This ARP describes recommended sampling conditions, instrumentation, and procedures for the measurement of nonvolatile particle number and mass concentrations from the exhaust of aircraft gas turbine engines. Procedures are included to estimate sampling system loss performance. This ARP is not intended for in-flight testing, nor does it apply to engines operating in the afterburning mode. This ARP is intended as a guide toward standard practice and is subject to change to keep pace with experience and technical advances.