What is the difference between parameter codes 88101 and 88502 for PM2.5 monitors?

The 88101 monitors include both manually operated Federal Reference Methods (FRMs) and automated Federal Equivalent Methods (FEMs) and each are used for determining compliance with the PM2.5 standards. The 88502 monitors are “FRM-like” but are not used for regulatory purposes. Both 88101 and 88502 monitors are used for reporting daily Air Quality Index values.