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.