Summary of topic 5.8
Acid deposition occurs when sulfur and nitrogen oxides emitted from fossil fuel combustion react with water, oxygen, and other chemicals in the atmosphere to form acids. These acids can be washed out of the atmosphere as acid rain or deposited as dry particles. Acid deposition harms aquatic ecosystems by making lakes and streams acidic, damaging fish populations. It also damages forests by interfering with photosynthesis in trees and causing them to drop leaves prematurely. The areas most affected are those downwind of heavy industrial regions and have geology that cannot neutralize acids like granite. Management strategies to reduce acid deposition include using cleaner fuels, adding pollution controls to power plants, and international agreements to limit cross-border air pollution.
Summary of topic 5.8
- 1. Topic 5 Pollution Management 5.8 Acid Deposition http://www.youtube.com/watch?v=v09KnqiYi-c
- 2. Acid Rain • NOx andSOx may either fall to the ground as particles, aerosols or gases (dry deposition) or else forms acid rain (wet deposition) • The longer they remain suspended in the air, the more likely they will be oxidised to HNO3 and H2SO4 • Wet deposition may occur thousands of kilometres from the pollution source (especially now that chimney stacks may be hundreds of metres tall)
- 3. Effects of Acid Rain • Lakes – – – – – Reduced biodiversity Acidity may cause death of fish fry Decreased turbidity Growth of white moss on lake beds Increased concentrations of dissolved metals (including Cd2+, Cu2+, Al3+, Zn2+, Pb2+) – this makes them bioavailable to water plants and also allows them to enter drinking water • Forests – Damage to lipids and membranes leading to plant death – SOx interferes with photosynthesis especially in coniferous plants – Acidity causes conifers to shed needles too rapidly – Low soil pH causes damage to root hairs and and inhibits water and nutrient uptake
- 4. Distribution of Acid Deposition • • • • • • • It is a global rather than localised problem, since deposition may occur thousands of kilometres from source There are natural sources of acidity, including plants which acidify soils (heather and bog moss), volcanic eruptions and the dissolution of carbon dioxide in precipitation (carbonic acid) There also exist natural sources of buffering, including chalk and limestone deposits Conversely, granite deposits are naturally acidic and have low buffering capacity The areas most affected by anthropogenic acid deposition are Sweden, Norway, Denmark, Scotland, Germany, The Netherlands, Austria and The East Coast of the U.S. This appears to be largely due to prevailing winds and levels of rainfall They are also areas rich in lakes and rivers with
- 5. Management Strategies • Prevention – – – – – – – Burn less fossil fuels Reduce numbers of private vehicles Increased use of public transport and bikes Switch to low emission fuels (or electric cars?) Remove sulphur before combustion or SOx after (scrubbing) Burn coal with a neutralising agent (such as limestone) Use chemicals to buffer soil and allow decomposition of plants to offset the acidification process – International agreements are necessary since the polluter and the victim of the pollution may be different countries (e.g. The Gothenburg Protocol, 1999)
- 6. Questions 1. Describe how acid rain is caused 2. Describe the effects of acid deposition on living things 3. Describe and evaluate strategies to control acid rain