State the word equation for photosynthesis, carbon dioxide + water $ ightarrow$ glucose + oxygen

Chemistry of the Environment – Air Quality and Climate

Learning Objective

State the word equation for photosynthesis.

Word Equation for Photosynthesis

Carbon dioxide + water → glucose + oxygen

Purpose: photosynthesis removes CO₂ (a greenhouse gas) from the atmosphere and produces O₂, linking it directly to air‑quality and climate topics.

Balanced Molecular Equation (reference only – not required for the Core)

6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂

Composition of Clean, Dry Air (IGCSE 0620 10.3 Core)

• ≈ 78 % nitrogen (N₂)
• ≈ 21 % oxygen (O₂)
• ≈ 1 % argon (Ar) and other trace gases
• Trace gases include carbon dioxide (CO₂) ≈ 0.04 % and very small amounts of neon, helium, methane, etc.
• “Dry” air means water vapour has been removed; the percentages above refer to the dry‑air mixture.

Major Anthropogenic Sources of Air Pollutants

Adverse Effects of Each Pollutant (limited statements – AO1)

• CO₂ – greenhouse gas; enhances the greenhouse effect → global warming and sea‑level rise.
• CO – toxic; interferes with oxygen transport in blood → headaches, nausea, death at high levels.
• CH₄ – potent greenhouse gas (≈ 28 times more effective than CO₂ over 100 years) → accelerates climate change.
• NO_x – forms tropospheric ozone and smog; contributes to acid rain → respiratory problems, vegetation damage.
• SO₂ – primary cause of acid rain; harms aquatic life and corrodes buildings.
• Particulate Matter – inhalable particles cause respiratory and cardiovascular disease; reduce visibility (haze).

Mitigation Strategies (knowledge of applications – AO1)

Climate‑change mitigation (CO₂, CH₄, N₂O, etc.)

• Use renewable energy (wind, solar, hydro).
• Improve energy efficiency in industry, transport and buildings.
• Afforestation and re‑forestation.
• Capture landfill gas and use it for energy.
• Seal leaks in natural‑gas pipelines.

Acid‑rain mitigation (SO₂, NOₓ)

• Use low‑sulphur fuels.
• Install flue‑gas desulphurisation (FGD) units or scrubbers.
• Employ low‑NOₓ burners and selective catalytic reduction (SCR) in power plants.
• Promote public transport and low‑emission vehicles.

Other pollutant‑specific measures

• CO – install catalytic converters; maintain engines; promote electric vehicles.
• Particulate Matter – fit diesel particulate filters (DPF); enforce dust‑control on construction sites; adopt clean‑fuel technologies.

Basic Greenhouse‑Gas Mechanism

Solar short‑wave radiation passes through the atmosphere and warms the Earth’s surface. The warm surface emits infrared (IR) radiation upward. Greenhouse gases (CO₂, CH₄, N₂O, water vapour) absorb part of this IR radiation and re‑emit it in all directions, including back toward the surface. This “trapping” of heat raises the temperature of the lower atmosphere – the greenhouse effect.

Why Photosynthesis Matters for Air Quality & Climate? (syllabus answer)

1. Removes CO₂, a major greenhouse gas, from the atmosphere.
2. Produces O₂, essential for aerobic life.
3. Creates glucose, the primary energy source for the food chain, supporting ecosystems that stabilise soils and water cycles.
4. Forests, crops and algae act as large‑scale carbon sinks, helping to mitigate climate change.

Comparison of Equation Forms