0018933 eo back of the filter screen except during the sampling periods, 2.2.3 Discussion of Possible Errors in Sampling. Polydisperse aerosols contain an aggregate of particles whose sizes are arranged in accordance with a characteristic frequency distribution, When the aerosol is sampled under | ideal conditions, the ratios of the numbers of particles in the varjous size ranges will be preserved unchanged in the collectors However, a departure from the initial size distribution: may be encountered if the collecting device has'a dimensional bias (non-isokinetic condition), or if some of the particles are broken up during the sampling operation. Isokinetic sampling conditions will be achieved with a filtering device moving through the aerosol at subsonic speeds if the air velocity into the intake of the filter is identical with the flow rate past the outside, As used in Project 2.8, both the wing tank and coincident samplers were close to isokinetic since the velocity ratios were respectively 0.8 (or greater) and - 0.7-0.9. calculated However, in a few cases, the/velocity ratios for the coincident units were much less,due to malfunction of the sanupling equipnent - (see Appendix B), The E-1 sampler used on the WB-50's was'poor isokinctically, but this was considered to be immaterial for height line sampling where the particles in a given region should be fairly uniform in size, Samplers, such as the project rockets, which move at supersonic speed with respectto the aerosol are expected from aerodynamic theory to be unbiased, 49 pinelHDeREITER LIES Sao a a Slaw in = — —_— — Rietiete. tor6fee Er eG e