A volatility-tandem differential mobility analyzer (VTDMA) was designed to monitor the non-volatile fraction of reaction chamber-generated organic aerosol particles. Using a coiled-tube heater for particle volatilization, an analysis of the carrier gas temperatures was made for wall temperatures of 100, 150, and 200 degrees C. Oligomerization in organic aerosol particles generated from irradiations of alpha-pinene/NO(x)/H(2)O/pure air in a reaction chamber shows a strong linear relationship with time and has an oligomerization rate of 1.3%h(-1) for the 100 degrees C wall temperature case. This rate is almost three times slower than the previously published rate for irradiations of 1, 3, 5-trimethylbenzene/NO(x)/H(2)O/pure air. In addition, experiments using the VTDMA demonstrated that oligomerization of nebulizer-generated methylglyoxal particles can occur in the absence of NO(x), propene, and irradiation. The oligomerization of organic aerosol particles has implications which are highly relevant to the atmosphere, such as influencing hygroscopic growth and cloud condensation nuclei activation. (C) 2005 Elsevier Ltd. All rights reserved.