Dynamic shape factors: measurement techniques and results on aggregates of solid primaries

Two different methods for measuring dynamic shape factors kappa of aerosols are described: (A) using aerodynamic size classification by means of e.g. the spiral centrifuge, (B) using aerosol decay curves of mass and number concentrations. Limited attention is given to a third method which uses the spatial dimensions of more spherical aggregates. Comparison between results from (A) and (B) for solid aggregates of U3O8 and copper oxide has yielded good agreement. These results and additional experimental data from method B on gold and copper oxide aerosols lead to a proportionality between kappa and the cube root on the number n of primaries per aggregate for n up to about 104. The different results on kappa from literature, (A) and (B) mainly for the range n > 104 are discussed. Shape changes of aggregates in humid atmospheres like the human respiratory tract lead to a drastic increase of the aerodynamic diameter. (author)