Ozone Layer and Depletion

Ozone Layer

• Ozone (O3O_3O3​) is a pale blue gas with a pungent odor.
• Ozone is located in the upper layer of the atmosphere, which surrounds the Earth.
• The ozone layer acts as a barrier against harmful ultraviolet (UV) radiation from the sun.
• Chlorofluorocarbons (CFCs), containing chlorine, fluorine, and carbon, are used in aerosol propellants and refrigerants.
• CFCs contribute to ozone layer depletion.
• CFCs rise to the stratosphere and break down into chlorine atoms due to sunlight.
• Chlorine atoms react with ozone, forming chlorine oxide and oxygen, reducing ozone concentration.

Ozone Depletion

• Ozone layer depletion allows more UV radiation to reach Earth's surface.
• Excessive UV radiation increases the risk of skin cancer, premature aging of the skin, and eye damage (cataracts).

Reducing Air Pollution

• Catalytic converters in vehicle exhaust systems reduce pollutants like carbon monoxide, nitrogen oxides, and unburnt hydrocarbons.
• Flue gas desulfurization removes sulfur dioxide from the waste gases produced by power plants burning sulfur-containing fossil fuels.
• Using low-sulfur fuels minimizes sulfur dioxide emissions from vehicle engines.

Catalytic Converters

• Catalytic converters use transition metals like platinum and rhodium as catalysts.
• Redox reactions in the converter convert harmful exhaust gases into harmless ones.
• Nitrogen monoxide reacts with carbon monoxide to form nitrogen and carbon dioxide.
• Carbon monoxide oxidizes to carbon dioxide.
• Nitrogen oxides reduce to nitrogen.
• Unburnt hydrocarbons like octane oxidize to carbon dioxide and water vapor.

Flue Gas Desulfurization

• Flue gas desulfurization removes sulfur dioxide from flue gas, reducing atmospheric sulfur dioxide levels.

Air Pollutants

• Common air pollutants include unburnt hydrocarbons (CxC_xCx​ HyH_yHy​), ozone (O3O_3O3​), sulfur dioxide (SO2SO_2SO2​), and nitrogen oxides (NOxNO_xNOx​).

• Sources of air pollutants include vehicle engines, chemical plants, and fossil fuel combustion.

• Effects of air pollutants on health and the environment include respiratory problems, eye irritation, photochemical smog, and acid rain.

• Unburnt hydrocarbons cause eye and lung irritation, breathing difficulties, and contribute to photochemical smog.

• Ozone causes eye and lung irritation, breathing difficulties, headaches, chest pain, and affects plant photosynthesis.

Acid Rain

• Acid rain is rainwater with high levels of sulfuric acid and nitric acid.
• Sulfur dioxide (SO2SO_2SO2​) and nitrogen dioxide (NO2NO_2NO2​) are acidic oxides that react with oxygen and water to form sulfuric acid and nitric acid, respectively:
  • 2SO2(g)+O2(g)+2H2O(l)−>2H2SO4(aq)2SO_2(g) + O_2(g) + 2H_2O(l) -> 2H_2SO_4(aq)2SO2​(g)+O2​(g)+2H2​O(l)−>2H2​SO4​(aq)
  • 4NO2(g)+O2(g)+2H2O(l)−>4HNO3(aq)4NO_2(g) + O_2(g) + 2H_2O(l) -> 4HNO_3(aq)4NO2​(g)+O2​(g)+2H2​O(l)−>4HNO3​(aq)
• Acid rain damages metal structures, buildings, aquatic life, and soil nutrients.