Sampling Versus Monitoring
Sampling refers to acquiring a sample in the field using any variety of pollutant collection devices - filter, aqueous absorbents, solid adsorbents, etc. The pollutant is removed from the sample gas stream and concentrated. The collection device, which is now the sample, is recovered after the test run and submitted to an accredited 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. LEHDER also possesses newer technology, Extractive Fourier Transform Infrared Spectroscopy, which can monitor several gas compounds simultaneously and can be valuable for some testing programs.