2. Environment pollution
Environmental chemistry is the multidisciplinary
science involving chemistry, physics, life science,
agriculture, medical science, public health and
sanitary engineering. In broader terms it is the study
of the sources, reactions, transport effect and fate of
chemical species in air, water, soil and the effect of
human activity upon these.
The objective of environmental education is to
enlighten the public, particularly students and social
workers, about the importance of protection and
conversation of our environment and the need to
restrain human activities which lead to
indiscriminate release of pollutants into the
environment.
3. Environment pollution
A wave of concern for the environmental swept across the
developed countries in the sixties & reached its climax in 1970
with the celebration of earth day under the auspices of the
United Nations. Then from 1972 onwards with the conclusion of
United Nations conference on human environment of Stockholm
this wave started sweeping across India & other developing
nations. At present there are many environmental issues, which
have grown in size & complexity day by day, threading the
survival of mankind on earth. However several Japanese killed
by eating fish from Minamata Bay in the sixties. Why did 3000-
4000 people die in London in 1952? Why are historic marble
status in Greece & Italy getting damaged by rain water? How did
the Mediterranean Sea polluted river in India? Should plutonium
breeder reactors be developed? Is saccharin a dangerous food
additive? These are some typical chemical issues which can be
best handled in their chemical perspective. Of course the issues
are linked with ecological, social, political and economic
questions which have also to be taken into account.
4. Environment pollution
Nomenclature:
Pollutant: a substance present in nature, in greater than
abundance due to human activity, which ultimately effect on the
environment and therefore on living organisms and mankind.
E.g. Pb, Hg, SO2, CO2 etc.
Contaminant: a material which does not occur in nature, but is
introduced by human activity into the environment, affecting its
composition. A contaminant is classified as a pollutants when it
exerts a detrimental effect
Receptor : The medium which is affected by a pollutant. Man
is the receptor of photochemical smog causing irritation of the
eyes and respiratory tract.
Sinks: The medium which retain and interacts with a long-lived
pollutant. A marble wall will act a sink for atmospheric. The
ocean are sinks for atmospheric CO2 & H2SO4 and ultimately
damaged H2SO4 + CaCO3 = CaSO4 + H2O + CO2
5. Pathways of pollutant : The mechanism by which the pollutant is
distributed from its source into the environment segments.
Pb(C2H5)4 ( in gasoline / in automobile petrol) PbCl2 + PbBr2(Air)
PbCl2 + PbBr2(soil)
Speciation : The different chemical forms or species of inorganic,
organic or organometallic compounds present in the environment is
known as specification. It is important to identify the chemical species
of a pollutant since some species are more toxic than others. Thus
methyl mercury (CH3Hg)⁺, (CH3)2Hg are deadly poison compared to
others species of Hg.
Dissolved oxygen : Oxygen is a vitally important species in water. It is
consumed by oxidation of organic matter/ reducing agents. It is an
important water quality parameter. The optimum value for good water
quality is 4-6 mg/L of DO, which ensures healthy aquatic life in water
body. Lower DO values indicate water pollution. In natural & waste
waters DO levels depend on the physical, chemical & biological
activities of the water body.
Environment pollution
6. Chemical oxygen demand (COD): This is and index of the organic content of
water (oxygen demanding substances in water ) and is important water quality
parameter. It is a rapidly measurable parameter for stream, industrial waste
studies & control of water treatment plants.
Bio-chemical oxygen demand (BOD): Based on oxidation of organic matter in
water. This is also a water quality parameter for organic matter in water, which
is empirical in nature. It is measured by the quality of oxygen utilized by
suitable aquatic microorganisms during a five-day period.
Threshold limit value(TLV): This indicates the permissible level of a toxic
pollutant in atmosphere to which a healthy industrial worker is exposed during
an eight hour day without any adverse effect. TLV values for Be , Zn, are 0.002
and 1.000 mg/ m3 respectively.
Environmental segments :
Environment consists of four segments- atmosphere, hydrosphere, lithosphere
and biosphere.
Atmosphere : It is the protective blanket of gasses surrounding the earth, which
contains life on earth and saves it from the hostile environment of outer space.
It absorbs most of the cosmic rays, major portion of the electromagnetic
radiation from the sun. It transmits only neat ultraviolet, visible, infrared
radiation (300-2500 nm) and radio waves (0.10-40µ) while filtering out tissue-
damaging ultraviolet radiation below about 300 nm.
Environment pollution
7. Hydrosphere : This means all types of water resources-oceans, seas,
rivers, lakes, stream, reservoirs etc.
Lithosphere : This is the outer mantle of the solid earth, consisting
minerals occurring in the earth crust & the soil.
Biosphere : This denotes the realm of the living organisms & there
interactions with environment.
Environmental pollution
Air pollution water pollution Land pollution
Surface water Underground water Marine water
pollution pollution pollution
Environment pollution
8. Air pollution
There are five primary pollutants which together contribute more than 20% of global air
pollution . These are (i) CO, (ii) NOx (Nitrogen oxides), (iii) HC (Hydrocarbon), (iv) Sox
(Sulphur oxides), (v) particulates, part.
CO : It is a colorless, odorless and tasteless gas , It is 96.5% as heavy as air and is not
soluble in water.
The basic chemical reactions yielding CO are-
Incomplete combustion of fuel or C- containing compounds.
2C + O2 2CO2
Reaction between CO2 and carbon–containing materials at elevated temps. in industrial
process e.g. in blast furnace.
CO2 + C 2CO
Dissociations of CO2 at high temperatures.
CO2 CO + O
Natural process, e .g. volcanic action , Natural gas emission , electrical discharge during
storm & seed germination , marsh-gas production etc. contribute CO in the atmosphere.
The significant contribution is from human activities.
a) Transportations contribution about 64%
b) Misc sources (Agricultural burning , forest fires etc) 16.9 %
c) Industrial processes . 9.6 %
9. Control of CO pollution :
Modification of internal contribution engines to reduce the
amount of pollutants formed during fuel combustion.
Development of exhaust system reactors which will complete
the combustion process.
Development substitute fuels for gasoline.
Development of pollution – free power sources to replace
the internal engine.
Use of catalytic converters in two stages helps in eliminating
pollutants for exhaust gases before they are discharged into
the atmosphere.
Gasoline containing pb(C2H5)4 is the major source of Pb
pollution in the environment. Pb–free gasoline should be
introduced.
The possible approach to CO pollution is a substitute fuel for
gasoline . May be compressed natural gas (CNG) & Liquefied
natural gas (LNG).
10. Nitrogen oxides NOx :
NOx represents composite atmospheric gases, nitric oxides & nitrogen dioxide , which are
Primarily involved in air pollution . NO is colorless , odorless gas but NO2 has a reddish
– Brown-color and pungent suffocating odor .The basic chemical reaction leading to
Formation of NO & NO2 are
N2 + O2
1210-1765 º C 2NO
2NO + O2 2NO2
The 2nd reaction Is also favored at temps. About 1100⁰C
uv NO Air
NO2 sun light (O2) O3
O
O2
The distribution of NOx from natural sources is more or less uniform on a global basic lent
man- made sources varies depending Urban / rural areas . In Urban atmospheres ,
NOx is 10-100 times greater than in rural areas.
11. Nitrogen oxides NOx
The end product in HNO3. A possible mechanism for the formation of HNO3 is show below
in which O3 plays an important role.
O3 + NO2 NO3 + O2
NO3 + NO2 N2O5
N2O5 + H20 2HNO3
1. Before day light NO & NO2 levels remain fruity stable at concentration slightly higher
than the daily minimum .
2. As the traffic rush begins & increases (6-8 am) , the level of NO increases & becomes
maximum.
3. At mid-morning with increased ultraviolet light , the NO2 level increases due to
conversion of NO into NO2.
4. O3 build up as NO level drops below 0.1 ppm.
5. In the evening the No level again goes up during the evening traffic rush.
6. O3 accumulated during day times , reacts with NO during night with the result that NO2
concentration goes slightly up & O3 level drops.
Busy cities heavy automobile traffic has revealed that the maximum values of NO &
NO2 levels are 1-2 and 0.5 ppm, respectively.
12. Sources of NOx pollution :
Natural bacteria action discharges.
Man made source release 50*107 tones of NOx .man made some in combustion of coal,
oil, natural gas & gasoline.
By photo chemical reaction.
Control of NOx pollution :
a) The use of catalytic converts for control of automobile emissions provides
for removals of ( NO)x.
b) Power plants emit about 50-1000 ppm of (NO)x. Such emission can be
reduced to 90% by a two stage combustion process.
(i) The fuel (coal/gas/oil) is fired at a relatively high temp .whit a sub-
stoichiometric amount of air, say 90- 90 % of the stoichiometric requirement.
This yield of NO is limited in the absence of excess of O2.
(ii) Fuel burnout is completed at a relatively low temperature in
excess air,Under this condition NO is not favored. A possible approach to
NOx removed from stack gas is the chemical sorption process using H2SO4
solutions or alkaline scrubbing solution containing Ca(OH)2 &
Mg(OH)2.Simultaneously SO2 is also removed. NO is converted into N2O3
which is easily absorbed.
Nitrogen oxides NOx
13. Control of NOx pollution :
Then NO2 + NO N2O3
NO2 is recycled. Four steps are involved in scrubbing process . Flue gas and
NO2 and introduced into an oxidizer.
NO2 +SO2 +H2O H2SO4 +NO
NO & +NO2 react to form N2O3 which is scrubbed by H2SO4 in a scrubber.
The cleaned flue gas is released into the atmosphere.
NO2 + NO N2O3
N2O3 + 2H2SO4 2NOHSO4 + H2O
The reaction product is decomposed & the resulting H2SO4 recycled to the
scrubber.
2NOHSO4 + ½ O2 +H2O 2H2SO4 + 2NO2
NO2 produces HNO3 in HNO3 reactor.
3NO2 + H2O 2HNO3 +NO
Excess NO2 & NO are recirculated through the oxidizer in first step.
Nitrogen oxides NOx
14. Sulphur dioxide so2 :
It is colorless gas with a pungent odour. It is produced from the
combination of sulphur-bearing material.
S + O SO2
2SO2 + O2 2S03
SO3 + H2O H2SO4
Natural process e.g. volcanoes. Provide 67% SOx pollution distributed all
over the globe. Men sources 33%. Fuel combustion, transportation,
coal fired power station.
+H2O
SO2 + O2 SO3 + O2 H2SO4 (H2SO4)n aerosol droplet.
SO2 + 1/2 O2
Soot dust SO3
+ H2O H2SO4 (H2SO4)n aerosol droplet
Or metal oxide
This gives rise to the phenomenon of acid rain.
15. Control :
4 possible ways to the removal & control of SOX emissions.
Removal of Sox from flue gases.
Removal of S from fuel before burning.
Uses of low sulphur fuels
Substitution of other energy sources of fuel combustion.
Sox from flue gases can be conveniently eliminated by using chemical scrubbers. The flue
stack are passed through a slurry of limestone, CaCO3, which absorbs SO2 quite
efficiently.
CaCO3 + SO2 + O2 CaSO4 + CO2
An alternate process is based on a reaction between HSO3⁻ ions (from SO2) and citrate ions.
The flue gas is cooled to 50⁰C or lower and freed from particulates and traces of H2SO4.
Then pass to a Absorption tower into a solution containing citrate ions (H2Cit⁻)
SO2 + H2O HSO3⁻ + H⁺
HSO3 + H2Cit¯ (HSO3.H2Cit)⁻²
Passed into,
closed vessel where
H2S is bubbled
H2S + H⁺
2S + H2Cit⁻ + 3H2O
16. Acid rain :
Much of the NOx and SOx entering into the atmosphere are converted into HNO3 &
H2SO4 respectively. The detailed photochemical reactions in the atmosphere
are summarized:
NO + O3 NO2 + O2
NO2 + O2 NO3 + O2
NO2 + NO3 N2O5
N2O5 + H2O HNO3
HNO3 in removed as precipited or as particular nitrates after reaction with bases
(NH3, particulate lime)
HC, NOX
SO2 +1/2 O2 + H2o Soot particles (metal oxide) H2SO4
HNO3 & H2SO4 Combine with HCl emission (both by natural and anthropogenic
sources) to generate acidic precipitation which is widely known as acid rain.
Acid rain now a major pollution problem in some areas.
Acid rains causes extensive damage to buildings & sculptural materials of marble,
limestone, slate, mortar etc. These materials become pitted and weakened
mechanically as the soluble sulphates are leached out by rainwater.
17. Particulates : Small, solid particles and liquid droplets are collectively termed particulates.
These are presents in the atmosphere in fairly large numbers and sometimes pose a serious air
pollution problem.
Sources: Numerous natural processes injecting particulate matter in the atmosphere (800-2000
million tones each year) volcanic eruption, blowing dust & soil by the wind, spraying salt &
other solid particles by the seas & oceans.
Man-made:
Fly ash from power plants
smelters from mining operation
smoke from incomplete combustion process
Effects of particulates on materials:
Air borne particles including soot, fumes and mist are potentially harmful for a variety of materials.
The extent & type of damage depend upon chemical composition & physical state of the
pollutant. Extensive damage occurs when the particulates themselves are corrosive or when
they carry toxic substances along with them.
Control: There are 4 types of equipment used for the control of particulates.
Gravity setting chamber
cyclone collector
wet scrubbers
Electro static precipitators.
18. Inorganic particulate matter: Metal oxide comprise a
major class of inorganic particles in the atmosphere. They
are produced whenever fuels containing metals are burnt.
Thus particulate Fe3O4 in formed during the combustion of
pyrite containing coal.
3FeS2 + 8O2 Fe3O4 + 6SO2 & V converted to V2O5, CaCO3 CaO + CO2
Pb(C2H5)4 + O2 + C2H4Cl2 + C2H4Br2 CO2 + H2O + PbCl2 + PbBrCl + PbBr2
dichloroethane dibromoethane
then Pb-halides which are volatile & emerge through exhaust
system which condenses to form particles. This is basic of
Pb pollutions in the atmosphere. Due to presence of H2SO4
(SO2 + O2 + 2H20 H2SO4) & basis air pollutant, such as
NH3 OR CaO, Salts are formed
H2SO4 +NH3 (NH4)2SO4
H2SO4 + CaO CaSO4 + H2O
19. Organic particulate matter :
These are benzene extracted substances poly cyclic aromatic
hydrocarbon (PAH) are important components of organic
particulate matter because of their carcinogenic nature. Some
typical PAH compounds are Banzo pyrene, chrysene etc.
Most of PAH compounds are absorbed into soot particles.
Monitoring
Analysis of CO : (i)Infrared spectrosphotometry. It is based on
the principle that CO strongly absorbs infra-red radiation at
certain wavelengths. When IR radiation is passed through a long
cell containing a trace of CO, part of the energy is absorbed by
the gas. At higher CO level more of the IR energy is absorbed.
(ii)Gas chromatography : 10 ppm or lower levels of CO can be
conveniently measured by gas chromatography.
20. Hydrocarbon and photochemical
smog:
Natural source :
Natural sources, particularly trees, emit large
quantities of hydrocarbons in the atmosphere.
Methane is the major naturally occurring
hydrocarbon emitted into the atmosphere. It is
produced in considerable quantities by bacteria in
the anaerobic decomposition of organic matter in
water, sediments and soil.
2{CH20} bacteria CO2 + CH4
Man-made source:
Automobiles are the major sources of hydrocarbon
emitted to the atmosphere.
21. Control:
Hydrocarbons are removed from the atmosphere by several
chemical & photochemical reactions. The end product are CO2,
solid organic particulate matter that settles from the atmosphere
or water- soluble products e.g. acids & aldehydes which are
washed by rain .The majority of the harmful effects of
hydrocarbon pollution are not due to the hydrocarbon
themselves, but the products of photochemical reactions. An
important characteristics of atmosphere which are loaded with
large quantities of automobiles exhausts, trapped by an
inversion layer (stagnant air masses) and at the same time
exposed to intense sunlight, is the formation of photochemical
oxidants in the atmosphere. This gives rise to the phenomenon
of photochemical smog. Photochemical smog is characterized
by brown, hazy fumes which irritate in eyes & lungs, lead to the
cracking of rubber and extensive damage of plant life.
22. Control:
The probable mechanism of smog forming reactions as follows.
a) Reactive hydrocarbon ( those with C=C group ) from auto
exhaust interact with O3 to from a hydrocarbon free radical
RCH2•
b) RCH2• rapidly reacts with O2 to from another free radical
RCH2O2•
c) RCH2O2• reacts with NO to produce NO2 & the free radical
RCH2O•
d) This new free radical next interacts with O2 to yield a stable
aldehyde, RCHO, and hydroperoxyl radical, HO2•
e) HO2• then reactive with another molecule of NO to give NO2 &
HO•
f) HO• is extremely reactive & rapidly reacts with a stable
hydrocarbon RCH3 to yield H2O & regenerate the hydrocarbon
free radical RCH2• , thereby completing cycle.
24. Route of PAN formation
RCHO
HO•
RC• = C acyl radical
O2 peroxyacyl radical
RC = O
OO•
NO2
RC = O
OONO2
peroxyacyl nitrate (PAN)
25. The aldehyde RCHO may initiate another route by
interaction with the HO• Radical, leading to the formation
of an acyl radical RC=O, peroxyacyl radical RCOO2 ( by
reaction with O2) & finally peroxyacyl nitrate PAN ( by
reaction with NO2). PAN is one of the most potent eye
irritants found smog.
Control of hydrocarbon & photochemical pollutants.
O3 & PAN secondary pollutants, so their control ultimately
depends on the control of their primary precursors,
hydrocarbons & nitrogen oxides. The control of NOx has
been described earlier & that of HC in connection with the
control of auto exhaust emissions.
