Notes

Atmosphere and the environment

1. AIR:

Air is a mixture of gases. This is the composition.
Nitrogen: 78%
Oxygen: 21%
Noble gases: 0.97% (mainly argon)
Carbon dioxide: 0.03%

2. AIR POLLUTION:

Air pollution is caused by human activity, harmful gaseous chemicals are released into the atmosphere

i. Carbon Monoxide (CO)
Carbon monoxide is a colourless and odourless gas. Much of the carbon monoxide in the air comes from the incomplete combustion of petrol in car engines.
; Reacts with haemoglobin to form carboxyhaemoglobin which reduces the ability of haemoglobin to transport oxygen to the rest of the body. Causes headaches, fatigue, breathing difficulties and even death.
Solution: CO emissions can be minimised by ensuring the complete combustion of fuels. Motor vehicles fitted with catalytic converters oxidise CO to relatively harmless CO2

ii. Sulfur Dioxide (SO2)
Fossil fuels such as coal, crude oil and natural gas contain sulfur. When they are burnt in motor vehicles, power stations and factories, sulfur is converted to sulfur dioxide. Naturally comes from volcanic eruptions
; irritate the eyes and lungs and cause breathing difficulties, high levels lead to inflammation of the lungs (bronchitis), react with water in the atmosphere to form acid rain, which corrodes buildings and harms aquatic life and plants.
Solution: CaCO3 can be used to remove SO2 produced as flue gas from power stations and other industries.

iii. Oxides of Nitrogen (NO, NO2)
In a car engine or chemical factory, where temperatures are very high, nitrogen combines with oxygen in the air to form nitrogen monoxide or nitric oxide (NO)
N2(g) + O2(g) ---> 2NO(g)
Nitrogen monoxide reacts with oxygen to form a brown gas, nitrogen dioxide (NO2)
During thunderstorms, the heat energy released by lightning causes nitrogen and oxygen in the air to react to form oxides like nitrogen monoxide and nitrogen dioxide.
; irritate the eyes and lungs and cause breathing difficulties, high levels lead to inflammation of the lungs (bronchitis), react with water in the atmosphere to form acid rain, which corrodes buildings and harms aquatic life and plants.

iv. Unburnt hydrocarbons, methane and ozone
Unburnt hydrocarbons are released in car exhaust fumes and chemical plants,
Methane is a colourless and odourless gas, which is produced when plant and animal matter decay. Sheep and cows give off methane due to the digestion of food. Methane is also produced from the decay of rubbish in landfills.
Ozone is formed when nitrogen dioxide in the air reacts with unburnt hydrocarbons in the presence of sunlight.
; (respectively) Some hydrocarbons are toxic, e.g. benzene is a carcinogen. Resulting in the formation of ozone and photochemical smog. Traps heat to contribute to global warming. Causes eye irritation and respiratory problems.