The objective of this research was to characterize the ability of the pDR-1200 real-time aerosol monitor to measure aerosols of varying size, composition, and origin. Particle aspiration and transmission efficiency was characterized at airflow rates of 2 L/min, 5 L/min, and 10 L/min in a wind tunnel in both static and orientation-averaged configurations. At 10 L/min, the particle cut point for 50% penetration of particles through the device (d(50)) was approximately 6 micro m, while at 2 L/min and 5 L/min the d(50) was significantly larger, about 9 micro m (p = 0.01). There was no significant difference in particle penetration efficiency between facing-the-wind and orientation-averaged configurations (p(avg) = 0.66). The pDR-1200 response factor, which is defined as the ratio the time-averaged, monitor-reported concentration to a gravimetric filter concentration measured directly downstream of the sensing zone, was evaluated for four aerosol types: Arizona road dust, background ambient aerosol, environmental tobacco smoke, and diesel particulate matter. These aerosols, each of varying refractive index and particle size distribution, produced significant changes in the measured response factor (p < 0.01). The pDR-1200 both overestimated and underestimated (up to a factor of 7) the gravimetrically determined aerosol concentration. These discrepancies further reinforce the need to calibrate the instrument in situ for each aerosol of interest. Inter-instrument variability was generally low for co-located monitors.