The following article contains the modification of a NOX-analyzer (APNA-370) for monitoring of hazardous ammonia in ambient air at agricultural sites. HORIBA’s APNA-370 was originally designed to determine NOX/NO/NO2in ambient air, using the reduced pressure Chemiluminescence (CLD) method with a cross flow modulation (according to EN 14211). With the implementation of an additional converter, ammonia is transformed into nitrogen monoxide at an efficiency rate of 95 %. Therefore the modified NOX-analyzer is suitable for quantitative determination of ambient ammonia. The Hessen Agency for Environment and Geology (HLUG) used the method of ammonia permeation, which has been proven to produce a reliable span gas. The evaluation of the permeation method has revealed an error range of approximately 1 %. Currently a type approval for a NH3-analyzer does not exist in Europe. Therefore we related to the next relevant criteria. The instrument was validated according to the conforming standards of the German (VDI 4202-1/4203-3) and European (EN 14211) type approval test.