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Wednesday, 15 July 2015
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 monoxide is odourless and colourless.
It is highly toxic, as it prevents haemoglobin in blood from
2.2. Nitrogen oxides
Nitrogen oxides are formed from lightning activity and internal
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
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
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
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).
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. Questions - Quizzes and Tests on Air and Atmosphere Videos - Causes and Effects of Global Warming