1. Acid rain

2. Hydrologic cycle Evaporation Transpiration Condensation Precipitation Processes that cycle water between air and earth surface

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 is basic.

4. Acid rain Rainwater has a pH of 5.7 if CO 2 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. H 2 SO 4 and HNO 3 are the major contributors to acid rain.

5. pH of acid rain H 2 SO 4 and HNO 3 are the major contributors to acid rain.

6. Sources for H 2 SO 4 and HNO 3 in the air Both substances are formed in the air –Precursor to H 2 SO 4 : SO 2 –Precursor to HNO 3 : NO 2 Concentrations of the precursors SO 2 and NO 2 are greatly increased by man-made activities, especially fossil fuel combustion.

7. Formation of sulfuric acid from SO 2 Gas-phase SO 2 +. OH + M  HSO 3. + M HSO 3. + O 2  HO 2. + SO 3 (fast) SO 3 + H 2 O + M  H 2 SO 4 + M (fast) Aqueous phase (cloud and rain) Dissolved SO 2 is oxidized to sulfate by O 3 and/or H 2 O 2 –O 3 (dominant pathway when pH>5) –H 2 O 2 (dominant pathway when pH<5) –Organic peroxides –O 2 catalyzed by iron and manganese

8. 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, and fungi and mosses that thrive under acidic conditions; –Stunts growth of crops such as tomatoes, soybeans, carrots, and cotton

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

10. Effects of acid rain (Continued) Damage of materials and structures –building materials, statues, metals, cars. –CaCO 3 + H 2 SO 4 --> CaSO 4 + CO 2 + H 2 O –CaSO 4 occupies more volume than CaCO 3 and is more soluble than CaCO 3. Harm to human beings –irritation to eyes, inflammation of lung tissue, respiratory illness, etc.