Ambient air quality monitoring and
High volume sampler
Instruments needed for
Wind speed Anemometer
No unit (Expressed
Millibars or mm of
The Aim of Sampling:
•The principal requirement of a
sampling system is to obtain a sample
atmosphere at a particular place and
time and that can be evaluated as a
mass or volume concentration.
•The sampling system should not alter
characteristics of the sample in an
The major components of most
sampling systems are:
1) An inlet manifold
2) An Air mover (Blower)
3) A collection medium
4 ) Flow measurement device
material from the ambient atmosphere to
the collection medium or analytical
device in an unaltered condition, all inlet
of ambient air must be rainproof.
(2)The air mover (Blower) provides the force
to create a vacuum or lower pressure at
the end of the sampling system (pumps).
(3) The collecting medium, may be
dissolving gases a filter surface for
(4)The flow device measures the
volume of air associated with the
• Gravitational method
• For collecting dust particles of 1µ
(micron) or larger 40 µ (micron ) in
the atmosphere, clean glass jars are kept
in the area where dust fall is to be
determined and after a few hours or days,
the dust is collected from each jar and
• The average weight of dust in each jar
is estimated and the dust fall is
expressed as weight of dust per unit
area per unit time.
• Containers, generally conical plastic jars,
10-15 cm in diameter, open at the top
• The jars are kept in strategic locations
throughout a community or in the vicinity
of particulate sources under study.
• Grit and dust fall into the jars which
sometimes have water to hold the dust.
After a one month exposure, the jars are
collected and brought into the laboratory
where their contents are analysed.
• In most cases only the total
particulate matter is determined, and
the results are expressed in terms of
tons per square kilometer per
month or g/sq. m / month.
• Monthly isopleth maps can be
constructed showing the variation of
dust fall throughout the area.
• A fibrous filter which is woven with randomly
oriented fibers acts as a target for the
collection of fine particles. When airborne
particles enter a filter and flow around the
fibers, they are subjected to aerodynamic
forces which result in their collection on the
• The principal mechanisms operating are
gravitation, inertia, interception and diffusion.
• Many types of filters are available for
removal of particulate matter from gas
• The chief variations are in the filter media
material and in the shape of the
• One common type is the thimble filter
• The filter paper thimble is filled with wellfluffed cotton which operates at a
sampling rate of 2 cf/min.
• By determining the change in
weight of the dried filter after
exposure, dust concentration in the
gas stream is determined.
• The paper thimble cannot be used
with high temperature gases; an
alundum thimble is useful in this
• Cyclones are a special type of impactors where
the impaction (on the side walls of the cyclone)
is combined with the gravitational settling of
the large particles.
• The effect is that the large particles will get
trapped before they reach the collecting filter
and thus giving a cut off size dependent of the
size, geometry and air flow velocity through the
• Cyclones (often) have the advantage of being
both small and cheap but still accurate enough
for most modern requirements.
• Cascade impactors are consists of a
number of impactor stages connected
in series with smaller and smaller cutoff diameter.
• The cut-off diameter in each stage
depends on the air velocity and
geometry of the stage (i.e. the
distance from the nozzle to the
• Cascade impactors often have up to
some ten stages ranging from a
cut-off diameter on the first stage
of 10 – 30 m to a diameter of 0.1
m or lower on the backup filter in
• This gives the opportunity to
analyse (e.g. chemical or
gravimetrical) a number of small
• Some drawbacks are the risk of bounce off
from one stage to the next (i.e. particles of
wrong size at some of the stages) as well as
the problem of obtaining sharp cut-off
diameters in the last stages (cut-off diameter
less than 0.1 – 0.2 m).
• Coating the impaction plates with oil or some
other sticky substance, which catches the
particles more effectively, can reduce the risk
of bounce of.
• This will then prevent or severely complicate
direct mass concentration calculations of the
• An electrostatic precipitator consists of an
ionizing electrode charged with a high negative
potential and a collector to be maintained at
positive potential produced by a special
transformer and rectifier.
• A known volume of air is allowed to pass
through the precipitator where the incoming
particles become negatively charged by the
electrode and adhere to the positively charged
• The collected particles are weighed and
their number can also be counted
accurately by using a microscope.
• This method of collection of particulate
matter is very efficient as high flow
rates with small pressure drops can be
• In thermal precipitators the particles in the
sampled stream move past a very hot wire
and are repulsed to the nearby cold plate
where they are collected.
• However, it can operate only at very low
sampling rates-approximately 50 mililitres
per minute and is useful only for R&D work.
Figure shows a thermal precipitator of the
type supplied by Casella Company Ltd.,
• High Volume Samplers are the basic
instruments used to monitor Ambient Air
• They are in widespread use all over the
world to measure air pollution in industrial
areas, urban areas, on the shop floor,
near monuments and other sensitive
• The High Volume Sampler is a vital tool
for studies relating to impact of
industrialisation to the air analysis, and
for work related diseases of the
respiratory system to air pollution.
• These are very much essential for
various Environmental Impact
Components of HVS
• Heavy Duty Blower,
• Orifice flow meter- measures flow,
• Time Totaliser-records time,
• Programmable Timer- measures time,
• Instrument Cabinet- acts as protection,
• Filter Holder assembly- holds the filter in
• Voltage Stabiliser- guards against
• Detachable Gable roof- allows passage of
air and protects filter.
PRINCIPLE OF OPERATION
• In these samplers, air-borne suspended
particulates (SPM) are measured by passing air
at a high flow-rate of 1.1 to 1.7 cubic meters
per minute through a high efficiency filter
paper which retains the particles.
• The instrument measures the volume of air
sampled, while the amount of particulates
collected is determined by measuring the
change in weight of the filter paper as a
consequence of the sampling.
• The passage for air reaching the filter is
designed to prevent heavier settleable dust
particles from reaching the filter (by provision
of cyclone) thus measuring the concentration of
Suspended Particulate Matter (SPM) in
• In high volume sampler provisions have
been made for simultaneous sampling of
• Here the air is passed through suitable
reagents that would absorb specific gases
where gaseous pollutants like SO2, NOx,
Cl2, H2S, CS2, NH3, etc. are analysed
subsequently by simple wet chemistry
method to determine the concentration of
Applications of HVS
• Routine Monitoring by air monitoring
• Open Spaces like forests and national park
• Monitoring around ecologically sensitive
• Data reporting for monthly and
yearly averages by local area air
Site Monitoring by industries.
Calculation of SPM concentration
Q1. State principles used for sampling of
particulate matter. Explain any one in detail.
(Nov 2008, May 2009, 8 marks)
Q2. Explain working of high volume sampler with
sketch. (May 2011, 8 marks).
Q3. Explain various principles used in particulate
matter sampling. (May 2011, 8 marks)
Q4. Explain procedure for determining
concentration of SPM in ambient air.