Introduction- Troposhere and stratosphere

1. OPEN COURSE:ESSENTIALS OF
CHEMISTRY (CH 1551.1)
MODULE 6: ENVIRONMENTAL
CHEMISTRY

2. ENVIRONMENTAL CHEMISTRY:
TOPICS TO BE COVERED
• Air Pollution: Types, Source And Influence.
• Acid Rain, Green House Effect, Ozone Layer and
Its Depletion.
• Water Pollution: Factors affecting purity of
water, sewage water, industrial waste,
agricultural pollution- pesticides, fertilizers,
detergents. Hard and soft water, removal of
hardness. Disadvantages of hard water.
• Soil Pollution: Pesticides, Herbicides, Fungicides,
Long Term Use Of Fertilizers, Plastic Waste.

3. INTRODUCTION
In Greek, (atmos sphaira)‘atmos’ means
gas and ‘sphaira’ means sphere
In general, atmosphere refers to
gases around a massive solid
sphere.
Atmoshpere:

4. Earth’s Atmosphere
• Gases in layers covering the earth’s
surface.
• They are held as a result of gravitational
attraction.

5. Atmosphere and life..
 Life is possible only with
atmosphere, with appropriate
composition of gases.
 Thus an atmosphere serves as an
umbrella for the life.
 Atmospheric science/aerology :
Study of atmosphere and its
effects on other systems.

6. Atmosphere and life..
Atmosphere plays an important
role in maintaining life-
 By absorbing harmful radiations
(e.g. UV radiation and by
maintaining almost constant
temperature and pressure by
various phenomena.
 By the exchange of gases in
various processes like breathing,

7. Earth’s
Atmosphere
Earth is surrounded by mixture of
gases (often referred to as ‘air’
from Greek word for ‘mixing’)
with varying amounts of water
vapour.
 Mass of atmosphere is
estimated as ~5×1018 Kg

8. Composition of Earth’s
atmosphere

9. The massive atmosphere of earth
varies in thickness with
altitude.(generally decreases)
 However the temperature profile
is somewhat complicated.
~ 75% of atmosphere is with in 11
Kms from earth’s surface.

10. Different Layers...

11. Troposphere:
 Begins from the surface –
extends upto 9-10 Kms at the
poles and 10-15 Kms at the
equator
 The boundary between
Troposphere and Stratosphere-
Tropopause

12. Troposphere contd...
 The upper limit of troposphere may
vary by a Km or more, depending
on- temperature, nature of
terrestrial surface etc.
 The temperature of the troposphere
falls off uniformly with altitude until
the cold layer (-57o C), tropopause is
reached.

13.  ~ 75% of the mass of the
atmosphere is associated
with the troposphere.
 The global energy flow
makes troposphere a
Turbulent region(In Greek
‘tropos’ means “turn”)
Troposphere contd...

14.  In the standard atmosphere
model, the average temperature
at the sea level is 150C
(59° F).
Typically, the temperature drops
about 6.5° C with each increase in
altitude of 1 km (about 3.6° F per
1,000 feet).
Troposphere contd...

15.  The rate at which the temperature
changes (usually fall in temperature) with
altitude is called the "lapse rate".
 Mathematically, Lapse rate (Γ) = [Change
in Temperature (ΔT)]/[Change in altitude
(ΔZ)] ; Γ= -ΔT/ ΔZ
 Thus a positive lapse refers to fall in
temperature with altitude.

16. Temperature profile of troposphere

17. Stratosphere
 The second layer of Earth’s
atmosphere.
 It begins at 10-15 Km from the
earth’s surface and extends up to
~50-60 Kms.

18. Stratosphere contd...
• In contrast to troposphere, it has a
negative temperature lapse rate. i.e.
It has warmer layers at top and
cooler layers at the bottom.
• With this layer, the inversion in
temperature begins.

20. • The temperature of the stratosphere increases
with altitude and ranges from -57oC to -3oC.
• This layer of atmosphere contains the highest
levels of ozone (O3), between 15-50 Kms- Ozone
layer.
Stratosphere contd...

21. OZONE
• Ozone is a molecule made up of three
oxygen atoms, with molecular
formula O3
• It is formed by the photolysis of
Oxygen by ultraviolet solar radiation
at wavelengths below 242.5 nm in
the stratosphere.

22. UV Radiation
UV ranges from 100-400 nm
• UV A: 400-315 nm
• UV B: 315- 280 nm
• UV C: 280-100 nm

23. UV Radiation
UV ranges from 100-400 nm
• UV A: 400-315 nm (significantly less
harmful to DNA, although there are
reports of skin burns and skin cancer)
• UV B: 315- 280 nm (harmful to the skin
and is the main cause of sunburn,
excessive exposure results in genetic
damage)
• UV C: 280-100 nm (very harmful to all

26. • Thus the most harmful UV to all living
things are completely absorbed and
screened out by the molecular oxygen
and the ozone layer.
• The ozone layer is mainly found in the
lower portion of the stratosphere from ~
20 to 30 kilometres above Earth’s surface.
• The thickness of the ozone layer varies
seasonally and geographically.

27. • The ozone layer was discovered by the
French physicists Charles
Fabry and Henri Buisson.(in 1913 )
• Gordon Miller Bourne Dobson,
(G.M.B.Dobson)-
a British physicist and meteorologist
designed a spectrometer, which could
measure the ozone from the earth’s
surface.

28. Ozone molecules are capable of
absorbing UV light between 200
and 310 nm.
Upon absorption of the UV
radiation, Ozone is split-up into an
oxygen atom and a molecule of
oxygen.
Ozone Depletion
O3 → O2 + O

29. • Now, this Oxygen atom recombine
with Ozone (O3) to give O2
O3 + O → 2O2
• Thus, the overall ozone in the
stratosphere is balanced by the
photochemical production and
recombination.