A novel bioaerosol amplification unit (BAU) that increases the size of viral particles by condensational growth has been designed and evaluated for improved viral aerosol collection. In the BAU, water was used as the condensing vapor to preserve viability of virus, and supersaturation conditions for condensational growth of particles were achieved by either conductive cooling or mixing with hot, water-saturated air. MS2 bacteriophage (28 nm) was used as the test agent, and changes in collection efficiency of an SKC Biosampler with and without the BAU were determined by assaying plaque-forming units (PFUs) in the collection medium. Results showed that the mixing-type BAU (mBAU) was a promising device for improved viral aerosol sampling. The number of viruses (PFU) collected in the Biosampler increased 2-3 fold after passing through the mBAU. However, PFU increases in the cooling-type BAU (cBAU) were insignificant. APS results likewise showed that the mBAU was better in growing particles than the cBAU. After growth, number concentrations of particles larger than 327 nm in the cBAU and mBAU increased 1.3 and 15.0 fold, respectively. The relatively high molecular diffusivity of water vapor compared to the thermal diffusivity of air and the temperature gradient in the cBAU tube limited particle growth by causing condensation to occur predominantly at the colder wall. (C) 2010 Elsevier Ltd. All rights reserved.