1. Environmental Chemistry Some Chemical Equations

2. Environmental chemistry • study of the effect of human activity on the chemical processes in the environment • concerns political and natural borders • global issues • applied chemistry

3. carbon monoxide: reduction (1) Lean burn engines: Decrease fuel /air ratio, from 1:14.7 (stoichiometric ratio/green band in diagram) to 1:18. Why? (or increase air /fuel ratio to 18:1)

4. Catalytic converter

5. Car Exhaust Reduction catalytic converter in car exhaust system: • reduction of nitrogen oxide • oxidation of CO and un-burnt hydrocarbons/VOCs • equations: CO (g) + O2(g) CO2(g) NO (g) + CO (g) CO2(g) + N2 (g) C8H18(g) + O2(g) CO2(g) + H2O(g)

6. carbon monoxide: reduction (2) CO (g) + O2(g) CO2(g) NO (g) + CO (g) CO2(g) + N2 (g) C8H18(g) + O2(g) CO2(g) + H2O(g)

7. sulphur oxides: sources • Natural: • volcanoes • sea spray • biological decay of organic matter that contains sulphur • reduction of sulphates • Man-made: • coal-burning power stations (equation starting from S in coal) • roasting of metal sulphides e.g. ZnS and Cu2S (equation)

8. sulphur oxides: health effects • acidic oxides • formation of sulphuricacid

9. sulphur oxides: methods of reduction • use of “low-sulphur content” fuels or removal of sulphur before burning coal/oil • removal of SO2from fumes before they are released: • limestone based fluidised bed(equations showing decomposition of calcium CaCO3reaction of CaO with SO2) • alkaline scrubbing (wet scrubber) (also called flue gas desulphurization, FGD): (equations showing reaction of CaO and Mg(OH)2)

10. sulphur oxides: methods of reduction • limestone based fluidised bed(equations showing decomposition of calcium CaCO3reaction of CaO with SO2 • Treatment of basic solutions with sulfur dioxide affords sulfite salts: • SO2 + NaOH → Na2SO3 + H2O • calcium oxide (lime) reacts with sulfur dioxide to form calcium sulfite: • CaO + SO2 → CaSO3

11. Sulphur oxides: reduction (1) Wet scrubber

12. sulphur oxides: methods of reduction • alkaline scrubbing (wet scrubber) (also called flue gas desulphurization, FGD): (equations showing reaction of CaO and Mg(OH)2)

13. Controls on CO2 • CO2 is controlled by a global scale feedback loop with a time scale of >10,000 years • Consider the following reactions: Generic Weathering Reaction Generic Precipitation Reactions Generic Mantle Reactions

14. Global O2 • oxidation is long-term sink of atmospheric O (e.g., oxygen stored as SO42-or CO32-salts) • C & S most important • model past O2 from these reactions

15. OxidationReduced species react with free O2

16. Oxidative Pyrite Weathering

17. Acidic Hydrolysis Reaction H+ replaces cations in mineral structure Main acid sources: • carbonic acid (H2CO3 from CO2 dissociation in natural waters) • organic acids (from CO2 respiration in soils) • sulfuric acid (volcanic, anthropogenic H2S) …typical mechanism of silicate dissolution.

18. Feldspar Hydrolysis Solid - Clay (“Secondary Mineral”) Dissolved Species Similar for: Anorthite (Ca2Al2Si2O8) K-Feldspar (KAlSi3O8) Most common weathering reactions on Earth…