The objective of this study was to compare two methods that are used to separate the solid and volatile components of an aerosol: the thermal denuder (TD) and catalytic stripper (CS). We challenged the TD and CS with atmospheric and laboratory generated aerosols. Laboratory generated particles were composed of tetracosane, tetracosane and sulfuric acid, and dioctyl sebacate and sulfuric acid. These compositions were chosen because they roughly simulate the composition of nanoparticles found in Diesel exhaust. The TD method produced semi-volatile particle artifacts due to the incomplete removal of evaporated compounds that nucleated and formed particles and solid particle artifacts that formed during treatment of the aerosol by the TD. Our results suggest that the differences in these methods will lead to different conclusions regarding the presence or absence, size, and concentration of solid particles in Diesel exhaust. (C) 2010 Elsevier Ltd. All rights reserved.