Determination of ecosystem exchange fluxes using the eddy covariance technique requires measurements with a fast time response. For ammonia, the time response is limited by adsorption and desorption processes on instrument surfaces, generally leading to a substantial underestimation of fluxes. Based on a 5-month flux dataset, we propose a new method to correct for the ammonia flux loss that is better suited to account for factors like surface aging and contamination than other approaches.