RESPONSE OF PARTICLE MEASURING SYSTEMS AIRBORNE ASASP AND PCASP TO NACL AND LATEX-PARTICLES

The response of a Particle Measuring Systems, Inc. (PMS) airborne Passive Cavity Aerosol Spectrometer Probe (PCASP)-100X and a PMS airborne Active Scattering Aerosol Spectrometer Probe (ASASP)-100X to nearly monodisperse aerosols of NaCl and polystvrene latex spheres in the size range 0.074-1.07-mu-m diameter (+/- 5%) are examined. Particles < 0.34-mu-m are size classified by electrical mobility using a Thermo System Inc. Electrostatic Classifier. The particles are also sized with the aid of a scanning electron microscope. Three equivalent diameters for the near cubic NaCl particles are considered: average of length and breadth, and cross section equivalent and volume equivalent diameters. For the linear diameter, the probes' response to latex and NaCl particles is quite similar. However, the use of cross section and volume equivalent diameter leads NaCl to be sized significantly less than the latex spheres consistent with reported differences between spherical (i.e., latex) and cubical geometry (i.e., NaCl). Using the linear diameter the lower detection limit of the ASASP-100X is found to be 0.175-mu-m +/- 5%, not 0.120-mu-m as given by the manufacturer. The lower detection limit of the PCASP-100X is found to be 0.125-mu-m +/- 5%, compared with the value of 0.10-mu-m suggested by PMS. In spite of this discrepancy the PCASP still represents a significant advancement for the airborne measurement of aerosol size distributions. Size distributions measured simultaneously with the two probes from an air craft agreed more favorably with the new calibrations than with those of the manufacturer.