Abstract: A saturator block assembly that is adapted for use with a condensation particle counter is described. The saturator block assembly is comprised of a member that is at least partially formed from a porous material that is adapted to absorb a working fluid. The saturator block assembly also includes at least one open column formed through the porous member. The open column is parallel with a length of the member and is adapted to emit the working fluid in vapor form from the porous material. The saturator block assembly is further comprised of an outer surface, and is adapted to operate at low pressure or low pressure transient applications. A volume of the porous material is configured so as to reduce the amount of air capable of being trapped in the pores of the porous material during low pressure or low pressure transient applications.