6.4 Acid Deposition

• Acid deposition – is the general term for acid coming down from the air

• 3 types of deposition• Dry – dry deposition comes down as ash or dry particles

• Wet – wet deposition comes down as rain/snow

Acidity – pH scale

• pH scale goes from 0-14

• 7 is neutral – pure water

• Less than 7 is acidic

• More than 7 is alkaline (basic)

Main acid deposition pollutants and source

• Pollutants – these are divided into: Primary and secondary air pollutants

• Primary pollutants are those pollutants that are emitted directly, for example:

• Leaving a chimney of a factory

• The exhaust of a car

• *Primary pollutants can react to form secondary pollutants

Main acid deposition pollutants and source

• secondary pollutants are made after the pollution leaves the chimney

• The main primary pollutants leading to acid deposition are sulpherdioxide (SO2) and nitrogen oxides (Nox)

• They react with water to form strong acids sulphuric (H2 SO4) and nitric acid (HNO3)

Main acid deposition pollutants and source

• Sources:

• Naturally Sulphur dioxide is produced from volcanic eruptions and nitrogen oxides by lightning

Main acid deposition pollutants and source

• Sources:

• The most important human activity that leads to the emissions of these pollutants are the combustion of fossil fuels in cars, industry, and power stations (which use coal, oil, or gas) to produce steam to drive the turbines

• Sulphur Dioxide is formed when Sulphur-containing fuels are combusted- Sulphur is common in coal and oil

• Nitrogen oxides are formed by the reaction of oxygen and nitrogen from the air, which readily takes place at the high temp. during combustion of fossil fuels. Nitrogen is not part of the fuel

• Sulphur dioxide can react with oxygen from the atmosphere and form Sulphur trioxide (SO3) both Sulphur dioxide and trioxide can react with water to form sulphurous acid (H2 SO3) and sulphuric acid (H2SO4)

• Nitrogen oxides react with water to form nitric acid (HNO3)

Effects of Acid Deposition

• Increases acidity of aquatic environments• Lakes, streams, wetlands

• Damages forests

• Removes nutrients from soil

• Reduces crop yields

• Decay of building materials and paints

acid deposition on forests

leaves lose protective

coating, become damaged

trees cannot produce enough

food

trees vulnerable to cold weather, disease, insects

Direct effect of Acid Deposition – on forests

• Can affect forests directly

• Coniferous trees are most at risk

Nutrient Effect of Acid Deposition – on soil

• Ca, K and Mg ions are leached or washed out of top soil.

• They go into the lower, inaccessible subsoil

• not available to vegetation

• Acid deposition speeds up this process

Toxic effect of Acid Deposition – on fish• Aluminum Ions

• Acid precipitation decreases the pH of the soil making aluminum more soluble.

• This aluminum enters the water

• Interferes with ability of fish to take in oxygen, salt and nutrients

• Fish die.

Toxic effect of Acid Deposition – Lichen• Symbiotic pairing of an alga and a fungus

• Found growing on trees

• Very sensitive to gaseous pollutants like Sulphur dioxide

• Used as an indirect measurement of pollution

• They are indicator species as distance from a polluted source increases so does the amount of lichen

Toxic effect of Acid Deposition – Nutrient removal effect on soil fertility• Affects soil by reducing the ability of soil

particles to hold on to nutrients:

• Calcium

• Magnesium

• Potassium

• Inhibits nitrogen fixing bacteria and thus their ability to add nitrate ions to the soil.

Toxic effect of Acid Deposition – Buildings

• Limestone or marble buildings and statues react with acid and simply dissolve

1908 1969

Effects of Acid Deposition are REGIONAL

• Most acid pollution emitted in one region ends up being deposited in the same region. (unlike other pollution which can be global, like CO2)

• At risk ecosystems – downwind of major industrial regions (wind blows dry deposition towards those ecosystems)

• Example: pollution in UK, Germany and Poland travels from west to east and ends up in Norway and Sweden.

Pollution management strategies for A.D.

• Replace: • reduce demand for electricity

• Move from fossil fuels to renewable energy

• Switch from private cars to public transport – reduce vehicle emissions

• Regulate• Clean up at “end of pipe” locations (points of emission, such as factories)

• Install “scrubbers” which trap pollutants in the smoke stacks

• Restore• Add ground up limestone to lakes to raise the pH

• Did this in Sweden in 1980s b/c lakes were too acidic. (14000 still are)

• To what extent should national governments think about the welfare of the citizens of other nations when developing environmental policies?

•Write a paragraph. • Make a claim.• Then support your claim with evidence• Justify your evidence using reasoning.