This study focused on the investigation of the effectiveness of negative air ionization (NAI), photocatalytic oxidation (PCO), and the combination of NAI and PCO on the removal of aerosolized Escherichia coli, Candida famata, and lambda vir phage under different relative humidity. The experiments were conducted with a stainless steel reactor equipped with a negative air ion generator, a photocatalytic filter, and two ultraviolet lamps with 365 nm wavelength. The removal efficiency (eta), defined as one minus the ratio of the outlet concentration to the inlet concentration of the appropriate bioaerosol, was used to evaluate the effectiveness of the removal methods. The combination of NAI and PCO was the most efficient removal method for aerosolized E. coli (eta = 0.304 +/- 0.06-0.364 +/- 0.008), C. famata (eta = 0.433 +/- 0.08-0.598 +/- 0.047), and lambda vir phage (eta = 0.689 +/- 0.02-0.903 +/- 0.06). In this removal method, the contributions of NAI were higher than those of PCO for the removal of E. coli and C. famata; for the removal of lambda virus phage the contributions of NAI and PCO were comparable NAI was the least efficient removal method for bioaerosols, and the removal efficiencies are: eta = 0. 175 +/- 0.04-0.245 +/- 0.03 for E. coli; 0.216 +/- 0.007-0.297 +/- 0.044 for C. famata; and eta = 0.299 +/- 0.12-0.384 +/- 0.02 for lambda vir phage. (C) 2008 Elsevier Ltd. All rights reserved.