Air and Atmosphere

1. Composition of Air
The volume composition of gases present in dry air is approximately 78% nitrogen and 21% oxygen. The remainder are noble gases (with argon as the main constituent) and carbon dioxide.

Nitrogen and oxygen can be separated by fractional distillation of liquid air.
Oxygen is often used in the manufacture of steel, and in welding.

2. Common atmospheric pollutants.
Common atmospheric pollutants include carbon monoxide (CO), methane, nitrogen oxides, ozone, sulfur dioxide, and unburnt hydrocarbons.

2.1 Carbon monoxide
Carbon monoxide is produced from incomplete combustion of carbon-containing substances.
Carbon monoxide is odourless and colourless.
It is highly toxic, as it prevents haemoglobin in blood from absorbing.

2.2. Nitrogen oxides 
Nitrogen oxides are formed from lightning activity and internal combustion engines.
When dissolved in rainwater, they form acid, which makes rain water acidic (acid rain).

2.3. Sulfur dioxide
Sulfur dioxide is produced from volcanoes and combustion of fossil fuels.
When dissolved in rainwater, sulfur dioxide form acid, which makes rain water acidic (acid rain).

3. Catalytic converters

Catalytic converters are installed in car engines to covert the harmful gases to less harmful ones. These converters consist of catalysts such as platinum and rhodium.
The following are some reactions that take place in the catalytic converter:
Oxides of nitrogen are converted to nitrogen.
Carbon monoxide is converted to carbon dioxide.
Unburnt hydrocarbons are converted to carbon dioxide and steam.
Note that the catalytic converters have no effect on sulfur dioxide.

4. Flue gas desulfurisation
Sulfur dioxide is a gas responsible for the formation of acid rain. Flue gas desulfurisation is a process for removing sulfur dioxide from flue gas. Calcium carbonate reacts with acidic sulfur dioxide to form calcium sulfite (a solid).
calcium carbonate + sulfur dioxide ---> calcium sulfite + carbon dioxide
CaCO3 + SO2 ---> CaSO3 + CO2

5. Chlorofluorocarbons (CFCs) and the ozone layer
The ozone layer prevents excessive ultra violet (UV) light from entering the atmosphere. Excessive UV radiation may result in an increased chance of humans getting skin cancer. CFCs are found to be responsible for depleting the ozone layer.

6. Combustion, respiration and photosynthesis
During combustion, and respiration, oxygen is absorbed while carbon dioxide is released into the atmosphere. During photosynthesis, carbon dioxide is absorbed by plants, and oxygen is liberated.
These processes keep the earth's carbon dioxide level in balance.

7. Greenhouse Gases and Global Warming

Methane and carbon dioxide are greenhouse gases. This means that they trap heat during the night, and keep earth warm. However, when there is excess greenhouse gases, the climate temperature will rise. This is what we call global warming. Global warming could cause the ice caps at the north and south poles to melt, increasing the sea level, and ultimately flooding low lying areas. Some animals may not be suited for the warmer temperatures and may become endangered or extinct.

- Quizzes and Tests on Air and Atmosphere

- Causes and Effects of Global Warming

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