This part of ISO 8573 specifies purity classes of compressed air with respect to particles, water and oil, independent of the location in the compressed air system at which the air is specified or measured. This part of ISO 8573 provides general information about contaminants in compressed air systems as well as links to the other parts of ISO 8573, either for the measurement of compressed air purity or the specification of compressed air purity requirements. In addition to the above-mentioned contaminants of particles, water and oil, this part of ISO 8573 also identifies gaseous and microbiological contaminants. Guidance is given in Annex A as to the application of this part of ISO 8573.