ENERGY NOTES ENVIROMENTAL SCENCE SLC (OPT SUBJECT)

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A. Write answers to the following questions.

1. What is energy? Mention any four forms of energy with examples.notesblognepal.blogspot.com
2. Describe in short why energy is important for the development of a nation.notesblognepal.blogspot.com
3. What is meant by furl? Mention any three common sources of energy in rural parts of Nepal.notesblognepal.blogspot.com
4. Explain in brief the importance of energy in industrial development.notesblognepal.blogspot.com
5. What is meant by the source of energy? Mention any four major sources of energy in urban parts of Nepal.notesblognepal.blogspot.com
6. What is a renewable source of energy? Give three examples also.notesblognepal.blogspot.com
7. What is a non-renewable source of energy? Give three examples also.notesblognepal.blogspot.com
8. What is a bio-fuel? Is it a renewable source of a non-renewable source of energy? Give reasons to support your answer.notesblognepal.blogspot.com
9. Explain briefly any three ways of conservation of energy.notesblognepal.blogspot.com
10. Describe in short in what way the environment is affected due to lack of energy conservation.notesblognepal.blogspot.com
11. Can the energy crisis of Nepal be solved by the use of alternative energy resources? Explain.notesblognepal.blogspot.com
12. What are the environmental consequences of over use and misuse of energy resources? Explain.
13. What are the methods to conserve the energy sources? Explain.notesblognepal.blogspot.com
    notesblognepal.blogspot.com
14. What are non-renewable energy resources? Explain in brief about the ways of conservation of non-renewable energy resources.notesblognepal.blogspot.com

B. Write down the differences between following terms

15. Bio-energy and Hydro-electricitynotesblognepal.blogspot.com
16. Renewable energy source and non-renewable energy sourcenotesblognepal.blogspot.com
    notesblognepal.blogspot.com
17. Solar energy and Mineral oilnotesblognepal.blogspot.com

C. Explain with reasons;

18. Solar energy helps in the conservation of non-renewable energy resources.notesblognepal.blogspot.com
19. Use of fuel should be reducednotesblognepal.blogspot.com
20. Mines of mineral oils should be conservednotesblognepal.blogspot.com
21. Production of bio-gas helps in the conservation of mineral oil.notesblognepal.blogspot.com

D. Write short note on:

22. Energy crisisnotesblognepal.blogspot.com
23. Hydro-electricitynotesblognepal.blogspot.com
24. Mineral oilnotesblognepal.blogspot.com
25. Nuclear Energynotesblognepal.blogspot.com
26. Solar Energynotesblognepal.blogspot.com

Some major concepts to be understood:

Global warming is the observed increase in the average temperature of the Earth's near-surface air and oceans in recent decades and its projected continuation.

Global average air temperature near Earth's surface rose 0.74 ± 0.18 °C (1.3 ± 0.32 °F) during the last century. The Intergovernmental Panel on Climate Change (IPCC) concludes, "most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations," which leads to warming of the surface and lower atmosphere by increasing the greenhouse effect. Other phenomena such as solar variation and volcanoes have probably had a warming effect from pre-industrial times to 1950, but a cooling effect since 1950. These conclusions have been endorsed by at least 30 scientific societies and academies of science, including all of the national academies of science of the major industrialized countries. The American Association of Petroleum Geologists is the only scientific society doubting the predominant opinion, but a few individual scientists also disagree with parts of it.

Models referenced by the IPCC predict that global temperatures are likely to increase by 1.1 to 6.4 °C (2.0 to 11.5 °F) between 1990 and 2100. The range of values reflects the use of differing scenarios of future greenhouse gas emissions as well as uncertainties regarding climate sensitivity. Although most studies focus on the period up to 2100, warming and sea level rise are expected to continue for more than a millennium even if no further greenhouse gases are released after this date. This reflects the long average atmospheric lifetime of carbon dioxide (CO₂).

An increase in global temperatures can in turn cause other changes, including sea level rise, and changes in the amount and pattern of precipitation. There may also be increases in the frequency and intensity of extreme weather events, though it is difficult to connect specific events to global warming. Other consequences may include changes in agricultural yields, glacier retreat, reduced summer streamflows, species extinctions and increases in the ranges of disease vectors.

Remaining scientific uncertainties include the exact degree of climate change expected in the future, and especially how changes will vary from region to region across the globe. A political and public debate also has yet to be resolved, regarding whether anything should be done, and what could be cost-effectively done to reduce or reverse future warming, or to deal with the expected consequences. Most national governments have signed and ratified the Kyoto Protocol aimed at combating greenhouse gas emissions.

Terminology

The term global warming is a specific example of the broader term climate change, which can also refer to global cooling. In principle, global warming is neutral as to the period or causes, but in both common and scientific usage the term generally refers to recent warming and implies a human influence.^[5] The United Nations Framework Convention on Climate Change (UNFCCC) uses the term "climate change" for human-caused change, and "climate variability" for other changes. The term "anthropogenic climate change" is sometimes used when focusing on human-induced changes.

Causes

Carbon dioxide during the last 400,000 years and the rapid rise since the Industrial Revolution; changes in the Earth's orbit around the Sun, known as Milankovitch cycles, are believed to be the pacemaker of the 100,000 year ice age cycle.

The climate system varies through natural, internal processes and in response to variations in external "forcing" factors including solar activity, volcanic emissions, variations in the earth's orbit (orbital forcing) and greenhouse gases. The detailed causes of the recent warming remain an active field of research, but the scientific consensus identifies increased levels of greenhouse gases due to human activity as the main influence. This attribution is clearest for the most recent 50 years, for which the most detailed data are available.

Greenhouse gases create a natural greenhouse effect without which temperatures on Earth would be an estimated 20 °C (36 °F) lower, so that Earth would be uninhabitable. It is therefore not correct to say that there is a debate between those who "believe in" and "oppose" the greenhouse effect as such. Rather, the debate concerns the net effect of the addition of greenhouse gases when allowing for positive or negative feedback.

The primary greenhouse gases are water vapor, carbon dioxide (CO₂), and methane (CH₄). Water is the most abundant in the atmosphere by concentration, but it is a short-term greenhouse gas and in a dynamic equilibrium in the atmosphere. Great quantities of water can be added to the atmosphere by evaporation or subtracted by precipitation in a period of weeks. Methane is an intermediate-term greenhouse gas and in the atmosphere is converted to CO₂ in a period of months to years. CO₂ is a long-term greenhouse gas and, once added to the atmosphere can remain in the atmosphere for hundreds of years.

Adding CO₂ or CH₄ to Earth's atmosphere, with no other changes, will make the planet's surface warmer. The concentration of CO₂ in the atmosphere, currently 380 parts per million (ppm), might be naïvely taken to be too low to have much effect. However, the importance of CO₂ arises from a feedback effect: a little of the long-term CO₂ injected into the atmosphere causes a little warming, which causes a little more of the potent short-term water vapor to be evaporated into the atmosphere, which causes still more warming, which causes more of the potent water vapor to be evaporated, and so forth, until a new dynamic equilibrium concentration of water vapor is reached at a slightly higher humidity and with a much larger greenhouse effect than that due to CO₂ alone. This feedback effect is reversed only as the CO₂ is slowly removed from the atmosphere.

Ozone depletion describes two distinct, but related observations: a slow, steady decline of about 4 percent per decade in the total amount of ozone in Earth's stratosphere since around 1980; and a much larger, but seasonal, decrease in stratospheric ozone over Earth's polar regions during the same period. The latter phenomenon is commonly referred to as the ozone hole.

Ozone cycle overview

Three forms (or allotropes) of oxygen are involved in the ozone-oxygen cycle: Oxygen atoms (O or atomic oxygen), oxygen gas (O₂ or diatomic oxygen), and ozone gas (O₃ or triatomic oxygen). Ozone is formed in the stratosphere when oxygen molecules photodissociate after absorbing an ultraviolet photon whose wavelength is shorter than 240 nm. This produces two oxygen atoms. The atomic oxygen then combines with O₂ to create O₃. Ozone molecules absorb UV light between 310 and 200 nm, following which ozone splits into a molecule of O₂ and an oxygen atom. The oxygen atom then joins up with an oxygen molecule to regenerate ozone. This is a continuing process which terminates when an oxygen atom "recombines" with an ozone molecule to make two O₂ molecules: O + O₃ → 2 O₂

Ozone-oxygen cycle in the ozone layer.

The ozone-oxygen cycle is the process by which ozone is continually regenerated in Earth's stratosphere, all the while converting ultraviolet radiation into heat energy. In 1930 Sidney Chapman resolved the chemistry involved.

Formation

In the first step, an ozone molecule's life begins when ultraviolet solar radiation (with high energy; less than 240 nm in wavelength) breaks apart an oxygen molecule (O₂) into two oxygen atoms. These atoms react with other diatomic oxygen molecules to form ozone molecules.

O₂ + (radiation < 240nm) → 2 O

O₂ + O + M → O₃ + M

In the second reaction, "M" is a so-called "third body collision partner", a molecule (usually nitrogen or oxygen) which undergoes no chemical change, but carries off the excess energy of the reaction. Ozone is formed primarily in the upper stratosphere, since the radiation at wavelengths less than 240 nm is absorbed efficiently already at about 30 km height.

How the ozone layer works

The ozone molecules formed by the above reaction absorb ultraviolet radiation having wavelengths between 240 and 310 nm. The triatomic ozone molecule becomes diatomic molecular oxygen plus a free oxygen atom:

O₃ + (radiation < 310 nm) → O₂ + O

The atomic oxygen produced immediately reacts with other oxygen molecules to reform ozone:

O₂ + O + M → O₃ + M

where "M" once again denotes the third body that carries off the excess energy of the reaction. In this way, the chemical energy released when O and O₂ combine is converted into kinetic energy of molecular motion. The overall effect is to convert penetrating UV light into heat, without any net loss of ozone. This cycle keeps the ozone layer in a stable balance while protecting the lower atmosphere from UV radiation, which is harmful to most living beings. It is also one of two major sources of heat in the stratosphere (the other being the kinetic energy released when O₂ is photolyzed into O atoms).

Removal

If an oxygen atom and an ozone molecule meet, they recombine to form two oxygen molecules:

O₃ + O → 2 O₂

The overall amount of ozone in the stratosphere is determined by a balance between production by solar radiation, and removal by recombination. The removal rate is slow, since the concentration of O atoms is very low.

Certain free radicals, the most important being hydroxyl (OH), nitric oxide (NO), and atoms of chlorine (Cl) and bromine (Br), catalyze the recombination reaction, leading to an ozone layer that is thinner than it would be if the catalysts were not present.

Most of the OH and NO are naturally present in the stratosphere, but human activity, especially emissions of chlorofluorocarbons (CFCs) and halons, has greatly increased the Cl and Br concentrations, leading to ozone depletion. Each Cl or Br atom can catalyze tens of thousands of decomposition reactions before it is removed from the stratosphere.

Ozone can be destroyed by a number of free radical catalysts, the most important of which are the hydroxyl radical (OH·), the nitric oxide radical (NO·) and atomic chlorine (Cl·) and bromine (Br·). All of these have both natural and anthropogenic (manmade) sources; at the present time, most of the OH· and NO· in the stratosphere is of natural origin, but human activity has dramatically increased the chlorine and bromine. These elements are found in certain stable organic compounds, especially chlorofluorocarbons (CFCs), which may find their way to the stratosphere without being destroyed in the troposphere due to their low reactivity. Once in the stratosphere, the Cl and Br atoms are liberated from the parent compounds by the action of ultraviolet light, e.g.

CFCl₃ + hν → CFCl₂ + Cl

The Cl and Br atoms can then destroy ozone molecules through a variety of catalytic cycles. In the simplest example of such a cycle^[2], a chlorine atom reacts with an ozone molecule, taking an oxygen atom with it (forming ClO) and leaving a normal oxygen molecule. A free oxygen atom then takes away the oxygen from the ClO, and the final result is an oxygen molecule and a chlorine atom, which then reinitiates the cycle. The chemical shorthand for these gas-phase reactions is:

Cl + O₃ → ClO + O₂

ClO + O → Cl + O₂

The net reaction is: CFCl₃ + hν + O₃ + O → Cl + CFCl₂ + 2O₂, the "recombination" reaction given above.

Interest in ozone depletion

While the effect of the Antarctic ozone hole in decreasing the global ozone is relatively small, estimated at about 4% per decade, the hole has generated a great deal of interest because:

• The decrease in the ozone layer was predicted in the early 1980's to be roughly 7% over a sixty-year period.
• The sudden recognition in 1985 that there was a substantial "hole" was widely reported in the press. The especially rapid ozone depletion in Antarctica had previously been dismissed as measurement error.
• Many were worried that ozone holes might start to appear over other areas of the globe but to date the only other large-scale depletion is a smaller ozone "dimple" observed during the Arctic spring over the North Pole. Ozone at middle latitudes has declined, but by a much smaller extent (about 4–5% decrease).
• If the conditions became more severe (cooler stratospheric temperatures, more stratospheric clouds, more active chlorine), then global ozone may decrease at a much greater pace. Standard global warming theory predicts that the stratosphere will cool.
• When the Antarctic ozone hole breaks up, the ozone-depleted air drifts out into nearby areas. Decreases in the ozone level of up to 10% have been reported in New Zealand in the month following the break-up of the Antarctic ozone hole

Biological effects of increased UV

The main public concern regarding the ozone hole has been the effects of surface UV on human health. So far, ozone depletion in most locations has been typically a few percent. Were the high levels of depletion seen in the ozone hole ever to be common across the globe, the effects could be substantially more dramatic. As the ozone hole over Antarctica has in some instances grown so large as to reach southern parts of Australia and New Zealand, environmentalists have been concerned that the increase in surface UV could be significant.

Effects on Humans

UVB (the higher energy UV radiation absorbed by ozone) is generally accepted to be a contributory factor to skin cancer. In addition, increased surface UV leads to increased tropospheric ozone, which is a health risk to humans.

1. Basal and Squamous Cell Carcinomas -- The most common forms of skin cancer in humans, basal and squamous cell carcinomas, have been strongly linked to UVB exposure. The mechanism by which UVB induces these cancers is well understood — absorption of UVB radiation causes the pyrimidine bases in the DNA molecule to form dimers, resulting in transcription errors when the DNA replicates. These cancers are relatively mild and rarely fatal, although the treatment of squamous cell carcinoma sometimes requires extensive reconstructive surgery. By combining epidemiological data with results of animal studies, scientists have estimated that a one percent decrease in stratospheric ozone would increase the incidence of these cancers by 2%.

2. Malignant Melanoma -- Another form of skin cancer, malignant melanoma, is much less common but far more dangerous, being lethal in about 15% - 20% of the cases diagnosed. The relationship between malignant melanoma and ultraviolet exposure is not yet well understood, but it appears that both UVB and UVA are involved. Experiments on fish suggest that 90 to 95% of malignant melanomas may be due to UVA and visible radiation whereas experiments on opossums suggest a larger role for UVB.^[13] Because of this uncertainty, it is difficult to estimate the impact of ozone depletion on melanoma incidence. One study showed that a 10% increase in UVB radiation was associated with a 19% increase in melanomas for men and 16% for women. A study of people in Punta Arenas, at the southern tip of Chile, showed a 56% increase in melanoma and a 46% increase in nonmelanoma skin cancer over a period of seven years, along with decreased ozone and increased UVB levels.^[15]

3. Increased Tropospheric Ozone -- Increased surface UV leads to increased tropospheric ozone. Ground-level ozone is generally recognized to be a health risk, as ozone is toxic due to its strong oxidant properties. At this time, ozone at ground level is produced mainly by the action of UV radiation on combustion gases from vehicle exhausts.

Effects on Crops

An increase of UV radiation would also affect crops^.. A number of economically important species of plants, such as rice, depend on cyanobacteria residing on their roots for the retention of nitrogen. Cyanobacteria are sensitive to UV light and they would be affected by its increase.

Effects on Plankton

Recent research has analyzed a widespread extinction of plankton 2 million years ago that coincided with a nearby supernova. Researchers speculate that the extinction was caused by a significant weakening of the ozone layer at that time when the radiation from the supernova produced nitrogen oxides that catalyzed the destruction of ozone (plankton are particularly susceptible to effects of UV light, and are vitally important to marine food webs)