A mathematical model is presented relating the presence of NO2 in the oxidant stream to the fuel cell performance loss. Both contamination and recovery processes are considered. The model is validated using cell voltage/current density distribution and cell voltage change as a function of NO2 concentration transient data. The model is used to discuss NO2 threshold concentrations and contaminant screening. General and NO2 specific gaps in contaminant characterization methodology are also highlighted. (c) 2008 The Electrochemical Society.