The document discusses air pollution sampling and measurement techniques, focusing on stack sampling, particulate and gaseous sampling methods. It outlines the importance of sampling conditions, types of pollutants, and specific analytical methods for measuring common air pollutants like SO2, NOx, CO, and hydrocarbons. Different techniques and instruments for both manual and continuous measurement of these pollutants are detailed, emphasizing their principles and detection capabilities.

1. AIR POLLUTION SAMPLING
AND MEASUREMENT
Presented by:
S. Sudheer (A21126502032)
B. Gnana Sai (A21126502004)
K. Lokesh (A21126502029)

2. STACK SAMPLING
• The major problem in stack
sampling is of obtaining a
representative sample.
• The important factors are:
• 1) Selection of Sampling site
• 2) Number of sampling points
required
• The flow in stack should be of
turbulent flow
• A circular opening of with
various transverse points at
different radii are located for
non turbulent flows

3. • STACK SAMPLING
Sampling system
Particulate
sampling
Gaseous sampling

4. SAMPLING SYSTEM
• Stack sampling is carried out by diverting
part of gas stream through a sampling
train.
• Sampling train consists of various parts
as shown in figure.
• A nozzle placed in the gas stream, a
sampling probe through which sample is
drawn, collector, flow measuring device
and a prime mover such as vaccum
pump.
• The nozzle is generally sharp edged and
made of stainless steel with glass and
Teflon.
• This type of analysis is mainly used for
collecting gases and particulate matter at
high temperatures

5. PARTICULATE SAMPLING
• The common technique employed for sampling particulate gas stream is called
isokinetic technique.
• In the method a sample is drawn into the probe such that the conditions at the tip of
the probe are the same as those in free gas stream.
• At greater velocities errors are small and 20% of errors are acceptable.
• If a gas velocity (up), less than the free stream velocity (uꚙ)(Sub-isokinetic), is
maintained inside the probe,the static pressure at the tip of the probe is greater than
the free stream static pressure at the same cross section.
• So finer particles approaching the probe tip are carried away with the gas
streamlines and larger particles (3 µm or greater) in this portion of the gas travels in
straight-line trajectories due to their higher inertia and enter the probe tip and
continue into the probe. In this case the particle- capture efficiency of the probe will
be less than one and the sample will indicate high concentration of coarse particles.

6. • On the other hand if the up > uꚙ (Super-isokinetic), the static pressure at
the tip of the probe is less than free stream pressure, and too much gas
will be sampled in proportion to the probe area.
• So the capture efficiency will be greater than one and the sample will
contain a large amount of finer particles.
• Only when the sample is iskinetic, the capture efficiency will be one.

7. GASEOUS SAMPLING
• Gaseous sampling from stack is similar to the particulate matter sampling, but it
is not necessary to sample at isokinetic conditions.
• The sample can be withdrawn at a constant rate independent of flow rate in the
stack.
Precautions taken for sampling:
• Particulate matter must be filtered upstream of the collection system to
prevent blocking and reaction with gaseous on cooling.
• Sampling is heated so as to avoid water from condensation.
• Tube should be made of sampling materials(stainless steel)
• Suction through the nozzle draws a known volume of gas from the stack into
collection devices, which removes the constituents gas of interest and is sent
for analysis.

8. GASEOUS SAMPLING

9. ANALYSIS OF AIR POLLUTANTS
• Air quality measurement is generally done by continuous automatic
analyzers.
• But convectional laboratory analysis is being carried out for spot checking.
• It is done by 2 ways
 Chemical(by chemical reactions):
In chemical methods the pollutant being measured undergoes
chemical transformations and the product is then with appropriate
analytical techniques.
 Physical principles:
In the physical methods of measurement, a physical property of the
pollutant is utilized-such as the ability of the gas to absorb infrared
radiation. The mount of radiation is detected.

10. TYPES OF GASEOUS POLLUTANTS
Sulphur
dioxide
Nitrogen
oxides
Carbon
monoxid
e
Oxidants
and
ozone
Hydrocarbo
ns
pollutants

11. SULPHUR DIOXIDE(SO2)
• The most common manual methods for measuring atmospheric SO2 are based on
colourimetry, iodimetry, or turbidimetry.
• There are several automatic instruments for monitoring sulphur dioxide, the most
common of these are based upon conductometric, colourimetric, and flame
photometric principles.
• In the conductometric technique, the sampled air containing SO2 is passed through a
dilute solution of hydrogen peroxide in dilute sulphuric acid. SO2 is oxidised to H2SO4
thereby increasing the electrical conductivity of the solution. The increase in
conductivity, which is measured, is proportional to the concentration of SO2 in the
sample.
• With this technique, as low SO2 concentrations as 0.01 ppm can be detected.
• However, the conductometric analyzers suffer from a wide variety of interferences.
Acidic gases such as hydrogen chloride give positive errors, while ammonia
interferes negatively.
• One of the best method used for autometric monitoring of SO2 is coulometry.

12. SULPHUR DIOXIDE(SO2)
• In the bromocolourimetric
analyser, air containing SO2 is
drawn continuously through an
electrolytic cell which contains
acidified bromine solution and
two sets of electrodes.
• SO2 in the air sample is oxidized
by bromine, causing a reduction
in bromine concentration, this
changes in oxidation-reduction
potential of the reagent.
• A voltage is developed and is
compared to reference voltage,
and is calibrated to SO2
concentration.

13. NITROGEN OXIDE
• Colourimetric method (Griess-Saltzman)– reaction with sulphanilic acid to
form diazonium salts, this is coupled with ethylenediamine dihydrochloride
to get a pink coloured dye complex, the amount absorbed is measured in a
spectrophotometer.
• It is also used for analysis of NO, but firt it s oxidized to NO2 .
• This method is not suitable for the collection of 24-hour samples, because
the dye complex is fairly unstable.
Continous analyzer:
• Several continuous analyzers are available for the measurement of NO and
NO2 based on colourimetric, nondispersive infrared and chemiluminescent.
• Among these chemiluminescent is accurate and cheap.
• This has wide range of 0.004ppm to more than 1000ppm.

14. • In the chemiluminescent technique,
NO reacts rapidly with ozone to form
NO2 and oxygen.
• About 7% of the NO2 produced is in
excited state and reverts to the
ground state with the emission of
radiant energy.
• This emitted radiation is received by
a photomultiplier tube whose output
is amplified and fed to a recorder.
• The intensity of radiation is
proportional to amount of nitric
oxide.
• This reaction is specified for NO only
if any
• NO2 is present it dissociates into NO
before entering.

15. CARBON MONOXIDE
• Nondispersive infrared spectrophotometry(NDIR)
• It is based on continuous absorption of infrared
radiations by CO molecules
• It consists of two cells one is reference cell filled
with non-absorbing gas(nitrogen) and another is
sample cell continuously sent with carbon
monoxide.
• The detector consists of two compartments
separate by a thin metal diaphragm and filled with
CO.
• Since more radiation passes to reference cell side
compartment, the CO therein expands more
compared to other causing pressure difference
across the diaphragm, in turn causes it to pulse
back and forth.
• The magnitude of the diaphragm vibration is a
function of the absorbing CO concentration in the
sample cell.

16. OXIDANTS AND OZONE
• The standard method for the net determination of total oxidants is the neutral
phosphate-buffered KI colourimetric technique of Saltzman.
• In this method, a sample of air at a known flow rate is passed through a
solution of 1% neutral buffered potassium iodide and the liberated iodine is
measured colourimetrically at 352 nm.
2KI+O3+H2O→ O2+2KOH+I2
• Since one mole of ozone releases one mole of iodine, the I₂ concentration
measured is directly related to the total oxidant concentrations in the rage of
0.01 to 10 ppm (as ozone).
• Automatic monitoring of ozone, is based on the chemiluminescence of the
ozone-ethylene reaction .
• In this method, ozone is exposed to a large excess of ethylene in a reaction
vessel. The chemiluminescent light released during the reaction is then
measured using a photomultiplier tube, and related to the ozone
concentration.
• There are no interferences from other atmospheric components and the
device is capable of measuring concentrations less than 0.001 ppm. However,

17. HYDROCARBONS
• The total hydrocarbon content is generally reported on a non-methane basis.
• It is most commonly determined by flame ionisation technique (FID).
• In this method the sample gas is injected into the flame created by burning
hydrogen in either air or oxygen.
• When hydrogen alone burns, relatively few ions are generated but when
hydrocarbons are present, the flame produces a complex ionisation in which a
large number of ions are present.
• An electric field is set up in the vicinity of the flame by making the burner jet
positive with respect to a wire loop.
• The electric field induces ion migration in such a manner that a small ionisation
current is established between the electrodes, and this current is proportional
to the concentrations of ions in the flame.
• The data are usually expressed in units of the gas used in calibration, e.g. "ppm
of C as methane".
• The FID is uniquely suitable for hydrocarbon analysis because it does not
respond to other gases such as CO, CO2, H2O, SO2 and nitrogen oxides. The
recording range of these analysers varies from approximately 2 to 3000 ppm
hydrocarbons as methane. Ordinarily, the 0 to 20 ppm range is most useful for
ambient-air analysis.

18. • The non-methane hydrocarbon analysis can be accomplished by a differential
measurement. The sample is passed through a charcoal column which is
saturated with methane but is still capable of retaining other hydrocarbons. This
column can then be used with FID as an analyser for the analysis of methane
only. By differences between the results obtained, the non-methane
hydrocarbons can be assessed.

19. THANK YOU