now again considering the mass of the
atmosphere almost 75% of the mass of the
atmosphere are in troposphere right here
and again usually the heavier gas
molecules accumulate close to the
surface because of the gravitational
force right and another about 24% or
something in here in the stratosphere
and all of the mass actually almost 99%
of the mass are in these two layers but
we have gas molecules mesosphere
thermosphere even actually in EXO
spheres we have right we have to
remember that now in other things is how
high the satellites are do you know how
many kilometers from the earth
satellites that orbit in earth now the
satellites are usually between 700
kilometers to 10,000 kilometers now the
for example the space station in the
earth and that's about four hundred and
thirty kilometres four hundred thirty
kilometres up here as a matter of fact
why this one is something is happening
there I guess anyhow now how about the
pressure you see again the pressure
changes decreases as we go up here and
the pressure values I have for example
that about hundred kilometers 100
kilometers up here the pressure is about
ten to the minus three
Torr and if you go to about 200
kilometers the pressure is 10 GM
- six stores so that is a very very low
pressure actually very very low pressure
what does that means that simply means
that we have gases above those layers
but the density of gas is very very low
actually there's one gas molecule here
there's another gas molecule probably 10
kilometers away in other gas molecules
is you know 5 kilometers actually it
says that for example in the
thermosphere and a bow a gas molecule
trail was about sometimes hundred
kilometers before it collides in other
gas molecules so we have to remember
that the number of gas molecules per
unit volume up there particularly as the
temperature and thermosphere where the
temperature is 1500 degree centigrade is
very very very small and the kinetic
energy actually the temperature
determines the kinetic energy of the
molecules now the kinetic energy 1 over
2 MV squared this is one molecule
kinetic energy is equal to 3 over 2 and
0 Avogadro's number R times T you can
calculate that so that means that the
kinetic energy is directly proportional
to the temperatures and it really
doesn't matter at the same temperature
remember that all molecules have the
same kinetic energy even you know
doesn't matter whether the molecule is a
big molecule it's a small molecule the
kinetic energy of all molecules are the
same again considering the ideal gas
behavior because the kinetic energy is
only determined by the temperature now
so what happens like a nitrogen which
has a molar mass 28 grams and a hydrogen
molar mass of 2 grams and one hydrogen
molecule h2 + 1 + 2 molecule has the
same kinetic energy at the same
temperature at the same temperature what
does that means consider in this
equation here for the kinetic energy
that means that
the hydrogen molecule is moving much
faster than the nitrogen molecules even
though the kinetic energies are the same
but the velocities of those are
different velocities are different now
when you simply let's say stand here
like this or put your hands like here
now how you feel cold and how you feel
hot actually if the temperature here in
room temperature is higher than the body
temperature right somewhere about higher
than body temperatures then the
molecules with high kinetic energy comes
and hits to the surface of your hand or
your skin and then they actually they
heat to the molecules in your skin and
they transfer their kinetic energy to
the molecules in the skin right and this
way you feel hot because the energy heat
is simply flowing from the surrounding
to your body and you feel hot but now
the amount of heat that absorbed or
transferred from the kinetic energy of
the gas molecules to your body depends
on how many gas molecules are hidden to
your skin per unit time and since there
is huge number of molecules in the air
at this when the pressure is one
atmosphere huge numbers right so that
huge number of collusion means will
transfer a lot of heat and you will feel
hot and if the temperature actually of
the gas is hundred degrees that will be
very very hot but if there are only few
molecules heat to your skin per unit
time and suppose that the kinetic energy
of those molecules is very very high put
their 1500 it would making a difference
because the amount of energy that they
will transfer will be yes compared to
one molecule at room temperature would
be very very high but the number of
collisions will be very low that means
that very very small amount of heat will
be transferred to your body even though
the molecules that hit your skin has
kinetic energy equivalent to 1500
degrees centigrade right so that's why
actually up to there when the density of
the gas is so low even 1500 to 15,000
degree centigrade temperature will not
make you feel hot if you just walk in
there I mean or being there as a matter
of fact this is what you know the
temperature and the gas molecules and
the kinetic energy of the gas molecules
so that's why I said that 1500 there
know may not be very hot for us because
very very small number of molecules will
simply hit to your skin or to your body
which will transfer certain amount of
kinetic energy okay now when you say
space what do you mean is that actually
up to ten thousand up to ten thousand
kilometers there are atoms or ions in
the form of ions nitrogen hydrogen
no because there's so few molecules
there that wouldn't really bother
actually now those the space shuttle's
remember they're space shuttles they go
into the space right when they enter the
atmosphere of the sphere now off the
earth they feel the atmosphere at about
120 kilometers about the earth that
means about that even though there are
gas molecules there is no effect almost
yeah let's not say there's no effect
there is certainly a fact but in terms
of space shuttle in fact no no thanks
but at 120 kilometers then they feel the
atmosphere actually and there is a heat
actually due to the between between the
gas and the space shuttle it goes into
the atmosphere okay so there are gas
molecules but they're not much actually
there from one standpoint very very
important from what as we will see they
protect us from very high energy
radiations
or high energy particles that comes from
the Sun they prevent those particles
reach into the surface and making hazard
to the living organisms actually you
know that we will see that as a matter
of fact yes
no no no because if you calculate the
kinetic energy of one molecule that will
be something like ten to the minus
eleven ten to the minus joule something
like that it's very very small right so
when you multiply it by Avogadro's
number then it becomes like kilojoules
and things like that so that's very very
low energy I mean for one molecule but
if you have Avogadro's number then
that's a different story it's a
different story
okay now let's continue here now now the
composition of the atmosphere these are
the compositions we have nitrogen
highest mole fractions point seventy
eight this is the mole fractions
actually remember or in a number of mole
wise you can say it's a 78% and then the
oxygen next one is about twenty point
twenty-one and then we have argon noble
gas and then we have carbon dioxide
actually up to here almost 99.99% of the
atmosphere is accounted by these four
actually three four carbon dioxide
compound the other elements again then
we have neon helium remember neon helium
and argon they're all noble gases so
they are in the form of atoms then we
have methane gas right ch4 and then we
have the Krypton Krypton is again noble
gas right and hydrogen we have hydrogen
and we have nitrous oxide and we have
xenon another noble gases you see again
we have quite a number of noble gases in
the atmosphere the amounts are small but
that's not really they're still there as
a matter of fact now in other things
here particularly these gases when they
if fuse or goes from one layer to the
another layer due to that temperature
change the escape of the gas from one
layer into the other is very very small
so you can say the diffusion between the
layers like over here for example the
diffusion from this - they're from the
troposphere to the stratosphere is very
very low and then diffusion here is low
diffusion there is also low right but
there are actually mixing of those so
actually the mixing is you know very
very low mostly you have the gases here
in the troposphere as I said the mass
wise okay now let's look at remember the
largest amount in the atmosphere is
nitrogen and then the oxygen right any
gases let's look at the properties of
those nitrogen and oxygen now nitrogen
is largely unreactive due to the bond
energy associated with breaking there no
nitrogen nitrogen actually to have a
reaction with nitrogen molecule first
you have to break that bond and that
bond is very very strong and I guess it
is about 900 something yes it is about
941 kilojoules per mole to break that
bond there you have to give that much
energy that's very very high so it is
almost difficult impossible to break the
nitrogen nitrogen there in the
atmosphere I mean have any reaction even
though there are some nitrogen atoms
there are some dissociations of the
nitrogen now the oxygen has much lower
bond energy and the value is about 495
compared to 900 almost twice so that
means that it is possible to break the
oxygen oxygen bond and when you break
the oxygen oxygen bond then the oxygen
becomes reactive that's why we say that
the ox
is more reactive than the nitrogen and
we know that the oxygen reacts with
almost all elements to form oxides right
and then we have the non metal oxides
with the nonmetals and we have metal
oxides with the metal remember we also
said that the non metal oxides are
acidic and non metal oxides particularly
active metal oxides like sodium oxide or
calcium oxide are basic right they are
basic now this is the Aurora lights that
sometimes they called North lies and
that those are the lights that comes out
from the nitrogen and oxygen atoms
nitrogen and oxygen atoms simply when
they bombarded with the photon coming
from the Sun they excite the electron to
upper level and when that electron falls
down to lower level it emits light again
in the visible region and we have those
in fact usually in the North Pole and
South Pole we see those lies and they're
called Aurora Aurora means rose garden
right all different colors actually okay
now photochemical reaction in the
atmosphere
what is the photochemical reaction if a
reaction is taking place by the
bombardment of photons by absorbing the
energy or from the photons that reaction
those kind of reactions are called photo
chemical reactions photochemical
reactions and here beyond the
stratosphere where the alter defense it
says of the earth against the radiation
and high-energy particle occurs that
simply means that beyond the
stratosphere mesosphere thermosphere the
four are chemical reactions are taking
place by what by absorbing these
high-energy photons or high-energy
particles that's coming from the sponsor
Sun so what happens due to that
photochemical reactions the energy of
those or I should say those high-energy
radiation
are all absorbed and it is prevented to
reach to the surface of the area that's
what it says it said defense kind sort
of a defending the earth actually from
those now chemical changes which occur
can be described as photodissociation or
photo ionization x' you can guess again
photodissociation simply means breaking
the bonds and photo ionization means
ejecting an electron from the molecule
for example if you simply break the
oxygen oxygen bond it will be
photodissociation if you simply remove
an electron if a photon removes an
electron from the oxygen molecule it
will be photo ionization x' photo
ionization now this this picture let me
see if I can explain you this this is
the spectrum solar spectrum at the sea
level and this is the solar spectrum
outside the atmosphere actually now what
it simply shows this the intensity
particularly off the UV radiation this
is the UV radiation that's where the
high-energy photons are or the shorter
wavelength than the UV actually the the
intensity of those are simply decreased
from that to that as they reach to the
surface of the earth right what does
that mean that means we still have some
UV radiation reaching to the surface and
that's why we get the sunburns you know
the Sun birds actually is due to the UV
radiation that our skin absorbs that
light and then then it really harms your
body reactions are taking place because
it's a high-energy photons but it is
still decreased in fact quite a bit
before it reaches to the earth and all
of those are possible by photo
ionization and photochemical reactions
that means those gases observe those
photons and then reactions are taking
place those photo reactions
photochemical reactions are simply
taking place now here is
again the rupture of a bomb due to the
absorption of a photon ions are not
formed always radicals are formed this
is again what what it says is this when
you simply break the oxygen molecule
into two oxygen atoms by a photon but
that photon should should have enough
energy to break that actually the energy
of the photon should be greater than the
energy bond energy of the oxygen oxygen
double-bond in fact and when it breaks
you see again the electrons in the bonds
are half as on this and half on that
that means we have neutral oxygen atoms
neutral oxygen atoms and these are
actually called radicals why it is
radical because the what we have there
is this rather than the if I show the
loose diagram of the oxygen atom it
would not be like this but would be like
this right to two paired paired and then
we have unpaired when you have unpaired
electron it on an anthem that atom is
called radical and that atom actually is
more reactive than the others as a
matter of fact so that's actually why
it's called radical so one of the most
important reaction in the upper
atmosphere is the forward associations
of oxygen molecules the oxygen atoms
like this actually by simply knowing the
bond energy of the oxygen molecule we
can calculate what should be the photons
energy minimum to make this
photodissociation reaction to take place
we can calculate it right now photo
ionization x' are again rejecting an
electron from the molecules and here is
the nitrogen ejecting an electron there
becomes an n2 plus oxygen o2 plus in an
electron oxygen atom and OH two plus and
an elect
and this is the n-no actually nitric
oxide we call that nitric oxide and we
remove an electron to get the nitronium
ion here now the ionization energies in
kilojoules per mole are given like this
remember I said we can calculate the
wavelength of the photon that minimum
weight this will be again I should say
the maximum wave them because there's
the wavelength decreases the energy
increases eighty point one nine ah
meters ninety nine point three
nanometers ninety one point to nano
meters and this one is larger one
hundred thirty-four but all of these are
very high-energy photons that means if
you have bombarded with that photons it
will be disaster actually will kill you
as a matter of fact so all of those
high-energy photons are absorbed by
these molecules in the upper atmosphere
and they are not able to reach to the
surface of the earth as a matter of fact
now I guess the ozone layer everybody
heard about the ozone layer ozone layer
ozone is very very important again for
the life on Earth because ozone absorbs
some of the high-energy photons coming
from the Sun and actually prevents
preventing the hazards that we will have
if they reach to the surface as a matter
of fact now the ozone absorbs the
radiation between 240 and to 310
nanometers now remember in the previous
slide those wavelengths were much lower
than this what does that means that
means the photons which are used in
photodissociation and photo ionization
reactions are much much more energetics
much more in the energetics but these
are also hazardous UV radiations
actually 240 and 300 nanometers
and the ozone protects us from that by
simply absorbing that and we will see
what before a chemical reactions taking
place involved in the ozone and the
oxygens now where is the ozone ozone
actually the highest concentration is
about at 35 kilometers above the earth
about the earth and this is in
stratosphere here again now the ozone
here is good for us because it simply
screens the high-energy photons but the
ozone at the surface close to the layer
I mean to to the earth is very very
hazardous we don't want to have the
simply goes on in our atmosphere that we
inhale particularly the people who have
asthma are very badly affected by the
ozone so the ozone has to be there and
that ozone is naturally produced but
there are also an oak actually in the
pollutant air above the cities and that
is what the human beings are simply
produced those Ozone's
now the reaction is actually taking
place up in the atmosphere is an oxygen
atom remember the dissociation of the
oxygen simply molecule produces the
oxygen atom and that oxygen atom is
simply collides with another oxygen atom
and then forms the ozone this is how the
ozone is formed now the ozone layer
occurs in the atmosphere then about 30
25 kilometers it says I said about 35 25
okay 25 or 35 kilometers somewhere there
now you probably remember the ozone
depletion in Turkish this is called what
in Turkish what is that called goes on
ozone daily hose on Oh actually it's a
hole there that means the ozone layer is
very very thin and this is in the South
Pole they find out and they find out
that the reason that the ozone layer is
very thin here almost disappeared goes
on depleted due to the
chlorofluorocarbons that we left into
the atmosphere
what are those chlorofluorocarbons those
are simply the compounds which have
let's say fluorine and chlorine like
this or you can have let's say f3 + CL 3
or others these are chloro fluoro carbon
in fact in hydrocarbons the hydrogen is
replaced by the chlorine or the fluorine
all of them them they are called
chlorofluorocarbons and when you have
those chlorofluorocarbons in the
atmosphere they react with the ozone and
the ozone layer gets thinner and thinner
as a matter of fact and now
chlorofluorocarbons were used for years
as aerosol propellants and refrigerants
what is the aerosol propellants remember
those shaving cream for example all of
those the gas that push the cream out is
the aerosol and that is the
chlorofluorocarbons or refrigerators
uses the chlorofluorocarbons they are
not water-soluble that means they do not
wash out of the atmosphere by a rain and
are quite unreactive they stay in the
atmosphere for a long time because
they're very very unreactive and very
very stable as a matter of fact and the
carbon chlorine bonds is easily broken
by light with a wavelength between 190
and 225 nanometer in this stratosphere
where the ozone layer exists that means
that this reaction simply that
dissociation that rupture of the carbon
and chlorine and getting a chlorine atom
that chlorine atom
is taking place here somewhere here
where the ozone is and then the chlorine
reacts with the OHS on to form the
chlorine oxide and oxygen molecule and
now instead of the ozone reacting with
the high-energy photons to dissociate
and it uses chlorine atoms actually to
dissociate and that simply lowers the
concentrations of the ozone and
depletions of the ozone that's why in
fact those chlorofluorocarbons are not
used anymore I guess since 1995 it has
been decided that the
chlorofluorocarbons will not be used
instead of that we use floral hydro
fluorocarbons no chlorines but fluorine
and hydrogen actually fluorine and
hydrogen for example instead of that
this one we have this pre fluoro methyl
actually it is the fluoro hydrocarbon
naturally now let's look at the
pollutants yes
yes
no no but no but if you consider the
amount of chlorofluorocarbons or the
amount of the UV radiation is absorbed
to break that it's very very small
amount compared to the ozone reaction
that right because very very small
amount of those chlorofluorocarbons
actually up there
now our pollutions again is another
important area and also related to the
chemistry of the atmosphere and the
atmosphere now what are the pollutants
that considered pollutants in the
atmosphere carbon monoxide and
concentration has to be 10 ppm parts per
million if it is greater than that
that means it's harmful right and then
we have the hydrocarbons
what are these hydrocarbons just the
organic compounds organic compounds like
benzene Octane's and other things methyl
methane these are high hydrocarbons
there and that should be again at about
3 parts per million 3 ppm again in the
atmosphere these are the safe amounts I
should say for the human beings and
sulfur dioxide 0.08 parts per million
and nitrogen oxides 0.05 and total
oxidants 0.02 percent and then we have
the ozone and the others they are - it
says but you see again the most
hazardous ones are what sulfur dioxide
and nitrogen oxides and total oxidants
because this is 0.02 ppm and this is
0.05 ppm on 0.08 ppm that's very very
small amount even that is you know
considered to be very hazardous if it
goes over that values then we have to
take precautions to reduce the amount of
those pollutants
in the air yeah here I guess it says it
assumes no major smog problems now smog
is that sort of a brownish color fume
that floats over the big cities and you
can probably have seen that on over on
current especially in in the winter time
in the summertime too and that smug sort
of brownish color and that is actually
nitrogen dioxide mostly nitrogen dioxide
is a very very bad stuff this month
and although the typical value of SOT is
low it is considered the most serious
hazard health hazard on the list
sulfur dioxide very bad stuff for the
health for the human beings actually so
we have to keep the sulfur dioxide low
and where we get the sulfur dioxide from
burning coal and burning gasoline's the
coal has sulfur and gasoline also
contains sulfur burning those we simply
introduce into the atmosphere sulfur
dioxide as a matter of fact it's a bad
stop very bad
now that sulfur dioxide and also some
nitrogen oxides reacts with the oxygen
in the in the atmosphere and for example
this first forms sulfur trioxide and
that sulfur trioxide reacts with the
water rain in the atmosphere and forms
sulfuric acid or nitric nitrous oxides
and nitrogen oxides actually reacts with
the water to form nitric acids so when
the rain falls down it becomes acidic
due to the presence of the sulfuric acid
or nitric acid and we call those acid
rains and what happens when you have
acid rains they simply make a lot of
hazards to the buildings like this for
example or to the goods or living
organisms and the plants usually the
trees are very badly affected in the for
by these acid rains and they actually
dry up they die actually if the acid
rains a force takes the acid green so we
should simply be careful reducing the
sulfur dioxide in the atmosphere
as a matter of fact it reacts with the
moisture in the air to form sulfuric
acid as we said and it is primarily
responsible for acid rain even though
the nitrogen oxide also contribute acid
rain they are also we formed some nitric
acid and highly acidity in rainfall
causes corrosion in the building
materials which shows here but the the
plants are also affected by those acid
rains too now how can we prevent the
sulfur dioxide going into the atmosphere
first of all we should remember that the
source of sulfur dioxide in the
atmosphere is burning coal particularly
in the power plants or burning gasoline
in a cars and in the power plant the
prevention of the sulfur dioxide letting
into the gas Inlet and into the
atmosphere is done by adding calcium
carbonate to the furnaces of the coal
with the coal actually powder calcium
carbonate and that calcium carbonate is
converted to the calcium oxide at high
temperatures about 900 degree centigrade
in the furnace and that calcium oxide
reacts with sulfur dioxide gas to form
the calcium sulphide this calcium
sulfide is solid and it actually
precipitates with the ash now then you
also take that calcium oxide and put it
in solution and pass the gas containing
sulfur dioxide through that solution and
that also takes the sulphur dioxide
left in the gas exhaust gas
and again precipitate as calcium sulfite
calcium sulphide and we simply prevent
the pollution of the atmosphere with the
sulfur dioxide by using calcium
carbonate here again in the furnaces now
nitrogen oxides again smug here is that
the brownish gas that hangs about large
cities is primarily nitrogen dioxide
remember when we talked about the
decompositions of the dinitrogen
tetroxide to the no.2 right and we said
that the dinitrogen tetroxide is
colorless but the nitrogen dioxide is
brown color so from the color actually
we watch how the equilibrium shifts to
the left or to the right from the
intensity of the color in the mixture of
the nitrogen dioxide and dinitrogen
tetroxide so the main constituent of the
smog this is what we call that smug that
means polluted air about the city and
this takes place when the weather
conditions is called inversions that
simply like the temperature opera is
warmer than the temperature lower and
then you can't get the pollutants going
upward as a matter of fact due to that
inversion and that's the no.2 it forms
the oxidation of nitric oxide and all
and component of the car exhaust which
is this in oh and these nitrogen oxides
are just some components of the
photochemical smog that means there are
also others particularly the ozone
carbon monoxide and hydrocarbons are
also contributes to air pollution that
causes very spiritual problems in many
people's in that smog actually now how
do we prevent the nitrogen oxide going
into the atmosphere in the automobiles
remember in the automobiles we have
catalyzed right or it is called
catalytic converters
that's before the exhaust pipe in the
exhaust pipe and the gas that comes out
from the engine which contains the
oxygen oxides of the nitrogen nitrogen
oxides there is with the help of the
catalyzed reaction with the oxygen and
actually decomposes to the nitrogen and
the carbon dioxide and water again with
the now these nitrogen oxides are just
some components of the photochemical
smog he says I mean they are also these
they're okay I guess we will stop here
continue next time any questions I'm
tired
I can't hear you have to come back night
yes would you please get also true yes
yes yes but sure sure definitely
definitely the unreactive 'ti of the
nitrogen is due to the triple bonds
between the nitrogen atoms in the
nitrogen molecule that's the question
yes the answer is yes because to break
that bond requires a lot of energy and
that's why the nitrogen is quite
unreactive nitrogen molecule