In the original report on our FTIR approach for measuring ammonia emissions after land spreading of anaerobic digestates a systematic error has occurred. In our quantitative analysis of single-beam FTIR spectra, subtraction of background IR radiation has been missed out, which is necessary for the bistatic OP FTIR configuration used in the study. This is mandatory because the thermal emission of near field objects contributes to the spectral continuum, while the NH3 absorption lines are not equally enhanced.

Therefore now, prior to quantitative analysis of single-beam spectra, passive FTIR spectra (IR source off) were subtracted from the single beam spectra to compensate for background IR radiation (Jarvis, 2003). After this correction, the NH3 background concentration (i.e. the NH3 concentration before AD field spreading) was determined to be 5.19 ppb, which was taken into account during the flux calculation.