Sampling Plane or Sampling Section
A plane normal to the centreline of the duct at the sampling position.

Sampling Point
The point(s) on the sample plane where the sample is collected.

Sampling Ports or Access Ports
Holes in the wall of the stack through which access to the emission gas can be gained.

Sampling Position
A suitable position on the site where representative samples can be obtained.

STA
Source Testing Association.

Stack
A structure through which pollutants are released to the atmosphere.