Environmental Chemistry Part VI: Advanced Atmospheric Chemistry
General Overview
- This section explores the detailed mechanisms of free-radical reactions in the atmosphere.
- Focus areas include:
- Tropospheric and stratospheric chemistry.
- Photochemical smog and its autocatalytic nature.
- Free-radical oxidation of hydrocarbons and sulfur compounds.
- Ozone depletion and the role of "loose" oxygen atoms.
Chapter 17: The Detailed Free-Radical Chemistry of the Atmosphere
Key Topics
- Introduction
- Reviews basic concepts: free radicals, photochemical reactions, and atmospheric layers.
- Importance of hydroxyl radicals (OH) as initiators of oxidation reactions.
- Tropospheric Chemistry
- Free-Radical Reactions in the Troposphere
- Most atmospheric gases are oxidized by reactions initiated by OH radicals.
- Decision trees guide the fate of gases (e.g., methane, CO).
- Oxidation of Methane
- Sequence from methane to CO₂ through intermediates (e.g., CH₃O•, HCHO).
- Photochemical Smog
- Synergistic oxidation of hydrocarbons and NOx to produce ozone and aldehydes.
- Late-stage reactions yield oxidants (H₂O₂, PAN, HNO₃).
- Stratospheric Chemistry
- Processes Involving Loose Oxygen Atoms
- Role of species like O₃, HO₂•, ClO•, and their interactions with NOx.
- Mechanisms for ozone destruction through catalytic cycles.
- Oxidation of SO₂
- Gas-phase reactions convert SO₂ to H₂SO₄ via intermediates (HSO₃•, SO₃).
- Importance of aqueous-phase reactions with H₂O₂ and O₃ in polluted air.
Teaching Suggestions
- Visual Aids
- Decision trees for gas fates (Figure 17-1).
- Reaction sequences for methane oxidation and smog formation.
- Mechanisms for ozone depletion (Table 17-1).
- Interactive Activities
- Draw Lewis structures for free radicals.
- Solve problems predicting reaction sequences (e.g., methane to CO₂, ethylene to formaldehyde).
- Real-World Applications
- Discuss policies to mitigate photochemical smog (e.g., reducing VOC emissions).
- Analyze the impact of catalytic converters on NOx reduction.