| adsorbents etc.
The pollutant is removed from the sample gas stream
and concentrated. The collection device, which is
now termed the sample, is recovered after the test
run and submitted to a laboratory for analysis.
The advantage of this technique is that very low
levels of air toxic compounds can be evaluated.
The detection limit can be reduced by increasing
the sample run period and the sample volume. Additional
or repeat analysis can also be carried out on the
sample if required. The disadvantage is that there
is normally a long lag period between acquisition
of the sample and reporting the pollutant emission
data.
Monitoring refers to continuous and “real
time” analysis of pollutant concentrations
using instrumental analyzers. The analyzer is
typically calibrated using certified or EPA Protocol
gases to ensure accurate and representative data.
The outputs from the analyzer are either printed
to a strip chart recorder or to an electronic
data logger for data processing.
The obvious advantage of utilizing monitoring
techniques is that real time data can be acquired
continuously. This allows the facility to evaluate
the effect of process changes and conditions over
time. The disadvantage is that there are a limited
number of gas specific analyzers for routine stack
testing. The most frequently used analyzers are
for the measurement of combustion gases: NO, NO2,
SO2, CO, CO2, O2
and total organic matter. Newer technology such
as Extractive Fourier Transform Infrared Spectroscopy
can monitor several gas compounds simultaneously,
which can be valuable for some testing programs.
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