Response characteristics of the particle measuring systems active scattering aerosol spectrometer probes

Predictions of the size response of various light-scattering aerosol counte rs manufactured by Particle Measuring Systems are reported. Models that exp loit the high intensity of light available within the cavity of a He-Ne gas laser (generically referred to by the manufacturer as "active scattering a erosol spectrometer probes") are considered. The new response function prop erly averages over particle trajectories through nodes, antinodes, and inte rmediate regions of the intracavity laser beam. Our studies address probes having two basic scattering geometries: those that collect light scattered over a relatively narrow solid angle (subtending angles between 4 degrees a nd 22 degrees from the laser beam axis, as in the model ASASP-300 and ASASP -300X probes) and those that collect light over a rather large solid angle (between 35 degrees and 120 degrees, as in the ASASP-X, ASASP-100X, LAS-250 X, LAS-X, and HS-LAS probes). The theoretical response predictions for both narrow-angle and wide-angle probes are compared to previous measurements o f monodisperse test aerosols of polystyrene latex, dyoctylphthalate, nigros in dye, and carbon black. The new response function predicts smoother depen dence on particle size than the previous response function of Pinnick and A uvermann (1979) and is in better agreement with measurement. Response calcu lations for common atmospheric aerosol (water, sulfuric acid, ammonium sulf ate, and black carbon) reveal the considerable sensitivity of the response to particle dielectric properties. Response functions for internal mixtures (black carbon inclusions in water droplets, quartz in sulfuric acid, carbo n in ammonium sulfate, and metal in sulfuric acid) are somewhat different t han those for homogeneous particles. Comparison of response calculations wi th the manufacturer's calibration reveal conditions for which the manufactu rer's calibration is most appropriate and the potential for errors (as much as a factor of two in sizing) when it is blindly applied. Finally, respons e functions for multiline laser operation, as the manufacturer suggests mig ht be appropriate for the HS-LAS and LAS-X probes, are nearly the same as f or single-line lasing. These results should help the user of these instrume nts to more realistically interpret size distribution measurements.