The use of estimation techniques is a key aspect of a PRTR programme. These techniques are different ways of measuring the amount of a chemical released into the air or water or on land. Releases and transfers are usually estimated rather than calculated through exact quantifiable measurements because estimation provides accurate results and is generally easier and less expensive.
Different estimation methods are used depending on the industrial process, equipment and operating conditions at each factory or specific source.
Sources of chemical releases and transfers include both "point" and "diffuse". Point sources are such things as factories and industrial plants that emit chemicals from a fixed location. Diffuse sources include agriculture, small and medium-sized enterprises, households, and cars and have more variable and sporadic emissions.
The aim of this project is to help countries develop and implement PRTR systems by making the data about chemical releases and transfers easier to find and use. It does this through a two-pronged approach: 1) creating a general, over-arching view of available release estimation techniques; and 2) identifying individual industrial processes that do not have a reliable or acceptable estimation technique. A Task Force on Release Estimation Techniques was created in 2000 with these aims in mind.