| Composition of Earth's atmosphere | |||
|---|---|---|---|
| Gases having fairly uniform concentrations |
Percent by volume | Gases having variable concentrations | Percent by volume |
| Nitrogen, N2 | 78 | Water vapor, H20 | 0 to 4 |
| Oxygen, O2 | 21 | Carbon dioxide, CO2 | 0.034 |
| Argon, Ar | 0.9 | Ozone, O3 | 0.000004* |
| Neon, Ne | 0.0018 | Carbon monoxide, CO | 0.00002* |
| Helium, He | 0.0005 | Sulfur dioxide, SO2 | 0.000001* |
| Methane, CH4 | 0.0001 | Nitrogen dioxide, NO2 | 0.000001* |
| Hydrogen, H2 | 0.000005 | Particles(dust, pollen) | 0.00001* |
| * Average value in polluted air. | |||
Life on Earth would not be possible without air. We need oxygen from the air to breathe. Plants need carbon dioxide from the air to prepare food through photosynthesis. Humans get energy due to the combustion of food inside the body, which is supported by air.
Composition of air:
Air contains mostly nitrogen and oxygen, and small
amounts of argon, carbon dioxide and water vapor.
Other gases namely hydrogen, methane, nitrogen dioxide,
ozone, helium, neon, krypton, xenon, carbon monoxide and
sulfur dioxide are present in traces. The percentage
of all these components also varies, but only
slightly, from one location to another. The
average composition of air by volume is given in the table.
Function of air:
- Nitrogen: It dilutes the activity of oxygen and helps in the combustion of fuels and food at moderate rate. If nitrogen were not there, burning would be so fast and violent that any fire would be very difficult to control. Nitrogen reacts with oxygen during lightning, forming oxides of nitrogen. These react with water to form the acids of nitrogen, which come down to the Earth with rain. These nitrogenous substances are converted into compounds by symbiotic bacteria in leguminous plants. These compounds help in the growth and development of plants as nitrogen is the essential constituent of proteins.
- Oxygen: It is essential for the combustion of fuel required for release of energy. Oxygen burns food inside our body, releasing energy. Therefore, it is essential for our survival. It supports all plant and animal life.
- Carbon dioxide: It enables plants to manufacture food by photosynthesis. It maintains the temperature of atmosphere by not allowing the Earth to radiate heat rapidly at night time, as it reflects back heat radiations.
- Water vapor: The presence of water vapor in the atmosphere is responsible for weather phenomena. It controls evaporation from the bodies of plants and animals. It provides moisture to plants, which is essential for their growth.
- Dust particles: Acts as nucleus for precipitation of water vapor, and this is how clouds are formed.
Air pollution
The air pollution is also known as the atmospheric pollution. Air pollution may be global risk factor
for cardiovascular diseases.
Smog
Smog is a form of air pollution. Smog can form in almost any climate where industries or cities
release large amounts of air pollution, such as smoke or gases.
Air Pollution:
An undesirable change in the physical,
chemical or biological characteristics of air is
called air pollution. Any material in the atmosphere
that is harmful to health is defined as an air pollutant.
The pollution of air may be caused by natural processes
or by human activities.
- Aerosols and particulates: Airborne solid particles such as ash, soot, metal oxides and even sea salts play a major role in air pollution. Particles up to 0.01 millimeter in diameter (too small to be seen with the naked eye) attract water droplets and thereby form aerosols that may be visible as fog or smoke. Larger solid particles suspended in air are called particulates. Dust, fumes, mist and fly ash are the examples of particulates in air.
- Smog: Smog has grown to be a major problem, especially over urban areas where industrial and human activities abound. Smog is the combination of smoke particles with the tiny droplets of fog containing poisonous gases discharged by the burning of fossil fuels in homes, industries and automobiles. Smog is a deadly air pollutant. Weather plays an important role in smog formation. Smog usually occurs in winter season.
Industrial air pollution
Its emissions include particles, hydrocarbons, carbon monoxide, ammonia and fluorides, as well as
sulphur dioxide and nitrogen oxides which are components of acid rain.
- Industrial smog: There are two
general types of smog namely industrial smog and
photochemical smog. Industrial smog, produced
largely from the combustion of coal and oil, is
high in particulates. Its main chemical ingredient
is sulfur dioxide, which accumulates in
aerosols and is transformed to sulfuric acid.
Airborne sulfuric acid is also a leading cause of acid rain. Prime source of the photochemical smog is internal-combustion engine. Photochemical smog is produced by the action of sunlight on nitrogen oxides, hydrocarbons and other pollutants created from fossil fuel combustion. Photochemical smog consists of pollutants that participate either directly or indirectly in chemical reactions induced by sunlight. These pollutants are predominately nitrogen oxides, ozone, and hydrocarbons. - Ozone is a molecule of three oxygen atoms bound together (O3). Ozone is a pungent pollutant. It causes eye irritation and at high levels can be fatal. Plant life suffers when exposed to even relatively low concentrations of ozone. If a freed atom collides with an oxygen molecule, it becomes ozone. Stratospheric ozone has been called “good” ozone because it protects the Earth's surface from dangerous ultraviolet light.
Greenhouse effect
Solar radiation is absorbed by Earth and the objects on it. Earth then emits infrared radiation.
Carbon dioxide, water vapor, and other greenhouse gases in the atmosphere absorb and re-emit heat that would otherwise be
radiated from the Earth into space.
Effects of air pollution:
- Many of the deaths are due to acute respiratory infections in children; others are due to cardiovascular diseases, lung cancer and chronic respiratory diseases in adults. If emissions are high and ventilation is poor, household use of coal and biomass can severely affect the indoor air quality.
- Global Warming: The term “global warming” refers to the increase in the average temperature of global surface air and oceans since about 1950, and to continuing increases in those temperatures. As Earth warms up, the oceans warm up too very slowly but significantly. Water expands as it warms so, as the oceans are heated, the water they contain takes up more volume, and this makes the level of the seas rise. The seas also rise when glaciers and ice sheets melt, feeding more water into the oceans. Sea level rise is one of the major impacts of global warming. To reduce the impact of climate change, everybody should adopt preventative measures to minimize global warming.
Trees reduce air pollution
Trees and other plants make their own food from carbon dioxide (CO2) in the atmosphere, water,
sunlight and a small amount of soil elements. In this process, they release oxygen (O2) for us to breathe. Managing
and protecting forests and planting new trees reduce CO2 levels by storing carbon in their roots and trunk and
releasing oxygen into the atmosphere.
Prevention of air pollution:
Some of the steps you can take as an individual or
a group of individuals to improve upon the air quality
around you are as follows:
- Do not use bags made from plastics. Use only cloth and jute bags. Don't burn dried leaves, branches of trees, paper and garbage in the open. Instead find ways and means for their safe disposal. For example, recycle the used paper.
- Save electricity. In the long run, it will amount to burning less fossil fuels.
- Reduce the use of aerosols (they are particles of solid or liquid matter that can remain suspended in air from a few minutes to many months depending on the particle size and their weight) such as perfumes, deodorant sprays, cosmetics and other similar sprays in your homes.
- Grow more trees. They are nature's lungs.