Q.35. Discuss the
problem of ‘ozone layer depletion’ and present a summary of international
efforts taken up so far to address the problem. (AKTU. - 2009 - 10)
Related Question -
Q. Discuss the effects of ozone
depletion on environment. What remedial measures do you suggest? (AKTU. - 2011 - 12)
Ans. The
following adverse effects can be observed: (AKTU. - 2010 - 11)
Effect
On Terrestrial Plants: -
Increased UV radiation affects
plants by reducing leaf size and increasing germination time. This could
decrease crop yield of corn, rice, soybeans, peas, sorghum, and wheat. It also
leads to loss of chlorophyll in leaves, and thus reduction of photosynthesis.
Loss of agricultural productivity may lead to severe social and political
consequences at global level.
Effect
On Aquatic Community: -
UV radiation can penetrate 10 to
20 m deep in water. The radiation kills many planktonic organisms. Death of
phytoplankton adversely affects the aquatic food chain. Mass-scale elimination
of phytoplankton due to UV radiation will reduce CO2 uptake at the
global scale, which in turn, will increase atmospheric CO2 and
consequently cause global temperature to rise.
Effects
On Human Beings: -
Ozone depletion may increase the
rate of skin cancer and cause the skin to freckle and age faster. It increases
the frequency of cataracts and other eye diseases in humans and animals. The
ability of the human system to fight diseases (immune system) is also weakened.
Effect
On Climate: -
Ozone depletion will disturb the
temperature gradient. In addition, both the UV radiation reaching to the
Earth’s surface and the presence of ozone-destroying chemicals will add to
global warming with further harmful effects.
Effect
On Materials: -
Increase in UV radiation damages
paints and fabrics, causing them to fade faster. Plastic furniture, pipes,
etc., also deteriorate faster when exposed to the sun.
International
Efforts: -
Intergovernmental negotiations
for an international agreement to phase out ozone-depleting substances started
in 1981 and concluded with the adoption of the Vienna Convention for the
Protection of the Ozone Layer in March 1985.
The Vienna Convention encourages
intergovernmental cooperation on research, systematic observation of the ozone
layer, monitoring of CFC production, and the exchange of information. The
Convention commits the signatories to taking general measures to protect human
health and the environment against human activities that modify the ozone
layer. It is a framework agreement and does not contain legally binding
controls or targets.
Governments now recognize the
need for stronger measures to reduce the production and consumption of a number
of CFCs and several halons. As a result, the Montreal Protocol on Substances
that Deplete the Ozone Layer was adopted in September 1987.
Ninety-six chemicals are
presently controlled by the Montreal Protocol and are subjected to phase-out
schedules under it. The Protocol was designed so that these schedules could be
revised on the basis of periodic scientific and technological assessments.
Governments are not legally
bound by the Protocol until they ratify it as well as the Amendments to it.
Unfortunately, while most governments have ratified the Protocol, ratification
of the Amendments, with their stronger control measures, still lags behind.
Q.36. What is meant by ozone shield. How CFCs
and ozone depleting substances effects ozone shield. (AKTU. - 2012 - 13)
Ans. Ozone
shield is the stratospheric ozone layer, giving protection to the earth's
surface due to intense absorption of harmful solar ultraviolet radiation by the
gas.
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·), atomic chlorine ion (Cl·) and atomic bromine ion
(Br·). The dot is a common notation to indicate that all of these species have
an unpaired electron and are thus extremely reactive. All of these have both
natural and man-made 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 levels of 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 + electromagnetic radiation ® 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,
a chlorine atom reacts with an ozone molecule, taking an oxygen atom with it
(forming ClO) and leaving a normal oxygen molecule. The chlorine monoxide
(i.e., the ClO) can react with a second molecule of ozone (i.e., O3) to yield another chlorine atom and two molecules of
oxygen. The chemical shorthand for these gas-phase reactions is:
Cl + O3 ® ClO + O2 – The chlorine
atom changes an ozone molecule to ordinary oxygen
ClO + O3 ® Cl + 2 O2 – The ClO from
the previous reaction destroys a second ozone molecule and recreates the
original chlorine atom, which can repeat the first reaction and continue to
destroy ozone.
