A new tool to determine the Specific Nitrogen Accumulation Rate (SNAR expressed in gNH3 h−1 m-3packingmaterial) in the washing liquid of a biotrickling filter for treating ammonia (NH3) emissions is proposed. The tool is based on the relationship which exists between the electrical conductivity (EC) of the water and the amount of nitrogen salts dissolved in the water (i.e. ammonium NH4+, nitrite NO2–, and nitrate NO3–). The methodology was applied experimentally by carrying out EC measurements for 5 months in a lab-scale biotrickling filter treating gaseous ammonia emissions. In addition to the EC measurements, the temperature and pH of the liquid phase were recorded. The temperature, NH3 and N2O concentrations (inlet and outlet) were also measured in the gas phase. It was demonstrated that the continuous EC record over time would appear to be a valuable tool in determining the amount of nitrogen actually accumulated into the liquid phase of the biotrickling filter. Thus, the parameter SNAR could be used to characterize the ability of the biotrickling filter to remove ammonia without measurement on the gas phase. It was also shown that high values of the ionic strength of the water (EC > 25 mS cm−1) dramatically affects the nitrogen accumulation rate.