An instrument for semi-quantitative real-time measurement of polycyclic aromatic hydrocarbons (PAH) on airborne fine particles was evaluated. The instrument operates on the principle of photoelectric ionizaton of PAH adsorbed on particle surfaces, with resulting loss of photoelectrons and subsequent measurement of the remaining positively charged particles. The authors investigated the characteristic performance of the instrument in both chamber and field studies. This performance included: selectivity for fine particles, response to PAH only on particles versus response to PAH in the vapor phase, accuracy compared to integrated sampling, interferences, rapidly of response, limits of detection, bias, ease of operation, reproducibility, calibration, reliability, and ease of field operation and maintenance. The instrument performed well and appears to be suitable for screening air for particle-bound PAH in a variety of microenvironments, as well as for use in estimating human exposure related to various activities that may generate PAH.