This part of ISO 18611 specifies the quality characteristics of the marine NOx reduction agent, aqueous urea solution at 40 % concentration (AUS 40), which is needed to operate so-called SCR (selective catalytic reduction) converters. In marine applications, for example, for engine exhaust gas treatment, SCR converters are particularly suitable for selectively reducing the nitrogen oxide (NOx) emissions of internal combustion engines and boilers.

This International Standard is covering quality requirements and guidelines for AUS 40 for marine applications, irrespective of manufacturing method or technique.

In the remaining parts of ISO 18611, the term “NOx reduction agent” will be abbreviated to “AUS 40”.