Video Transcript
In this video, we will learn about common air pollutants, where they come from, and how they affect our world.
Air pollutants can be gases or particulates. Particulates are tiny solid particles, for example, tiny particles of carbon called soot. Soot you will commonly see coming off smoky fires. And it’s also a product of incomplete combustion of fossil fuels, which we will investigate just now. Common gaseous air pollutants include carbon monoxide gas, sulfur dioxide gas, and various oxides of nitrogen. These gaseous pollutants are also produced from the burning or combustion of fossil fuels. These substances negatively impact our environment as well as human, plant, and animal health. Let’s investigate how these pollutants are produced and how they each specifically impact our environment and organisms.
Where do these air pollutants come from? Most come from the burning of fossil fuels. Fossil fuels such as coal, oil, gasoline, which is derived from oil, and natural gas are burnt, for example, in industrial processes at factories and in car engines. The main products are water vapor and carbon dioxide gas. But carbon monoxide gas or sooty carbon particulates can also be produced. The last two are products of incomplete combustion, where there is insufficient oxygen gas to convert all the fuel to water vapor and carbon dioxide gas. When carbon dioxide is a product, we say the combustion was complete.
This equation shows the complete combustion of propane gas. There is sufficient oxygen, and so carbon dioxide is produced. The corresponding equation for the incomplete combustion of propane shows two very different products, carbon monoxide and sooty carbon. You may have seen both of these reactions occurring in the lab. The fuel gas in a Bunsen burner, which consists of propane mixed with butane, gives a nice, clean blue flame when the air hole of the Bunsen burner is fully open. But when the air hole is not fully open and there is insufficient oxygen, the flame is orange and gives off much sooty smoke. In industry, factories and cars, similar reactions occur, giving off these air pollutants.
Fossil fuels often contain other elements and impurities such as sulfur. When the fuels are combusted, sulfur compounds are produced. For example, sulfur in fossil fuels can be oxidized to sulfur dioxide gas, another type of air pollutant. Fossil fuel combustion releases much energy and generates very high temperatures. This can cause the production of another class of air pollutants, various oxides of nitrogen whose general formula we write as NO subscript X. These are sometimes commonly referred to as NOX gases.
Now, nitrogen and oxygen do not usually react with each other under normal conditions. Nitrogen especially is usually inert and unreactive. But the very high temperatures in engines supply enough energy to induce a reaction between nitrogen and oxygen. At these high temperatures, nitrogen and oxygen from the air in the car engine can react to produce nitrogen monoxide, which can further react with oxygen gas to produce nitrogen dioxide gas. These are two different examples of the general formula NOX. Nitrogen monoxide and nitrogen dioxide can react even further with the energy from sunlight in the atmosphere to produce other toxic substances.
When leaded fossil fuels are combusted, some hazardous lead compounds can be produced. Since the 1970s, lead additives such as tetraethyl lead used in gasoline and some petrols began to be restricted by some countries. Nowadays, most countries highly restrict or don’t use at all these lead additives in gasoline and petrol, even though these leaded compounds can increase engine performance and fuel economy. This is because research has shown the toxicity of lead and lead compounds.
Now that we know about the common pollutants in the air and how they are produced, let’s investigate how they negatively impact the world.
Building damage is the first unfortunate influence of air pollution. The carbon in soot can cause buildings to blacken over time. Over time, soot build-up can block pipes in water heaters, furnaces, and boilers, which can create a potential fire hazard. Sulfur dioxide can react with water in tiny droplets in clouds to form sulfurous acid, which can react further with oxygen to produce sulfuric acid. When nitrogen dioxide reacts with water in clouds, nitric acid is produced. These substances fall as acid rain, damaging limestone buildings and metal structures.
Most modern cars contain a catalytic converter in their exhaust or tailpipe. The catalytic converter converts the harmful oxides of nitrogen to harmless nitrogen gas and water vapor. So building damage is the first problem resulting from air pollution.
Health problems is another big result of air pollution. Carbon monoxide gas is highly toxic. It binds strongly to hemoglobin in red blood cells, hindering the binding of oxygen gas to red blood cells. And in this way, less oxygen gas is carried to the cells of the body. Prolonged exposure to high concentrations of carbon monoxide can lead to sluggishness, unconsciousness, and even death. The fine particles of carbon soot, if breathed in, can cause breathing problems. Soot particles are extremely small, even smaller than dust particles. They can enter the bloodstream, causing a wide variety of health issues. These include asthma, strokes, heart attacks, and even cancer.
Nitrogen dioxide gas is toxic. It affects the lungs and can cause coughing. It can also contribute to some cases of bronchitis. These three substances are some of the components of smog. Smog is that yellow-brown smoky haze often seen hanging over cities and industrial areas, especially when it hasn’t rained for a while. Smog is a mixture of dust, carbon monoxide gas, soot, oxides of nitrogen, sulfur dioxide gas, and may even contain some VOCs, which are volatile organic compounds. These chemical pollutants in smog can inflict all the harmful damage and health influences we have investigated so far, such as building damage and harm to the body, for example, harm to lung function and irritation to eyes, nose, and throat.
Hazy smoke can also block sunlight partially causing global dimming. Less sunlight is allowed to reach the Earth’s surface, and this has a cooling effect. Though the cooling effect of global dimming may seem like a good thing because it could counteract the effects of possible global warming from greenhouse gases, it’s a very artificial cooling effect, bringing with it these health problems, acid rain, and building damage.
Damage to plants and aquatic life is another effect of air pollution. We have seen that SO2 gas and NO2 gas produce acid rain when they interact with water and clouds. Acid rain can increase the acidity of rivers and lakes. And this has a harmful effect on the aquatic life, sometimes even making those bodies of water too acidic for those organisms to live. Acid rain can also cause trees and plants to drop their leaves and can change soil conditions, which sometimes results in plants not thriving but even dying. Carbon soot and other particulate matter from a pollution can smother plant leaves. This can reduce their ability to take in sunlight and carbon dioxide for photosynthesis.
What about lead and lead oxide released from the burning of fossil fuels that contain lead additives. Research has shown that lead, lead oxide, and other lead compounds can accumulate in the body over time, can cause brain and kidney damage, and can cause problems in the gastrointestinal tract and male reproductive system. Most countries restrict or have phased out lead additives in gasoline and petrol, although a few countries still do use these additives.
Although air pollution can cause many unwanted effects on the environment and our health, it is important to remember that these problems are generally localized problems. Acid rain does not fall everywhere. Smog does not cover the whole Earth. Global dimming only occurs when there is much particulate matter in the air. And there are many parts of the world that do not have building damage or serious health problems from air pollution. Nevertheless, air pollution can indirectly affect us all. We can all play a role in improving the air quality of our planet by making wise choices in our daily lives.
Let’s look at the key points that we have learnt about air pollution. We learnt that the common air pollutants include carbon monoxide gas, sulfur dioxide gas, gaseous oxides of nitrogen, carbon soot, and lead compounds. We saw that these substances are produced during the combustion of fossil fuels. And this results in building damage, health problems, smog, and global dimming, as well as injury to plant and aquatic life.
