6.4 - Acid Deposition

Acid Deposition

Can impact living systems and the built environment. The general term for acid coming down from the air

The pollution management of ______ often involves cross-border issues.

Acids

Chemicals that are able to give a hydrogen ion away.

Normal unpolluted rain is slightly acidic and has a pH of about 5.6, cause by the presence of carbon dioxide in the atmosphere

Wet deposition

When acid comes down in the form of rain or snow. Occurs at slightly longer distances from the sources of the primary pollutants.

It consists of sulphurous acid, sulphuric acid, and nitric acid

Dry deposition

When acid comes down as ash or dry particles. Usually occurs quite close to the source of the acidic substances.

It consists of sulphur dioxide, sulphur trioxide, and the nitrogen oxides

Primary Pollutants

Those that are directly emitted from the chimney of a factory or the exhaust pipe of a car, such as:

• Sulfur Dioxide - SO₂

• Nitrogen Oxide - NO_x

Secondary Pollutants

Primary pollutants react with other substances in the atmosphere and create different pollutants such as

• Sulfuric acid - H₂SO₄

• Nitric acid - HNO₃

Sulphur Dioxide

Naturally formed by volcanic eruptions and nitrogen oxides by lightning. _____ is formed when sulphur-containing fuels are combusted since sulphur is common in coal and oil

Direct effect

For example, acid on aquatic organisms and coniferous forests, such as:

• chlorophyll loss & yellowing of tree leaves and buds leads to diminished growth

• thinning cuticle (the waxy coating on needles)

• symbiotic root microbes killed (ex. Rhizobium) limits nutrient uptake

Indirect toxic effects on fish

• When the pH of rain drops below 5, aluminum ions which are normally insoluble, become soluble

• This leads to the Al ions dissolving and leaching out of the soil and into streams

• Aluminum disrupts salt, water, and oxygen-regulating systems in fish

  • It can also adhere to fish gills, causing suffocation

• Lichens are sensitive to SO₂ gases and may therefore be used as an indicator species

Effect of acid deposition on coniferous forests

1. Leaves and buds show yellowing (loss of chlorophyll) and damage in the form of thinning wax cuticles

2. These and other changes reduce growth, allowing nutrients to be leached out and washed away and pathogens and insects to gain entry

3. Symbiotic root microbes are killed and this greatly reduces the availability of nutrients, further reducing tree growth

4. It reduces the ability of soil particles to hold on to nutrients (Calcium, Magnesium, Potassium) ions which are then leached out

5. It releases toxic aluminum ions from soil particles which then damage root hairs

= trees are weakened and may die

Indirect nutrient effect

When soil can’t retain Calcium, Magnesium, Potassium ions, in an acidic environment. This leads to these nutrients leaching out of the soils and thus are unavailable to the trees.

• Dissolved Aluminum ions damage root hairs (the smallest roots are the most effective at absorbing nutrients), so the trees are unable to absorb many nutrients

• N-fixing bacteria don’t function as well, so less Nitrogen is added to the soil matrix

Pollution management strategies that include altering human activity

• Switch to renewable energy sources to reduce fossil fuel use

• Increase energy efficiency of household appliances

• Use more public transportation to reduce the number of cars on the road

• Use low-sulfur fuels

Pollution management strategies that include regulating and monitoring the release

• Install scrubbers on smokestacks of coal-fired power plants to remove SO₂

• Catalytic converts installed on automobiles to remove SO₂ and NO_x (required by law in US, Canada, and Europe)

Pollution management strategies that include Cleanup and restoration

• Add lime to acidified lakes and streams

• Add lime to forestry plantations

• UN Convention on Long-Range Transboundary Air Pollutants (LTRAP) - 1979; later ammended and modified by US, Canada, and Europe

The effects of acid deposition on soil, water, and living organisms