The Federal Immission Control Ordinances (BImSchV) specify the requirements of the BImSchG for particular types of installations and industries. While TA Luft is a general administrative regulation, the various BImSchVs have the force of law. In exhaust gas cleaning, the 31st BImSchV (Solvent Ordinance) and the 44th BImSchV (medium combustion plants, gas turbines and internal combustion engine installations) are particularly relevant. The latter, for example, very strictly regulates emissions of nitrogen oxides and formaldehyde from biogas plants and combined heat and power plants (CHP). Compliance with these ordinances is monitored by regular official measurements. Catalytic systems are specifically designed to guarantee, in continuous operation, the limits set out in the relevant BImSchV. For plant operators, understanding which ordinance applies to them is essential in order to base investment decisions on cleaning technologies on a sound legal footing.