Separated measurements of volatile and non-volatile fractions of atmospheric aerosols have become more important due to possible effects of non-volatile particle on respiratory diseases. Measurements of non-volatile particle fractions with considerable size and time resolution are therefore needed. The combination of a thermodenuder (TD) with aerosol size spectrometers can provide size distributions of non-volatile particles. TDs usually consist of two units: a heating and a cooling tube. Unfortunately, available TDs have some disadvantages concerning the heated tube, where volatile material should be desorbed from the particles. The residence time in the heating zone might be too short to completely evaporate the volatile material or the temperature at the exit of the heating tube might be below the condensation temperature of the evaporated species. Here, a new TD was developed with a longer residence time at the requested temperature and a more effective insulation to prevent recondensation at the end of the heating unit. Additionally, the TD was calibrated for size-dependent particle losses at different heater temperatures. (C) 2002 Elsevier Science Ltd. All rights reserved.