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Water in the atmosphere- Acid rain

Water in the atmosphere- Acid rain. Ions in pure water. autoionization. H2O. H + + OH -. neutralization. pH value of pure water. In pure water, autoionization is the only source of ions, therefore:. A pH of 7 defines neutrality, pH<7 means acidic and pH>7 is basic. .

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Water in the atmosphere- Acid rain

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  1. Water in the atmosphere- Acid rain

  2. Ions in pure water autoionization H2O H+ + OH- neutralization

  3. pH value of pure water In pure water, autoionization is the only source of ions, therefore: A pH of 7 defines neutrality, pH<7 means acidic and pH>7 is basic.

  4. What is the pH of natural rain water? pH of natural rain water is determined by acidic and basic species that are naturally present in the atmosphere. Unit: M Equilibrium constant CO2 partial pressure in unit of atm CO2: 370 ppm

  5. What is the pH of natural rain water? (Continued) Rainwater is naturally acidic because its equilibrium with carbon dioxide.

  6. Acid rain • Rainwater has a pH of 5.7 if CO2 is the only species that affects its acidity. • When additional acidic species are present at appreciable levels as a result of man-made activities, pH of rain water becomes lower than 5.7. Acid rain. • H2SO4 and HNO3 are the major contributors to acid rain.

  7. pH of acid rain H2SO4 and HNO3 are the major contributors to acid rain.

  8. Sources for H2SO4 and HNO3 in the air • Both substances are formed in the air • Precursor to H2SO4: SO2 • Precursor to HNO3: NO2 • Concentrations of the precursors SO2 and NO2 are greatly increased by man-made activities, especially fossil fuel combustion.

  9. Role of NH3 in acid rain • Ammonia dissolved in rainwater scavenges H+: • NH3 (aq) + H+= NH4+ • Ammonia input lowers the acidity in rain. Ion Rural New York Southwest Minnesota (meq/l) (meq/l) H+(pH) 46 (4.34) 0.5 (6.31) SO42- 45 46 NO3- 25 24 HCO3- 0.1 10 NH4+ 8.3 38 The larger input of NH3 in MN is responsible for the lower rain acidity than in NY.

  10. Production of NH3 • Animal waste, • ammonification of humus followed by emission from soils • losses of NH3-based fertilizers from soils • industrial emissions.

  11. Acid Rain: Cross-boundary Pollution A large portion of SO2 and NO2 produced in one country is exported to others by prevailing surface winds. • Canada-U.S.A: More than half the acid deposition in heavily populated southern Canada originates from seven central and upper midwestern states-Ohio, Indiana, PA, IL, Missouri, WV, and TN, where coal and oil-burning power and industrial plants are concentrated. • Asian-Pacific

  12. Effects of acid rain • Acidification of surface water (lakes, rivers, etc), and subsequent damage to aquatic ecosystems. • kills aquatic plants, fish and microorganisms in lakes and streams by releasing ions of Al, Pb, Hg and Cd from soils and sediments. • Damage to forests and vegetation • Weakens or kills trees, especially conifers at high elevations; • Makes trees more susceptible to diseases, insects, drought, and fungi and mosses that thrive under acidic conditions; • Stunts growth of crops such as tomatoes, soybeans, spinach, carrots, broccoli and cotton

  13. Acid rain has scarred the pine forest at Clingman’s Dove in the Smoky Mountain

  14. Effects of acid rain (Continued) • Damage of materials and structures • building materials, statues, metals, cars. • CaCO3 + H2SO4--> CaSO4 + CO2 + H2O • CaSO4 occupies more volume than CaCO3 and is more soluble than CaCO3. • Harm to human beings • irritation to eyes, inflammation of lung tissue, respiratory illness, etc. • Degradation of regional visibility

  15. Study questions • Why is natural rainwater acidic, with a pH value of 5.7? • What are the major pollutants that can alter the natural rain water pH? • Statues made of lime stone have been observed to lose their original fine features. Explain the reason behind this phenomenon.

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