L2 according to ISO 15957 dust goes by a variety of names. In ISO 12103-1 it is called A2 Fine Test Dust or sometimes "ISO Fine"– different names for the same dust! This dust is also specified in other standards including ISO 29461-1:2021 and ISO 16890:2016.
AC Fine and SAE fine are two designations for another type of test dust widely used in filter testing. AC Fine was introduced in the United States in the 1940s as a test dust for air cleaners. The Society of Automotive Engineers later adopted it as a test dust for air cleaners in their SAE J726 specification. However, the processes used to manufacture and characterize this test dust have undergone changes over the years.
Currently, the terms AC Fine or SAE Fine are often used synonymously with ISO Fine, A2, or L2.
