The accuracy of the European Emissions Standard Method to determine the amount of diesel particulate matter (DPM) emitted to the atmosphere is questioned. Results obtained using an experimental fixed bed installation show that the main mechanism involved in the formation of DPM is gas phase saturation and later liquid adsorption, and that gas adsorption is not important under the mini-tunnel sampling conditions. Based on this finding, a new theoretical model is developed assuming accumulation of hydrocarbons in the mini-tunnel. The model reproduces the amount of particulates emitted as a function of dilution ratio and filter temperature. Results prove that these parameters must be specified in the emissions standard method to carry out an accurate homologation of the different vehicles. (C) 2002 Elsevier Science Ltd. All rights reserved.