ISO 18611-1:2014规定了船用氮氧化物还原剂的质量特性，即浓度为40%的尿素水溶液（AUS 40），这是操作所谓的SCR（选择性催化还原）转换器所需的。例如，在船舶应用中，对于发动机废气处理，SCR转换器特别适合选择性地减少内燃机和锅炉的氮氧化物（NOx）排放。 本国际标准涵盖了适用于船舶应用的AUS 40的质量要求和指南，与制造方法或技术无关。 在ISO 18611的其余部分中，术语“NOx还原剂”将缩写为“AUS 40”。

ISO 18611-1:2014 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".