The effect of environmental contamination (NO,, SO,) on the performance of proton exchange membrane fuel cells (PEMFC) was studied. The performance of PEMFCs was tested for 100 h with different cathode reactants. According to the Ambient Air Quality Standard of PRC, three kinds of cathode gases were applied to operate the fuel cells, which were 1 ppm NO2/air, 1 ppm SO2/air and a mixture of contaminant gases. The gas mixture contained 0.8 ppm NO2, 0.2 ppm NO and 1 ppm SO2. Finally, the poisoning behavior and the mechanisms were analyzed by constant-current discharging and cycle voltammetry (CV). During the 100 h test, the potentials of the fuel cell degraded by 65%, 77% and 90% with 1 ppm SO2/air, a gas mixture and 1 ppm NO2/air, respectively. (c) 2007 Elsevier B.V. All rights reserved.