This part of ISO 22241 specifies the quality characteristics of the NOx reduction agent AUS 32 (aqueous urea solution) which is needed to operate converters with selective catalytic reduction, so-called SCR (selective catalytic reduction) converters, in motor vehicles with diesel engines. SCR converters are particularly suitable for selectively reducing the nitrogen oxide (NOx) emissions of diesel engines. In the remaining parts of ISO 22241, the term “NOx reduction agent AUS 32” will be abbreviated to “AUS 32”.