To increase the particle-measurement size range of a differential mobility analyzer (DMA), a new type of DMA has been developed with a continuously variable column length L (i.e. nominal distance between the aerosol inlet and outlet) between 0 and 300 mm. Critical design features of the DMA are precise control of the electrode length and avoiding eccentricity of the electrode during length adjustment. The tandem DMA calibration demonstrates a precise control of L. The transfer function of the DMA for 1-nm particle size is obtained from the mobility distribution of the C-60 monomer. The transfer function of the DMA at each L is described by the diffusing transfer theory (An ultrafine aerosol size distribution measuring system. Ph.D. thesis, University of Minnesota). We also show that the DMA can measure particle size from 1 nm to hundreds of nanometers by adjusting L corresponding to the particle size. (C) 2002 Elsevier Science Ltd. All rights reserved.