The law establishes that companies emitting substances into the atmosphere must regularly check the quality of air issuing from their chimneys. These checks are normally carried out at stations located in precise points of the chimneys, where the flow and components are homogeneous, according to specific UNI directives.
Operative spaces for sampling emissions are subject to specific methods designed to guarantee worker safety and sample accuracy, while minimising the uncertainty of sample quality.

Particular standards and specifications exist also regarding sample point outlets and their locations. Different characteristics may be required, depending on the case, type and quantity of emissions.