CONCERN ABOUT OUR ENVIRONMENT

Structure of the atmosphere

The atmosphere is a protective layer of gases that shelters all lives on the earth.

The atmosphere has five different layers that are determined by the changes in temperature that happens with increasing altitude.

1.Troposphere: Living at the surface of the earth, we are usually only aware of the events happening in the lowest layer, the troposphere. It contains most of our weather clouds, rain, snow. In this part of the atmosphere, the temperature gets colder as the distance from the earth's surface increases. The top of the troposphere is called the tropopause. This is lowest at the poles, where it is about 5 km above the earth's surface. It is the highest (about 16 km) near the equator.

2.Stratosphere: This extends upwards from the tropopause to about 50 km where jet aircraft fly. It contains much of the ozone in the atmosphere. The increase in temperature with height occurs because of the absorption of ultraviolet (UV) radiation from the sun by this ozone.

3. Mesosphere: The region above the stratosphere is called the mesosphere. Here the temperature again decreases with height, reaching a minimum of about -90°C at the "mesopause".

4.Thermosphere and ionosphere: The thermosphere lies above the mesopause and is a region in which temperature again increases with height. This temperature increase is caused by the absorption of energetic ultraviolet and X-ray radiation from the sun. Thermosphere also includes the region called the ionosphere. It is a region of the atmosphere that is filled with charged particles. The high temperature in the thermosphere

can cause molecules to ionize. The temperature in the ionosphere just keeps getting hotter as you go up.

5. Exosphere: The region above about 500 km is called the exosphere. It contains mainly oxygen and hydrogen atoms. This is the region where atoms and molecules escape

into space.

OZONE LAYER

Causes of ozone depletion: 

Chlorofluorocarbons (CFC) are commonly used as coolants in refrigerators and air-conditioners, in blowing plastic foams, and in spray cans. But during the last decade, these were found to be responsible for ozone depletion in the stratosphere. It has been established that one molecule of CFC can destroy one lakh O3 molecules in the stratosphere.

The extreme chemical stability and non-toxicity of CFCs enable them to persist for years

in the atmosphere. In the stratosphere, CFCs are subjected to photochemical dissociation

by intense UV radiation which results in the generation of Cl radicals. One Cl radical can

destroy one lakh O3 molecules in the following way-

Cl·+03→C10·+02

C1O·+ClO·+M→(ClO)2+M

（＇M'represents another molecule

（ClO)2+E→Cl·+C10O·

which remains unchanged)

C1OO·+M→Cl·+O,+M (E= energy)

Cl·+O3→C1O·+02

Net reaction:203+hv→302

Over the past few years, the atmospheric concentration of nitrous oxide has recorded

a consistent increase due to the large scale combustion of fossil fuels and enhanced use of

nitrogenous fertilizers. Nitrous oxide, as well as other oxides of nitrogen, are also emitted

by supersonic transport aircraft.

In the stratosphere, nitrous oxide is photochemically converted into more reactive nitric oxide.

（N2O+E→NO+N)

This nitric oxide formed then undergoes the following chain reactions

NO+O3→NO2+O2

O3+hv→O2+O

NO2+0→NO+O 2

Net reaction:203+hv→3 O 2

Harmful effects of ozone depletion:

① Human Health: UV radiations are sufficiently energetic to break apart important

biological molecules.

（a) Skin: Exposure to UV radiation causes the connective tissue of the skin to damage.

Thus skin becomes wrinkled and loses its elasticity. If the exposure continues, the

skin becomes coarsely furrowed and lumpy. Besides, it has been estimated that 1%

the decline in the ozone layer could lead to a 4-6% increase in the probability of skin cancer.

（b) Eyes: UV radiation can damage the lens of the eye. Cataract, even blindness can result.

② Leaves of the plant will be discolored as photosynthesis will be affected.

③ Marine organisms will be destroyed.

④  Agricultural productivity will be reduced.

Greenhouse effect and global warming

The glass roof of a greenhouse is permeable to radiations from the sun. Once inside

the greenhouse, the radiations strike a surface and are transformed into heat. The glass on the roof of the greenhouse impedes the heat from passing out. Since much heat is trapped, the inside of a greenhouse is warmer than the outside. Like glass, a few gases-mainly carbon dioxides, but also methane, nitrous oxide, ozone, water vapor, and chlorofluorocarbons allow the sun's radiation to pass through and strike the surface of the earth. But like the glass roof of a greenhouse, these gases create a canopy to prevent the resulting heat from escaping. The net result is the warming up of the earth's atmosphere.

The greenhouse effect is a phenomenon in which solar radiation of shorter wavelength (frequencies of visible light) largely passes through the atmosphere but the heat energy

of longer wavelength(lower frequencies of infrared ray) emitted by the surface is absorbed

by the gases like CO,, CHa, water vapor, etc., and reflected back to the earth in all

directions, causing warming of the atmosphere. It is to be noted, the wavelength of

visible light → 400-700 nm, IR ray→700-1000 nm The primary greenhouse gases in the earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Oxygen and Nitrogen are not greenhouse gases.

The main sources of greenhouse gases due to human activities are: 

① A number of factories all over the world burn immense quantities of coal, oil, and natural gases and produce a huge quantity of carbon dioxide. 

② Power stations based on fossil fuels are major sources of man-made carbon dioxide. 

③ A large fleet of automobiles, railways, aircraft, etc. use an immense quantity of diesel and petrol releasing a huge amount of carbon dioxide every year. 

④ Burning of firewoods and deforestation are the major sources for the production of carbon dioxide. 

⑤ Chlorofluorocarbons are released from coolants.

Consequences of the greenhouse effect:

Climatic Changes:

① Due to global warming, the oceans get warm up and sea levels would rise flooding low-lying regions. 

② In temperate regions, the winter will be shorter and warmer but the summer will be longer and hotter. 

③ There will be an enormous increase in rainfall but the problems of desertification, drought, and soil erosion will further worsen. 

④ The tropics may become wetter but the subtropics, which are already dry, are expected to be drier. 

Other Changes : 

① Melting of ice-caps will be found over polar regions.

②Due to the greenhouse effect and much warmer tropical oceans, there may occur more cyclones, and hurricanes and snow-melting mountains will cause more floods during monsoon.

③ A rise in atmospheric temperature will increase the evaporation of seawater increasing the humidity. 

Measures to control the greenhouse effect:

① To reduce the consumption of fossil fuels such as coal and petroleum. 

② To depend more on non-conventional renewable sources of energy such as wind, solar, biogas, etc.

 ③ There should be a restriction on the emission of CO2 and CFCs from factories and automobiles.

Rational Use of Energy

Harnessing energy resources for sustainable development

A natural resource is anything that people can use which comes from nature. People do not make natural resources but gather them from the earth. Examples of natural resources are air, water, wood, oil, wind energy, hydroelectric energy, iron, and coal.

The calorific value of fuel: The energy contained in fuel or food is determined by

measuring the heat produced by the complete combustion of a specified quantity of it.

The amount of heat released by a unit weight or unit volume of fuel during its complete combustion is called its calorific value. 

Unit: It is generally expressed in joules per kilogram (J/kg).

Conservation of resources: 

Conservation refers to reducing the rate at which

resources are used. Conservation is one of the biological principles of sustainability.

A concept of conservation plans to achieve a balance between production and protection

and is against any unplanned development that flouts ecological principles.

Sustainable development is the development that meets the needs of the present

without compromising the ability of future generations to meet their own needs.

Alternative sources of energy:

Solar Energy : 

Man has been using solar energy purposefully for millennia. This Sun

is the source of most of our energies. Solar energy, being non-polluting and non-depletable

is considered as renewable energy and thus fits into the principle of sustainability. Only

0.2 to 0.5% of the solar energy reaching the earth is trapped by photosynthesis. Thus only

a small percentage of the solar energy reaching the earth could sustainably supply all the

energy needs of human societies.

Some solar devices:

Solar Cooker : 

In a solar cooker, sunlight is converted to heat energy that is retained

for cooking. Dark surfaces get very hot in sunlight whereas light surfaces do not. Food

cooks best in dark, shallow, thin metal pots with dark, tight-fitting lids to hold in heat and

moisture. This occurs in much the same way that a greenhouse retains heat or a car with

its windows rolled up.

Solar cells:

Solar power is produced by collecting sunlight and converting it into

electricity. This is done by using solar panels, which are large flat panels made up of many

individual solar cells. It is most often used in remote locations, although it has become

popular in urban areas as well.

The disadvantages of solar energy are :

① It is available only during the daytime,

② It is not available in cloudy weather.

Wind Power :

Wind power is extracted from air flow using wind turbines or sails to produce mechanical or electrical power. Windmills are used for their mechanical power, windpumps for water pumping, and sails to propel ships. But a large number of wind generators covers a large area for the production of a comparatively low amount of electric power. When the wind does not blow, wind generators remain dead.

Tidal Power :

The tides move a massive amount of water and the energy from

the moving water, known as tidal energy, can be captured and converted into electricity.

Advantages : 

① Other forms of renewable energy, such as wind and solar energy are dependent on random weather patterns. But tidal energy is based on the rise and fall of tides, which is more uniform and reliable. 

② It does not release greenhouse gases or other pollutants into the air.

Disadvantages:

① Tidal energy development is hampered by high upfront costs. There are also limited suitable locations for tidal energy.

⑦ The energy which is obtained from the strong currents of water produced by the rise

and the fall of sea level due to tidal action is called tidal energy.

Geothermal Energy:

Geothermal energy is thermal energy generated and stored in the earth. Resources of this energy range from the shallow ground to hot water and hot rock found a few miles beneath the earth's surface and down even deeper to the extremely high temperatures of molten rock called magma. This geothermal energy can be used for space heating or for boiling water and generate steam to drive turbogenerators. The energy which is generated by utilizing the heat of the earth's interior is called geothermal energy.

Biomass energy and biogas:

The term "biomass" refers to organic matter that has stored energy through the process of photosynthesis. These fuels, however, do not produce much heat on burning and a lot of smoke is given out when they are burnt. Therefore, technological improvement is necessary to improve the efficiency of these fuels. Biogas typically refers to a mixture of different gases produced by the biochemical decomposition of organic matter such as agricultural waste, manure, municipal waste, plant material, sewage, green waste, or food waste in absence of air. Since it is mainly produced from cow-dung(gobar), it is popularly known as gobar-gas.

Biogas is an excellent fuel as it contains a high percentage of methane.

Compressed Natural Gas (CNG) is biogas that has been compressed and can be used as a fuel for vehicles.

Electricity from waste :

Scientists are developing new ways to recycle waste by generating electricity from landfill waste.

Coalbed methane (CBM):

Coalbed methane (CBM), coalbed gas, coal-mine methane (CMM) are the forms of natural gas that is stored ('"adsorbed”） in deeply buried coal seams. In recent decades it has become an important source of energy. CBM is generated either from a biological process as a result of microbial action or from a thermal process as a result of increasing heat with the depth of the coal.

Methane hydrates: Methane hydrates are white, ice-like solids inside of which are trapped molecules of methane. Here the methane molecules are enclosed in microscopic cages composed of water molecules. If methane hydrate is either warmed or depressurized, it will revert back to water and natural gas. When brought to the earth's surface, one cubic meter of gas hydrate releases 164 cubic meters of natural gas.