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Ambient Air Quality Monitoring |
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Ambient Air Quality Monitoring is done to measure the common
air that we breath day to day anywhere or at work room environment.
Depending on the location chosen, the standards of National Ambient Air
Quality (NAAQS) or Work Area (Factory / industrial battery limits)
Environment Standards (such as OSHA/ STEL/ TWA) are applicable.
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The Respirable Dust Sampler (RDS) is modified High Volume
Sampler (HVS) with capability to separate the below 2.5 or 10 micron dust
respectively. The design of the RDS has to be developed and certified by the
recognized institute. |
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the ground. Care has to be taken to choose the location so
that it is representative of the target sample area. Undue traffic,
proximity to roadside, or material handling yard will give the true results
for that location, but not “ representative” for the area in general. As
such the objective of Ambient Monitoring has to be clear before selecting
the location.
If you are trying to measure the impact of an industry on the surrounding
environment, the location has to be in the downwind direction, where the
emission from that industry is probably hugging the ground. This distance
varies depending on weather conditions. It is generally within 50 to 100
times the stack height. |
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The duration of sampling has to match with the one specified
in the standard being used for comparison. Depending on the concentration of
various pollutants, the sampling duration may have to be reduced to shorter
interval. As such the monitoring may be continued for 24 hours, by changing
the absorbing solutions after every 8 hours. The average daily results can
be calculated for comparison. Gaseous pollutants are analyzed by standard
methods in the laboratory. |
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Sampling rate for Respirable Particulate Matter (RPM) /
Suspended Particulate matter (SPM) has to be minimum of 1000 liters/minute
and periodic adjustment may have to be done or the filter paper has to be
changed at shorter interval. The sampling rate may fall below minimum due to
heavy pollution load and therefore clogging of filter paper. Calculations
can be also done by taking the mean average flow rate of sampling.
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The machine requires 230 V supply and the motor is DC type.
It is not of flame-proof type and hence precautions are to be taken while
sampling in prohibited area. During operation, the Noise Level is around 65
dB 2 m away from the RDS/ HVS Sampler. |
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Sound
Level Monitoring |
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Noise
v/s Sound:
These two words are quite often used interchangeably, which is not very
correct. Noise has been defined as unwanted sound. A good lyrical song may
be liked by us and hence is not a noise. But the same song can be unwanted
during examination study time. What we measure with these instruments is the
general total sound level in the area, and not Noise. Noise is subjective
concept. |
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Noise
Level Measurements:
A young, audiometrically healthy normal male adult responds to sound waves
of frequency range of 20 to 16,000 Hz, where as children and women have
capacity to respond to 20,000 Hz. The speech zon lies in the range of 500
to 2,000 Hz. The human ear is most sensitive in the range of 2,000 to 5,000
Hz. |
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Weightings:
The writers of the acoustical standards have established three weighting
characteristics and these are A, B & C. The “A” weighting net work filters
out very low frequencies very severely, “B” moderately and “C” hardly
filters out any.
Time Weightings:
The two
time weightings are called Fast and Slow responses. Slow responses refer to
averaging time of up to 1 second to 0.5 seconds (500 ms) and the Fast
response is 125 ms to 200 ms. However, it may vary as per requirement of the
purchaser specifications. dB(A) Fast meets the requirements of Human ear
sensitivity. |
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Noise
Rating Systems:
The
human response to Noise depends upon the frequency of the sound, the type of
noise (continuous, intermittent or impulsive) and the time (day or night) it
occurs. Thus the Noise rating system should take frequency into account,
differentiate between day time and night time noise and be capable of
describing the cumulative noise exposure. The following two systems are
Presently in vogue:
The LN
Concept: If measurements are made over a period of time, the parameter LN
represents or indicates as to how frequently a particular sound level is
exceeded. Say L30 = 70 dB A, then it represents that 70 dB A was exceeded
30% of the measuring time.
The
Leq Concept:
The
equivalent continuous equal energy level, Leq can be applied to any
fluctuating Noise Level. It is that constant Noise Level that over a given
time, expends the same amount of energy as the fluctuating level over the
same time period.
General Sound Level Monitoring:
Sound Level Measurements at workplace are done using simple instruments
capable of having ‘A’ and ‘C’ weightings and ‘Slow’ and ‘Fast’ response
selection switch. The sound level measurement has to be done where human
employee is facing the sound or at employee’s place of working. It may be
near or far from the actual Noise Source.
Standards:
These are depending on the location and period of day. Industrial areas
obviously have somewhat higher acceptable sound levels than those prescribed
for residential areas. The collected night standards are stringent than the
day time standards. |
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