Ozone Layer Depletion & Air Pollution PDF

## What is the Ozone Layer? - Discuss why the ozone layer is important. - Describe the depletion of ozone by chlorine-containing compounds called chlorofluorocarbons (CFCs). 1. Ozone (${O_3}$ ) is a pale blue gas with a pungent odour. 2. Ozone is found in the upper layer of the atmosphere. The atm...

## What is the Ozone Layer? - Discuss why the ozone layer is important. - Describe the depletion of ozone by chlorine-containing compounds called chlorofluorocarbons (CFCs). 1. Ozone (${O_3}$ ) is a pale blue gas with a pungent odour. 2. Ozone is found in the upper layer of the atmosphere. The atmosphere is a layer of air that surrounds the Earth. 3. The ozone layer acts as a barrier to filter out harmful ultraviolet (UV) radiation from the sun. 4. Chlorofluorocarbons, commonly called CFCs, are compounds containing the elements chlorine, fluorine and carbon. They are used as aerosol propellants and refrigerants. 5. CFCs cause the depletion of the ozone layer. - When released into the air, CFCs float upwards to the stratosphere. - In the presence of sunlight, they decompose to form chlorine atoms. - These chlorine atoms react with ozone to form chlorine oxide and oxygen. - The loss of ozone and depletion of the ozone layer allows ultraviolet radiation to reach the Earth's surface. - Excessive ultraviolet radiation can increase the risk of skin cancer, premature aging of the skin, eye damage (cataract). ## Worked Example 22.3 The depletion of the ozone layer is mainly caused by chlorofluorocarbons (CFCs). An example ## Reducing Air Pollution 1. Some ways to reduce air pollution are shown below: - Using a catalytic converter to remove certain air pollutants from exhaust gases. - Carrying out flue gas desulfurisation to remove sulfur dioxide. - Using low sulfur fuels to reduce the emission of sulfur dioxide from vehicle engines. ## Catalytic Converters Fitting catalytic converters to exhaust pipes can help to reduce the amounts of air pollutants such as carbon monoxide, oxides of nitrogen and unburnt hydrocarbons. The catalysts used in catalytic converters are transition metals like platinum and rhodium. - In the catalytic converter, redox reactions convert harmful exhaust gases into harmless gases. - Nitrogen monoxide reacts with carbon monoxide to form nitrogen and carbon dioxide. - Carbon monoxide is oxidised to carbon dioxide. - Oxides of nitrogen are reduced to nitrogen. - Unburnt hydrocarbons such as octane are oxidised to carbon dioxide and water vapour. ## Flue Gas Desulfurisation The exhaust or waste gases produced by power plants that burn sulfur-containing fossil fuels are known as flue gas. Flue gas desulfurisation is the process of removing sulfur dioxide from the waste gases formed when fossil fuels undergo combustion. This reduces the amount of sulfur dioxide that is released into the atmosphere. ## Air Pollutant | Air Pollutant | Source | Harmful Effects | |:---------------------------------------|:----------------------------------------------------------------------------|:--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | Unburnt hydrocarbons (${C_x}$ ${H_y}$) | Combustion in engines of vehicles and chemical plants. | They cause irritation of the eyes and lungs and breathing difficulties. They react with oxides of nitrogen in the presence of sunlight to form photochemical smog which pollutes the air. Photochemical smog appears as a brown haze. | | Ozone (${O_3} $) | Reaction between oxides of nitrogen and unburnt hydrocarbons in the presence of sunlight. | It causes irritation of the eyes and lungs and breathing difficulties. It causes headache and chest pain. It slows down photosynthesis, thus affecting crops. | ## Acid Rain 1. Acid rain is rainwater containing high levels of sulfuric acid and nitric acid. 2. Both sulfur dioxide and nitrogen dioxide are acidic oxides and react with oxygen and water to form sulfuric acid and nitric acid respectively. - $2SO_2(g) +O_2(g) +2H_2O(l) -> 2H_2SO_4(aq)$ - $4NO_2(g) +O_2(g) +2H_2O(l)-> 4HNO_3(aq)$ 3. The harmful effects of acid rain include the following: - Corrosion of metal bridges and structures - Corrosion of buildings or monuments made of calcium carbonate - Acidification of lakes and rivers, which harms aquatic life - Leaching of nutrients from the soil, which affects the growth of plants # What are Air Pollutants? - Identify some common air pollutants and their sources. - Discuss some effects of the air pollutants on health and the environment. - Describe the chemical reactions that can be used to reduce the level of air pollutants. 1. Air pollutants are substances which harm living things and affect the environment. 2. Air pollutants are also known as atmospheric pollutants. 3. Some common air pollutants and their sources and harmful effects are shown below. | Air Pollutant | Source | Harmful Effects | |:-----------------------------------------------|:----------------------------------------------------------------------------------|:------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | Carbon monoxide (CO) | Incomplete combustion of carbon-containing fuels. | It combines with haemoglobin in red blood cells and reduces its ability to transport oxygen, thus causing death. | | Sulfur dioxide (${SO_2}$) | Combustion of sulfur-containing fossil fuels, volcanic eruptions. | They cause irritation of the lungs and eyes and breathing difficulties. They react with oxygen and water to form acid rain. Acid rain kills plants and aquatic life and corrodes marble and metal structures. | | Oxides of nitrogen (${NO}$, ${NO_2}$) | Combustion in engines of vehicles. | They react with oxygen and water to form acid rain. Acid rain kills plants and aquatic life and corrodes marble and metal structures. | | Methane (${CH_4}$) | Decomposition of dead organic matter, waste gases released due to digestion in cattle. | It is a greenhouse gas that contributes to global warming. |