3. PRINCIPLE OF OPERATION
• High Volume Sampler is a basic instrument
used primarily for measuring concentration of
suspended particulate matter in atmospheric
air. By definition, suspended particulates are
too small in size to have an appreciable falling
velocity and are likely to remain in the
atmosphere for significant periods of time.
These particulates usually range from 1
micron to approximately 100 microns in size.
4. • It may be caused by a variety of processes
such as incomplete combustion of solid,
liquid, or gaseous fuels, wastes from
metallurgical, chemical and refining
operations, iceneration, etc.
• Moreover, natural sources also contribute
suspended materials like spores, salt water
spray and pollens.
5. • High Volume Sampling is an internationally
accepted standard technique for monitoring
the concentration of suspended particulates.
In these systems a large volume (1500 cubic
meters) of atmospheric air is passed through a
suitable filter medium over a period of upto
24 hours. They will thus yield measurable dust
samples in areas with dust levels as low as one
microgram per cubic meter of air. However,
where dust concentrations are high, shorter
sampling times may suffice.
6. Measurement of Particulate
Concentrations
• The mass concentration of suspended
particulates in ambient air, expressed in
micrograms per cubic meter, is calculated by
measuring the mass of collected particulates
and the volume of air sampled.
• In APM 430, the flow rate of air passing
through the filter is monitored by measuring
the pressure drop across an Orifice Plate
placed between the filter holder and the
blower.
7. • The scale of the manometer used to measure
the pressure drop is calibrated in air flow units
of cubic meters per minute. A Time Totalizer
records the time in minutes/hours for which
the system has sampled air. Hence the volume
of air sampled is known.
• The mass of particulates collected is measured
gravimetrically, using a balance capable of
reliable measurement to the nearest
milligram.
8. • One must remember, however, that
particulate matter which is oily, such as wood
smoke or photochemical smog, may block the
filter and cause a rapid decrease in air flow at
a non-uniform rate. Even fog or high humidity
can severely reduce the air flow through the
filter since even though glass fiber filters are
insensitive to changes in relative humidity, the
collected particulates may be hygroscopic.
9. • Hence, it is recommended that filter mediums
must be carefully conditioned, both before
and after sampling, prior to the measurement
of their weight.
10. Measurement of Particulate
Concentrations
• The mass concentration of suspended
particulates in ambient air, expressed in
micrograms per cubic meter, is calculated by
measuring the mass of collected particulates
and the volume of air sampled.
• The flow rate of air passing through the filter
is monitored by measuring the pressure drop
across an Orifice Plate placed between the
filter holder and the blower.
11. • The scale of the manometer used to measure
the pressure drop is calibrated in air flow units
of cubic meters per minute. A Time Totalizer
records the time in minutes/hours for which
the system has sampled air. Hence the volume
of air sampled is known.
• The mass of particulates collected is measured
gravimetrically, using a balance capable of
reliable measurement to the nearest
milligram.
12. • One must remember, however, that particualte
matter which is oily, such as wood smoke or
photochemical smog, may block the filter and
cause a rapid decrease in air flow at a
nonuniform rate. Even fog or high humidity can
severely reduce the air flow through the filter
since even though glass fibre filters are
insensitive to changes in relative humidity, the
collected particulates may be hygroscopic.
Hence, it is recommended that filter mediums
must be carefully conditioned, both before and
after sampling, prior to the measurement of
their weight.
13. Measurement of Gaseous Pollutants
• The APM 430 Sampler is designed to monitor
only the concentration of suspended
particulates in atmospheric air, and the APM
411 gaseous sampling attachment must be
used if gaseous pollutants are also to be
monitored. An attempt has been made to
make the two units as independent of each
other as possible. Hence, users who are not
interested in gaseous pollutants need not
acquire the APM 411 attachment.
14. • However, each APM 430 system is provided
with all the fixtures needed for using the
gaseous sampling attachment, so that the
APM 411 system can be fitted at any stage.
• APM 411 gaseous sampler uses wet chemical
methods for the absorption and detection of
gaseous pollutants. Hence, atmospheric air
must be passed through absorbers containing
suitable reagents which would absorb relevant
gases like Sulphur dioxide, Nitrogen oxides,
Hydrogen sulphides, etc.
15. • The absorbing reagents must be analyzed in a
laboratory to work out the quantity of gas
absorbed.
• The APM 411 system has been provided with
a set of four midget impingers for gaseous
sampling. A gas manifold with separate flow
control valves allows independent flow rates
to be set in individual impingers. A flow-meter
has been incorporated which allows a precise
measurement of sampling rate when the
system is being set up. The impingers have
been kept in an ice-tray to improve the
absorption efficiency of the system and
prevent loss of absorbers by evaporation.
16. OPERATING INSTRUCTIONS
• Selection of Sampling Site. The High Volume
Sampler is usually operated at ground level. In
normal usage it is never operated more than
15 meters above ground level. In order to
obtain a representative sample, the Sampler
should not be positioned near a wall or other
obstructions that would prevent free air flow.
17. • In excessively turbulent conditions or in the
presence of strong surface winds or otherwise
inclement weather, the sampling rate is likely
to decrease rapidly and perhaps in a non-
linear fashion due to filter choking. If the
sampler is operating in the vicinity of a source,
day-to-day variations in the measurement are
expected due to varying meteorological
conditions and changing atmospheric
phenomena, like wind speed and direction,
disperal, diffusion, etc.
18. Selection of Filter Medium
• For most cases where interest is limited to a
gravimetric determination of the total
suspended particulate concentration, glass
microfibre filters having a low resistance to
airflow, a low affinity for moisture and a 98%
collection efficiency for particles of 0.5 micron
or larger size are suitable.
19. • However, where further analysis of the
particulates is to be attempted to detect
specific elements/radicals, care should be
taken to choose special filter mediums having
a low background concentration of the
substances of interest. For instance, special
grades of glass microfibre filters are available
which have a controlled and low
concentration of metals like Iron, Zinc,
Cadmium, Lead, Arsenic, Nickel, etc.
20. Preparing the Filter
• Prior to use, expose each filter to a light
source and inspect for pinholes, particles and
other imperfections. Filters with visible
defects should not be used. A small brush is
often used to remove stray particles adhering
to the surface of new filters. Always handle
filter papers from their edges and do not
crease or fold the filter medium prior to use.
21. • Both blank and samples should be
conditioned at 20 to 25 degrees Centigrade,
and relative humidity below 50% for at least
16 hours prior to weighing. It is usual to put
an identification number and date of sampling
on the filters. Weigh the filters to the nearest
milligram and record the weight and filter
identification number.
22. Installation of the Filter
• Always install or remove the filter only when the
Sampler is OFF. Open the gable roof of the shelter,
loosen the wing nuts and remove the face plate from
the filter holder. Place a numbered, pre-weighed
filter in position with its rough side up. Replace the
face plate without disturbing the filter and fasten
securely. Under tightening will allow air leakage, over
tightening will damage the rubber face plate gasket.
A very light application of talcum powder may be
used on the rubber gasket to prevent the filter from
sticking. Close the roof of the shelter
23. Operation of the Orifice Meter
• The Orifice meter is really a differential
manometer used to measure the pressure
drop across an Orifice Plate. It uses distilled
water as the indicating fluid which must be
topped up from time to time. The brass screw
mounted on the meter plate is a filling plug
which must be opened to fill in the
manometer fluid. Use the syringe provided
with the instrument to fill distilled water upto
the “zero” mark on the meter scale.
24. • When adequate fluid has been filled into the
system, close the filling plug. Do not over
tighten the plug since it would damage its seal
ring. A drain plug has been provided on left
side of cover in order to drain out excessive
water.
26. TIMER OPERATION
• SETTING UP THE TIMER FOR MANUAL
OPERATION
Pullout all the pins on the timing dial outwards.
Use the main ON-OFF switch on the instrument
panel / manometer plate to manually switch the
blower ON or OFF. (Note : with the pins in
outward positions, the timer remains connected
to the mains but is unable to control operation of
the Sampler.)
27. SETTING UP THE TIMER FOR
AUTOMATIC OPERATION
Pull outwards all the pins located on the timing
wheel. Rotate the wheel clockwise until it is
synchronized with the real time of the day. e.g.
Rotate the timing wheel clock-wise until the
number aligned to the pointer (marked as a
triangle- ) on the center wheel corresponds to
the real time of the day. For example, if the
actual time is 10 A.M., the pointer should be
aligned to number 10.
28. Similarly, if the actual time is 3 P.M. the pointer
should be aligned to number 15. At this position
the timer is ON as in the manual position.
Decide the OFF time and push all the pins on
dial from selected OFF time to the start time
inwards. This will switch off the blower at
desired time. The sampler may now be left
unattended and will automatically operate for
the desired time. (Caution : The timing wheel
provides and endless loop, and so the timer will
repeat the operation after 24 hours, unless the
sampler is externally switched off.)
29. Each pins of the tuning dial corresponds to
approximately 15 minutes. It enables to select
many ON time and OFF time intervals as per
requirement.
• Caution :
In case the timer function not to be use
then pullout all the pins on the timing dial
outwards.
30. Using the Time Totalizer
The Time Totalizer uses a clock motor to drive a geared
numerical display. As shown in Drg. No 43015-00, the
system has been wired so that it operates only when
the heavy duty blower receives power. Hence its
display indicates the true time, in minutes/hours for
which the Sampler has sampled atmospheric air.
The Time Totalizer performs two important functions :
(a) it keeps check on the actual sampling time when the
instrument is operated, and
(b) it facilitates timely preventive maintenance.
31. Time Totalizer readings must be noted before
and after each air-sampling, so that the exact
duration of the sampling can be worked out. The
same readings can be used to determine when
the Orifice-meter system is due for cleaning. As
such, we strongly recommend that Time-
Totalizer readings be recorded in the form of a
Log and used to establish a preventive
maintenance schedule as per maintenance
instructions given in section 5 of the manual.
32. In the event of power failure, both the Timer
and Time Totalizer (as also the Sampler) stops.
Hence, when power is restored, the Sampler will
continue to operate for the balance time period
set on the Timer. It will, however, loose
synchronicity with the real time of the day. The
Time Totalizer will still indicate the actual
number of hours and fraction of hours (i.e., ....x
x.xx hrs) for which the Sampler has operated.
33. Sampler Start-up Sequence
Before commencing any air sampling operations using the APM
430 High Volume Air Sampler, check the following :
(1) The system is suitably located as per section 4.1
(2) A fresh, pre-weighed filter is installed in the filter holder.
(3) The fluid in the orifice meter is at ‘Zero’ level.
(4) In case both particulate and gaseous pollutants are to be
sampled, check that impingers with suitable reagents are in
place and are connected as per Section 4.12. If only suspended
particulates are to be sampled, the entire APM 411 gaseous
sampling attachment can be removed.
34. • Connect the mains chord of the sampler to a
live 220 V.A.C. outlet. Switch on the machine.
• Allow the Blower to run for a minute so that it
attains full speed and then record the
sampling rate indicated by the orifice meter. In
case gases are also to be sampled, set the
desired flow rates (for gaseous sampling)
using the needle valves of the gas manifold.
Record the sampling rates for gases.
35. Sampler Shut-off Sequence
(1) Record the flow-rate indicated by the orifice
meter.
(2) Record the flow-rate indicated by the
rotameter (for gaseous sampling).
(3) In case the system was operating under the
control of the Timer and the blower has already
been shut off, restart the blower using the ON-
OFF switch and allow the flow rate to stabilize
for a minute before recording the flow rates
mentioned above.
36. (4) Switch off the sampler using the MCB switch.
(5) Record the final sampling time indicated by
the Time Totalizer.
(6) Open the filter-holder and carefully remove
the Filter Paper. Fold the paper along its length
so that the soiled sides are in contact and are
facing inwards. Store the filter paper in a clean
envelope.
(7) Remove the Sampler from the Sampling Site
to a safe storage area.
37. Calculations (For Suspended
Particulate Sampling)
Weight of suspended particulates (W)
W = W2 - W1 (grams)
W2 = Weight of the filter paper after sampling (grams)
W1 = Weight of fresh filter paper (grams)
Note: Both W2 and W1 are to be measured after filter
conditioning as mentioned under heading , preparing
the filter
Volume of Air Sampled (V)
V = Q x T (Cubic Meters)
Q = Average sampling rate (Cubic meters per minute)
38. T = Sampling Time (Minutes)
Q = (Q1 + Q2) / 2
Q1 = Initial sampling rate indicated by the
Orifice Meter at the start of sampling
Q2 = Final Sampling rate indicated by the Orifice
Meter just before the end of sampling.
Concentration of Suspended Particulate Matter=
W/V(grms/cubic meter)
