👉Smog:
The word smog is derived from smoke and fog.
This is the most common example of air
pollution that occurs in many cities
throughout the world. There are two types of
smog:
👉(a) Classical smog occurs in cool humid
climate. It is a mixture of smoke, fog and
sulphur dioxide. Chemically it is a
reducing mixture and so it is also called
as reducing smog.
👉(b) Photochemical smog occurs in warm, dry
and sunny climate. The main components
of the photochemical smog result from the
action of sunlight on unsaturated
hydrocarbons and nitrogen oxides
produced by automobiles and factories.
Photochemical smog has high
concentration of oxidising agents and is,
therefore, called as oxidising smog.
👉Formation of photochemical smog:
When fossil fuels are burnt, a variety of
pollutants are emitted into the earth’s
pollutants are emitted into the earth’s
troposphere. Two of the pollutants that are
emitted are hydrocarbons (unburnt fuels) and
nitric oxide (NO). When these pollutants build
up to sufficiently high levels, a chain reaction
occurs from their interaction with sunlight in
which NO is converted into nitrogen dioxide
(NO2). This NO2 in turn absorbs energy from
sunlight and breaks up into nitric oxide and
free oxygen atom.
Oxygen atoms are very reactive and
combine with the O2 in air to produce ozone
The ozone formed in the above reaction
reacts rapidly with the NO(g) formed in the
reaction to regenerate NO2. NO2 is a brown
gas and at sufficiently high levels can
contribute to haze.
Ozone is a toxic gas and both NO2 and O3
are strong oxidising agents and can react with
the unburnt hydrocarbons in the polluted air
to produce chemicals such as formaldehyde,
acrolein and peroxyacetyl nitrate (PAN).
👉The common components of photochemical
smog are ozone, nitric oxide, acrolein,
formaldehyde and peroxyacetyl nitrate (PAN).
Photochemical smog causes serious health
problems. Both ozone and PAN act as powerful
eye irritants. Ozone and nitric oxide irritate the
nose and throat and their high concentration
causes headache, chest pain, dryness of the
throat, cough and difficulty in breathing.
Photochemical smog leads to cracking of
rubber and extensive damage to plant life. It
also causes corrosion of metals, stones,
building materials, rubber and painted
surfaces.
👉How can photochemical smog be controlled ?
Many techniques are used to control or reduce
the formation of photochemical smog. If we
control the primary precursors of
photochemical smog, such as NO2 and
hydrocarbons, the secondary precursors such
as ozone and PAN, the photochemical smog
will automatically be reduced. Usually catalytic
converters are used in the automobiles, which
prevent the release of nitrogen oxide and
hydrocarbons to the atmosphere. Certain
plants e.g., Pinus, Juniparus, Quercus, Pyrus
and Vitis can metabolise nitrogen oxide and
therefore, their plantation could help in this
matter.
👉What is smog? How is classical smog different from photochemical smogs?
👉Write down the reactions involved during the formation of photochemical smog.
👉What are the harmful effects of photochemical smog and how can they be
controlled?
.High concentration of which of the following in atmosphere
leads to stiffness of flower buds which eventually fall off
from plants?
(a) NO2 (b) SO2
(c) CFC (d) Smog
.
.
Answer ▽ ✅ Verified
(b) High concentration of SO2
leads to stiffness of
flower buds
Oxides of Sulphur: Oxides of sulphur
are produced when sulphur containing fossil
fuel is burnt. The most common species,
sulphur dioxide, is a gas that is poisonous to
both animals and plants. It has been reported
that even a low concentration of sulphur
dioxide causes respiratory diseases e.g.,
asthma, bronchitis, emphysema in human
beings. Sulphur dioxide causes irritation to
the eyes, resulting in tears and redness. High
concentration of SO2 leads to stiffness of flower
buds which eventually fall off from plants.
Uncatalysed oxidation of sulphur dioxide is
slow. However, the presence of particulate
matter in polluted air catalyses the oxidation
of sulphur dioxide to sulphur trioxide.
are produced when sulphur containing fossil
fuel is burnt. The most common species,
sulphur dioxide, is a gas that is poisonous to
both animals and plants. It has been reported
that even a low concentration of sulphur
dioxide causes respiratory diseases e.g.,
asthma, bronchitis, emphysema in human
beings. Sulphur dioxide causes irritation to
the eyes, resulting in tears and redness. High
concentration of SO2 leads to stiffness of flower
buds which eventually fall off from plants.
Uncatalysed oxidation of sulphur dioxide is
slow. However, the presence of particulate
matter in polluted air catalyses the oxidation
of sulphur dioxide to sulphur trioxide.
The reaction can also be promoted by
ozone and hydrogen peroxide.
⬆️Prev____@organised notes_____Next⬇️
.The irritant red haze in the traffic and congested places
is due to presence of which of the following ?
(i) Oxides of sulphur
(ii) Oxides of nitrogen
(iii) Carbon dioxide
(iv) Mists, smoke and dust
(v) Smog
(a) (i), (iv) and (v) (b) (iii) only
(c) (ii) only (d) (ii) and (v)
.
.
Answer ▽ ✅Verified
(c) The irritant red haze in the traffic and congested
places is due to presence of oxides of nitrogen.
places is due to presence of oxides of nitrogen.
👉Oxides of Nitrogen: Dinitrogen and
dioxygen are the main constituents of air.
These gases do not react with each other at a
normal temperature. At high altitudes when
lightning strikes, they combine to form oxides
of nitrogen. NO2 is oxidised to nitrate ion, NO₃−
which is washed into soil, where it serves as a
fertilizer. In an automobile engine, (at high
temperature) when fossil fuel is burnt,
dinitrogen and dioxygen combine to yield
significant quantities of nitric oxide (NO) and
nitrogen dioxide ( NO2 ).
NO reacts instantly with oxygen to give NO2
👉Rate of production of NO2 is faster when
nitric oxide reacts with ozone in the
stratosphere.
👉The irritant red haze in the traffic and
congested places is due to oxides of nitrogen.
Higher concentrations of NO2 damage the
leaves of plants and retard the rate of
photosynthesis. Nitrogen dioxide is a lung
irritant that can lead to an acute respiratory
disease in children. It is toxic to living tissues
also. Nitrogen dioxide is also harmful to
various textile fibres and metals.
👉Acid rain refers to the ways in which acid
from the atmosphere is deposited on the
earth’s surface. Oxides of nitrogen and
atmosphere and finally settle down either on
the ground as dry deposition or in water, fog
and snow as wet deposition.
from the atmosphere is deposited on the
earth’s surface. Oxides of nitrogen and
sulphur which are acidic in nature can be
blown by wind along with solid particles in theatmosphere and finally settle down either on
the ground as dry deposition or in water, fog
and snow as wet deposition.
Ammonium salts are also formed and can
be seen as an atmospheric haze (aerosol of fine
particles). Aerosol particles of oxides or
ammonium salts in rain drops result in wet deposition.
SO2 is also absorbed directly on
both solid and liquid ground surfaces and is
thus deposited as dry-deposition.
👉Formation of photochemical smog:
When fossil fuels are burnt, a variety of
pollutants are emitted into the earth’s
When fossil fuels are burnt, a variety of
pollutants are emitted into the earth’s
troposphere. Two of the pollutants that are
emitted are hydrocarbons (unburnt fuels) and
nitric oxide (NO). When these pollutants build
up to sufficiently high levels, a chain reaction
occurs from their interaction with sunlight in
which NO is converted into nitrogen dioxide
(NO2). This NO2 in turn absorbs energy from
sunlight and breaks up into nitric oxide and
free oxygen atom.
Oxygen atoms are very reactive and
combine with the O2 in air to produce ozone
The ozone formed in the above reaction
reacts rapidly with the NO(g) formed in the
reaction to regenerate NO2. NO2 is a brown
gas and at sufficiently high levels can
contribute to haze.
Ozone is a toxic gas and both NO2 and O3
are strong oxidising agents and can react with
the unburnt hydrocarbons in the polluted air
to produce chemicals such as formaldehyde,
acrolein and peroxyacetyl nitrate (PAN).
⬆️Prev____@organised notes_____Next⬇️
.Photochemical smog is due to the presence of
(a) oxides of sulphur (b) oxides of nitrogen
(c) oxides of carbon (d) lead
.
.
Answer ▽ ✅Verified
. (b) The oxidised hydrocarbons and ozone in presence of humidity cause photochemical smog.
👉Smog:
The word smog is derived from smoke and fog.
This is the most common example of air
pollution that occurs in many cities
throughout the world. There are two types of
smog:
👉(a) Classical smog occurs in cool humid
climate. It is a mixture of smoke, fog and
sulphur dioxide. Chemically it is a
reducing mixture and so it is also called
as reducing smog.
👉(b) Photochemical smog occurs in warm, dry
and sunny climate. The main components
of the photochemical smog result from the
action of sunlight on unsaturated
hydrocarbons and nitrogen oxides
produced by automobiles and factories.
Photochemical smog has high
concentration of oxidising agents and is,
therefore, called as oxidising smog.
👉Formation of photochemical smog:
When fossil fuels are burnt, a variety of
pollutants are emitted into the earth’s
pollutants are emitted into the earth’s
troposphere. Two of the pollutants that are
emitted are hydrocarbons (unburnt fuels) and
nitric oxide (NO). When these pollutants build
up to sufficiently high levels, a chain reaction
occurs from their interaction with sunlight in
which NO is converted into nitrogen dioxide
(NO2). This NO2 in turn absorbs energy from
sunlight and breaks up into nitric oxide and
free oxygen atom.
Oxygen atoms are very reactive and
combine with the O2 in air to produce ozone
The ozone formed in the above reaction
reacts rapidly with the NO(g) formed in the
reaction to regenerate NO2. NO2 is a brown
gas and at sufficiently high levels can
contribute to haze.
Ozone is a toxic gas and both NO2 and O3
are strong oxidising agents and can react with
the unburnt hydrocarbons in the polluted air
to produce chemicals such as formaldehyde,
acrolein and peroxyacetyl nitrate (PAN).
👉The common components of photochemical
smog are ozone, nitric oxide, acrolein,
formaldehyde and peroxyacetyl nitrate (PAN).
Photochemical smog causes serious health
problems. Both ozone and PAN act as powerful
eye irritants. Ozone and nitric oxide irritate the
nose and throat and their high concentration
causes headache, chest pain, dryness of the
throat, cough and difficulty in breathing.
Photochemical smog leads to cracking of
rubber and extensive damage to plant life. It
also causes corrosion of metals, stones,
building materials, rubber and painted
surfaces.
👉How can photochemical smog be controlled ?
Many techniques are used to control or reduce
the formation of photochemical smog. If we
control the primary precursors of
photochemical smog, such as NO2 and
hydrocarbons, the secondary precursors such
as ozone and PAN, the photochemical smog
will automatically be reduced. Usually catalytic
converters are used in the automobiles, which
prevent the release of nitrogen oxide and
hydrocarbons to the atmosphere. Certain
plants e.g., Pinus, Juniparus, Quercus, Pyrus
and Vitis can metabolise nitrogen oxide and
therefore, their plantation could help in this
matter.
👉What is smog? How is classical smog different from photochemical smogs?
👉Write down the reactions involved during the formation of photochemical smog.
👉What are the harmful effects of photochemical smog and how can they be
controlled?
⬆️Prev____@organised notes_____Next⬇️
.The secondary precursors of photochemical smog are
(a) SO2 and NO2
(b) SO2 and hydrocarbons
(c) NO2 and hydrocarbons
(d) O3 and PAN
.
.
Answer ▽ ✅Verified
(d) O3 and PAN
primary precursors of
photochemical smog, such as NO2 and
hydrocarbons, the secondary precursors such
as ozone and PAN,
⬆️Prev____@organised notes_____Next⬇️
.The main element of smog is
(a) O3 and PAN (b) O3
(c) PAN (d) PPN and PBN
.
.
Answer ▽ ✅Verified
a
primary precursors of
photochemical smog, such as NO2 and
hydrocarbons, the secondary precursors such
as ozone and PAN,
⬆️Prev____@organised notes_____Next⬇️
.The smog is essentially caused by the presence of
(a) Oxides of sulphur and nitrogen
(b) O2 and N2
(c) O2 and O3
(d) O3 and N2
.
.
Answer ▽ ✅Verified
(a) Smog is caused by oxides of sulphur and nitrogen.
⬆️Prev____@organised notes_____Next⬇️
Air pollution causing photochemical oxidants production
include
(a) Carbon monoxide, sulphur dioxide
(b) Nitrous oxide, nitric acid fumes, nitric oxide
(c) Ozone, peroxyacetyl nitrate, aldehydes
(d) Oxygen, chlorine, fuming nitric acid
.
.
Answer ▽ ✅Verified
(c) Ozone, peroxyacetyl nitrate, aldehydes
Ozone is a toxic gas and both NO2 and O3
are strong oxidising agents and can react with
the unburnt hydrocarbons in the polluted air
to produce chemicals such as formaldehyde,
acrolein and peroxyacetyl nitrate (PAN)
⬆️Prev____@organised notes_____Next⬇️
.Photochemical smog formed in congested metropolitan cities
mainly consists of
(a) ozone, peroxyacetyl nitrate and NOx
(b) smoke, peroxyacetyl nitrate and SO2
(c) hydrocarbons, SO2 and CO2
(d) hydrocarbons, ozone and SOx
.
.
Answer ▽ ✅Verified
(a) ozone, peroxyacetyl nitrate and NOx
⬆️Prev____@organised notes_____Next⬇️
.Photochemical smog occurs in warm, dry and sunny climate.
One of the following is not amongst the components of
photochemical smog, identify it.
(a) NO2
(b) O3
(c) SO2
(d) Unsaturated hydrocarbon
.
.
Answer ▽ ✅Verified
(c) SO2
⬆️Prev____@organised notes_____Next⬇️
.The main element of smog is
(a) O3 and PAN (b) O3
(c) PAN (d) Both (a) and (b)
.
.
Answer ▽ ✅Verified
(a) O3 and PAN
⬆️Prev____@organised notes_____Next⬇️
.Which of the following statements is not true about classical
smog?
(a) Its main components are produced by the action of
sunlight on emissions of automobiles and factories.
(b) Produced in cold and humid climate.
(c) It contains compounds of reducing nature.
(d) It contains smoke fog and sulphur dioxide
.
.
Answer ▽ ✅Verified
(a) Its main components are produced by the action of
sunlight on emissions of automobiles and factories.
⬆️Prev____@organised notes_____Next⬇️
.Which of the following statements about photochemical
smog is wrong?
(a) It has high concentration of oxidising agents
(b) It has low concentration of oxidising agent
(c) It can be controlled by controlling the release of NO2,
hydrocarbons ozone, etc.
(d) Plantation of some plants like pinus helps in controlling
photochemical smog.
.
.
Answer ▽ ✅Verified
(b) It has low concentration of oxidising agent
⬆️Prev____@organised notes_____Next⬇️
.
.Which of the following can control the photochemical
smog ?
(A) Use of catalytic converters in automobiles.
(B) Plantation of trees like pinus, pyrus vitis etc.
(C) Using less sulphur containing fossil fuels.
(a) A and C (b) B
(c) A and B (d) A, B and C
.
Answer ▽ ✅Verified
(c) A and B
Usually catalytic converters are used in the
automobiles, which prevent the release of nitrogen
oxide and hydrocarbons to the atmosphere. Certain
plants e.g., Pinus, Juniparus. Quercus, Pyrus and
Vitis can metabolise nitrogen oxide and therefore,
their plantation could help in this matter.
⬆️Prev____@organised notes_____Next⬇️
.Which of the following statement(s) is/are correct ?
(i) Classical smog is a mixture of smoke, fog and
sulphur dioxide.
(ii) Classical smog is also called oxidising smog
(iii) Hydrocarbons, NO2 and PAN are components of
photochemical smog.
(a) (i) and (iii) (b) (i) and (ii)
(c) (iii) only (d) (i), (ii) and (iii)
.
.
Answer ▽ ✅Verified
(a) Classical smog is also called reducing smog.
⬆️Prev____@organised notes_____
Question: From NCERT | NEET 2014 || [Difficult level:Easy] |||
.A gas that is not common component of photochemical smog is-
1. Ozone
2. Acrolein
3. Peroxyacetyl nitrate
4. Chlorofluorocarbons
.
.
Answer ▽ ✅Verified
4. Chlorofluorocarbons
