Global Warming & Acid Rain (WJEC GCSE Chemistry: Combined Science)

• There are no simple solutions to the environmental problems caused by burning fossil fuels
• The effects of global warming and acid rain are far-reaching
  • Therefore, strategies are needed to reduce the carbon dioxide and sulfur dioxide emissions responsible for these global issues

Addressing global warming

• Carbon dioxide emissions need to be reduced to avoid or slow global warming 
• Some measures that can be taken include being more ‘responsible consumers’ of energy by:
  • Using hydrogen and renewable energy supplies such as solar or wind energy instead of burning fossil fuels
  • Using more fuel-efficient vehicles, e.g. electric and hybrid cars
  • Reducing the number of vehicles on the road, e.g. using public transport, car-sharing
  • Recycling or reusing products made from crude oil and its derivatives
  • Reducing household energy consumption, e.g. turning lights out, using more efficient appliances
• Reducing deforestation and / or re-forestation, i.e. planting more trees, can help reduce the amount of atmospheric carbon dioxide
• Governments and economies in developed nations are slowly switching to greener and sustainable sources of energy and often offer financial incentives to companies to convince them to “go green"

Addressing acid rain

• Sulfur dioxide emissions need to be reduced to avoid or reduce the amount of acid rain 
• The same ‘responsible consumers’ of energy ideas for addressing global warming apply to acid rain
• Sulfur dioxide emissions can be reduced by the use of low sulfur fuels
• Weak alkalis can be used to neutralise soil and rivers / lakes affected by acid rain
  • Farmers will add 'lime' to reduce the acidity of their soil

Higher tier

Carbon capture and storage (CCS)

• This is another method to reduce carbon dioxide emissions but it is only performed on a large scale
  • For instance, in coal / natural gas fired power stations and steel / cement factories
• The three steps in the CCS process are:
  1. Capture
     • Carbon dioxide is separated from the other waste gases produced in industrial processes
  2. Transport
     • The carbon dioxide is compressed and transported to a storage site
     • Transport methods include pipelines, road transport and shipping
  3. Storage
     • The carbon dioxide is injected into rock formations deep underground for permanent storage
     • These are typically old oil / gas reservoirs and old coal mines 

• Any method to reduce carbon dioxide emissions that involves using less fossil fuels will also reduce sulfur dioxide emissions

Reducing sulfur dioxide emissions

• The main way to reduce sulfur dioxide emissions is to treat the waste gases from coal fired power stations 
• The waste gases are passed into a scrubbing chamber which sprays a wet slurry of calcium oxide and calcium carbonate into the gases
  • This process is also known as sulfur scrubbing or flue gas desulfurisation
• The calcium compounds react with the sulfur dioxide to produce calcium sulfate

Sulfur dioxide scrubber

The scrubber sprays a lime slurry over the waste gases to remove 90 - 95% of the sulfur dioxide