Virtual impactors are widely used for sampling aerosol particles. Conventionally, vertical aerosol inlet is used for virtual impactors. In this study, a modified aerosol inlet, that is, horizontal aerosol inlet, was applied to virtual impactors. The cut-off size and wall loss of the virtual impactors were determined through numerical method and then validated through experiments. It was found that the horizontal aerosol inlet was helpful for lowering both cut-off size and wall loss of the virtual impactors (ysjnuri@hanyang.ac.kr)