A continuous photo-electric aerosol sensor (PAS) was used to characterize the particle-bound polycyclic aromatic hydrocarbons (p-PAHs) content at a heavily trafficked roadside site in Hong Kong. The measurements at the roadside station were performed for nine months from January to September 2005. For the total quantified p-PAHs, the PAS output shows good correlations to the data obtained with the offline quartz-fiber aerosol filter collection method. The average concentration of corrected p-PAHs was 5.3 ± 3.7 ng/m3, ranging from 0.2 to 22.0 ng/m3. The p-PAHs concentrations increased in the daytime in accordance with the heavy amount of road traffic, and decreased in the nighttime due to less traffic. Hourly p-PAHs concentrations had high correlation coefficients with all goods vehicles (> 0.9) and large buses (~0.8), showing that diesel vehicle emissions are the primary source of p-PAHs. The day-to-day variation of p-PAHs is significant, because it was influenced by various factors (e.g., traffic levels, mixing height, and potential pollution sources).