Measurement of accurate particulate emission factors in ducted sources with particle size segregation involves a compromise between two conflicting requirements. In order to avoid anisokinetic sampling bias over a duct traverse, the flow rate of gas entering the sampling nozzle must vary with the local duct velocity. However, to maintain constant cuts in an inertial particle sizing device, the flow rate through the device must remain constant. Furthermore, if a specific size cut (such as ten micrometers) is specified, the flow rate of the sampler is fixed by the stack gas temperature and composition. A sampling train has been constructed which introduces an adjustable amount of clean, reheated, recycled stack gas between the sampling nozzle and the inertial sizing device. The EGR train was tested at three coal-fired utility boilers using inertial samplers without recycle gas and EPA Method 17 trains for reference measurements.