ISO 8573-8:2004 specifies test methods for determining the solid particle mass concentration in compressed air, expressed as the mass of solid particles with maximum particle size limits. The methods' limitations are also specified. One of a series of standards aimed at harmonizing air contamination methods, it identifies sampling techniques and also gives requirements for evaluation, uncertainty considerations and reporting for the air purity parameter solid particles by mass concentration. The test methods are suitable for determining the purity classes in accordance with ISO 8573-1. (Particle content based on counting particles is dealt with in ISO 8573-4.)