Acid Deposition
Acid Rain
What is it?Why do we care?
Acid Rain: History
• Evidence of increased pH level in the atmosphere can be found in glacier ice.
• The Ice show a sudden decrease in pH from the start of the Industrial Revolution
What is Acid Rain
• Term first used in 1872 by a Scottish chemist, Angus Robert Smith
• The more accurate name is acid deposition– “Acid rain” includes both wet and dry acidic
deposits
• Acid deposition refers to all types of precipitation--rain, snow, sleet, hail, fog--that is acidic in nature
• Acid deposition is precipitation with a pH lower than 5.6
What is Acid Rain?
• Acid Rain is formed when particles of gases, such as Nitrogen oxides NOx and Sulphur dioxide SO2 mix with water droplets in clouds to form diluted acids.
Examples
• When CO2 reacts with water, carbonic acid is formed.
When SO2 reacts with water, sulfurous acid is formed.
When NO2 reacts with water, nitric acid is formed.
Acidity
• Acidity is measured on the pH scale
• Each drop is a tenfold increase in acidity• Normal rainfall is about 5.6• In some areas including Ontario, rain has a pH
of 4 or less
Sources of Acid Deposition
• Sulfur dioxide and nitrogen dioxide particles are emitted from utility plants, especially coal-fed electric plants
• Automobiles also emit acid rain causing pollution
•Atmospheric pollutants do not recognize international boundaries, and therefore pollutants put into the atmosphere in one area might affect a different region.
Sources of Acid Deposition
• SO²– Power plants– Iron smelters – Other heavy industry– Volcanoes
• NO2
– Engine Exhaust– Agricultural
lands
Worldwide:
Natural: 75-100 million tons per year (volcanoes)
Human sources: 75-100 million tons per year
But in Europe and N. America, human sources contribute 95% of total load
Sources of Acid Deposition
Effects of Acid Deposition
Effects of Acid Deposition
• Acid Deposition effects:
– BIOLOGICAL: Forestry, fisheries, wildlife, and farming
– ANTHROPOLOICAL: buildings and other structures, vehicles, and human health
Plants and Forests
1. Effects on Forests
• Damages leaves and needles
• reduce tree's ability to withstand cold
• inhibits plant germination
• depletes nutrients from soils.
• Acid rain affects animals in the water.
2. Effects on Lakes and Rivers
• increases acidity
• Cannot support variety of life– Plants grow best between pH 7.0 and 9.2– At pH 6, freshwater shrimp cannot survive. – At pH 5.5, bottom-dwelling bacterial
decomposers begin to die – Below a pH of about 4.5, all fish die. – Populations of water birds dwindle with loss of
fish
Effects on Lakes
• Some life benefits from the increased acidity. – i.e Lake-bottom plants and mosses, and
blackfly larvae.
• Some lakes with limestone rock are able to neutralize acid– Eastern Canada is underlain by granite, therefore
cannot neutralize acids.
• According to Environment Canada, 150 000 lakes are being damaged in eastern Canada,
Areas (In Black) With Low Acid-neutralizing Capacity
3. Effects on Farming
• In eastern Canada, particularly Ontario, 84% of productive farmlands affected by acid rain.
• Root systems unable to absorb nutrients
• crop yields fail millions of dollars are lost.
Effects on Building and Vehicles
• Causes corrosion of buildings, monuments, stained glass, railroad line, airplanes, cars, steel bridges and other man-made structures
• sulfur pollutants react with minerals in stone to form a powdery substance that is washed away by rain (especially sandstone or limestone, or marble)
• This powdery substance is called gypsum.
Sandstone portal Figure on Herten Castle in Ruhr district of Germany. Sculpted 1702; photographed in 1908.
Same sandstone portal figure photographed in 1969.
4. Effects on Human Health
• causes toxic metals to break loose from their natural chemical compounds.
• toxic metals can be absorbed by the drinking water, crops, or animals that human consume.
• Can cause nerve damage to children or severe brain damage or death. – Scientists believe that one metal, aluminum, is
suspected to relate to Alzheimer's disease.
Effects on Human Health
• respiratory problems
• sulfur dioxide and nitrogen oxide emission can cause dry coughs, asthma, headaches, eye, nose, and throat irritation
• Acid rain can aggravate a person's ability to breathe and may increase disease which could lead to death.