Strategies to Manage Impacts of Acid Rain (Cambridge (CIE) IGCSE Environmental Management): Revision Note

Strategies to manage impacts of acid rain

Flue gas desulphurisation (FGD)

• FGD is important because SO₂ emissions are a health and environmental hazard

• FGD systems can remove up to 95% of SO₂ from flue gases

• FGD is the main way to reduce sulphur dioxide emissions from coal-fired power stations

  • Emissions are passed into a scrubbing chamber where

    • They are sprayed with a wet slurry of calcium oxide and calcium carbonate 

    • The calcium compounds react with sulphur dioxide to produce calcium sulphate

    • The cleaned gas is then emitted from the chimney

Flue gas desulphurisation

• Scrubbers remove building exhaust gases and particles

• Wet scrubbers

  • Wet scrubbers use limestone to neutralize sulphur dioxide before it leaves exhaust stacks

  • These pipes pass gases through a water-sprayed chamber

  • Particulates and dissolved gases are then filtered from the liquid

  • After cleaning (scrubbing), the exhaust is emitted

  • There is a sludge collection system that traps polluted water for later disposal

• Dry scrubbers

  • Exhaust gases are neutralised or converted by dry chemical scrubbers

  • The converted materials are recovered from the gas stream, with the cleaned gases being emitted

  • Calcium oxide is a common dry scrubber additive which reacts with SO₂ to form calcium sulphite

Catalytic converter

• Catalytic converters are devices fitted to petrol and diesel vehicles and sometimes on kerosene heaters and stoves to reduce harmful emissions

• They contain a series of transition precious metal catalysts, such as platinum and rhodium

• The metal catalysts are in a honeycomb within the converter to increase the surface area available for reaction

• The system is attached to the exhaust system and converts toxic gases like CO, NOₓ, and hydrocarbons into less toxic compounds like CO₂, O₂, N₂, and water

Transport policies

• Transport policies can help mitigate the effects of acid rain by using fewer fossil fuels

• In many countries, it is compulsory for vehicles to have catalytic converters

• By providing larger subsidies, governments can promote the use of public transport

• Walking, cycling, and carpooling reduce emissions

• Increasing the number of electric vehicles (EV) on the road can also help

Benefits & limitations of strategies to manage impacts of acid rain

Flue gas desulphurisation

• They help lower harmful gases released into the air

• They can reduce SO₂ emissions by up to 90%

• However, the flue gas exiting the absorber is highly corrosive because it's saturated with water and still contains SO₂ that can damage equipment

• Using corrosion-resistant materials or reheating the gasses above dew point minimises corrosion but adds to the costs

Catalytic converters

• Motor vehicles generate more air pollution than any other single human activity

  • Catalytic converters may improve air quality; however, they are expensive to replace and can increase fuel consumption, as extra fuel is needed to keep the converter hot enough to work

  • Also catalytic converters are a target for thieves who remove them for the precious metals

Transport policies

• Carpooling leads to a reduction in the number of cars in city centres and is also a more economical way to travel

  • Leeds city council operates a policy to encourage car sharing by the use of high-occupancy vehicle lanes, available for cars carrying two or more passengers, hence encouraging people to share cars to enable them to get to work quicker

  • However, carpooling offers limited flexibility and can cause additional wear and tear on vehicles, leading to increased maintenance costs

• Using public transport

  • The introduction of bus lanes and improved transport information services has made public transport more attractive and sped up journey times

  • However, in some countries, the cost, availability and reliability of public transport means people will continue to use their cars

• Cycling can often be the quickest way to make short journeys

  • But cycle tracks in towns and cities need improvement and expansion

• Walking

  • The introduction of pedestrianisation in city centres has increased the number of walkers

  • As with cycling, walking is also a healthy way to travel as it increases physical fitness with no emissions

• Promoting efficient motoring

  • Maintaining slower speeds, fuel is conserved, and less carbon dioxide is emitted

  • However, many people will and do ignore speed restrictions

• Electric vehicles (EVs)

  • An EV’s electric motor is highly efficient compared to an internal combustion engine

  • EVs produce no tailpipe emissions but still contribute to emissions when the raw materials are mined, refined and manufactured

  • EVs may also source energy from a grid that uses fossil fuels

  • EVs are fitted with lithium-ion batteries that use a lot of energy and raw materials

• Traffic management schemes

  • Traffic management schemes reduce the amount of traffic in city centres

    • Paris has experimented with a scheme that allows cars with an even number plate to enter the city on one day and those with odd number plates on the next