The effluent pollutants emitted to the atmosphere from a source may contain many different pollutant materials. Effluent measurements and sampling procedures follow specific test methods and protocols to ensure representative and accurate emission data. Test methods are pollutant specific, sometimes industry specific and originate from a variety of sources and jurisdictions such as USEPA, Environment Canada, State Agencies, Provincial Agencies, Trade Organizations, etc.

Source sampling provides a great deal of important data on the operating parameters and emissions of an industrial source. This information is used as the basis for decisions on a variety of issues. The data taken during a source test experiment must therefore be a precise representation of the source emissions. This task requires a thorough knowledge of the recommended sampling procedure in conjunction with an understanding of process operations. The typical industrial process may vary conditions at the source for a variety of economic or logistical reasons.

The source sampling program must be designed to prevent process variation from biasing the source sample and to ensure the safety of the field personnel. Consequently, source testing is an endeavor that should be performed only by trained personnel.