AICE ENVIRO UNIT 7

7.1 Acid Deposition

Definition:
A mix of air pollutants that deposit from the atmosphere; occurs as acidic wet deposition (pH < 5.6) or dry deposition. Acid deposition plays a significant role in environmental degradation by altering ecosystems and affecting health.

Types of Acid Deposition:

Wet Deposition:

Includes forms of precipitation such as snow, rain, hail, and fog. Wet deposition is critical in transporting acids away from the atmosphere and can significantly lower the pH of the receiving water bodies.

Major secondary pollutants:

• Sulfuric Acid ($H<em>2SO</em>4$):

  • Formed primarily from the oxidation of sulfur dioxide ($SO_2$).

  • Major contributor to acid rain and can lead to widespread damage in aquatic and terrestrial ecosystems.

• Nitric Acid ($HNO_3$):

  • Produced through the oxidation of nitrogen oxides.

  • Impacts similar to sulfuric acid; however, it dissociates more easily in water.

These compounds can travel far from the source, leading to regional environmental issues.

Dry Deposition:

Involves dust and gases. Dry deposition is significant as it occurs without precipitation, depositing pollutants directly onto surfaces.

Primary pollutants include:

• Sulfur Dioxide ($SO_2$):

  • Emitted from burning fossil fuels like coal and oil, as well as during volcanic eruptions.

• Nitrogen Oxides ($NO_x$):

  • Produced from combustion processes in vehicles and power plants.
    These typically fall close to the emission source, contributing to localized pollution.

Formation Process:

Sources of sulfur and nitrogen:

• Fossil fuels contain sulfur compounds that contribute to acid deposition upon combustion.

• Nitrogen from the atmosphere reacts with oxygen at high temperatures, such as in internal combustion engines, to produce nitrogen monoxide, which contributes to nitrogen oxides upon further reactions.

Chemical Reactions:

• The oxidation of sulfur dioxide can be represented as:
  $SO<em>2 + H</em>2O + O<em>2 \rightarrow H</em>2SO_4$

• The formation of nitric acid is shown as:
  $NO + H<em>2O + O</em>2 \rightarrow HNO_3$

Environmental Effects:

Aquatic Life:

• Acid deposition notably kills larva of fish, mollusks, and amphibians, which can disrupt food chains and lead to declines in species diversity.

• Alters morphology in aquatic species, leading to issues like impaired fish gill health, which affects respiration.

Vegetation and Crops:

• Acid rain causes significant defoliation in sensitive crops and trees, damaging chloroplasts and reducing overall photosynthesis efficiency.

• Alters soil chemistry, affecting nutrient availability and reducing productivity and crop yield.

Built Environment:

• Erodes stone buildings and structures, particularly those made of limestone and marble, leading to loss of cultural heritage.

• Damage to vehicles from acid deposition enhances chemical weathering and causes rust.

• Can erase historical inscriptions on monuments, impacting cultural preservation.

Prevention Strategies:

• Promoting the use of renewable energy sources like wind, solar, and geothermal to reduce reliance on fossil fuels.

• Enhancing public transport systems and encouraging walking, biking, or carpooling to reduce vehicular emissions.

Legislation:

• Clean Air Act (1990): Established emissions trading for sulfur dioxide to mitigate acid rain effects.

• Utilize scrubbers in industrial emissions systems to remove pollutants before they are emitted into the atmosphere.

• Promote the development and adoption of cleaner-burning vehicles and innovative technologies that reduce emissions.

7.2 Photochemical Smog

Definition:
Photochemical smog is a complex mixture of air pollutants, primarily ground-level ozone formed through the chemical reaction of nitrogen oxides and volatile organic compounds (VOCs) in the presence of sunlight. It is mainly a problem in urban areas with high traffic.

Sources:

• Common sources include products such as paints, fuel at gas stations, and activities like plastic manufacturing.

• Other contributors are vehicle emissions and industrial discharges.

Impacts:

• Health impacts like eye irritation, respiratory problems, lung damage, and exacerbation of conditions such as asthma.

• Causes significant reductions in agricultural yields by harming crops directly.

• Degrades materials such as plastics and rubber, leading to increased maintenance costs.

• Reduces visibility, contributing to transportation safety issues and challenges for aviation.

7.3 Managing Air Pollution

Technological Approaches:

• Sulfur Dioxide (SO2): Managed through flue gas desulfurization technologies (scrubbers) that remove SO2 from exhaust gases.

• Nitrogen Oxides (NOx): Reduced via the introduction of catalytic converters in vehicles that convert NOx into harmless nitrogen and oxygen.

• Particulates: Utilized electrostatic precipitators to control particulate emissions from industrial sources.

• VOCs: Promote the safe usage and disposal of household products containing VOCs to minimize releases.

Policy Measures:

• Strategies aiming to reduce fossil fuel consumption through incentivizing alternative energy sources.

• Implement stringent legislation regarding vehicle emissions and urban usage restrictions to control pollution sources.

• Adhere to the "Polluter pays" principle to hold polluters accountable for environmental degradation.

7.4 Ozone Depletion

Mechanism:
Chlorofluorocarbons (CFCs) found in products like aerosols and refrigerants are stable at sea level, allowing them to rise into the stratosphere. There, UV light breaks them down, releasing chlorine atoms that react with ozone molecules, leading to ozone depletion.

• The chemical reaction can be represented as:
  $Cl + O<em>3 \rightarrow ClO + O</em>2$

• Chlorine's ability to react multiple times with ozone demonstrates its catalytic effect, significantly affecting the ozone layer.

Effects:

• Increased UV radiation results in various human health issues, including higher rates of cataracts and skin cancer.

• Reductions in agricultural productivity due to damage to crops from increased UV exposure.

• Loss of biodiversity as ecosystems are disrupted due to changing conditions.

• Economic impacts resulting from material degradation, such as increased costs in healthcare and agriculture.

International Actions:

• Vienna Convention: Promotes international cooperation and sharing of information regarding ozone depletion to encourage global awareness and intervention.

• Montreal Protocol: A significant global initiative targeting the phaseout of ozone-depleting substances to protect the ozone layer from further damage.

• Alternatives:

  • Hydrochlorofluorocarbons (HCFCs) are introduced as a less harmful alternative to CFCs, though they still have some ozone depletion potential.

  • Fluorinated gases, while not damaging the ozone layer, contribute significantly to global warming as potent greenhouse gases.

• Research:
  The Rowland-Molina hypothesis first established CFCs as the primary cause of ozone depletion, later confirmed by subsequent scientific research, leading to policy changes and international agreements to curb CFC use.