Despite the rapid growth in nanotechnology, very little is known about the unintended health or environmental effects of manufactured nanomaterials. The development of nanotechnology risk assessments and regulations requires quantitative information on the potential for exposure to nanomaterials. The objective of this research isto characterize airborne particle concentrations during the production of carbonaceous nanomaterials, such as fullerenes and carbon nanotubes, in a commercial nanotechnology facility. We measured fine particle mass concentrations (PM2.5), submicrometer size distributions, and photoionization potential, an indicator of the particles' carbonaceous content, at three locations inside the facility: inside the fume hood where nanomaterials were produced, just outside the fume hood, and in the background. The measurements were not selective for engineered nanomaterials and may have included both engineered nanomaterials and naturally occurring or incidental particles. Average PM2.5 and particle number concentrations were not significantly different inside the facility versus outdoors. However, large, short-term increases in PM2.5 and particle number concentrations were associated with physical handling of nanomaterials and other production activities. In many cases, an increase in the number of sub-100 nm particles accounted for the majority of the increase in total number concentrations. Photoionization results indicate that the particles suspended during nanomaterial handling inside the fume hood were carbonaceous and therefore likely to include engineered nanoparticles, whereas those suspended by other production activities taking place outside the fume hood were not. Based on the measurements in this study, the engineering controls at the facility appear to be effective at limiting exposure to nanomaterials.