This document discusses various procedures for sampling air pollutants, including classification of sampling methods, difficulties encountered, instruments used, duration and location of sampling. It describes correct sampling methods such as statistical methods, sample size, continuous vs intermittent sampling. Devices discussed include meters, suction devices, probes, absorbers, adsorbers, condensers and collectors. Factors like sampling period, atmospheric vs source sampling, and choosing representative sampling sites are also summarized.

1. Sampling Procedures
By Vipul
Shankar,MGLI,Ahmedabad

2. Subjects Areas
Introduction
Classification of Sampling methods
Difficulties encountered in Sampling
Instruments for Sampling Waste Gases
and for atmospheric Sampling
Duration of Sampling Period
Location of Sampling Sites

3. Subjects Areas(cont)
Sampling Method
Sampling Suspended Particulates by high
volume sampler
Stack Sampling Techniques
Recent Trends in Sampling of Stack
Effluents

4. Introduction
 Difficulty in collection of representative samples
has to be kept in mind
 Sample collection is a first tool for measurement
of any air pollutant from ambient environment
 Procedure used for measuring gaseous emission
from a stack or a vent depend upon on the nature
of compound and the purpose for making the
measurement
 The composition &,temp of the carrier gas stream
effect the selection of a sampling technique,
analytical method and sampling plan

5. Classification Of Sampling Methods
Sampling of impurities of every nature eg
gas,particulate matter
Sampling under various environmental
condition eg sampling taken from
chimney or in the open air
Sampling methods :intermittent or
continuous( depend upon time factor)

6. Difficulties Encountered in Sampling
Collecting samples of true representative
character
Errors created from methods used for
the collection and separation of various
components of pollution
Difficulty in preventing any change in the
conc of particulate matter in suspension
as a resulting of sampling operations

7. Methods of Correct Sampling
 (1)Statistical Method:It is based on probability
theory.ie It gives the data in percentage
probability that indicate series of data accurate in
within certain limits.
 (2)Size of Samples:Large sample size is required
for accurate analysis
 (3)Changes of sample during and after
sampling:Investigator must try to avoid such
serious sources of error

8. Methods of Correct Sampling(Cont)
 (4)Continuous and intermittent Sampling
:Continuous recording instruments combine the
operation of sampling and analysis.It is much
faster and accurate. And become more
popular.Intermittent sampling can be tried
 (5)Sampling of volatile constitutes: it is better to
carry out sampling with large volume of air to
avoid sources of error
 (6)Sampling of Particulates(A);Sampling should
be carried out in iso -kinetic condition

9. Methods of Correct Sampling(Cont )
(b)gas stream should be sampled as far as
possible in the same direction and same
speed(c) collecting surface should be as
close as possible to the source of stream. To
avoid reducing the efficiency of sampling,
deposits and condensation should not be
allows to form in the walls of sampling
vessel.

10. Methods of Correct Sampling(Cont )
(7)Sampling of waste gas:Gas stream
should be sampled at several points and
maximum number of samples should be
taken to get average value as difficulty are
due to high temp,lack of uniformity in the
composition of gas flow and difference in
speed due to disturbance.

11. Methods of Correct Sampling(Cont )
 (8)Sampling in open air(a)high dilution of the
pollutant dispersed in air(b)Need to collect
large number of samples©difficulty of
sampling under iso kinetic condition
 It is necessary to collect more samples through
continuous recording instruments at various
places to minimize the error of sampling
 Metrological data like wind speed and direction
should be collected to know their effects on
dilution or concentration of pollutants in the
air

12. Basic Consideration of Air Sampling
 Sample collected must be representative in
terms of time and location
 Sample volume should be large enough to
permit accurate analysis
 Sampling rate must be such to provide
maximum efficiency of collection
 Duration of sampling and frequency of
sampling should reflect accurately the
occurrence of fluctuations in pollution levels
 Contamination must not be modified or altered
in the process of collections

13. General Devices for Sampling
 Meters :it is useful for determine the volume of gas
collected.They are fitted with manometers for pressure and
thermometer for temperature measurement of the gas
stream sampled.
 Suction Devices:Vacuum pump driven by electric motor is
commonly used
 Probes:A probe or tube( made of stainless steel,or glass or
quartz which can resist temp and non –corrosive)should
have suitable length and diameter. To ensure iso-kinetic
sampling,the opening of the probe should face the gas
stream to be sampled

14. Devices for Sampling Gases and Vapours
 A gas can be sampled by means of suitable
absorption reagent
 This absorbers are fitted with a porous partition,so
that the air or gas passes through the regent
solution in the form of fine bubblers thus ensuring
intimate contact
 Sampling is carried out at an average rate of about
100-150 liters per hours of gas stream

15. Devices for Sampling Gases and
Vapours(cont)
 Absorbers can be organized in series with two or three
elements containing same solution or two or more different
reagent solutions so as to absorb more pollutants
successfully from the same volume of gas or air sampled
 Typical sampling train comprising an
impinger,trap,manometer,flow meter,valve and pump(See
figure)
 SO2,NOx,NH3,H2S,HCL,HF,HCN etc can be measured as
low as o.1ppm
 This method can be useful for ozone,hydrocarbons,organic
solvents.

17. Adsorbers
 Silica gel,or activated charcoal or suitable reagent
are used as adsorbers in the columns for absorbing
gas or air.This can be extracted from the column
with using different solvents.
 Difficulty is in selecting suitable adsorbing
medium.
 Useful for hydrocarbons and ozone

18. Condensers
 Gas sampled will be cooled in suitable
container,which will condense the volatile
substance present.
 Condensations traps can be arranged in series or
parallel at decreasing temperatures
 Ice,liquid air or liquid nitrogen can be used as
coolants
 Components of gaseous pollutants can be
separated by fractional condensation
 This method is used for sampling of odoriferous
substances

19. Collectors Under Reduced Pressure
Nitric and aldehyde having a high
molecular weight,absorption in aqueous
solution is some time incomplete.In such
cases,it is preferable to use bottle of
known volume for collecting under
pressure reduced to 200mm Hg or less
This method is suitable for oxides of
nitrogen

20. Plastic Container
 Special Polythene bags are used for collecting and
transporting large volume of air.It has advantage
that they can be used for successive analysis of
small fraction of the sample taken
 Polythene is inert for many substances including
SO2 and formaldehyde
 Plastic begs have been used for grab sampling and
sample storage before analysis.

21. Duration of Sampling Period
 Two types of Sampling;(1)Short period or Spot
Sampling(2)Continuous Sampling
 Choice of sampling period depends upon(1)the
nature of compound under study(2)Its stability
to oxidation,light,or other factors(3)
Sensitivity,accuracy and precision of the
analytical method to be used

22. Short or Spot Sampling
 Usefulness:Random checking of pollution at
many points
 Disadvantages(1)this sampling have limited
values because pollution levels fluctuate
widely,depending on meteorological
condition,topographical features,and various
factors associated with sources of pollution.
(2)It does not give adequate data on the nature
and magnitude of an air pollution problem(3)
It may give information about maximum and
minimum and average values over definite time
period if series of data collected

23. Continuous Sampling
Advantages(1)Useful for the
systematic studies with regard to
nature and extent of Air
Pollution(2)Data are useful for
epidemiological study for evaluating
the hazards to man
,animals,vegetations(3)for evaluating
control programme.

24. Sampling for atmospheric air and
near emitting sources
 Generally atmospheric air contains trace
amount of pollutant compare to near emitting
sources
 Required longer times or higher flow rates in
atmospheric air compare to source material
 Very sensitive analytical procedures are
required to determine trace element present in
collected atmospheric air samples

25. Locations of Sampling Sites
Sampling sites/locations must be carefully
selected so as to be representative of the area
under study
Site must be located in a such way so that
collected sample must represent that air is
actually berthed by the exposed populations
groups for the study of health effect.
Concentrations of pollutant varies with
altitude,results obtained on the roofs of the
building may differ from ground level or
breathing level

26. Locations of Sampling Sites(cont)
Necessary numbers of sampling stations
and their locations depends upon(1)
objective of programme(2)size of the study
area(3)proximity of source of
pollution(4)topographical features and
weather condition
This information can be decided after
preliminary survey

27. Locations of Sampling Sites(cont)
Objective of preliminary survey(a)To
gather information on the nature and
magnitude of the emission from principal
source of pollution (b)to review available
climatologically and meteorological
data©To gather data on the
concentrations of pollutants in areas of
severe and slight pollution