Topic 2: Air

Air Composition of Clean Dry Air

• Composition: Clean dry air is primarily composed of the following gases by volume:

  • Nitrogen: 78%

  • Oxygen: 21%

  • Noble gases and Carbon dioxide: Remainder

Separation of Nitrogen and Oxygen

• Technique: Fractional distillation of liquefied air is used to separate nitrogen and oxygen.

Air Pollutants

• Sources:

  • Sulfur Dioxide: From combustion of fossil fuels containing sulfur compounds.

  • Oxides of Nitrogen: Emitted from car engines.

  • Carbon Monoxide & Particulates: From incomplete combustion of carbon-containing fuels.

  • Carbon Dioxide: Produced from complete combustion of carbon-containing fuels.

  • Methane: Generated from the decomposition of vegetation and waste, and from microbial digestion in animals.

Adverse Effects of Air Pollutants

• Sulfur Dioxide:

  • A poisonous gas causing irritation of the respiratory tract and breathing difficulties.

  • Contributes to acid rain.

• Oxides of Nitrogen:

  • Cause acid rain and photochemical smog.

  • Lead to respiratory problems.

• Carbon Monoxide:

  • A toxic gas that forms carboxyhemoglobin, reducing blood oxygen transport and causing asphyxiation.

• Particulates:

  • Increase the risk of respiratory diseases and cancer.

• Carbon Dioxide:

  • At elevated levels, it contributes to global warming and environmental changes.

• Methane:

  • Contributes to global warming.

Photochemical Smog

• Formation: Occurs mainly in automobile-dense areas due to reactions between nitrogen oxides and unburnt hydrocarbons catalyzed by sunlight.

• Products: Ozone gas is produced, which is toxic; nitrogen monoxide converts to nitrogen dioxide, giving the smog a brownish color.

• Effects:

  • Reduces visibility, damages plants, irritates eyes, and causes respiratory distress.

Acid Rain

• Formation: Sulfur dioxide and oxides of nitrogen react with water to form sulfuric and nitric acids, resulting in a lower pH than natural rain (pH ~ 5.5 vs. acid rain at pH ~ 4).

• Problems:

  • Corrodes metal structures and damages buildings/statues (e.g., erodes marble and limestone).

  • Increases water acidity, killing aquatic life.

  • Damages plants and contributes to mineral leaching in soils.

Greenhouse Effects and Global Warming

• Mechanism: The balance of heat received from the Sun and emitted into space affects the Earth’s temperature. Greenhouse gases like CO2 and methane trap heat, leading to warmer temperatures.

• Consequences:

  • Potential climate change disruptions, extreme weather, melting ice caps leading to rising sea levels.

Oxides of Nitrogen Production

• Details: Produced from high-temperature fuel combustion in car engines, leading to nitrogen oxides formation.

Strategies to Reduce Air Pollution

• For Climate Change:

  • Plant more trees and use alternative energy sources (e.g., hydrogen, renewable fuels like wind/solar).

• For Acid Rain:

  • Decrease sulfur dioxide emissions and enhance pollution control technologies (e.g., flue gas desulfurization).

  • Use low sulfur fuels and catalytic converters in vehicles.

Catalytic Converters

• Function: Convert harmful emissions into less harmful substances, targeting:

  • Carbon monoxide to carbon dioxide.

  • Oxides of nitrogen to nitrogen.

  • Hydrocarbons to carbon dioxide and water.

• Chemical Reactions:

  • $2CO(g) + O<em>2(g) ightarrow 2CO</em>2(g)$

  • $2CO(g) + 2NO(g) <br>ightarrow 2CO<em>2(g) + N</em>2(g)$

  • $2NO<em>2(g) + 4CO ightarrow 4CO</em>2(g) + N_2(g)$

Photosynthesis

• Process Overview: Plants synthesize food using carbon dioxide and water in the presence of sunlight, producing glucose and oxygen.

• Chemical Equation:
  $6CO<em>2(g) + 6H</em>2O(l) + ext{sunlight} <br>ightarrow C<em>6H</em>{12}O<em>6(s) + 6O</em>2(g)$

Respiration

• Process Overview: The burning of glucose for energy, producing carbon dioxide and water.

• Chemical Equation:
  $C<em>6H</em>{12}O<em>6(s) + 6O</em>2(g) <br>ightarrow 6CO<em>2(g) + 6H</em>2O(l) + ext{Energy}$

• Difference: Photosynthesis is endothermic, whereas respiration is exothermic.