Effects of Pollution - Environmental Chemistry Video Lecture - Class 11

you all must have heard of Hurricane
Katrina
Hurricane Katrina of the 2005 was the
costliest hurricane as well as one of
the five deadliest in the history of the
United States
the number of these destructive
hurricanes is increasing in number as
compared to earlier years
what is the reason why such hurricanes
are occurring frequently let's find out
in today's episode
hello and welcome I am do brother
Goswami today we will continue our
discussion about a major concern of
modern life yes I am talking about
pollution in our earlier episode we have
already discussed about tropospheric
pollution stratospheric pollution acid
rain and smog but today we will discuss
what to do about it in this episode we
will take a look at the depletion of
ozone layer greenhouse effect and global
warming finally we will look at
important questions and answers in the
exam decoded section I am sure you have
heard about the depletion of ozone layer
and it's After Effects environmentalists
keep mentioning terms like ozone
depletion and ozone hole what do they
mean well let's begin at the beginning
ozone is a gas with the formula or 3
it occurs in two layers of the
atmosphere troposphere and stratosphere
the layer closest to the Earth's surface
is the troposphere
it generally extends up to ten
kilometres from sea level ozone present
in troposphere is harmful as it may lead
to difficulty in breathing causing
nausea and headache it also leads to
damage of crops trees and other
vegetation another important fact about
ozone is that it is also a common
component of smog the stratosphere lies
above the troposphere that is between 10
and 50 kilometer above sea level ozone
present in the stratosphere protects
life on earth from the harmful
ultraviolet radiations coming from the
Sun so now the logical question is how
is ozone formed in the stratosphere the
answer is very simple at a height of
about 20 kilometers ozone is formed from
atmospheric oxygen in the presence of
sunlight take a look at the reaction on
your screen
formation of ozone in stratosphere
region begins with the photodissociation
of oxygen molecules by UV radiations
the oxygen atoms then combined with
oxygen molecules to form ozone but since
ozone is thermodynamically unstable it
decomposes thus a dynamic equilibrium
exists between the production and
decomposition of ozone molecules but
this equilibrium is being destroyed by
the chlorofluorocarbons also known as
CFCs and it is the root cause of ozone
layer depletion now the question is how
do these chlorofluorocarbons reach the
atmosphere I will give an answer to this
but before that let me tell you how we
use CFCs CFCs are used as coolants in
refrigerators and air conditioners
in the past they were also used in the
manufacture of disposable foam products
such as cups and plates and as aerosol
propellants in spray cans and as
solvents to clean newly soldered
electronic circuit boards the
chlorofluorocarbons from all these
household and industrial goods are
released in the atmosphere in due course
of time these CFCs mix with the normal
atmospheric gases and eventually reach
the stratosphere in stratosphere they
get broken down by powerful ultraviolet
radiations and release chlorine free
radicals the chlorine radicals then
react with stratospheric ozone and
causes the breakdown of ozone which
leads to its depletion so CFCs are the
transporting agents for continuously
generating chlorine radicals into the
stratosphere and damaging the ozone
layer since mid 1970s scientists have
been concerned about the harmful effects
of these CFCs on the ozone layer you
must know that in 1980s
atmospheric scientists working in
Antarctica reported the depletion of
ozone layer
commonly known as ozone hole over the
South Pole this has led to many efforts
including the Montreal Protocol treaty
to decrease the production of substances
believed to be responsible for ozone
depletion that was all about ozone and
its depletion later in the episode we
will figure out how to counter this but
that's after a short break but in the
meantime here is a question for you from
our website www.weg.net away
welcome back I am the brother and today
again we are discussing pollution before
the break we were talking about the
depletion of ozone layer and had asked
you a question
when is the world ozone Day celebrated
if you knew its 16th September then give
yourself a green salute because you are
environmentally conscious and if we are
talking green we must discuss the term
that environmentalists use very often
yes greenhouse effect I am sure you have
heard this term but let me explain its
significance you might have observed
that when you park your car out on a
sunny day the inside of the car becomes
very very warm even more than the
outside any guesses why this happens let
me explain what happens is that the
sun's rays entered through your car
windows some of the heat from the Sun is
absorbed by the seats the dashboard the
carpeting and floor mats when those
objects released this heat all of it
doesn't get out through the windows some
heat is reflected back in so a certain
amount of energy is going in and less
energy is going out the result is a
gradual increase in the temperature
inside your car
in the same way earth also stays warm
enough for life to survive with the help
of a phenomenon called greenhouse effect
the greenhouse effect was discovered by
Joseph Fourier in 1824 so if you thought
this was a new term think again but what
is a greenhouse some plants especially
flowers vegetables and fruits need a
warmer climate to thrive but how can a
farmer grow them in a cold climate
simple he sets up a greenhouse that is
how poor kids are grown in Himachal
Pradesh
in a greenhouse the visible light passes
through the glass reaches the plants and
soil and warms them the warm soil and
plants emit infrared radiations since
the glass is opaque to the infrared
radiations it partly reflects and partly
absorbs these radiations this mechanism
keeps the energy of the Sun trapped in
the greenhouse this helps in keeping the
greenhouse warm just as the glass in the
greenhouse holds the sun's warmth inside
the atmosphere traps the sun's heat near
the Earth's surface and keeps it warm
this is called natural greenhouse effect
it maintains the temperature and makes
the earth perfect for life so now you
know what greenhouse effect is and how
it's beneficial to mankind but before we
go further let's take a call from a
young friend what difference would it
make to the Earth's temperatures without
the greenhouse effect hmm what would the
earth be like without the greenhouse
effect
well the Earth's average surface
temperature is 14 degrees Celsius in
absence of greenhouse effect it would be
about minus 18 degrees Celsius so is the
greenhouse effect only dependent on the
sun's rays actually no various gases
also contribute to it take a look on the
graphics shown on your screen carbon
dioxide methane
nitrous-oxide chlorofluorocarbons and
water vapor in the atmosphere are termed
greenhouse gases out of these the
maximum contribution to the greenhouse
effect is by carbon dioxide gas coming
to another hot topic of today that is
global warming what is it and what does
carbon dioxide have to do with it well
as you know carbon dioxide is present in
the Earth's atmosphere increase amounts
but surprisingly it plays a critical
role in controlling the climate if its
amount crosses a delicate proportion of
0.03 percent the natural greenhouse
balance may get disturbed and this may
lead to global warming due to
industrialization urbanization and
increasing density of vehicles and the
use of hydrocarbon products millions of
tons of carbon dioxide has been released
into the atmosphere and this amount is
increasing as a result of this the
proportion of carbon dioxide in the
atmosphere has increased by about 13
percent and this increase in the amount
of carbon dioxide has raised the
temperature of the earth by 0.5 degrees
Celsius
it has been estimated that by the year
2030 the Earth's average temperature
would be increased by about 2 degrees
Celsius this increase in temperature of
atmosphere is called global warming the
other greenhouse gases may also lead to
the heating of the atmosphere and cause
global warming this change in the
Earth's temperature will adversely
affect the monsoon rains and cause
excessive melting of the polar ice
thereby raising the level of water in
seas and oceans this may also cause
flooding and submerging of many
low-lying areas
till now we have studied and discussed
the reason for the depletion of ozone
layer greenhouse effect and global
warming now let me take you back to the
question I asked at the beginning of the
episode
why has the number of destructive
hurricanes increased compared to the
earlier times here is your answer during
summers the atmospheric temperature
increases the air above the ocean which
is full of moisture becomes warm and
rises over the oceans due to this
low-pressure air from surrounding areas
moves to the low-pressure area in an
inward and outward rotating pattern the
rising of warm air leads to evaporation
and this results in cooling of the ocean
when the warm air rising above condenses
it results in the formation of clouds
and rains condensation releases heat to
the surroundings
this cycle of evaporation and
condensation brings the oceans heat
energy into the vortex that is a
powerful circular current of water
powering the storm and we have
hurricanes so what is the moral of
today's discussion simple it is very
important to realize the importance of
protecting our environment so we should
adopt methods and activities which help
us in doing so and believe that we can
make a difference with this we come to
the end of the theory for today for more
information about this topic do log on
to www.wymt.com
welcome back
I am de Brito and you are watching
chemistry 11 over the course of this
episode we have learnt effects of ozone
depletion greenhouse effect global
warming it's time now for exam decoded
but before I put you to the test here is
a quick recap of all that we have
learned today in this episode we learned
that ozone occurs in two layers of the
atmosphere troposphere and stratosphere
ozone present in the stratosphere
protects life on the earth from the
sun's harmful ultraviolet radiations
chlorofluorocarbons are the main reason
of ozone layer depletion the atmosphere
traps the sun's heat near the Earth's
surface and keeps it warm this is called
natural greenhouse effect some of the
greenhouse gases are carbon dioxide
methane nitrous oxide
chlorofluorocarbons and water vapor in
the atmosphere
the presence of greenhouse gases in
large amounts may also lead to the
heating of the atmosphere and cause
global warming the increase in
temperature due to the greenhouse effect
is called global warming
now that we are fortified with the facts
there is no reason to delay moving on to
exam decoded
welcome to exam decoded where I will
give you some tips and some analysis all
designed to max your scores you know
answering exam questions doesn't always
have to be stressful it can also be an
invigorating challenge a lot like our
rapid fire round let's go over the rules
this round has five questions for one
marked each you will get no more than
five seconds for each answer track your
scores carefully and I will tell you
what they mean your first question is
the gas of vital importance to all
living organisms present in the
stratosphere is Jay carbon dioxide G
nitrogen C ozone G carbon monoxide and
the correct answer is C ozone let's move
on to the second question the gas that
contributes the most to the greenhouse
effect is a carbon monoxide be water
vapor C ozone G carbon dioxide if your
answer is D carbon dioxide you bagged
one more mark now the third question
coming your way the increase in
temperature due to the greenhouse effect
is known as J global warming the ozone
hole C acid rain T none of these the
correct answer is a global warming the
second last question
ozone present in stratosphere acts as
pollutant true or false
this is false at the end a simple
question for you
methane is a greenhouse gas true or
false
if you said true you are right time now
to see how you have feared if you have
got all five answers right then you are
a high flier and this is definitely your
strong subject if you have scored four
or three then you are an achiever you
are doing well but a bit more practice
is needed if you have scored less than
three then you are a learner who must
keep studying hard to master this topic
but no matter how you did in our
rapid-fire round do log onto
www.koco.com for many more tests and
question papers it's important to know
that the topic effects of pollution
comes under the chapter pollution which
carries a weight age of three marks
making it an important part of your exam
paper the questions asked from this
topic can be very short answer type
questions for one mark and short answer
type questions for two marks the
questions covered from this topic
usually test your knowledge ability
let's take a look at one such question
for two marks it's a knowledge-based one
so I would lead you through the various
steps what do you understand by
greenhouse effect what are the major
greenhouse gases this question is for
two marks so let's see how you can get
both of them while answering this
question you must write when the
radiations from the Sun reach the
Earth's surface the atmosphere traps the
sun's heat near the Earth's surface and
keeps it warm this is called greenhouse
effect
it maintains the temperature of the
earth this explanation will fetch you
one mark carbon dioxide and other gases
like methane nitrous oxide and CFCs are
some examples of greenhouse gases these
examples will fetch you the other mark
that's all we have in store for you
today
I do hope that now you will act as a
catalyst of change for protecting the
environment for more on the concepts of
this topic
log onto www.koco.com
it's now time to say goodbye but let me
leave you with an interesting piece of
information freons
which were once used in dry-cleaning are
now phased out this is because freons
being nonreactive rises up in the
atmosphere along with other gases and
leads to destruction of ozone by
photodissociation take care keep
thinking
you