Photochemical smog is formed when sunlight reacts with nitrogen oxides and volatile organic compounds in the atmosphere. It causes a brown haze and health issues. Acid rain is caused by emissions from industries and vehicles reacting with water, moisture, and oxygen in the air to form acids. It harms plants and ecosystems. Chlorofluorocarbons are man-made gases used in aerosols and refrigerants that contribute to global warming and deplete the ozone layer, which protects the Earth from ultraviolet radiation.

1. Photochemical smog
Acid rain its Theory and
Adverse Effects
Chlorofluorocarbons and
its Effects
Represented To: Mam Saima Shehzadi
Represented By: Rabia Batool (Roll No: 14)
Sundas Shehzadi ( Roll No:17)

2. What is Photochemical Smog?
 Photochemical smog: is a type of smog produced when ultraviolet light
from the sun reacts with nitrogen oxides in the atmosphere. It is visible as a
brown haze, and is most prominent during the morning and afternoon.
 Photochemical Smog can also be defined as a mixture of various gases with
dust particules .

3. How is Photochemical Smog Formed?
1)Nitrogen dioxide (NO₂) can be broken down by sunlight to form
nitric oxide (NO) and an oxygenradical (O):
NO2 + sunlight → NO + (O)
2) Oxygen radicals can then react with atmospheric oxygen (O₂)
to form ozone (O3).
(O) + O2 → O3
3) Ozone is consumed by nitric oxide to produce nitrogen dioxide
and oxygen.
O3 + NO → No2 + O2
4) Harmful products, such as PAN, are produced by reactions of
nitrogen dioxide with various hydrocarbons (R), which are
compounds made from carbon, hydrogen and other substances:
NO₂ + R → products (such as PAN)

4.  5) The main source of these hydrocarbons is the VOCs.
Similarly, oxygenated organic and inorganic compounds (RO)
react with nitric oxide to produce more nitrogen oxides

5. Types of pollutants Causing Photo-
chemical Smog
 Primary pollutants: The two major primary pollutants,
nitrogen oxides and VOCs, combine to change in sunlight in a
series of chemical reactions, to create what are known as
secondary pollutants.
 Secondary pollutants: The secondary pollutant that
causes the most concern is the ozone that forms at ground level.
While ozone is produced naturally in the upper atmosphere, it is
a dangerous substance when found at ground level. Many other
hazardous substances are also formed, such as peroxyacetyl
Nitrate (PAN).

6. Sources of photochemical Smog
1)Biogenic Sources:
In nature, bushfires, lightning and the microbial processes that occur in soil
generate nitrogen oxides. VOCs are produced from the evaporation of naturally
occurring compounds, such as terpenes, which are the hydrocarbons in oils that
make them burn. Eucalypts have also been found to release significant amounts of
these compounds.
2)Anthropogenic Sources:
Nitrogen oxides are produced mainly from the combustion of fossil fuels, particularly
in powerstations and motor vehicles. VOCs are formed from the incomplete
combustion of fossil fuels, from the evaporation of solvents and fuels, and from
burning plant matter such as backyard burning and wood burning stoves.
 In Adelaide in 2000, an estimated 66% of nitrogen oxides (NO and NO₂) came from
motor vehicles, and a further 20% from fuel combustion. Motor vehicles
contributed 44% of VOC emissions.

7. Effects of photochemical smog:
1. Effects on Environment:
 Photochemical smog has devastating effects on the environment. The
collection of chemicals found in photochemical smog causes problems for
plants and animal life.

8. 2.Effect on plants
 Deposition of particulate matter containing toxic metals affects the
growth of plants.
 The particulate matter after deposition in plants leaves block stomata
opening of plants and reduce growth.
 Decrease the pH of the soil which makes the soil infertile.
 Can lead to extensive damage to crops, trees.and vegetation.
 Some plants such as tobacco, tomato and spinach are highly responsive
to ozone, so photochemical smog can decimate these sensitive crops,
trees and other vegetation.

9. Brown Necrotic leaves
 Brown Necrotic leaves: Ozone causes necrotic (dead) patterns on
the upper surfaces of the leaves of trees. Ground-level ozone also can
interfere with the growth and productivity of trees.

10.  It can cause anything from minor pain to
deadly diseases such as lung cancer
,wheezing.
 High levels of smog also trigger asthma
attacks because the smog causes increased
sensitivity to allergens, which are triggers
for asthma.
3.Effects On Human Health

11. Precautions To Reduce photochemical Smog
Take precautionary steps to safeguard against the ill effects of
photochemical smog.
1. Keep your motor vehicle regularly serviced .Reduce your daily pollutant
emissions by driving less, making use of carpools.
2. Other small actions, such as tightly sealing the lids of chemical products
like garden chemicals, solvents, and household cleaners.
3. Use energy efficient appliances and Look for the Energy Star logo when
buying an electricical Appliances.
4. If renovating or buildings use energy-efficient designs and materials. Turn
off unnecessary electrical appliances.
5. Limit your wood fires at home.

12. What is Acid Rain?
Introduction To Acid Rain:
 Normal rain water is always slightly acidic
because CO₂ present in atmosphere and get
dissolved in it form carbonic acid.
H₂O (1) + CO₂ (g) ⇒ H₂CO3(aq)
 Carbonic acid then can ionize in water
forming low concentrations of carbonate and
hydronium ions.
H₂O (1) + H₂CO3 (aq) ⇒ HCO3 (aq) + H30+
(aq)
 Unpolluted rain can also contain other
chemicals which affect its pH (acidity level).
 The pH of rain is further lowered to as this
type of Precipitation is called as ACID RAIN.
Acid rain is the combination of H₂SO4, HNO3
and HCI

15. Types of Acid Rain
1)Wet Deposition
2) Dry Deposition
1) Wet Deposition:
This type of deposition occurs when any form of condensation removes acids
from the environment, leading to acidic deposition on the earth's surface.
2) Dry Deposition:This type of deposition occurs when polluted
particles and gases begin to stick to the surface of the earth through smoke and
dust in the absence of precipitation.Wet deposition is more dangerous than dry
deposition, as it washes all the pollutants, and carries it to the lakes and rivers.

17. Causes Of Acid Rain
NATURAL CAUSES:
 Volcanic Emissions
 Biological processes
 Lightning
Anthropogenic Causes:
 Factories (industrialization)
 Motor vehicles, Automobile Exhaust
 Coal based power plants
 Domestic fires
 Smelters

18. Theory of Acid Rain
ROBERT ANGUS SMITH :
 The phrase acid rain was first used in 1852 by Scottish chemist Robert
Angus Smith during his investigation of rainwater chemistry near
industrial city Manchester in England and Scotland. The phenomenon
became an important part of his book Air and Rain The Beginnings of a
Chemical Climatology.
 ROBERT ANGUS SMITH was first to show relation between acid rain &
atmosphere pollution. Term acid rain was generated by SMITH in 1872.
 Father of acid rain.
 The earliest report about acid rain in the United States came from
chemical evidence gathered from Hubbard Brook Valley public awareness
of acid rain in the US increased in the 1970s.

19. Sundas shahzadi
Roll number 17
Effects ofAcidRain

20. Effects on trees
• The needles andleaves of the trees turn brown and falloff.
• Trees can also suffer from stuntedgrowth;and havedamagedbark and leaves,which
makes them vulnerable toweather
.
• Direct contactbetween trees and acid rain but it also happenswhen trees absorb soil
water thathas come into contactwith acid rain.
• The soil poisonsthe tree with toxic substancesthat the rain has deposited into it.

22. Effectson plants
• Causing brown necrosis of plants andtrees
• causing the yellowing of Leaf tissue(chlorosis)
• Direct effecton plantsgrowth due to toxifIcationof soil.
• It takes awaysoil nutrients causing stuntedgrowth.
• Block stomatal pores ofleaves.
• BiochemicalreactionsdominatedbypH are effected.
• Degradationof chlorophyll in plants.

24. Effects on vegetation
• Leaches nutrientsfrom soil,slowing plantgrowth.
• increase acidityin soil.Leachout toxins from the soil ,poisoning plants.
• impedingphotosynthesis
• allows organismsto infectthrough broken leaves.

31. • In the US many Coal burningpower plantsuse fluegas desulfurizationto remove sulphur
containing gases from their stack gas.An example of FGD is wet scrubber.Wet scrubber
is basically areaction tower equipped with afanthat extract hot smoke stack gases from
a power plantinto the tower.Limestone is also injectedinto the tower to mix with stack
gases and combine with the Sulphur Dioxide present, the calcium carbonate of the
limestone produces pH neutral calcium sulphate that is physically removed from the
scrubber,thatis how the scrubber turnssulphur pollutioninto industrialsulphates.
PREVENTION METHODS TECHNICAL
SOLUTION

33. CHLOROFHLOROCARBONS AND THEIR EFFECTS
Introduction:
• A chlorofluorocarbon (CFC) is an organiccompoundthatcontainsonly carbon,chlorine,
and fluorine,producedas a volatilederivativeof methane,ethane,andpropane.
• The Chlorofluorocarbons(CFCs) are man-madechemicalsthat exist as gases or liquids.
• Thy are non-toxic&non-flammable in nature.

34. SOURCES OF CHLOROFHLOROCARBONS
• They do not occur naturally
,theyare alwaysmanufactured.
• The most common source of CFCs are refrigerantsbutfire suppressionsystem for
aircraftsandaerosol also emitCFC into the atmosphere.
• Aerosol cansare also asource of CFC,as CFC are used as propellantsin these cans.
• Halonsthat are used in protectionsystem,are also asource of CFC.

35. EFFECTS OF CHLOROFHLOROCARBONS
• Chlorofluorocarbons have these major effectsonatmosphere.
1.Greenhouse effect:
• CFCs are greenhouse gases
• Absorb heat in the atmosphere, sending some of the absorbed heat back to the surface of theearth
• Contribute to global warming and climate change
2.Ozone-depletion effect:
• UV radiation in stratospherecauses CFC molecules to dissociate into free radicalsthat contains one or more unpaired
electrons.
• Thus contributingto the thinningof the protective ozone layer
.