Acid deposition refers to acidic particles and gases that deposit or fall to the Earth.
e.g. WET deposition: acidic gases like oxides of sulphur and nitrogen and acidic particles brought down by precipitation by rain, fog and snow. DRY deposition: absense of precipitation.
Pure rain water has a pH of ≈5.6, because carbon dioxide dissolves in rain to form carbonic acid. As a result, environmental pollution called acid rain is any rain with pH less than 5.6, and occurs commonly in industrailised areas (pH≈4-5 [4 to 40 times greater than pure rain water]). Extreme case of acid rain resulted in pH of 1.7 (LA, Dec 1982), and also a pH of 4.0 can kill fish life to form dead lakes (North America, China, Russia).
Acid deposition is associated with parts of a country with heavy industries and down-wind from industrial sites. Oxides of sulphuur and nitrogen are mostly responsible for this acidity and precipated become contaminated with acids when these oxides are present as pollutants.
Formation from sulphur oxides:
- sulphur dioxide + water --> sulphurous acid (stronger than carbonic acid)
-sulphur dioxide+ oxgyen--> sulphur trioxide (formed in the presence of oxygen, ozone, hydroxyl free radical and sunlight)
sulphur trioxide + water --> sulphuric acid
Formation from nitrogen oxides:
-nitrogen dioxide + water --> nitric acid + nitrous acid (absence of oxygen)
-nitrogen dioxide + water + oxygen --> nitric acid (consists of more complicated steps, summarised in this equation)
- other pollutants like the hydroxyl free radical (formed during photochemical smog) can react with nitrogen dioxide (also a free radical with a lone electron) to form nitric acid [accelerates conversion of nitrogen dioxide to nitric acid].
E.2.2 Discuss the environmental effects of acid deposition and possible methods to counteract them.
Acid deposition affects humans, aquatic life, materials, soil, vegetation and visibility.
Humans:
· Irritates whole respiratory tract and the eyes.
· Sulphate particles penetrate the lungs where they become embedded, adverse effects on asthmatics, the elderly and the young. (Sulphate aerosols are powerful irritants)
· Increased concentrations of aluminum ions in water due to acidic conditions may lead to Alzheimer’s disease.
· Irritates whole respiratory tract and the eyes.
· Sulphate particles penetrate the lungs where they become embedded, adverse effects on asthmatics, the elderly and the young. (Sulphate aerosols are powerful irritants)
· Increased concentrations of aluminum ions in water due to acidic conditions may lead to Alzheimer’s disease.
Aquatic life:
· Eutrophication from nitrates in acid deposition.
· Aluminum ions from leaching of soil by acid rain affect the function of the gills.
· Acidification of water bodies may result in the death of some species of fish.
· Eutrophication from nitrates in acid deposition.
· Aluminum ions from leaching of soil by acid rain affect the function of the gills.
· Acidification of water bodies may result in the death of some species of fish.
Materials:
· Corrosion of basic materials (e.g. marble, limestone, dolomite).
· Insoluble carbonates are converted to more soluble sulphates that then dissolve- destroys structural and artists’ stone (stone leprosy).
· Corrosion of iron and steel promoted by acid rain, worsened by high humidity, high temperatures, presence of particulates.
· Leaching of toxic heavy metals (e.g. Lead, Cadmium, Mercury) into the water system.
· Bleaching and weakening of fabrics and leather.
· Dicolouration and embrittlement of paper.
· Deterioration of electrical appliances.
· Corrosion of basic materials (e.g. marble, limestone, dolomite).
· Insoluble carbonates are converted to more soluble sulphates that then dissolve- destroys structural and artists’ stone (stone leprosy).
· Corrosion of iron and steel promoted by acid rain, worsened by high humidity, high temperatures, presence of particulates.
· Leaching of toxic heavy metals (e.g. Lead, Cadmium, Mercury) into the water system.
· Bleaching and weakening of fabrics and leather.
· Dicolouration and embrittlement of paper.
· Deterioration of electrical appliances.
Soil and vegetation:
· Acute injury from short term exposure to high acid concentrations consists of dead areas of leaves which dry out and usually become bleached.
· Chronic injury from long term exposure to low acid concentrations consists of bleached spots, yellowing of leaves, suppression of plant growth and reduction in yield (acid rain disrupts chlorophyll synthesis).
· Leaching and removal of important nutrients such as magnesium ions from the soil.
· Acute injury from short term exposure to high acid concentrations consists of dead areas of leaves which dry out and usually become bleached.
· Chronic injury from long term exposure to low acid concentrations consists of bleached spots, yellowing of leaves, suppression of plant growth and reduction in yield (acid rain disrupts chlorophyll synthesis).
· Leaching and removal of important nutrients such as magnesium ions from the soil.
Visibility:
· Mist can causes great loss of visibility and affect air flights.
· Mist can causes great loss of visibility and affect air flights.
METHODS OF COUNTERACTING ACID DEPOSITION:
-pre-combustion methods or post-combustion methods can be used to prevent the formation of acidic particles/gases.
-Promotion of alternative energy sources and conserving energy would decrease combustion of fossil fuels.
-Adding calcium carbonate or calcium hydroxide to soil and lakes neutralizes acidity.
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