Principles of Sampling and Analysis -Gaseous Pollutants

Gaseous pollutant monitoring can be accomplished using various measurement principles. As an example, sulfur dioxide monitoring can be accomplished with dynamic samplers for average concentrations over a 24-hour period and with static samplers for longer periods, e.g., 30 days. Some of the most common techniques to analyze gaseous pollutants include spectrophotometry, chemiluminescence, gas chromatography-flame ionization detector (GC-FID), gas chromatography-mass spectrometry (GC-MS), and Fourier transform infrared spectroscopy (FTIR).

With all sampling and analysis procedures, the end result is quantitative data. The validity of the data depends on the accuracy and precision of the methods used in generating the data. Accuracy is the extent to which measurements represent their corresponding actual values, and precision is a measurement of the variability observed upon duplicate collection or repeated analysis. To ensure the validity of data, various quality control measures are employed for each reference method. The primary quality control measure is calibration. Calibration checks the accuracy of a measurement by establishing the relationship between the output of a measurement process and a known input. Each of the reference methods has precise calibration procedures that must be followed to ensure accurate results.

EPA has also developed extensive quality assurance programs to ensure validity of data. An essential component of the quality assurance program is the implementation of audits. In an audit, one lab or many labs would analyze a known standard sample of a pollutant. If the labs obtain the expected result, they can be assured that their methods and procedures are accurate.