To eliminate these sources of pollution, the IMO (International Maritime Organization) began a long time ago to set binding limit values for air pollutants, like those for power plants on land. In addition, some coastal regions in America, Europe and Asia have issued even stricter emission limit values and prohibit ships that do not comply with these limit values from entering their coastal waters and ports. National authorities use so-called sniffers to monitor emissions from the air and / or at stationary points such as bridges and port facilities.

Since January first, in the year of 2020, a limit value of 0.50% applies to SO₂ emissons in international waters and alimit value of 0.10% in coastal waters (ECAs = Emission Control Areas). The ECAs include e.g. also North and Baltic Sea.

In order to comply with the new limit values, the regulations provide shipping companies with different options. This includes the fundamental change in the type of fuel, e.g. from HSFO to MGO (Marine Gas Oil) or LNG (Liquid Natural Gas) as well as equipping or retrofitting ships with desulphurization systems, so-called SOx scrubbers.

For the shipping companies, these scrubbers have the advantage that they can continue to burn the HSFO, which is considerably cheaper in relation to MGO or LNG, in the existing drive machines with manageable investment and operating costs.

Similar to the desulphurization systems in the stationary power plant area, the scrubbers work as air washers. In the so-called open-loop process, the alkalinity of the sea water is used to neutralize the sulfur from the engine exhaust gases. The closed-loop and the dry porcess, as well as a combination of the two, are less common. These are closed circuits in which the exhaust gas is desulfurized using chemicals and minerals. In order to comply with the regulations and obtain the required certificates, all systems without exception must be equipped with suitable, also certified emission monitoring systems. These constantly measure compliance with the limit values for SO₂ and CO₂ and also provide the relevant documentation. This must be proven when entering ECAs and ports. The documentation also includes the proper disposal of the residues resulting from the desulfurization process.

As is common in almost all areas of the maritime shipping for insurance reasons, all components and devices involved in the scrubber system must be certified by an internationally recognized classification society. The acceptance tests are based on the special operating conditions on ships and the climatic ambient conditions. For example, the components must withstand vibrations of up to 4g, depending on the location, and their electromagnetic radiation must not interfere with any on-board systems or sensors.