CBSE Class 11 Chemistry Environmental Chemistry

3. Main Primary
Pollutants
Carbon
monoxide
Sulphur
oxides
Nitrogen
oxides
Particulates
Secondary
Pollutants
Ground
level Ozone
Acid Rain
Nutrient
Enrichment
1
2

4.  Environmental chemistry is the scientific study of the chemical and biochemical
phenomena that occur in natural places. It should not be confused with green
chemistry, which seeks to reduce potential pollution at its source. It can be defined
as the study of the sources, reactions, transport, effects, and fates of chemical
species in the air, soil, and water environments; and the effect of human activity
and biological activity on these. Environmental chemistry is
an interdisciplinary science that includes atmospheric, aquatic and soil chemistry, as
well as heavily relying on analytical chemistry and being related
to environmental and other areas of science.
 Environmental chemistry involves first understanding how
the uncontaminated environment works, which chemicals in what concentrations are
present naturally, and with what effects. Without this it would be impossible to
accurately study the effects humans have on the environment through the release
of chemicals.

5. Pollutants

6. The picture depicts how drastically era is changing?
 A pollutant is a substance that causes pollution. We can have
pollutants in liquid, solid or gaseous form.
 A substance becomes a pollutant when its concentration is
greater than the natural abundance and this increase in
concentration is either due to human activities or natural
phenomenon.
 There are pollutants which can be degraded and rapidly
broken down by natural processes similar to the degradation
of vegetables.
 We also have pollutants which take decades to degrade,
once released cannot be easily removed. for example,
DDT, plastic materials, heavy metals and nuclear waste.

7. Sources & Effects of
Environmental Pollution:
When there is an undesirable change in the
surrounding that has harmful effects on plants
and animals, it leads to environmental
pollution.

9. Tropospheric Pollution
 The presence of unwanted substances in the lowest
layer of the atmosphere results in tropospheric
pollution.
 Major gaseous pollutants include oxides of sulphur,
nitrogen, carbon and hydrocarbons.
Burning of fossil fuels (coal, automobile fuel) produce
oxides of Sulphur and nitrogen. They react with water
in presence of oxygen of air and form nitric acid and
Sulphuric acid. This causes acid rain which is harmful
to agriculture plants and trees. It causes various
respiratory ailments.
 Burning of hydrocarbons (carcinogens) produce oxides
of carbon. CO is poisonous and can lead to
death. CO2 is responsible for global warming.
Particulates of smoke dust mist and fume are harmful
for human health and cause respiratory ailments.

10. Chemical Reactions forming Oxides
 The presence of particulate matter in polluted air
catalyzes the oxidation of Sulphur dioxide to
Sulphur trioxide.
 The reaction can also be promoted by ozone and
hydrogen peroxide.
2SO2 (g) +O2 (g) → 2SO3(g)
SO2 (g) +O3 (g) → SO3(g) + O2 (g) SO2(g) +
H2O2(l) → H2SO4(aq)
 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 ) as given below:
 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
N2 (g) + O2 (g) → 1483K 2NO(g)
2NO (g) + O2 (g) → 2NO2 (g)
NO (g) + O3 (g) → NO2 (g) + O2 (g)

11. o Hydrocarbons are composed of
hydrogen and carbon only and are
formed by incomplete combustion of
fuel used in automobiles.
o Hydrocarbons are carcinogenic, i.e., they
cause cancer.
o They harm plants by causing ageing,
breakdown of tissues and shedding of
leaves, flowers and twigs.
Carbon monoxide (CO) is one of the
most serious air pollutants. It is a
colorless and odorless gas, highly
poisonous to living beings because
of its ability to block the delivery of
oxygen to the organs and tissues. It
is produced as a result of incomplete
combustion of carbon.

13. Classification of Air Pollution

14. The main Primary Pollutants are:

15. Mask can filter particles < 0.007
microns i.e. 10 times smaller than
PM2

16.  The primary pollutants are “directly”
emitted from the processes such as fossil fuel
consumption, Volcanic eruption and factories.
 The major primary pollutants are Oxides of
Sulphur, Oxides of Nitrogen, Oxides of Carbon,
Particulate Matter, Methane, Ammonia,
Chlorofluorocarbons, Toxic metals etc.
 Other Primary Pollutants
 Another category of the primary air pollutants is
toxic metals such as Cadmium, Lead and
Copper, which are products of the Industrial
processes. The Chlorofluorocarbons (CFCs) are
proved to be harmful to the ozone layer emitted
from products currently banned from use. In
agriculture process, Ammonia is emitted which
has characteristic pungent odor. It is a precursor
to foodstuffs and fertilizers. Ammonia is also a
building block for the synthesis of many
pharmaceuticals.

17. Secondary Pollutants:

18.  The upper stratosphere consists of
considerable amount of ozone (O3),
which protects us from the harmful
ultraviolet (UV) radiations (λ 255 nm)
coming from the sun.
 Ozone in the stratosphere is a product
of UV radiations acting on dioxygen
(O2) molecules. The UV radiations
split apart molecular oxygen into free
oxygen (O) atoms. These oxygen
atoms combine with the molecular
oxygen to form ozone.
 O2 (g) → O(g) + O(g)
 O(g) + O2 (g) ⇌ O3 (g)
 Ozone is thermodynamically unstable
and decomposes to molecular oxygen.
. UV radiations lead to ageing of skin, cataract, sunburn, skin
cancer, killing of many phytoplankton, damage to fish
productivity

19.  We are aware that normally rain water
has a pH of 5.6 due to the presence of
H+ ions formed by the reaction of rain
water with carbon dioxide present in the
atmosphere.
 When the pH of the rain water drops
below 5.6, it is called acid rain.
 Acid rain refers to the ways in which acid
from the atmosphere is deposited on the
earth’s surface
 H2O (l) + CO2 (g) ⇌⇌ H2CO3 (aq)
 H2CO3 (aq) ⇌ H + (aq) + HCO3 – (aq) HCO−
3

22. Number of days reaching ‘unhealthy for sensitive groups’ level or
above on the air quality index

23. Air pollution is a leading contributor to
noncommunicable diseases (NCDs)
 A new World Health Organization
(WHO) report highlights the links
between air pollution & the
epidemic of non-communicable
diseases (NCDs) that is affecting
people worldwide. Children are most at risk with
growing evidence indicating that
early life exposure to environmental
risks like chemicals & air pollutants
increases the lifetime risk of
developing NCDs.
Environmental factors are main causes of NCDs with 12.6
million deaths a year linked to the environment
 Heart disease, stroke, lung disease &
cancers, are among the top five
causes of death today, & one-quarter
to one-third of deaths from these
diseases are due to air pollution
ambient (outdoor) and household
(indoor) air pollution caused more
than 6 million deaths from these
diseases in 2012.