4d) Human influences on the environment

Pollution of the air by sulfur dioxide and carbon monoxide:
Sulfur Dioxide-

1. Burning fossil fuels releases harmful gases like CO₂ and SO₂ 
2. The sulfur dioxide comes from sulfur impurities in the fossil fuels 
3. When this gas mixes with rain clouds it forms dilute sulfuric acid 
4. Then acid rain falls 
5. Internal combustion engines in cars and power stations are the main causes of acid rain

Carbon Monoxide- 

1. When fossil fuels are burnt without enough air supply they produce the gas carbon monoxide 
2. CO is a poisonous gas and when combined with red blood cells it prevents them from carrying oxygen 
3. Carbon monoxide's mostly released in car emissions. Most modern cars are fitted with catalytic converters that turn the carbon monoxide into carbon dioxide, decreasing the amount of CO that's released into the atmosphere. 

Greenhouse gases:
Some gases in the Earth's atmosphere prevent heat radiating into space from the Earth. This is called the greenhouse effect and the gases that are involved are called the greenhouse gases.
They include:

• water vapour 
• carbon dioxide 
• nitrous oxide 
• methane 
• CFC 

Human Activity and Greenhouse gases:

Carbon Dioxide:

- released into the atmosphere all the time as part of our everyday lives, in; car exhausts, industrial processes and as we burn fossil fuels 

- cutting down large forest areas (deforestation) can also effect the levels of carbon dioxide in the atmosphere 

Methane:

- produced from natural sources 

- also from cattle 

Nitrous Oxide: 

- released naturally by bacteria in soils and the ocean 

- a lot more is released from soils after fertiliser is used 

- also released from vehicle engines and industry 

CFCs:

- man-made chemicals that were once used in aerosol sprays and fridges 

- very powerful greenhouse gases 

- most countries no longer produce them as it damages the ozone layer (part of the upper atmosphere where ozone is found in higher concentrations) which then prevents UV radiation from reaching the Earth 

- some still remains from old fridges and are released through leaks 

Greenhouse gas results in an enhanced greenhouse effect and this may lead to global warming, which is a gradual increase of the Earth's overall temperature and consequences, examples are change in crop growth patterns or flooding due to polar ice caps melting.   

For Paper Two- Biological consequences of pollution of water by sewage:

• increases the number of micro organisms which then leads to the depletion of oxygen 
• causes eutrophication which is when the environment becomes enriched by nutrients 

Eutrophication:

When fertilisers leach into the water, it can cause eutrophication.

If too much fertiliser is applied into fields (like nitrates and phosphates) and it rains afterwards, nitrates can be easily washed through the soil into nearby rivers and lakes. 

1. Fertilisers enter the water, adding extra nutrients 
2. The extra nutrients cause algae to grow quickly and block out the sunlight 
3. Then plants in the water can not photosynthesise due to the lack of light and start to die 
4. With more food available, micro-organisms that feed on dead plants increase in number and deplete (use up) all the oxygen in the water 
5. Organisms that need oxygen, like fish, then start to die due to the lack of oxygen 

Deforestation Effects:

1. Leaching 
• when trees are removed nutrients get leached away, but don't get replaced so it leaves infertile soil 
2. Soil Erosion 
• when trees are removed, soil can be washed away by the rain (eroded), which can leave infertile ground 
3. Disturbing the water cycle
• Rainwater can run straight into the rivers which can lead to flooding 
• Makes the local climate drier when trees are cut down 
4. Disturbing the balance of carbon dioxide and oxygen
• When trees are cut down and burnt the stored carbon is released at once as Carbon Dioxide, this contributes to global warming.
• Fewer trees mean that less photosynthesis occurs releasing less oxygen. This causes the oxygen level in the atmosphere to drop