vegetation, while a higher percentage is resultant of transport, solvent use, and other industrial processes.
- Carbon (II) oxide (CO) – It is described as a colorless, odorless, but poisonous gas. It is a by-product of the incomplete combustion of wood, natural gas, or coal. The dominant source of CO in urban regions is the exhaust from gasoline or diesel-powered vehicles. On the other hand, in rural areas, the primary source of CO is the burning of biomass fuels used for residential heating and cooking.
- Nitrogen dioxide (NO2) – It is one of the primary air pollutants, especially in urban regions. It is a product of high-temperature combustion and electrical discharge produced from thunderstorms. It can be seen as a brown haze or a plume downwind over metropolitan areas. The human-made sources of NO2 include diesel-powered vehicles, heating, and power stations.
- Sulfur dioxide (SO2) – It is described as a colorless gas with a pungent, suffocating smell. It comes from natural processes, such as volcanic eruption and anaerobic degradation of organic material, and anthropogenic emissions (industrial processes). SO2 production in urban areas is primarily due to the burning of sulfur-containing fuels, and metal processing facilities roasting sulfide ores to make metal oxides. Furthermore, the gas reacts with water in the presence of nitrogen dioxide, a catalyst, to form acidic rain.
- Particulate matter (PM) – These are regarded as tiny particles in either liquid or solid form that are suspended in the atmosphere. The particles vary in size in that, such as soot, dust, and smoke are large enough to be visible to the naked eye; therefore, they are termed as coarse PM. Nonetheless, the most detrimental is the smaller particles referred to as PM10 and PM2.5. PM10 are those with diameters smaller than 10 microns, while the latter refers to those with diameters smaller than 2.5 microns, hence, are known as fine particles. Anthropogenic-based particulate matter comes from diesel and petrol engines, build work, industry, diesel engines. On the other hand, natural sources comprise sea sprays, volcanoes, soil, and pollen. Moreover, it is formed when gases like sulfur dioxide and nitrogen dioxide change in the air due to chemical reactions.
- Volatile toxic metals, including mercury and lead, and their associated compounds. They are heavy metals associated with severe health effects. Atmospheric mercury concentrations are significantly dominated by reactive gaseous mercury (RGM), gaseous elemental mercury (GEM), and particulate mercury (Hg-P). Hg-P and RGM are formed from the oxidation of GEM in the atmosphere. The GEM is a global pollutant with a period of decay ranging from months to years. Moreover, the concentration of GEM in the atmosphere varies from 2-10 ng/m3; on the contrary, the RGM and Hg-P levels range from tens to hundreds of pictograms per cubic meter.
- Odor from sewage, garbage, and other industrial processes.
These are defined as pollutants formed as a result of chemical reactions (International Agency for Research on Cancer, 2016):
- Nitrogen oxide produces nitric acid. After a high concentration of nitrogen oxide gas is released into the atmosphere, it reacts with water to form acidic compounds. The compounds are transported in the air by wind until they fall to the ground in either their dry or wet form.
NO2 + H2O HNO3
- Sulfur dioxide produces sulfuric acid. The atmospheric sulfur dioxide reacts with water vapor to form the weak sulfuric acid. This acidic compound is damaging to both infrastructure and human health.
SO2 + H2O H2SO4
- Ground-level ozone is formed through the chemical reactions between VOCs, sunlight, and nitrogen dioxide. It is a significant component of atmospheric smog. After nitrogen is released into the atmosphere, it splits in the presence of sunshine to release an oxygen ion (O). This released ion combines with an oxygen molecule (O2) to yield ozone gas (O3). It often reaches its highest level in the afternoon and early evening hours and during summer. Ozone is a vital component of the troposphere as it is the center of chemical and photochemical reactions occurring in the atmosphere. Unlike the stratospheric ozone that serves the function of absorbing harmful ultraviolet radiation emitted by the sun, the ground ozone is generally hazardous.
Effects of Air Pollution
Environmental Impact of Air Pollution
Air pollution is associated with an array of environmental effects, and these include but are not limited to global warming, acid rain, ozone depletion, and eutrophication. Acid rain is a form of precipitation containing high concentrations of sulfuric and nitric acid. It falls onto the Earth’s surface in its dry (gas and particulates) or wet (snow, rain, or fog) forms. Acid rain can cause the soil to acidify the soils and water bodies, which might be harmful to both plants on the Earth’s surface and aquatic organisms. Furthermore, it fastens the rate of decay of buildings, thus destroying infrastructure (Manisalidis, et al., 2020). The other environmental effect is ozone depletion, in which hydrofluorocarbons, chlorofluorocarbons, and halons deplete the ozone layer in the upper atmosphere. The reduction in the thickness of this layer allows the increase in the amount of ultra-violet radiation reaching the Earth’s surface. This can lead to impaired immune systems, cataracts, and even skin cancer (Manisalidis, et al., 2020). The radiation also damages sensitive crops by penetrating their stomata and inducing their closure. As a result, the process of CO2 transfer is blocked, thereby resulting in the reduction of photosynthesis. On the other hand, ground-level ozone adversely impacts agricultural yields and forest vegetation.
About global warming, the Earth’s atmosphere contains a balanced concentration of naturally occurring gases that are trapped under the ozone layer that keep the temperature stable. When high concentrations of carbon (IV) oxide are released from the Earth’s surface, they build up and form a blanket layer in the atmosphere. This layer prevents harmful terrestrial radiation reflected from the Earth’s surface to go back to the atmosphere; thus, it is trapping it. Therefore, this results in the accumulation of heat, which leads to increased surface temperatures. This brings about the disturbance of the usual climatic cycles, such as the melting of the ice caps, flooding, and rising sea levels (Manisalidis, et al., 2020). Lastly, the smog effect occurs when a dark fog is formed over the fields and cities. Photochemical and sulfurous smog is hazardous and harmful to human health (Manisalidis, et al., 2020).
Health Impact of Air Pollution
In addition to adverse environmental impacts, air pollution is also a significant risk factor for several health conditions. Overall, high pollution levels can result in immediate health problems, such as damaging cells participating in respiratory, aggravated respiratory and cardiovascular disease, and increased stress to the lungs and heart. On the other hand, long-term exposure is linked to permanent health effects, including a reduced life span, accelerated lung aging, development of diseases (bronchitis, asthma, emphysema, and even cancer), and loss of lung capacity and its decreased function. However, it is essential to note that specific pollutants are associated with particular health impacts. The ground-level ozone is a strong irritant that leads to the constriction of airways, hence, forcing the respiratory system to work harder to supply oxygen throughout the body (Azam, Riahi-Zanjani, & Balali-Mood, 2016). It also causes other health problems, such as increased fatigue, aggravated respiratory diseases (bronchitis, emphysema, and asthma), diminished athletic performance, lung damage even after the disappearance of sore throat, and coughing increased fatigue and immunosuppression.
Exposure to particulate matter is associated with the onset and progression of heart and lung diseases. PM2.5 has the highest probability of reaching the lower respiratory tract and, hence, has a more significant potential for causing respiratory diseases (Azam et al., 2016). Furthermore, based on the level of exposure, particulate pollutants might result in mild to severe illnesses. Dry mouth, cough, wheezing, and general body weakness are some of the prevalent mild symptoms of air pollution. Conversely, long-term exposure to PM concentrations leads to a reduced life expectancy, which is often brought about by the increased prevalence of lung and cardiopulmonary cancer and reduced lung function due to the development of chronic respiratory diseases (chronic bronchitis and chronic obstructive lung disease).
Symptoms of carbon (II) oxide pollution comprise dizziness, headaches, vomiting, nausea, and, finally, the loss of consciousness. CO competitively binds to the heme groups in hemoglobin to form carbaminohemoglobin. This compound does not have a high affinity to oxygen as compared to oxyhemoglobin. On the other hand, the major health concerns associated with exposure to sulfur (II) oxide comprise the exacerbation of pre-existent respiratory diseases, and respiratory irritation and dysfunction. The pollutant is often absorbed in the upper airway as it is deposited on this section and dissolves into the surface lining fluid, thereby forming sulfite. These compounds interact with other body receptors, thus resulting in local and centrally mediated bronchoconstriction.
Nitrogen oxide is regarded as a deep lung irritant that can induce pulmonary edema if exposed to high levels. The most common symptoms are coughing and wheezing; nevertheless, dyspnea, headaches, diaphoresis, irritations, chest pains, bronchospasm, fever, and pulmonary edema might also occur. Lastly, exposure to high concentrations of lead is often chronic as it bioaccumulates in the body; however, it lacks apparent symptoms (Azam et al., 2016). The metal is known for its neurotoxic capabilities, thus has the potential to cause memory impairment, mental retardation, hyperactivity, and learning disabilities in children. Although its main target is the nervous system, the pollutant can affect other parts of the body, including the renal, cardiovascular, and reproductive systems.
Measures to Reducing Air Pollution
Mitigation efforts are often challenging, and that is the reason for most measures being centered on prevention. With the world becoming increasingly industrialized, there is a dire need for people to become aware of the environmental and health hazards that air pollution poses. Controlling air pollution requires the participation of both the government and individuals.
Government Level Prevention
The government can control air pollution by enacting and implementing appropriate legislation and strict controls regarding the various types of anthropogenic activities that introduce pollutants into the air. These comprise standardizing motor fuel by identifying alternative, environmentally friendly sources. A significant portion of pollutants is produced from vehicle emissions, especially those with engines running on diesel and gasoline. Using a clean energy source, such as electricity, solar power, liquefied, and compressed natural gas, will reduce the amounts of pollutants being released into the atmosphere. Moreover, still focusing on vehicles, the government should support the standardization of the manufacture of engines with low fuel consumption. This leads to a decrease in the amount of fuel consumed by a vehicle, resulting in fewer emissions.
Third, the government should improve public transport systems, for instance, by installing more trams and subways, to encourage more people to use them and discourage them from buying personal vehicles. In addition, penalties should be imposed for polluting industries, while low tax policies levied on clean technologies. Waste dumping sites should also be located far away from residential areas as they produce bad odor upon decomposition. Continuous quality monitoring should be performed, and an extensive media campaign used to increase public awareness of air quality and related environmental and public health issues. The campaign should focus on concepts relating to indoor air pollution. These include outlining the adverse effects that air pollution has on human health and the environment. Furthermore, the public should be encouraged to use bicycles or public transport for commuting to reduce emissions. Moreover, people, especially those in the rural areas, should consider using fossil fuels (charcoal and firewood) wisely as this has the potential to minimize the concentration of pollutants released at the household level. Last but not least, the public should be encouraged to re-use and recycle items as this will decrease the need for manufacturing industries to produce new products.
Azam, G.A., Riahi-Zanjani, B., & Balali-Mood, M. (2016). Effects of air pollution on human health and practical measures for prevention in Iran. Journal of Research in Medical Sciences, 21(5), 1-12. Web.
International Agency for Research on Cancer. (2016). Sources of air pollutants. Web.
Manisalidis, I. et al. (2020). Environmental and health impacts of air pollution: A review. Frontiers in Public Health, 8(14), 1-13. Web.
United States Environmental Protection Agency. (2020). Criteria air pollutants. Web.