By:- ArjuN N.M OF 11th B
• Environmental Chemistry is the scientific study of the chemical
and biochemical phenomena that occur in natural places.
• 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
Pollution is the introduction of contaminants into a
natural environment that causes instability, disorder,
harm or discomfort to the ecosystem i.e. physical
systems or living organisms. Pollution can take the
form of chemical substances or energy, such as noise,
heat or light.
Tropospheric air pollution has impacts on scales
ranging from local to global. Reactive intermediates in
the oxidation of mixtures of volatile organic
compounds (VOCs) and oxides of nitrogen (NOx) play
(The atmosphere is divided into five layers)
The Troposphere (up to 10 km) It's the atmosphere that surrounds us.
The Stratosphere(10-50 km) Very little oxygen or water vapor. Aircraft
fly in the lower stratosphere. This is also where the ozone layer exists.
The Mesosphere(50-80 km) This is where most meteors burn up, because
the density is higher than the outer layers.
The Thermosphere(80-650 km) Practically a vacuum. Includes the
ionosphere (auroras) as well as space station orbits.
The Exosphere(500-2000 km ) The farthest any of Earth's atmosphere
Troposphere is a turbulent, dusty zone containing air, much water vapour
and clouds. This is a region of strong air movement and cloud formation.
The stratosphere, on the other hand, contains dinitrogen, dioxygen, ozone
and little water vapour.
The presence of ozone in the stratosphere prevents about 99.5per cent of
the sun’s harmful ultraviolet (UV) radiations from reaching the earth’s
surface and thereby protecting humans and other animals from its effect.
Tropospheric pollution occurs due to the
presence undesirable solids or gaseous
particals in the air. The major gaseous and
particular pollutants present in troposphere:
1.gaseous air pollutants :these are oxides of
sulphur, nitrogen and carbon, hydrogen
sulphide, hydrocarbons, ozone and other
2.particulate pollutants: these dust, mist,
fumes, smoke,smog ,etc.
Gaseous air pollutants
a) Oxides of Sulphur
b) Oxides of Nitrogen
d) Oxides of Carbon
i. Cabon monoxide
ii. Cabon dioxide
Global warming and green house effect
About 75% of the solar energy reaching the earth is absorbed by the
earth’s surface, which increases its temperature. The rest of the heat
radiates back to the atmosphere. Some of the heat is trapped by gases
such as carbon dioxide, methane, ozone, chlorofluorocarbon compounds
(CFCs) and water vapours in the atmosphere. Thus they add to the heating
of the atmosphere. This causes global warming.
Large amount of methane are released in paddy fields, coal mines, from
rotting garbage dumps and by fossil fuels. chlorofluorocarbons (CFCs) are
man-made industrial chemicals used in air conditioning etc.CFCs are also
damaging the ozone layer. if this trends continue, the average global
temperature will increase to a level which may lead to melting of polar ice
caps and flooding of low lying areas all over the earth. increase in the
global temperature increases the incidence of infectious diseases like
dengue, malaria, yellow fever, sleeping sickness etc.
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
H 2O (l) + CO2 (g) =H2CO3 (aq)
H2CO3 (aq) = H+ (aq) + HCO3- (aq)
When the H 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. Oxides of nitrogen and sulphur which are acidic in nature can be
blown by wind along with solid particles in the atmosphere and finally settle down
either on the ground as ground deposition or in water, fog and snow as wet
acid rain is a byproduct of a variety of human activities that emit the oxides of
sulphur and nitrogen in the atmosphere.
SO2 and NO2 after oxidation and reaction with water are major contributors to
acid rain, because polluted air usually contains particulate matter that catalyse the
acid rain is harmful for agriculture, trees and plants as it dissolves and washes
away nutrients needed for their growth. It causes respiratory ailments in human
beings and animals. it affects plants and animal life in aquatic ecosystem. It
corrodes water pipes resulting in the leaching of heavy metals such as iron, lead and
copper into the drinking water. Acid rain damages buildings and other structures
made of stone or metals. The Tajmahal in India has been affected by acid rain.
The word smog is derived from smoke and fog.
of Photochemical Smog Formation
Photochemical smog happens when nitrogen oxides and volatile organic
compounds react together in the presence of sunlight as a catalyst and
form ozone at lower levels. The nitrogen oxides are emitted from vehicle
exhausts and volatile organic compounds are generated by a multitude of
chemicals, such as paint and cleaning agents. The effects of smog on
human health and the environment are serious and harmful. The toxic
chemicals formed in a photochemical smog can irritate nasal passages
and eyes. Breathing problems can become aggravated due to prolonged
exposure to smog conditions. Some of the toxins generated by chemical
reactions in the photochemical smog are considered carcinogenic. The
acidic nature of the smog can also cause environmental damage and
structural decay in dwellings.
There are two types of smog:
a) classical smog occurs in cool humid climate. It is a mixure of smoke, fog and
sulphur dioxide. Chemically it is a reducing mixure and so it is also called a reducing
Winter smog is essentially created by the excessive use of fossil fuels to heat
up homes and buildings. Winter photochemical smog forms during extreme
weather conditions, particularly during the height of winter. This is because
during extremely cold conditions, populations of cities which have large number
of hearth-heated homes use coal or other combustibles that generate
considerable amounts of smoke and pollutants. These air pollutants are emitted
at the lower levels in the atmosphere. The cold and moist air retains the
emissions for a longer time through the chemical reactions that take place at a slower
rate. Cities boxed in by surrounding higher elevations which experience heavy snowfalls
face smog regularly.
b) Photochemical smog occurs in warm, dry and sunny climate. The main component of
the photochemical smog results from the action of sunlight on unsaturated
nitrogen oxides produced by automobiles and factories.Photochemical smog has high
concentration of oxidizing agents and is,therefore,called as oxidizing smog.
Causes of Summer Smog Formation
Cities with a geography that does not allow proper dispersal of emissions by wind
and helps the smoke get trapped by extreme weather conditions experience
The abundance of sunlight and high temperatures during the summer speeds up
chemical reactions in the atmosphere, which, mingled with humidity, creates dense
smog. At times,temperature inversions at higher altitudes lead to the formation of
summer photochemical smog by trapping a humid layer of air below a layer of warm
air, which holds up the pollutants. Coastal cities surrounded by hills or mountains
are prime candidates for summer smog.
Effect of photochemical smog
The common component of photochemical smog are ozone, nitric oxide, acrolein,
formaldehyde and peroxyacetyl nitrate(PAN).
Photochemical smog causes seriously health problems. Bothozone 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 surface
Primary gases in photochemical smog are nitrogen oxides. Nitrogen oxides are a
mixture of gases, two of which are significant in the production of photochemical
smog. These two are nitric oxide and nitrogen dioxide. Nitrogen oxides come from
combustion processes such as the burning of gas in motor vehicles, burning of coal
or even forest fires.
VOCs are organic compounds that easily turn to gases and are the result of gasoline
exhaust (from cars, trucks, buses and gasoline stations), industrial emissions or
paint fumes. They are composed of hydrogen, carbon and other elements such as
sulfur and nitrogen. VOCs are sometimes referred to as hydrocarbons.
The type of ozone found in photochemical smog is located in the troposphere, the
layer of the atmosphere that is closest to the Earth's surface. This type of ozone
is referred to as ground-level ozone and is harmful. Ground-level ozone forms from
a chemical reaction involving nitrogen oxides, VOCs and sunlight. When sunlight and
hot weather are present, ground-level ozone can reach harmful concentrations if
there is no wind.
PAN forms as the result of complex chemical reactions between nitric oxide (NO)
and VOCs. Scientists began studying PAN as early as the 1940s when plants on
farms near Los Angeles began showing ill effects, found to result from the city's
onset of smog. Scientists found PAN is 10 to 50 times more toxic than oxone to
plants and is a major eye irritant.
Forming Photochemical Smog
For photochemical smog to form, several chemical reactions need to take place
between nitrogen oxides, VOCs, and sunlight. Although photochemical smog is the
result of a series of complex chemical reactions, it can be illustrated by a simple
example that starts with heavy traffic during the morning commute. The byproducts of the fuel burning vehicles, nitrogen oxides and VOCs, are emitted in the
exhaust fumes coming from the vehicles. The nitrogen oxides and VOCs quickly
react to form nitrogen dioxide (NO2). Then, as the day progresses, the sunlight
becomes stronger and more intense. The sunlight reacts with the nitrogen dioxide
(NO2) to form ground-level ozone. The nitrogen dioxide (NO2) also reacts with
VOCs to form PAN. This combination of toxic gases makes up photochemical smog.
These chemical reactions are ongoing throughout the day and the photochemical
smog, under the right circumstances, increases as the day goes on and can get so
bad it can reduce visibility.
Formation and Breakdown of Ozone
The chlorine radicals are the continuously regenerated and cause the
breakdown of ozone. Thus, CFCs are transporting agents for
continuously generating chlorine radicals into the stratosphere and
damaging the ozone layer.
The Ozone Hole Depletion of ozone layer commonly known as ozone hole
over the south pole.
Effects of depletion of the Ozone layer
With the depletion of ozone layer, more UV radiation filters into
troposphere. UV radiations lead to ageing of skin, cataract, sunburn, skin
cancer, killing of many phytoplanktons, damage to fish productivity etc.
Causes of Water Pollution
International standard for drinking water
The international standard for drinking water are given below and they must be followed.
Fluoride:for drinking purposes, water should be tested for fluoride ion concentration. Its
deficiency in drinking water is harmful to man and causes diseases such as tooth decay
etc. However,F-ion concentration above 2ppm causes brown mottling of teeth.Excess
fluoride (over 10ppm) causes harmful effect to teeth n bones;
Lead : drinking water gets contaminated with lead when lead pipes are used for
transportation of water. The prescribed upper limit concentration of lead in drinking
water is about is 50ppb.lead can damage kidney,liver,reproductive system etc.
Sulphate: excessive sulphate more then 500ppm in drinking water causes laxative
effect ,otherwise at moderate levels it is harmless
Nitrate : the maximum limit of nitrate in drinking water is 50ppm.excess nitrate in
drinking water can cause disease such as methemoglobinemia(blue baby syndrome)
OTHER metAls: the maximum concentration of some common metals
India being an agriculture based economy gives high priority to
agriculture ,fisheries and livestock development. some insecticides n
pesticides for protection of our crops.
these insecticides and pesticides and herbicides cause soil pollution.
Prior to world war –II many natural occurring chemicals such as nicotine
(by planting tobacco plants in the crop field), where used as pest
controlling substance for major crops in agriculture practices
During world war –II ,DDTwas found to be of graet use in the control of
malaria and other insect borne diseases. therefore ,atter the war,DDT
was put to use in agriculture to control the damages caused by insects,
rodents, weeds, and various crop diseases how ever, due to adverse
effects its use has been banned in India.
Pesticides are basically synthetic toxic chemicals with ecological
repercussion. Most of the organic toxins are water insoluble and nondegradable. The concentration of toxins in higher animal reach a level
which causes serious metabolic and physiological disorders.
Industrial solid wastes are also sorted out as bio degradable n nondegradable wastes. Bio degradable wastes are generally by cotton
mills, food processing units ,paper mills and textile factories.
Non degradable wastes are generated by thermal power plants
which produce fly ash; integrated iron and steel melting slag.
Industries manufacturing aluminium, zinc and copper produce mud
The disposal of non-degradable industrial solid wastes, if not done
by a proper and suitable method, may cause serious threat to the
environment. Large quantity of toxic wastes are usually destroyed
by controlled incineration, whereas small quantities are burnt along
wit factory garbage in open bins.
Strategies to control environment pollution
There are household discards, there are medical, agricultural, industrial and mining
The improper disposal of wastes is one of the major causes of environmental
Collecting and disposal
Domestic wastes are collected in small bins, which are then transferred to
community bins by private or municipal workers. From these community bins, these
are collected and carried to the disposable site. At the site garbage is sorted out
and separated into biodegradable and non-degradable materials. Nonbiodegradable materials such as plastic, glass, metal scraps etc. are sent for
recycling. Bio-degradable wastes are deposited in land fills and are converted into
The waste if not collected in garbage bins, finds its way into the sewers. Some of it
is eaten by cattles. Non-biodegradable wastes like polythene bag, metal scraps,
etc. choke the sewer cause inconvenience. Polythene bags, if swallowed by cattle
can cost their lives also.