The Impactor sub-team have published several articles on this topic and have shared them here.
Roberts, D. L. and Mitchell, J. P. (2019) ‘Measurement of Aerodynamic Particle Size Distribution of Orally Inhaled Products by Cascade Impactor: How to Let the Product Specification Drive the Quality Requirements of the Cascade Impactor’, AAPS PharmSciTech. AAPS PharmSciTech, 20(2), pp. 1–10. doi: 10.1208/s12249-018-1276-9