A Comparison of Geometrical and Aerodynamic Sizes and Reliability of Size Distribution Curves of Airborne Particulates Collected by Andersen Samplers

The study was carried out for airborne particulates which were collected inside a chemical laboratory and on the roof of a building using two Andersen samplers of 8 stages. Geometrical, volume and arithmetic mean diameters of the particulates collected on each stage of the sampler were estimated from both optical microscopic photographs and the secondary electron images obtained by an X-ray microanalyzer. Volume mean diameters of the particulates were about 20% larger than the assigned aerodynamic diameters which were calculated as particle density of 1.0g/cm', and arithmetic mean diameters were about 30% smaller than the aerodynamic, diameters. The reliablity of particle size distribution curves was also discussed. from comparisons between the curves obtained by different drawers, different drawing methods, and two samplers. Two drawers gave up to 20% differences in the peak position (size) and height (frequency) of the curve using a graphic method. The application of Lagrange's interpolation equations of 4-9 th orders to the curve drawing gave good results except the both terminal regions of the curve, though it gave differences of less than 3.5% to the peak position and height of the curve depending on the order. The differences in the peak position and height were less than 12% between the curves of the particulates collected by two identical samplers. Fluctuations ( σ ) in the values, i. e. frequency, on vertical axis of the curve caused by weighing errors were less than 2.5% of the maximum peak height for 60 mg of a total sample from all stages and less than 4% for 21 mg of a total sample. The size distribution curves of the laboratory particu lates were similar to those of the outdoor particulates, though the former particulates were richer in small ones than in the latter.