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Mrs. Sealy APES VII. Acid Deposition • 1. “dilution solution” to air-pollution: to reduce local air pollution and meet government standards without having to add expensive pollution control devices, most coal-burning plants, ore smelters, etc. use taller smokestacks to emit sulfur dioxide high into atmosphere • 2. increases pollution downwind VII. Acid Deposition • • • • 3. chemicals reach ground: a. Wet: acid rain, snow, fog, cloud vapor b. Dry:acidic particles c. mixture causes acid deposition (acid rain) VII. Acid Deposition • 4. pH: a numerical measure of the concentration of hydrogen ions in a solution (1 digit change equals 10X change in acidity) • a. levels less than 7 - acid (natural precipitation) • b. levels greater than 7 - Base • c. typical rain in east US is now about 10 times more acidic (pH 4.3) Wind Transformation to sulfuric acid (H2SO4) and nitric acid (HNO3) Windborne ammonia gas and particles of cultivated soil partially neutralize acids and form dry sulfate and nitrate salts Nitric oxide (NO) Acid fog Sulfur dioxide (SO2) and NO Dry acid deposition (sulfur dioxide gas and particles of sulfate and nitrate salts) Wet acid deposition (droplets of H2SO4 and HNO3 dissolved in rain and snow) Farm Ocean Lakes in deep soil high in limestone are buffered Lakes in shallow soil low in limestone become acidic Fig. 17.9, p. 428 5. What areas are most affected by acid deposition? • occurs on a local rather than global basis b/c acidic components only remain in the air for a few days • areas downwind from coal and oil burning power plants, industrial plants and urban areas • ecosystems containing acidic soils without natural buffering of bases • growing problem in China (40% of its land), former Soviet Union, India, Nigeria, Brazil, Venezuela, Columbia Potential problem areas because of sensitive soils Potential problem areas because of air pollution: emissions leading to acid deposition Current problem areas (including lakes and rivers) Fig. 17.11, p. 429 6. What are the effects of acid deposition? • medium-risk ecological problem, high-risk to human health • human respiratory diseases (bronchitis, asthma), damages statues, buildings, metals, plastics and paints • damages tree foliage, makes trees more susceptible to cold temps, disease, insects, drought, fungi • harmful to aquatic species Effects of Weather Emissions Acid deposition Dry weather SO2 H2O2 NOX O3 PANs Others Low precipitation Increased susceptibility to frost, pests, fungi, mosses, and disease Increased evapotranspiration Direct damage to leaves and needles Increased transpiration Water deficit Bark damage Acids Potassium Calcium Aluminum Magnesium Sulfate Nitrate Lake Kills certain essential soil microorganisms Release of toxic metal ions Acids and soil nutrients Damage to fine roots Reduced photosynthesis and growth Nutrient deficiency Soil acidification Leaching of soil nutrients Dead leaves or needles Damage to tree crown Tree death Disturbance of nutrient uptake Disturbance of water uptake Groundwater Fig. 17.14, p. 432 D. What can be done to reduce acid deposition? • prevention • 1) reducing energy use & thus air-pollution by improving energy efficiency • 2) switching from coal to cleaner-burning natural gas • 3) removing sulfur from coal before it is burned • 4) burning low-sulfur coal • 5) removing SO2 particles, particulates, and nitrogen oxides from smokestack gases • 6) removing nitrogen oxides from combustion engines D. What can be done to reduce acid deposition? • reducing coal use is economically & politically difficult • clean-up approaches are expensive and mask symptoms w/ out treating causes • acidified lakes can be neutralized by treating them or the surrounding soil with large amounts of limestone or lime. This is an expensive and temporary remedy