Lecture 4 & Lecture 5 Book notes

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University of Toronto Scarborough
Environmental Science
George Archontitsis

LECTURE 4 CHAPTER 6 ACIDIC DEPOSITION -Subject of the chapter: Acidic substances and their precursors. Section I- Acid Pollutions -This section identifies the major pollutants responsible for acid deposition, and describes how they are formed. -Sulfur dioxide (SO2) and nitrogen oxides (NOx) are the major precursors of acid deposition. -With moisture these gases convert to sulphuric and nitric acids, deposited in rain, snow, and fog. - With dry conditions, sulfur dioxide= sulphate & nitrogen oxides= nitrate. -Half of acid deposition is dry, which is more likely to settle near emission sources. - Other chemicals can contribute to acid deposition, CO2 in moist temp= carbonic acid. Background -Acid deposition, first described in 1852. -First half of the twentieth century damage to tress and vegetation was seen near smelters (facilities that melts or fuses ores that contain metals in order to separate out the metals that ores contain). -Smelters release large quantities of sulfur dioxide from sulfur-rich metal ores. -To protect local communities, the 1970 US Clean Air Act required power plants and smelters to build emission stacks 1000 ft. (305 m) above ground level. -Pollutants released at this height would become so diluted that they would cause no harm anywhere. -High stacks were built, but another problem started: stack emissions of sulfur dioxide and nitrogen oxides are carried away by the wind for hundreds of miles. -Meanwhile, gases where converted to acid aerosols. - They rain out or settle on land, water, and on man-made materials. -Acid deposition, also stored in winter snow until spring snow melts and falls into water bodies, can also fall directly in water bodies. - Water can also become acidic enough to harm or kill fish and other aquatic organisms. - pH at 7 is neutral ---- pH decline can cause death from snails, to fish eggs, to fish species, to eventually flies and frogs - The US government spent half billion on National Acid Precipitation Assessment Program (NAPAP) - Carried by teams of scientists this study aimed to understand acid deposition and its effects. -These factors complicated the study: -Rain does not have a normal pH. Rain in the eastern US is naturally acidic -The pH of lakes and streams varies. - Difficult to determine whether acid rain was affecting forests, they can be affected by other stresses -1990, NAPAP reported that acid deposition did have adverse effects. Section II- Adverse Effects www.notesolution.comWater and Aqua Life -Fish, snails and crustaceans, had been affected in 15% of New England lakes. -Adirondack lakes in New York suffered most; more than 40% of lakes were chronically acid and had few fish. -2003, acid deposition continues to harm water quality, less habitable for fish and other organisms. - 1990 studies showed no fish at all lived in 346 of the most acidic lakes. Forests and Their Soils -Forests are damaged by acid deposition, ground-level ozone and heavy-metal pollution. -1980: NAPAP researchers saw red spruce trees growing at high elevations in NE US were in direct contact with acidic clouds; they showed reduced tolerance to winter cold. -Acid deposition could leave trees vulnerable to disease. -May die after many years - Sulfur and nitrogen containing acids are inorganic, they are persistent, and they continue to accumulate in soils and waters. How Acids Causes Damage -Hubbard Brook Experimental Forest in New Hemisphere described to have serious damage by acid deposition. - Data showed that level of organically bound calcium (a nutrient in forest soil) was only half of 1960 lvl. -By 1987 the forest stopped growing - Acid deposition can deplete calcium & magnesium: - Acid solubilises nutrients so they can wash away with rain and melting snow runoff. - More acid deposition promotes more calcium loss. - Calcium & magnesium are alkaline metals (base cations) that neutralize acid. Loss of= loss of acidic soil. -Soil aluminum, solubilised, can interfere with trees uptake of calcium and magnesium. When it runs into water bodies it can poison aquatic life. -Acid deposition continues over time, soils basic enough to have previously buffered the acid begin to acidify. Other Effects of Acid Deposition -Acid deposition can increase erosion rate of stone and metal structures. -Acid aerosols produce hazes that reduce visibility. (Health effects) Section III- Sources of Acid Precursors -Petroleum-fired power plants also emit SO2 and NOx. -Motor vehicles are major NOx source. -Acid pollution moves from Canada into the US. -Acid pollution moves from Eastern Europe to Scandinavia, also from China to Korea & Japan. www.notesolution.com
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