Below are the important questions and their solutions of CH 301 for Class Test 1 :
1. Define Green House Effect. And name some green house gases.
Ans.: Carbon dioxide (CO2) and other greenhouse gases act like a blanket, absorbing infra red (IR) radiation and preventing it from escaping into outer space. The net effect is the gradual heating of Earth’s atmosphere and surface, a process known as global warming.
Some greenhouse gases are : Carbon Dioxide (CO2), Methane (CH4), Nitrous oxide (N20) and Chlorofluro Carbon (CFC).
2. Explain the contribution of different green house gases in global warming.
Ans.: Contribution of different Greenhouse Gases on Global Warming
Water Vapour (H2O): Water vapour is the most important greenhouse gas. As the surface temperature increases by increase in the level of different greenhouse gases, the evaporation of surface water increases, thereby about 2/3 of the earth’s surface is covered with water vapour. It absorbs heat (IR absorption bands at less than 8 μm and greater than 18μm) and keep the atmosphere warm.
Carbon dioxide (CO2): Rapid industrialization and deforestation has created enormous increment of CO,, in the atmosphere. This gas absorbs heat OR absorption bands centered at 15 gm as well as at 2.7 gm and 4.3 gm) and keep the atmosphere warm.
Methane (CH4): It is produced by bacterial fermentation under anaerobic conditions as in rice paddies, swamps, marshes etc. Natural source of methane is wetlands, termites and oceans. Anthropogenic emissions of methane are the result of food production and fossil fuel use. Since food and energy production continuously increases therefore, methane emission will also continue to rise. CH4 absorbs IR (IR absorption bands centered at 3 μm and 8 μm) for a much longer time, increasing global temperature to a great extent.
Nitrous oxide (N2O): The increasing concentration of N2O is mainly due to human activity. The authropogenic N2O emissions are due to tropical agriculture. Other sources are production of nylon, combustion of fuel containing nitrogen. The IR absorption band 7.8 μm and 8.6 μm associated with stretching and bending of bonds.
Ozone (O3): Ozone has a strong absorption band at 9 μm in the stratosphere region, thus, an important greenhouse gas. The concentration of ozone varies from place to place and season to season.
Chlorofluro Carbon (CFC): CFCs have a long lasting life in the atmosphere. These molecules absorb approximately 9 μm with some bending and stretching bands in the vicinity of atmospheric window, making these as potent greenhouse gas.
3. What is Wein’s displacement law? Show how it can explain green house effect.
Wien’s displacement rule: A black body emits radiation with a different range of wave lengths that can be described with spectral distribution. Stefan-Boltzmann’s law gives the energy emission rate by black body but it cannot give any idea about the maximum intensity of radiation. Wien’s displacement rule can explain the wavelength at which the spectrum reaches its maximum intensity value.
λmax (µm)= 2898/T(K)
Where, λmax = maximum wavelength, T = Temperature
The surface of earth is around 34°C (288 K) which is much higher than the mathematical prediction. The Wien’s displacement rule is helpful here to understand the reason behind it. If we consider both Sun and Earth as a black body having average surface temperature 5800K and 288K respectively, then according to the Wien’s displacement rule their spectrum peaks will be at 0.5µm and 10.1 µm. If we analyse the spectrum curve of Black body radiation at 5800 K (for incoming solar radiation) and 288K (for out going radiation from earth surface), then we will notice that nearly all the incoming solar energy as it arrives just outside the earth’s atmosphere has wavelength less than 3 µm, while the outgoing radiation by the earth has essentially all of its energy in wavelength more than 3 µm. With so little overlap, it is convenient to say that incoming solar radiation has short wavelength while out going radiation from earth surface has long wavelength. The Infra Red (IR) portion of the spectrum strats about 0.7 µm extend -up to 100 µm. So, some of the incoming solar radiation and all of the out going earth’s radiation is IR.
4. What is black body radiation and Albedo effect? Explain how they cause air pollution.
Ans.: A black body (also blackbody) is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. A black body in thermal equilibrium (that is, at a constant temperature) emits electromagnetic radiation called black-body radiation. The radiation is emitted according to Planck’s law, meaning that it has a spectrum that is determined by the temperature alone, not by the body’s shape or composition. A black body in thermal equilibrium has two notable properties,
1. It is an ideal emitter: at every frequency, it emits ras much energy as — or more energy than — any other body at the same temperature.
2. It is a diffuse emitter: the energy is radiated isotropically, independent of direction.
Contribution in global warming : A blackbody when heated emits electromagnetic radiation. As temperature increases, the body emits a greater and greater portion of its radiation in the visible part of the spectrum. This radiation ultimately results in increasing the earth’s temperature.
Albedo is a measure of the reflectivity of a surface. The albedo effect when applied to the Earth is a measure of how much of the Sun’s energy is reflected back into space. Overall, the Earth’s albedo has a cooling effect. (The term ‘albedo’ is derived from the Latin for ‘whiteness’).
Contribution in global warming :
The most significant projected impact on albedo is through future global warming. With the exception of Antarctic sea-ice, recently increasing by 1% a year, nearly all the ice on the planet is melting. As the white surfaces decrease in area, less energy is reflected into space, and the Earth will warm up even more.
The loss of Arctic ice is of particular concern. The ice is disappearing quite fast; not only is albedo decreasing, but the loss triggers a positive feedback. By exposing the ocean surface to sunlight, the water warms up. This melts the ice from underneath, while man-made CO2 in the atmosphere warms the surface. Humidity also increases; water vapour is a powerful greenhouse gas. More ice therefore melts, which exposes more water, which melts more ice from underneath.
5. Derive an equation for Temperature change with altitude (Lapse Rate).
Ans.: Find solution from this gdrive link http://rebrand.ly/ch301ct1q5 .
6. What is ozone hole? Explain formation and depletion of ozone layer.
Ans.: Ozone hole is the area of the Earth’s atmosphere where abnormal reductions of ozone occur, it is an annual phenomenon observed during the spring in the Polar Regions and is usually followed by a recovery during the summer.
Ozone Formation : Ozone is formed by a photochemical reaction in the following way
O2 + hv (242nm) –> O+O
O + O2 + m (N2 or O2) –> O3 + M
The third body (M) absorbs the excess energy liberated by the above reaction and thereby stabilize the ozone molecules. Ozone strongly absorbs UV light in the region 220-330 nm.
Ozone Removal Mechanism : The mechanism of ozone removal is not clear but it is believed that ozone is eliminated from the atmosphere by reaction with atomic oxygen, hydroxyl radicals and mainly by nitric oxide.
(1) O3 + O –> O2 + O2
(2) O3 + HO• –> O2 + HOO•
HOO• + O –> HO• + O2
(3) O3 + NO –> NO2 + O2
NO2 + O –> NO + O2
Chlorofluro carbon (CFC) which is used as refrigerant they are inert in the troposphere but slowly diffuse into stratosphere where CFC form chlorine radical by absorbing ultraviolet radiation.
CFCl3 + hv –> Cl2FC• + Cl•
Cl• + O3 –> ClO• + O2
ClO• + 0 –> Cl• + O2
In a cyclic process ClO• can initiate a series of chemical reaction which lead to destruction of 100,000 molecules of O3 without being destroyed itself. Volcanoes – inject Cl2 and HCl directly into stratosphere. Here Cl2 on exposure of ultraviolet radiation (300-400 nm) forms Cl• and HO• reacts with HCl to give Cl•:
Cl2 + hv –> 2 Cl•
Cl• + O3 –> ClO• + O2
ClO• + O –> Cl• + O2
Part of the chlorine radical and ClO• can be removed through reaction with potent green hhouse gas CH4 and harmful NO2, producing HCl and ClONO2 which is rained out in the troposphere.
Cl + CH4 –> CH3• + HCl
CH3• + CH3• –> C2H6
ClO• + NO2 –> ClONO2
Hydrogen chloride(HCl) and chlorine nitrate (ClONO2) are inactive and do not remove ozone layer. But in the month of September (Antarctic winter) the atmosphere in the Antarctic becomes very cool (temperature < -90 degree C), and then the small ice crystals which make up polar clou9ds provide the surface to HCl and ClONO2 to stay for a longer duration and subsequent reaction follows :
ClONO2 + H2O –> HOCl + HNO3
HOCl + HCl –> Cl2 + H2O
ClONO2 + HCl –> Cl2 + HNO3
Once the sun rises (Antarctic Spring) the chlorine thus formed in winter undergo photolysis and forms chlorine radical.
Cl2 + hv –> 2Cl•
which subsequently remove ozone layer from the atmosphere.
Cl• + O3 –> ClO• + O2
1. What is Noise Pollution?
Ans.: Noise pollution or sound pollution refers to the presence of excessive and disturbing noise (from machines, transportation systems, aircrafts, trains, etc) in the environment that is very harmful to the physical and mental health of the living beings on earth.
2. Explain effect of noise pollution on Human health and migratory bird.
Effect on human life: Effects of noise include physiological and annoyance types. In the former category, there is evidence indicating that exposure to noise of sufficient intensity and duration can permanently damage the inner ear, with resulting permanent hearing loss. Loss of sleep from noise can increase tension and irritability; even during sleep, noise can lessen or diminish the relaxation that the body derives from sleep. In the annoyance category, noise can interfere with speech communication and the perception of other auditory signals: the performance of complicated tasks can be affected by noise. Noise can adversely affect mood, disturb relaxation, and reduce the opportunity for privacy. In all of the above ways, noise can detract from the enjoyment of our environment and can affect the quality of human life.
Effect on animals and birds: Noise pollution damage the nervous system of animal. Animal looses the control of its mind. They start behaving abnormally and become dangerous. Noise pollution results in decrease in population of birds as birds communicate mainly by sound, loud environments interfere with their communications and reduces pairing by almost 15 percent.
3. What is equivalent noise level?
Ans.: It is symbolically represented by Leq and it is accepted by ISO for measurement and rating of noise residential, industrial and traffic areas. The index implies mean noise level over a specified period of time i.e., the constant sound pressure level which would have produced the same total energy as the actual sound level over the given time.
Leq of 80 dBA means a steady noise over the whole period of time or noise level steady at 160 dBA for 50% of the time and zero noise for the remaining period.
4. Explain the source, path receiver concept for Noise Pollution Control.
Ans.: NOISE POLLUTION CONTROL:
The source, path receiver concept.
Noise pollution could be controlled by either reducing the noise at the source or by preventing its transmission or by protecting the receiver.
At the source: The first step in the prevention of noise pollution is to control the noise at the source itself.
(a) Lubrication of machines generally reduces the noise produced.
(b) Tightening the loose nuts.
(c) Reducing the eccentricity generally reduces vibration and noise.
In the path: It we are not able to control the noise at its source, the step is to try to prevent its transmission. The following are few examples of instances in which the noise pollution is controlled by modifying the path of transmission.
(a) Keeping the noisy machine covered in an enclosure so that the sound does not escape and reach the receiver.
(b) Construction of noise barriers on road sides for the benefit of the nearby residential communities.
(c) Sound – proof the building use heavy curtains on the windows, acoustical tile on the ceiling and walls, on the floors, seal all air leaks to reduce the noise coming in from outside.
Receiver: If we are not able to bring down the noise levels to the desired levels through source in noisy places. The following general measures may be taken to reduce noise pollution in a community.
(a) Don’t use horns except in an emergency. Keep auto and truck engines, air conditioners and appliances in good condition.
(b) Purchase the least noisy air conditioner or vacuum cleaner.
(c) Respect your neighbour’s right to silence.
(d) Tell your friends about the hazards of noise.
(e) Get organized.
(f) Become knowledgeable.
(g) Keep conversation and rest areas in the home away from sources of noise.
Sources : Organiser and Fundamentals of Environment and Ecology by Dr. Debapriya De and Dr. Debashish De.
Note : These are only important questions of CH 301 for Class Test 1. These are not the absolute questions which will be asked in test. So, don’t rely only on these questions.