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1. " AIR POLLUTION MONITORING"
(Dr. G.D. Agarwal, Director (Technical)
Envirotech Instruments Pvt. Ltd.,
A-271, Okhla Industrial Area Phase-1,
New Delhi)
1. FORWARD:
Awareness to the hazards of air-pollution and interest in preserving the quality of our
air- environment have by now grown to an extent where one does not any more
have to argue for the need for air-pollution control. However, partly due to the
traditional Indian way to basing our decisions on 'mental' analysis rather than
'instrument' analysis and partly because of the bureaucratic style of believing in facts
to emerge from statements of men in position, rather than from scientific
investigations, foe need for well planned and scientific investigations,,-the need for
well planned and scientifically conducted extensive and intensive environmental
monitoring is stiff hof appreciated .fully. Many among the well-educated and even
among the policy makers seem to think that some public speeches, a few well
written articles and TV shows alongwith some legislations, and followed by a few
prosecutions and jail sentences is all that is needed to protect the quality of
environment. It has-to be stressed and restressed the tnonitoring' is the key to any
and all rational steps in an environmental protections programme. Thus monitoring is
essential before any rational decisions on (i) objectives of environmental protection
programme (ii) laying down ambient quality and emission standards (iii) evaluating
current status and need for control measures (iv) selecting performance of control
measures (vii) fixing responsibility and initiating prosecution.
2. MONITORING PLANS:
Monitoring can be broadly classified into 2 groups:
A) Surveillance or Routine Monitoring:
Curried out with the purpose of finding out whether the ambient quality and/or the
emissions are within the prescribed limits. This shall essentially be a regulatory
function. Sometimes such monitoring may also be carried out to just evaluated the
state of environment and changes taking place in environmental quality with time,
with no specific limits or regulatory function in mind.
B) Investigative Monitoring:
Carried out to collect reliable information for deciding on standard, programmes,
control equipment etc.

2. The main difference between the two types is that of the time framework.
Investigative monitoring shall be an intensive effort over a relatively short period to
give the range and/or the critical values (e.g. maximum pollutional loads, minimum
achievable value etc.) for parameters relevant to the objective of the monitoring. The
selection of the monitoring locations, monitoring frequencies, monitoring parameters
and even the instruments and methods to be adopted, in essence the entire
'monitoring plan' shall have to be decided with a thorough understanding of the
objective concerned. Thus if the objective were to examine the validity of a
mathematical model for transport of pollutants from a single point source, it shall be
adequate to monitor a number of points all on the down-wind line at that particular
time: on the other hand if it is to examine the impact of a source on surrounding
environment the monitoring locations should be the critical targets (such as housing
agglomerations, Orchards, tree-groves etc.) in the near-by area, rather than a pre-
set distance in the downwind direction. In case the objective is to examine the
performance of pollution control devices, it shall be necessary to monitor both the
inlet and the outlet of these devices and in case of particulates also examine the size
distribution, and/or chemical composition to give clues to reasons for deviation from
expected performance and suggesting corrective steps. Experience of
ENVIROTECH on monitoring fluoride emissions from SSP fertilizer plants indicates
that while fluorides in gaseous from (HF or SiFu) are very small, almost negligible,
fluorides in mist form may be as high as 100-500 mg/nm3
indicating the need for
mist-eliminators on such streams.
In comparison planning surveillance or routine monitoring is fairly simple. In case it is
in compliance of regulatory requirements (as it almost always is), the matter is
straight-forward-the locations, the frequencies and the parameters have to be as
prescribed by the regulatory authority. In case of any doubts, difficulties or
disagreements go back to the prescribing authority. In case the monitoring is not as
regulatory requirement but is for general surveillance, the plan for the long-term
surveillance should be designed on the basis of an intensive study to determine the
most suitable locations, frequencies and parameters. The plan so evolved should be
periodically evaluated and revised if necessary.
3. CONTINUOUS/AUTOMATIC MONITORING VS DISCRETE SAMPLING:
Partly because of the much less human effort an attention needed by them and
partly because the glamour attached with high-technology and sophisticated devices
one tends to automatically prefer continuous and/or automatic devices for all types
of environment quality/pollution monitoring over methods that require collection of
samples to be analyzed later in a laboratory. The correct approach shall be to
evaluate all alternatives in a thorough scientific manner and choose the one that
shall serve the specific objectives at the optimal over-all costs. Some important
points that shall help a proper choice are mentioned below:
(i) Discrete sampling methods shall never be able to provide information on short-term
peak or worst concentrations and shall not even be suitable to indicate the periods

3. when concentrations were higher than a pre-set norm/standard. Thus for
surveillance monitoring to fix responsibility and seek corrective/compenciate action,
continuous recording type of instruments shall be most desirable. When control
equipment are installed the only alternative shall be an extremely high frequency of
discrete sampling, which may be impractical and a via-media shall be frequent
observations with a simple semi-automatic method. Monitoring of stack emissions to
ensure that these were within prescribed norms is one such example,
(ii) Automatic/Continuous Monitoring Devices are highly parameter specific. The
principles of operation of automatic instruments monitoring some common air-
pollutants are as follows:
Suspended Particulates
Carbon-mono-oxide
Hydrocarbons
Sulphur-di-oxide
Nitrogen-Oxides
Nephelometry
NDIR
Chromatography
Pulsed Flourescene
Chemiluminiscence
One can almost say that for each pollutional parameter, one shall need a separate,
costly and sophisticated instrument. This may not pose much of a problem in case of
stack monitorings where normally only one (or in rare cases two) pollutional
parameter shall be of interest and the locations where the monitoring is to be carried
out shall be only a few and fixed. Thus for surveillance of stationary sources,
continuous instruments shall be ideal, but for surveillance of ambient air-quality
where one may be interested in monitoring several parameters at a number of
points, continuous instruments shall be impractically costly.
(iii) Continuous/automatic instruments mounted on a Van shall not be much valuable for
serveillance of ambient air-quality in an area, since that Van can be at only one point
at a time and one can never ensure that the van would be at a particular location
during the critical period (which depending on meteorological factors, is highly
indefinite). Thus it appears that for ambient air quality surveillance nothing can beat
a well-planned network of High Volume Air Sampler stations.
(iv) Besides the high first cost (and often foreign exchange) involved
continuous/automatic monitoring systems also require sophisticated calibration,
probe cleaning and maintenance and repair facilities and often pose problems of
availability of spares.
(v) Continuous/Automatic Instrument may not be suitable for INVESTIGATIVE
monitorings where the exact monitoring conditions the parameters to be monitored,
the concentration etc. may not be known in advance and where one may wish to
monitor a number of parameters at a number of locations over relatively short
durations.
(vi) Discrete sampling methods shall require a much larger human effort and a number
of well-trained and reliable Technicians/Analysts. Often this becomes the most

4. serious limitations and drawback of these methods. Well one can go on and on. Like
most engineering decisions there is no generalization or simple choice and one has
to make a considered decision for his own objectives and circumstances.
4. DISCRETE (MANUAL) MONITORING SYSTEM:
As discussed above, the practical alternative for most monitoring objectives and
situations in India, is going to be using manual discrete sampling techniques which
are versatile enough to handle several parameters in vastly different concentration
ranges and monitoring conditions and also cheap enough to own and operate a
number of sets to monitor several locations simultaneously besides almost the entire
experience of ENVIROTECH and of this author has been on such instruments. As
such this paper shall deal with only manual discrete sampling methods in some
details.
AMBIENT (AIR- QUALITY) MONITORING:
For monitoring ambient air quality the High Volume Air Sampler is used. Figure-2
given a schematic diagram for ENVIROTECH High Volume Sampler. This
instrument consists of a heavy duty Blower which is used to such atmospheric air
through a filter paper. The volumetric flow rate of air drawn through the filter is
measured (by an orifice meter in case of Envirotech HVS) and the filter paper is
weighed before and after sampling to determine the amount of dust deposited on it.
The weight of suspended solids per unit volume of air can be calculated from these.
The deposited dust may also be subjected to chemical analysis to determine the
concentration of critical pollutants such as pesticides or heavy metals. Special high-
purity filter papers are also available for getting reliable results for trace elements.
Envirotech's APM 410 High Volume Air Sampler is an improved version of an earlier
model APM 400 and with more than 150 units in use, it has been widely accepted as
a standard instrument for measuring ambient air quality. Some of the unique
features of the APM 410 High Volume Sampler are mentioned below:-
(i) Unique flow measurement system using an orifice plate incorporated in the
Filter Holder casting ensure an exact measurement of the air passing through
the filter with minimum possibility of leakages or extraneous air flows affecting
the flow readings. The system has been calibrated at l.l.T. Delhi.
(ii) Special Cabinet design allows change of brushes without requiring the Blower
Assembly to be dismantalled. Brush replacement on the APM 410 could take
only a few minutes.
(iii) Special Hinge design allows easy separation of gable roof from the main
housing making the system more rugged and compact for transportation.
(iv) The system has been simplified by making the main unit of APM 410
essentially a particulate sampling system which alone needs the high flow-
rate. The gaseous sampling, which requires only a few LPM of air flow, is
performed through an attachable subsidiary unit APM 411. Keeping the

5. gaseous sampling module outside the main unit of APM 410 has the
advantages of: -
a) Easy manipulation on Impingers.
b) No heating up of absorbing solutions due to heat from the Blower.
o) Possibility of using ice or cold water bath around Impinger for complete
absorption of sparsely soluble gases,
d) Taking the Impinger tray directly to the Laboratory for safer transit of glass
parts.
The APM 410 system can sample particles down to 0.6 micron diameter and would
yield measurable samples in areas with a problem faced by consultants, regulatory
agencies and other users of the APM 410 High Volume Sampler who need to shift
the instrument from place to place is that the system tends to become rather bulky
and inconvenient for transportation. This led Envirotech to develop the APM 415
dwarf version of the standard HVS. The hardware used in the APM 415 sampler is
identical to the popular APM 410 but it is housed in a compact enclosure making the
system more portable.
RESPIRABLE DUST IS A BATTER INDEX THAN TSP.
High Volume Air Samplers like the APM 410 or APM 415 have been in use all over
the world for monitoring the Total Suspended Particulates (TSP) in ambient air. In
India over the past decade they have formed the backbone of the effort to monitor
ambient air quality. The volume of data accumulated over the past decade, indicates
that in the northern Indian planes TSP values are much higher than those
considered permissible, even in the absence of major anthropogenic causes. The
high TSP background is argued to be caused by the winds blowing from the western
deserts. Such dust however almost entirely consists of coarse particulates which
get quickly eliminated in the respiratory system and are hence not very harmful. The
same applies to most dusts caused by mining and agricultural activities. Moreover,
emissions for industries using even rudimentary control systems are likely to contain
predominantly finer particles. Similarly particulates emitted by vehicles are fine. The
coarser dust collected as part of the TSP would result in nuisance, soiling of
surfaces and perhaps some visibility problems but is unlikely to contribute
significantly to respiratory and other health effects associated with air pollution.
Health effects are caused primarily by Respirable particulates in the size range of
0.5 to 10 microns. As such when the main objective in Ambient Air Quality
monitoring is to protect the local community, measurement of TSP alone may be
often misleading.
Due to the above factors, air-monitoring programmes all over the world are
increasingly adopting the use of Respirable Dust Samplers in preference to the
traditional TSP samplers.

6. THE APM 451 RESPIRABLE DUST SAMPLER
In keeping with Envirotech's tradition of pioneering the development of indigenous
air monitoring instruments we have now introduced, for the first time in the country,
as Respirable Dust High Volume. The new system designated Envirotech APM 451
draws upon the field experience gained through more than 1000 installations of our
popular APM 410/415 High Volume Sampler and is based upon knowhow developed
at NEERI Nagpur the CSIR Laboratory and premier institution for environmental
research in India. The APM 451 sampler first separates the coarser particles (larger
than 10 mcirons) from the air stream before filtering it on the 0.5 micron pore-size
filter allowing a measurement of both the TSP and the Respirable fraction of the
suspended particulate matter (SPM).
Figure 45010-00 shows a schematic diagram of the APM 541 Respirable Dust
Sampler. Ambient air laden with suspended particulates enters the system through
the inlet pipe (1). As the air passes through the cyclone, coarse, non-respirable dust
is separated fro the air stream by centrifugal forces acting on the solid particles.
These separated particulates fall through the cyclone's conical hopper (2) and
collect in the sampling bottle placed at its bottom. The fine dust forming the
Respirable fraction of the Total Suspended Particulates (TSP) passes through the
cyclone and is carried by the air stream to the filter paper (3) clamped between the
top cover (4) and filter adaptor assembly (5) The Respirable dust (RSP) is retained
by the filter and the carrier air exhausted from the system through the blower.
RESPIRABLE SIZE CUT-OFF OF THE APM 451 SAMPLER
The Respirable Dust Standard recommended by the central pollution control board
(Govt, of India) recommends a 10-micron cut-off size for Respirable dust
measurements. However, it should be remembered that such size limits can be laid
only for particulates with uniform specific gravity and shape and usually refer to a
normalized situation of spherical particles with a specific gravity of one. Real life air
on the other hand contains a complex mixture of a variety of particles of different
materials having various densities and random shapes. Moreover the respiratory
tract like any other impaction/centrifugal separation system retains particulates with
varying densities at different levels. This implies that even relatively fine dust
particles of materials having a high specific gravity are likely to be retained in the
upper respiratory tract while larger particulates of lighter materials are likely to pass
deeper into the respiratory system.
The cyclone of the APM 451 Respirable Dust Sampler has been designed to provide
a cut-off at 10 microns for particulates commonly found in the urban environment. As
a centrifugal separation system this cut-off is bound to vary with the nature and
density of dust particles. The system has been extensively tested by NEERI for a
variety of dusts like Coal dust, Limestone, Cement, Fly-ash etc. Table (1) provides a
summary of the results of these tests.

7. NATURE OF DUST AND PARTICLE COLLECTIONS SIZE
S. No. Nature of Dust Specific Gravity Collection
Size
1. Coal 1 . 4 - 1 . 8 1 0 - 1 2
2. Road-Side Dust 2 . 0 - 2 . 2 8 - 1 0
3. Fly Ash 2 . 3 - 2 . 4 7 . 5 - 9
4. General Mining 2 . 5 - 2 . 7 7 - 9
(Limestone/Sandstone)
5 . Cement 3 - 3 . 3 6 - 8
6. Manganese Ore 3 . 5 - 4 5 - 7
Table 1
SHOP - FLOOR AIR QUALITY MONITORING
Air quality in the work environment is generally worse than the quality of community air.
Tolerance Limit Values (TLV) have been prescribed for almost 200 chemicals and
materials used on the shop-floor. However, to asses exposure levels of workers, for a
comparison against TLV levels, one needs to know the total dose received by a person
over a full work shift (usually 8 hours). In the course of their normal duties most workers
keep moving about on the shop-floor and are likely to be exposed to varying
concentrations of a given pollutant. Ideally the worker-exposure monitoring instrument
must be compact enough to be carried on the body of the person without causing undue
discomfort or hinderance to his activity. This also implies that such equipment should be
battery operated, if it requires any power. As such instrument like the HVS which are
suitable for monitoring community air are not usable for shop-floor monitoring simply
because they are not sufficiently portable.
Envirotech's APM 800 Personal Sampler is a portable instrument suitable for monitoring
worker exposure to different kinds of dusts, fumes or fibers on the shop-floor. Weighing
only about one kilogram the instrument can be conveniently belt worn. The APM 800
sampler is powered by rechargeable Nic-Cad batteries that can keep the instrument
operative for a full shift of 8 hours. A charger provided with each sampler is able to
recharge the batteries over-night. The APM 800 Personal Sampler provides a flow of
upto 2 LPM through a 25mm. diameter glass fibre or membrane filter. At the end of the

8. sampling the filter disk must be analyzed gravimetrically or by suitable chemical
methods to determine the levels of the aerosol of interest.
The Personal Sampler is essentially an instrument to monitor aerosols that can be
sampled by filteration. It is therefore quite effective for sampling pollutants like Silica
dust, Asbestos fibres, metal fumes etc. but is not usable for sampling gaseous
pollutants. Envirotech's APM 820 Handy Sampler is a portable, battery operated
instrument designed for monitoring gaseous toxicants in the work environment. The
instrument bubbles are through a set of midget impingers which contain suitable
reagents to absorb gases of interest. The instrument can maintain a flow of upto 1 LPM
through the impingers for a full shift of 8 hours. After sampling, the reagents must be
analyzed chemically to obtain the concentration of the pollutant. As in the case of the
APM 411 gaseous sampler the impingers of the APM 820 Handy Sampler are housed
in an ice-tray to reduce evaporative loss of absorbing solutions and the help
absorption of sparsely soluble gases.
Due to the presence of the ice-tray and wet chemicals the APM 820 system cannot to
worn on the body of the worker but is portable enough to be placed close to the actual
work Envirotech or even a fugitive emission source.
CONCLUSIONS
The most critical part of collection of data on environmental and particularly air-pollution
is a clear understanding of the objectives for which data is to be acquired and of the
environmental conditions prevailing in the area to be monitored. In the context of filed
conditions prevailing in most of the countries of the Indian subcontinent continuous air
monitoring instruments will prove to be prohibitive in cost and difficult to maintain. The
sampling type instrument which are now being locally manufactured. A well through out
and detailed plan for monitoring must be formulated and monitoring methods,
instruments and other hardware selected to suit the objectives and the monitoring plan
and last, but not the least, committed, reliable and well-trained monitoring personnel will
be needed to collect the field data.