The document discusses various environmental pollution monitoring devices. It describes infrared analyzers and gas chromatography techniques to measure carbon monoxide levels. For nitrogen oxide measurement, it covers colorimetry, chemiluminescence, laser techniques, and opto-acoustic spectroscopy. Sulfur dioxide analysis methods such as colorimetry and conductimetry are also outlined. Finally, it discusses flame ionization detectors and gas chromatography for estimating hydrocarbon levels.

1. ENVIRONMENTAL POLLUTION
MONITORING DEVICES
BY
N.P.DHARANI
ASSISTANT PROFESSOR

2. CONTENTS
• INTRODUCTION
• CO MONITOR
• NOX ANALYZER
• SULPHUR DIOXIDE MEASUREMENT
• HYDRO CARBONS ESTIMATION

3. INTRODUCTION
• Used to analyze the amount different gases present
in a mixture.
• 02,CO,CO2,NO2 can be analyzed from air.
• Gas analyzers used in industries are:
• In power plants oxygen and CO can be measured in
flue gas.
• In ammonia synthesis, presence of CO,
CO2,H2S,Water vapour will poison the synthesis
catalyst. So, these are analyzed and prevention are
taken to avoid the damage.

4. Instrumental Techniques and
measurements range
FROM R.S.KHANDPUR

5. CO MONITOR
• Non dispersive infrared analyzer
• Gas Chromatography

6. Non dispersive infrared analyzer
• It depends on characteristic energy of
absorption of CO molecule at wavelength of
4.6µ.
• It also absorbs other gases like CO2, H2O,SO2 and
NO2.
• Infrared radiation is passed through a sample
cell containing CO and a reference cell
containing a fixed quantity of nitrogen , CO and
water vapour.

7. Infrared Gas Analyzer
Construction:
• Two identical IR sources
emits beam of radiation
that are pulsed by a motor
driven chopper.
• The source of IR radiation I
shot wire spiral.
• For industrial analyzers,
the chopping frequency is
2-10Hz whereas for
medical application, it is 2-
50Hz.
FROM R.S.KHANDPUR

8. Block diagram of measuring system for
carbon monoxide
FROM R.S.KHANDPUR

9. • Reference cell contains a fixed quantity of the gases
whereas air sample is made to flow at about 150ml/min
though the sample cell.
• CO analyzer with IR absorption would give greater
sensitivity with larger cell path length.
• Instruments with 1mm cell length would measure from 1
to 50 ppm.
• Some latest instruments are capable of measuring 1 to
25 ppm even with cell path length of 10 cm.
• Response time of such instruments varies from 1 to 5
mins.
• Calibration is done by passing a known ppm
concentration of CO in nitrogen in the sample cell.
• The zero is set by using pure nitrogen as a sample.

10. Advantages
• Effect of flow rate is small.
• Response speed is high.
• High sensitivity measurements are possible.
• Effect of interfering components is small.
• Equipments are easy to maintain.

11. Gas Chromatography
• Gas chromatography (GC) is a common type of chromatography used
in analytical chemistry for separating and analyzing compounds that
can be vaporized without decomposition
• Air sample is passed though a stripper column, the heavy
hydrocarbons are retained, CO and methane are passed into
chromatographic column and then to catalytic reducing chamber.
• The methane pass through the reducing chamber unaffected, while CO
is reduced to methane.
• By using hydrogen flame ionization detector, both methane peaks can
be detected.
• The first peak is due to methane and second peak is due to CO.
• Accuracy is ±2%
• Peak heights of CO and methane give sensitivity of about 50ppb.

12. NOX ANALYZER
• COLORIMETRY
• CHEMILUMINESCENCE
• USE OF CO LASER
• LASER OPTO-ACOUSTIC SPETROSCOPY

13. COLORIMETRY
• This method can be used for the determination of nitrogen dioxide by
using Saltzman method.
• This method is based on a reaction in which a pink colored dye
complex is formed when air containing NO2 is passed in an absorbing
solution consisting of sulphanilic acid and diamine dissolved in the
acetic medium.
• Sensitivity is in ppm range.
• Nitric oxide may be determined by passing the sample through an acid
permanganate bubbler which oxidizes nitric oxide to nitrogen dioxide.
• Used for monitoring in stack sewages in concentration range of 5 ppm
to several thousand ppm, consists in passing sample into an evacuated
flask containing a solution of H2O2 in sulphuric acid.
• The oxides of nitrogen are converted into nitric acid and nitrate ions
react with phenoldisupluric acid to produce a yellow color, which is
measured calorimetrically.

14. CHEMILUMINESCENCE
• The phenomenon of emission of radiation from
a chemically excited species is known as
chemiluminescence. It results due to the
formation of new chemical bonds .The atoms in
the excited states posses higher energy levels
than the ground state & while returning to the
ground state they emit radiations.
• This phenomenon is useful for measurement of
air pollutants, particularly NO, NO2

15. CONT.,
• The following reaction uses for the measurement of
chemiluminescence emission.
• Since NO2 reacts slowly with ozone and the reaction
which produces NO3 is not done by chemiluminescence,
so it is necessary to reduce NO2 to NO before admission
into reactor.
NO2 NO +1/2 O2
• Light emission is measured with photmultiplier with high
gain and low dark current can have low levels of
radiation can be measured.
• The response of instruments based on this method is
linear from 1ppm to 1000ppm of NO.
• Used extremely in automative exhaust gases.

16. MEASUREMENT OF NITROGEN OXIDE
USING CO LASERS
FROM R.S.KHANDPUR

17. • This method detects nitric oxide in 0.25ppm.
• The apparatus consists of a CO laser, which emits
radiation that is absorbed by NO in the mixture, the
amount of absorption is proportional to the
concentration of NO present.
• The wavelength match between laser and NO is made
exact and hence the absorption is enhanced by placing
NO in a magnetic field.
• The CO laser used is a dc excited continuous working
laser, which operates at a single wavelength of 5.307µm.
• A diffraction grating is used at one end of the cavity as a
line selector.
• The laser yields 5-30mW of single line power.
• Absorption cell is made of pyrex (low thermal expansion
borosilicate glass) of diameter 15mm and 90cm length.

18. • Pressure applied is 10^-6- 10^-5 torr.
• To produce modulating audio frequency magnetic field
along the axis of the cell, insulated wire is closely wound
around the outside of the cell over about half its length.
• The coil is excited with a current of 1A in the frequency
range of 5-150KHz.
• This produces a varying magnetic field of about 50Guass P-
P intensity.
• The DC magnetic field is produced by a solenoid which
produce a field upto 2.5KGauss.
• The detector is a liquid nitrogen cooled Ge-Au element.
• The signal is amplied in a lock in amplifier(extracts a signal
with a known carrier wave from an extremely noise
environment) before given to recorder.
• The signal amplitude varies linearly with the concentration
of NO in the sample.

19. LASER OPTO-ACOUSTIC SPETROSCOPY
• Opto acoustic detectors combined with thermal IR sources has
been widely used in gas detection.
• This technique is used to measure trace amounts of nitrogen oxides
in the stratosphere.
• Opto acoustic detector involves the absorption of an AM beam of IR
by a gas which results in the generation of sound.
• The energy absorbed by the gas molecules from IR beam excites the
molecules to the rotational-vibrational energy levels above the
ground state.
• The main path for the delay of these excited states is collisional de-
excitation which results in the transfer of absorbed energy into heat
and raises the gas temperature.
• The temperature rise causes a corresponding pressure rise in the
gas.

20. Block Diagram of laser opto acoustic
detector for nitric oxides
FROM R.S.KHANDPUR

21. • When the beam intensity is modulated, the gas
temperature and pressure changes accordingly.
• Thus periodic pressure vibrations in the ags result in the
generation of sound.
• The arrangement uses CO2 laser, tuned by rotating a
diffraction grating at ine end of the laser cavity.
• It is tunable to 64 different emission lines in the range
from 927 to 1085cm-1
• The laser beam is focused at chopping wheel and then
focused into the detector.
• The chopping frequency is selected to optimize the SNR.
• The microphone is available and acoustic signal is
amplified in a preamplifier and displayed.
• The detector is highly sensitive and sample amount of
20pg may be detected.

22. SULPHUR DIOXIDE MEASUREMENT
• Colorimetry
• Conductivitimetry
• Gas chromatography
• Coulometry
• Flame photometric detector
• UV fluorescence method

23. Colorimetry
• A known volume of air is passed through an aqueous
solution,which contains reagents that absorb so2 and
produce a colored substance.
• The amount of colored substance is proportional to so2.
• The air to be analysed is passed through an aqueous
solution of 0.1M sodium tetracholromercurate.
• The so2 reacts with mercuric salt to form a
sulphatomercuric compound.
• The solution is further treated with acid bleached para-
rasoniline and formaldehyde, which forms a red purple
colour.
• The amount of color is determined photometrically.

24. • So2 can also be determined by means of
decolorisation of an aqueous starch iodine
solution which normally has deep blue color.
• When so2 is passed through the solution
containing starch iodine solution,the iodine
reduced by sulphur dioxide which in turn
results in decrease of intensity of starch iodine
color.

25. Conductivitimetry
• This technique is based
on measuring the change
in conductivity of a
solution, when a sample
of air containing so2 is
bubbled through it.
• C- cell
• P-perspex cap
• J-jet
• E-electrodes
FROM R.S.KHANDPUR

26. coulometry
• The ability of sulphur dioxide to reduce iodine can be
employed to monitor so2 by using iodine coulometry in an
aqueous solution.
• The mass of iodine reacted per unit time during any given
interval of time would indicate concentration of so2 in air.
• The coulometric arrangement requires two electrodes
made of platinum which acts as anode and cathode.
• These electrodes maintain a trace of iodine in equilibrium
with potassium bromide to maintain conductance.
• The shift in anode-cathode potential is sensed by a third
reference electrode, when so2 from sample air is bubbled
through the solution in a detector cell.

27. Flame photometric detector
• In Flame photometers, sample air is
introduced into hydrogen rich air flame by
using a narrow band interference filter shields
the PMT detectors, but 394nm emission
energy of flame excited sulphur atoms.

28. UV fluorescence method
• This method is based on the principle that so2
molecules absorb UV light and became excited
at a particular wavelength.
• These molecules then decay to a lower energy
sate emitting UV light at a different
wavelength.
• The intensity of fluorescence is proportional
to the so2 concentration.

29. Block diagram of fluorescence so2
analyser

30. Hydrocarbons estimation
• Flame ionization detector
• Gas chromatography

31. Flame ionization detector
• Organic compounds easily pyrolyse when
introduced into an air-hydrogen flame.
• The pyrolysis produces ions that can be
collected by having a cylindrical grid
surrounding the flame.
• The detector response would be in proportion
to the number of carbon atoms in the chain.

32. Schematic diagram of FID
FROM R.S.KHANDPUR

33. Working principle
• The sample gas containing hydrocarbons controlled at
a constant flow rate is mixed with hydrogen for fuel.
• The mixed gas is burned at the end of a very fine
nozzle.
• Two electrodes are placed on either side of the flame
and an appropriate electric field is applied to them.
• Ionic current will flow between the collector electrode
and the other electrodes.
• The current is then amplified and displayed on a meter.

34. Gas chromatography
• Gas chromatography has been applied for the
detection and measurement of hydrocarbons,
CO,CO2 in air.
• They are generally detected by FID since they
are not sensitive to CO and CO2.
• These are first converted into methane by
hydrogenation and then measured.