The emergence of nanotechnology has increased the concern of exposure to nanoparticles through inhalation. Studies have examined the performance of filtering facepiece respirators against engineered nanoparticles. This has been done by the generation and dispersal of certain particles in a given size distribution, which have then been run through experimental set-ups involving Condensation Particle Counters, Scanning Mobility Particle Sizers, and high efficiency performance filters for a set flow. Published studies have shown that the respirators used do provide expected levels of filtration protection against nanometer-sized particles. However, studies have not examined or applied different types of nanoparticle samples - different particle types have differing morphologies and physical characteristics that could affect filter performance. This study has exposed NIOSH-approved N95 facepiece respirators to six different types of engineered nanoparticles: aluminum oxide, iron oxide, single-walled carbon nanotubes, synthesized diamond, silicon dioxide, and titanium dioxide. In addition, N95 respirators have not been commonly exposed to differing concentrations of an aerosol in order to observe a shift in the primary penetrating particle size and a shift in the overall size distribution. This study challenged N95 respirators to four different concentrations of sodium chloride: 0.1, 1, 10, and 50 mg/ml. Another concern is whether or not a prolonged exposure of a single respirator affects the overall performance and protection from an aerosol, especially engineered nanoparticles, since very few studies have been done regarding this matter. N95 respirators were exposed to several types of engineered nanoparticles in a respirator testing apparatus at a set flow rate, examined for penetration with an SMPS, CPC, and DMA given these conditions: differing concentrations of sodium chloride, different engineered particles, and an extended duration of exposure to both sodium chloride and 15-nm titanium dioxide. This study showed that the primary penetrating particle size through an N95 facepiece respirator does increase and shift with increasing concentrations of an aerosol; however, the overall size distribution did not seem to shift much. Penetration decreased as sodium chloride concentration increased. Different nanoparticles had differing primary penetrating particle sizes through the respirator; however, penetration of these particles was similar to one another with the exception of iron oxide which had quite a high penetration percentage. A decrease in N95 respirator performance was observed when exposed to a 1 mg/ml solution of sodium chloride, as penetration increased with prolonged exposure. However, this did not seem to be the case when the respirator was exposed to a 6.67 mg/ml suspension of 15-nm titanium dioxide, as the penetration over the extended period of time was similar to one another.