The effects of different airborne particulate contaminants (oxalic acid, soot, ammonium sulfate, and sodium chloride) and the gaseous air impurity NOx on the performance of a passive air-breathing proton exchange membrane fuel cell (AB-PEMFC) were investigated by introducing the pollutants into the oxidant air fed to a small AB-PEMFC module. All contamination data were corrected for variations in air temperature and relative humidity. While 10 ppmv NOx degraded fuel cell performance by 22% within 4 h and showed partial recovery of 70% within another 11 h, the effects of the aerosol particles were considerably less severe. Only oxalic acid and ammonium sulfate exhibited significant performance degradation with upper limits of 24% 1000 h(-1) and 3% 1000 h(-1), respectively. Sodium chloride as well as soot particles did not cause any significant performance decline. Because diffusion is the main transport mechanism for aerosol particles into a passive AB-PEMFC, only a minor fraction of the total particle mass can actually deposit inside these fuel cells resulting in rather low effects even under very high aerosol loadings. Therefore, aerosol related effects seem negligible under ambient conditions. Copyright (c) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.