Acid Deposition Flashcards
What is acid deposition?
Acid deposition is the general term for acid coming down from the air
Wet deposition = acid comes down in form of rain (or snow)
Dry deposition = when acid comes down as ash or dry particles
What is the pH of normal unpolluted rain?
- Normal unpolluted rain is slightly acidic + has a pH of 5.6, caused by presence of co2 in atmosphere
- Precipitation is called acidic when its pH is well below pH 5.6
What are the main primary pollutants leading to acid deposition?
- sulphur dioxide
- nitrogen oxides
They react with water to form strong acids (sulphuric and nitric acids)
How are sulphur dioxide + nitrogen oxides produced naturally?
Sulphur dioxide by volcanic eruptions
Nitrogen oxides by lightning
How does burning fossil fuels lead to formation of primary air pollutants?
- Sulphur dioxide formed when sulphur-containing fuels (e.g. coal, oil) are combusted
- Nitrogen oxides formed by reaction of oxygen + nitrogen from the air, that takes place at high temp. during fossil fuel combustion
What are the effects of acid deposition?
- weakening tree growth in coniferous forests
- decreasing pH of water bodies, affecting aquatic organisms
- toxic effects eg. increased solubility of metal ions like aluminium (toxic to fish+plant roots)
- nutrient effects eg. leaching of nutrients
3 effects of acid deposition on coniferous forests
- Leaves + buds lose chlorophyll
- This reduces growth +allows nutrients to be leached out and pathogens to gain entry
- Symbiotic root microbes killed, reducing availability of nutrients
Toxic effects of acid deposition // aluminium ions - effect on fish and other aquatic organisms
- Decreased pH of soil makes aluminium more soluble
- Aluminium ends up in streams + rivers
- aluminium disturbs fish’s ability to regulate amount of salt in body, so salt content is slowly lost + fish die
Toxic effects of acid deposition // buildings
Limestone buildings + statues (w great archaeological + historical value) react w acid and dissolve
Toxic effects of acid deposition // peat bogs
- peat bogs affected by acid rain produce up to 40% less methane than before
- because bacteria that use sulphates as a food source outcompete the ones that use methane
Toxic effects of acid deposition // human health
- dry deposition in form of small particles of sulphates + nitrates penetrate into our lungs
- premature deaths from lung disease, asthma, bronchitis
Why are the effects of acid deposition regional in contrast to climate change // ozone depletion that affect all the Earth?
- Before the pollutants can spread over long distances, they return to the surface as dry or wet precipitation
- The acids seldom travel further than a few thousand kilometres
Where does dry deposition usually occur?
- occurs quite close to source of acidic substances
- consists of sulphur dioxide, sulphur trioxide + nitrogen oxides
Where does wet deposition usually occur?
- occurs at slightly longer distances from the sources of primary pollutants
- consists of sulphurous acid, sulphuric acid + nitric acid
It is mainly the downwind areas of major industrial regions that are strongly affected. Give 2 examples of this
- Scandinavian forests + lakes affected by acid rain originating in UK, Poland + Germany brought over by prevailing southwestern winds
- Industrial pollution from USA is blow by prevailing winds towards Canadian forests
Why does the impact of acid rain depend on the geology of the area on which it falls?
- Acid rain does little harm to limestone and chalk soils as they are alkaline soils + neutralise the acids
- But acid rocks produce soils that are v sensitive to acid rain
Pollution management strategies for acid deposition // altering human activity producing pollution ACTION
- replace fossil fuel use w ethanol for cars + renewable energy sources
- reduce overall demand fr electricity - education campaigns to turn off lights etc
- use less private transport
Pollution management strategies for acid deposition // altering human activity producing pollution (EVALUATION)
- we live in a fossil fuel reliant economy
- demand for power is every increasing, esp. in India + China as they industrialise
Pollution management strategies for acid deposition // regulating + reducing pollutants at point of emission (ACTIONS)
- Clean-up technologies at end of pipe locations e.g. scrubbing in chimneys to remove sulphur dioxide
- Catalytic converters convert nitrous oxides back to nitrogen gas
Pollution management strategies for acid deposition // regulating + reducing pollutants at point of emission (EVALUATION)
- Clean-up technologies are expensive + costs passed onto consumer
- Catalysers are cost effective if well maintained, but expensive to buy
Pollution management strategies for acid deposition // clean up and restoration
- liming acidified lakes (effective but expensive)
- recolonise damaged areas
- liming forestry plantations // trees acidify soils as they remove nutrients
- international agreements (difficult to establish + monitor)
What happened in 1999 in Europe?
27 countries signed up to new protocol on Long Range Transboundary Air Pollution to reduce + prevent air pollution
Evaluation of international agreement success in Europe
- avg of 50% reductions achieved by 2000
- but LEDCs rapidly industrialising + emissions set to increase unless MEDCs can help them to leapfrog to clean technologies
- due to regional character of acid deposition, international agreements are more regional
- but Kyoto Agreement will also help reduce acid deposition
Reducing effects of acid deposition // Liming lakes to neutralise acidity
> From 1950s, loss of many fish + invertebrate species in Scandinavian lakes linked to high levels of lake acidity
By 1990, 400+ lakes virtually lifeless
In 1980s, Sweden added limestone to lakes + rivers w mixed results
pH of treated lakes quickly raised but short-lived because of acidic nature of inflow of water
lime affected nutrient balance
Reducing effects of acid deposition // pre combustion techniques
- reduce sulphur dioxide emissions by removing sulphur from fuel before combustion
- sulphur obtained can be used in construction (as gypsum) or as the element sulphur in the chemical industry
