How is the grade of air compressor filter specifically divided?

The general filter grade can be divided into pre-filter, primary filter, fine filter and activated carbon filter. The pre-filter generally removes particles of 3~μm in diameter, the primary filter generally removes particles of 0.5~1μm in diameter and oil mist remaining content of 1PPM, the fine filter generally removes particles of 0.01μm in diameter and oil mist remaining content of 0.01PPM, and the activated carbon filter is mainly used to remove odor and oil vapor (oil mist remaining content of only 0.003PPM).