Environmental Science – Pollution, Ozone Depletion & Climate Change

Exam Logistics

• Upcoming assessment: Environmental Science Test
  • Scheduled for Thursday (exact date unspecified; confirm with instructor)
  • Structure:
  • 10 Multiple-Choice Questions
  • Short-Answer Section worth 21 marks
• Topics explicitly listed in teacher’s “Pollution Checklist”: definitions, sources & sinks of pollutants, CFCs/ozone depletion, enhanced greenhouse effect, global-warming impacts, mitigation strategies.

Pollution: Core Definition

• Pollution = “The presence in or introduction—due to human activities—into the environment of a substance which has harmful or poisonous effects.”
  • Key phrase: “due to human activities.” While natural phenomena release harmful substances, we label it pollution mainly when anthropogenic inputs exceed natural levels or overwhelm natural recovery.
• Pollutant = Any substance that, when released, causes harm or alters the environment in a negative way.
  • Includes gases, liquids, solids, energy (heat, noise, radiation).

Sources of Pollutants

Natural (background) sources

• Volcanic eruptions
  • Emit ash, $\text{SO}<em>2$, $\text{CO}</em>2$, metal particulates.
• Bushfires / wildfires
  • Produce smoke, particulate matter, $\text{CO}_2$.
• Animal waste
  • Releases $\text{CH}_4$ (methane) & nutrients (nitrates, phosphates).
• Pollen
  • Not toxic but can trigger allergies; counted when concentration becomes harmful.

Human (anthropogenic) sources

• Factories / industry
  • Emit toxic gases, heavy-metal particulates, acidic aerosols.
• Cars & transport
  • Produce $\text{CO}<em>2$, $\text{NO}</em>x$ (nitrogen oxides), unburnt hydrocarbons.
• Farming / agriculture
  • Fertilisers → nitrate & phosphate runoff (eutrophication)
  • Pesticides → bioaccumulation, endocrine disruption.
• Rubbish dumps / landfills
  • Anaerobic decomposition → $\text{CH}_4$ (explosive, greenhouse gas).
• CFCs from old refrigerators, aerosols, air-conditioning systems.

Pollutant Sinks

• Sink = Process or place that removes, absorbs, or stores a pollutant.
• Main natural sinks listed:
  • Forests & terrestrial vegetation
  • Photosynthesis absorbs $\text{CO}_2$ and stores carbon in biomass.
  • Soils
  • Adsorb/agglomerate chemicals; microbes convert nitrates to $\text{N}_2$ (denitrification).
  • Oceans
  • Dissolve $\text{CO}_2$, store nutrients, support planktonic uptake.
  • Wetlands
  • Act as biofilters—trap sediments, convert nitrates & phosphates.
  • Atmosphere (dilution)
  • Dispersion lowers local concentration; not removal—merely reduces immediate toxicity.
• Limitation principle: Rate of sink processes is finite. Human emissions often exceed sink capacity, leading to accumulation.

Case Study: CFCs & Ozone Layer Depletion

• CFCs (Chlorofluorocarbons)
  • Synthetic, stable, non-toxic in troposphere → popular as coolants & propellants.
• Mechanism of harm
  1. Molecules rise to stratosphere (10–50 km).
  2. UV radiation breaks CFCs → releases chlorine radicals (Cl·).
  3. Each Cl· catalytically destroys $\text{O}<em>3$ (ozone) via: $\text{Cl· + O}</em>3 \rightarrow \text{ClO· + O}<em>2$$\text{ClO· + O} \rightarrow \text{Cl· + O}</em>2$
  • Net: $\text{O}<em>3 + O \rightarrow 2\,\text{O}</em>2$; one Cl· repeats ~$10^5$ times before deactivated.
• Importance of ozone layer
  • Blocks ~99% of biologically damaging UV-B radiation.
• Consequences of depletion
  • Increased skin cancers & sunburn.
  • Higher incidence of cataracts & eye damage.
  • Reduced crop yields; phytoplankton damage → disrupts marine food webs.
• Policy connection: Montreal Protocol (1987) phased out CFCs—demonstrates global cooperation & precautionary principle.

Greenhouse Effect vs. Enhanced Greenhouse Effect

• Natural greenhouse effect
  • ~$66\%$ of incoming solar energy is re-radiated as infrared (longwave) from Earth’s surface.
  • Greenhouse gases (GHGs)—$\text{H}<em>2\text{O}$ vapour, $\text{CO}</em>2$, $\text{CH}<em>4$, $\text{N}</em>2\text{O}$—absorb & re-emit IR, maintaining average surface temp ≈ $15\,^{\circ}\text{C}$.
• Enhanced greenhouse effect
  • Human activities add extra GHGs, thickening the “blanket.”
  • Main anthropogenic drivers:
  • Burning fossil fuels (coal, oil, natural gas) → $\text{CO}_2$.
  • Deforestation → reduces carbon sinks; burning trees releases stored carbon.
  • Agriculture → livestock digestion emits $\text{CH}<em>4$; fertiliser use → $\text{N}</em>2\text{O}$.
• Result: Global warming—positive energy imbalance raising average temperatures.

Impacts of Global Warming (Observed & Projected)

• Reduction in alpine environments
  • Shorter snow seasons, upward shift of tree line, habitat loss for cold-adapted species (e.g., mountain pygmy possum).
• Melting ice caps & glaciers
  • Contributes to sea-level rise; reduces albedo (ice–albedo feedback).
• Sea-level rise
  • Threatens low-lying coastal communities & island nations; salt-water intrusion into aquifers.
• Increased frequency/intensity of bushfires & droughts
  • Warmer, drier conditions raise fire danger indices.
• Ecosystem & wildlife changes
  • Range shifts, coral bleaching, phenological mismatches (e.g., pollinators vs. flowering).
• Heatwaves & extreme weather
  • Greater risk to human health, agriculture, infrastructure.

Mitigation & Adaptation Strategies

• Energy transition
  • Expand renewables: solar PV, wind, hydro, geothermal.
  • Electrify transport; invest in grid storage & smart systems.
• Energy efficiency
  • Insulation, LED lighting, efficient appliances; industrial process optimisation.
• Reduce fossil-fuel dependence
  • Carbon pricing (tax or cap-and-trade); phase out coal power plants.
• Protect & restore forests
  • Halt land clearing; reforestation & afforestation projects sequester $\text{CO}_2$.
• Agricultural reforms
  • Methane-reduction feed additives; precision fertiliser use; regenerative practices enhancing soil carbon.
• Population stabilisation
  • Education, healthcare access, family-planning services help slow growth → lowers future emissions.

Ethical, Philosophical & Practical Considerations

• Intergenerational equity
  • Decisions today affect climate & ozone for centuries; duty to protect future generations.
• Precautionary principle
  • Act to prevent serious harm even if some cause-effect details remain uncertain (e.g., Montreal Protocol).
• Common but differentiated responsibility
  • Industrialised nations historically emitted more; equity demands they lead in mitigation & finance.
• Technological optimism vs. behavioural change
  • Debate: rely on innovation (carbon capture, geoengineering) or emphasise consumption reduction & lifestyle shifts.

Key Numerical & Scientific Facts to Memorise

• Test layout: 10 MCQs + 21-mark short answer.
• Ozone destruction catalytic cycle: 1 Cl· can destroy $\approx 10^5$ ozone molecules.
• Incoming solar energy: $100\%$ → ~$66\%$ re-radiated as infrared; trapped fraction determines warming.
• Major greenhouse gases (by contribution): $\text{CO}<em>2$ > $\text{CH}</em>4$ > $\text{N}_2\text{O}$ > CFCs (still potent but lower current concentration).

Quick-Recall Cheat Sheet

• Pollution = harmful substance; Pollutant sink = natural process/place that removes it.
• Natural sources → volcanoes, bushfires, animal waste, pollen.
• Human sources → factories, cars, farming, landfills, CFC appliances.
• CFCs → ozone layer depletion → UV exposure ↑.
• Greenhouse effect = natural; enhanced = human-amplified.
• Global warming effects: ice melt, sea-level rise, heatwaves, ecosystem shifts.
• Solutions mnemonic “R3E”: Renewables, Reduce fossil fuels, Reforest, Efficiency, Enteric (livestock) methane cut.