Air Pollution: Causes, Effects and Control Measures As the world grapples with the economic, environmental and health challenges of the 21st century, there is an urgent need to reassess our approach to air pollution. This is because air pollution is still one of the major issues affecting rapidly growing cities in low, middle and high income countries. Its impact is, however, not limited to health but may cut across the economic and sociopolitical sphere. According to the World Health Organisation (WHO), 4.2 million premature deaths was due to air pollution in 2016 alone, with SouthEast Asia and Western Pacific regions recording the highest number of deaths. Although prevalent in major cities, it is vital to know that the problem is not limited to cities alone since rural communities also contribute their fair share. Sources of Air Pollution Air pollution is the release of substances into the air that are detrimental to both our health and that of our planet. Most of these substances (pollutants) are a by-product of our personal, commercial, and industrial energy use and production. For instance, the energy needed to power our vehicles, trucks, and construction machinery comes from fossil fuels. Industrial power plants also use coal (fossil fuel) as an energy source. Burning of fossil fuels releases harmful gases and chemicals into the atmosphere. Some of these gases such as carbon dioxide (CO2) and methane (CH4) traps earth's heat and raises the global temperature bringing about climatic changes. Air pollution is not restricted to human activities alone but may also come from natural sources, for instance; volcanoes produce large amounts of particulate matter and gases which are released into the atmosphere during volcanic eruptions. Forest fires also produce moderate to high amounts of harmful gases and particulate matter, however, irrespective of the sources, pollutants can enter the atmosphere in two ways: Point Sources This is when the particulate matter or gases enter the atmosphere through a single source of origin, for instance, a single factory smokestack. Non-point Sources This is a term used when the pollutant comes from many sources e.g. all the power plants in Europe, all the vehicles in Nigeria e.t.c. We also differentiate pollutants depending on whether they cause direct harm once released or react further with atmospheric components to cause harm. Thus we have: Primary Pollutants These are gases and particulate matter that causes direct harm or that reacts further in the atmosphere to form harmful substances. Secondary Pollutants These harmful substances are the end product of the reactions between primary pollutants and other atmospheric components. Types of Air Pollutants There are many substances and gases that get released into the air that may qualify as pollutants. However, some substances pose more danger to humans than others, environmental and health experts identified the following six pollutants as posing the greatest threat to humans. Carbon monoxide (CO) Carbon monoxide (CO) is an odourless, colourless and poisonous gas produced from incomplete combustion of coals. C + 1/2O2 = CO (incomplete combustion) C + O2 = CO2 (complete combustion) About 62% of CO that gets released into the air is through emission from motor vehicles, the other 38% is through a combination of forest fires, burning of industrial and household waste e.t.c. Carbon monoxide is especially notorious for its ability to stop oxygen delivery to major organs in the body by interacting with haemoglobin, an oxygen carrying pigment in the blood. Specifically, it competes with and displaces oxygen for the same binding site in the Iron (ii) ion (Fe^2+) of the haemoglobin through the equation.. Carbon monoxide + haemoglobin = Carboxyhaemoglobin (abnormal and dangerous) Oxygen + haemoglobin = Oxyhaemoglobin (normal) Breathing air containing 0.02% concentration of Carboxyhaemoglobin for just 2hrs can result in serious headache or nausea , a much higher concentration of say 0.1% causes loss of consciousness after 1hr and death by asphyxiation after 4hrs. Toxic concentrations are prevalent in poorly ventilated environments such as garage, and coal power houses. Sulphur dioxide (SO2) The bulk of this pollutant (about 70%) is produced when sulphur from industrial plants reacts with atmospheric oxygen in the air. S + O2 = SO2 Characteristically it is a colourless highly reactive gas with a pungent suffocating smell. Sulphur dioxide and Nitrogen oxide falls within the category of noxious gases that react further with water, oxygen, and other chemicals in the atmosphere to produce sulphuric and nitric acid respectively, these acids get transported far and wide by air, mixing with other materials in the process and later falling back to earth as acid rain. Other sources of Sulphur dioxide (SO2) may include volcanoes, vehicles and heavy equipment, oil refineries e.t.c. The gas causes respiratory problems by: ● Causing irritation of the nose, throat and lung linings ● Narrowing the airway and thus reducing airflow to the lung ● Inducing coughing and chest tightness The effects can be especially fatal for people with pre-existing respiratory conditions such as asthma and other chronic obstructive pulmonary diseases. Oxides of Nitrogen (NOx) The term is used to describe a family of very reactive gases all of which pollute the air in various amounts, by far the most popular include nitric oxide (NO) and nitrogen dioxide (NO2), however NO is elusive, reacting further once formed to produce NO2 and as such NO2 is the most common. Characteristically, NO2 is a reddish - brown gas with pungent nasty smells. About 50% of this gas is produced through emissions from vehicles, especially diesel vehicles, perhaps the reason why roadside concentration is high where traffic is the busiest. Other major sources are industrial power stations and machinery, lighting discharge also contributes about 1% in the atmosphere. Both NO and NO2 play an active role in the formation of photochemical smog, NO2 also causes acid rain as stated earlier and affects the lungs the same way as sulphur dioxide. Particulate Matter (PM) Particulate matter is composed of a liquid and solid mixture including sulphates, nitrates, carbonates, mineral dusts, complex organic compounds and water suspended in thin air. They vary in sizes from those large enough to be visible such as dust, soot, dirt or smoke to the smaller particles classified as either PM10 for particles with diameters smaller than 10micron (10um) or PM2.5 for particles with diameter less than 2.5 micron (2.5um) known as fines. There is also ultrafine which are particles with diameter less than 0.1 micron (0.1um),they are the smallest fines. Particulate matters are mainly products of vehicular and industrial emissions from fossil fuel combustion, especially diesel engine, other sources are cigarette smokes, friction from brakes and tyres, dust from road surface building sites as well as natural sources like volcanoes, sea sprays, pollen and soil. Some particulate matters are formed by transformation of SO2 and NO2 through chemical reactions in the atmosphere. Where particulate matter ends up and the health impacts depends on the sizes: ● Larger particles may get trapped in the nose where it causes low to moderate but temporary respiratory problems ● PM10 may enter the airways causing a greater problem ● PM2.5 is 30 times thinner than human hair and can easily be inhaled deep into the lung breaching the breathing sac in the process, long term moderate to high damage may occur ● Ultrafines are known to cross into the blood streams Most particulate matters are carriers of toxic and carcinogenic chemicals and as such long term exposure may cause cancer, they are also associated with severe symptoms among asthmatics patients. Soot penetrates the lungs and bloodstream worsening bronchitis, heart attacks and hastening death. Ozone (O3) Ozone (O3) is useful in the upper atmosphere where it forms a blanket that absorbs most of the harmful ultraviolet (UV) radiations from the sun. It is basically a gas made up of 3 oxygen atoms. Near the earth's surface, it is produced by the reactions between the sun rays, organic gases and oxides of nitrogen emitted by cars, power plants, industrial boilers and refineries. Ozone irritates the airway of both healthy people and people with respiratory problems, at high concentration it also reduces the lung capacity, and can cause difficulties in breathing, wheezing, and coughing among people with lung conditions Volatile Organic Compounds (VOCs) These compounds, so called because they evaporate at or near room temperature are carbon containing compounds given off by paints, cleaning supplies, pesticides, glues etc. They are also released during combustion of coal, gasoline and natural gas, benzene and benzene - type compounds are also major sources. There is literally no escaping VOCs, drinking water is known to bear traces of these compounds due to industrial discharge and disinfection processes. VOCs react with oxides of nitrogen to form smog or ground-zero ozone. Common health effects include: ● Irritation to skin and eye ● Sensitization ● Central nervous system effects such as exaggerated visual disturbance ● Carcinogenicity ● Liver and kidney effects Other hazardous substances include lead, mercury, and dioxin. ● Lead in large quantities causes severe damage to the brain and kidney especially that of growing children. In trace quantities it affects the child's IQ and thus learning abilities ● Mercury has a long term effect on the central nervous system ● Dioxins are commonly present in food, but also occur in air in a trace amount where when inhaled, can harm the liver, affects CNS as well as the endocrine system. Other major effects of air pollutions are: Photochemical Smog Like stated earlier, photochemical smogs are mainly composed of ozone, nitrogen oxides and VOCs. The process of formation is straightforward and involves the following steps: Step 1 Nitrogen dioxide (NO2) produced from vehicle exhaust, is photolyzed by ultraviolet (UV) radiation hv from the sun, in the process the nitrogen dioxide is decomposed into unstable nitric oxide (NO) and oxygen radical O' according to the equation: NO2 + hv = NO + O⁻ Step 2 The oxygen radical released from step 1 above reacts with atmospheric oxygen molecules to form ozone, O3: O⁻ + O2 = 03 Step 3 Under normal atmospheric conditions, O3 will reacts with NO, given off NO2 and O2 as follows: O3 + NO = O2 + NO2 The process will thus become cyclical leading to net increase in ozone. However, to create photochemical smog, VOC must be present in the air such that the equation continues as follows. Step 4 The volatile organic compounds (VOCs) reacts with hydroxide in the air to form water and reactive VOC molecules: RH + OH⁻ = R⁻ + H2O Step 5 The reactive VOC combines with oxygen molecules(O2) in the air to form oxidized VOC: R⁻ + O2 = RO2 Step 6 Lastly the oxidized VOC can now bond with NO produced in step 1 above to form nitrogen dioxide and a reactive VOC molecules: RO2 + NO = RO⁻ + NO2 Note how NO from step 1 is oxidized in step 6 without destruction of any ozone, this implies that in the presence of VOC, step 3 is completely eliminated leading to a huge build up of photochemical smog in the lower atmosphere. Smog is prevalent in growing and densely populated cities such as Shanghai in China, New Delhi in India, as well as old and large cities like Los Angeles in the USA. Lagos in Nigeria have also witnessed some form of smog. Smog irritates the eyes and throat, it also damages the lung that is why it’s occurrence is preceded by warnings from health officials. Smogs can halt commercial activities when it occurs, like the case of Shanghai in 2018. GreenHouse Gases By trapping earth’s heat, greenhouse gases increase global temperature and drive climatic changes responsible for more extreme weather, rising seas, stronger storms, drought and heat related deaths. It also leads to an increase in infection disease like Lyme. Carbon dioxide produced from burning fossil fuel is the major greenhouse emitter contributing about 76%, followed by methane at 16% primarily from agriculture, and nitrous oxides from vehicle emissions contributing 6%. The remaining 2% comes from hydrofluorocarbons(HFCs), a very powerful greenhouse gas with a heat trapping ability thousands of times better than carbon dioxide. A 2016 agreement by a coalition of 140 countries aims to drastically reduce the use of this chemical in refrigerators and air conditioning units, replacing it with more environmentally friendly alternatives. This agreement according to NRDC will avoid the equivalent of more than 80 billion tonnes of carbon dioxide from being loaded into the atmosphere over the next 35 years. Tackling Air Pollution Over the years, there have been a concerted intergovernmental effort to curtail air pollution, these ranges from the 1979 UNECE convention on long range Transboundary Air Convention to the more recent 2015 Paris Climate Agreement. Others like the introduction of catalytic converters in automobiles helped reduce the emissions of more dangerous compounds from car exhaust, the 2016 HFCs phase down agreement is also significant, as well as the massive subsidization of renewable energy industries which has encouraged investment in alternative sources of energy. All these are responsible climatic policies with remarkable results and potentials to keep driving the changes that we need. However, more still needs to be done by the world governing body especially in ensuring that these treaties are sustained overtime as well as encouraging individual contributions through sensitization. This is because tackling air pollution cannot be left for the government alone since our everyday actions significantly impact our environment. Some of the simpler steps we can take as individuals include: ● Making good transportation choices by, walking, taking a bike and using public transportation when convenient ● Buying cars with better miles per gallon of gas or switching to electric car ● Making the right energy choice, request that your electricity get supplied by wind or solar if you have those options ● Buying your groceries locally and avoiding having to ride a truck across town for the same services you can get locally, this way you cut down on your carbon signatures ● Getting involved, joining the conversation, and electing environmentally responsible leaders whom will push for clean air and water You also need to be health conscious by: ● Following WHO air quality updates and staying inside when the air quality is bad ● Avoiding excessive sun exposure to avoid skin cancer or burn, wearing sunscreen when the sun is too hot and using an umbrella ● Staying clear of heavily trafficked road especially when exercising or avoiding such roads completely ● Showering and washing your clothes regularly to remove the particulate matter and ensuring that kids are not exposed to heavily polluted air References: [1] Miller, Jr., George Tyler (2002). Living in the Environment: Principles, Connections, and Solutions (12th Edition). Belmont: The Thomson Corporation. pp. 423. [2] Petrucci, Ralph H., William S. Harwood, and Geoff E. Herring. General Chemistry : Principles and Modern Applications. 9th ed. Upper Saddle River: Prentice Hall PTR, 2006. [3] Rodricks, Joseph V. Calculated Risks : The Toxicity and Human Health Risks of Chemicals in Our Environment. 2nd ed. New York: Cambridge UP, 2007. [4] World Health Organisation (WHO). 2018. Ambient (Outdoor) Air Pollution [5] D.V. Bates, G.M. Bell, C.D. Burnham, et al. Short term effects of ozone on the lung. Journal of Applied Physiology. 32. 176-181. (1976). [6] Godish, Thad. Air Quality. 4th ed. Florida: CRC Press LLC, 2004. [7] National Resources Defense Council (NRDC). 2012.Closing the Power Plant Carbon Pollution Loopholes [8] E.T. Wilkens. Air Pollution and the London Fog of 1952. Journal of the Royal Sanitary Institute. 74. 1-22. (1956). [9] National Geographic. 2019. What Step is Crucial in Fighting Cities’ Air Pollution?