Field emission properties of carbon black, carbon black and silica, and diesel engine exhaust were investigated and compared to multiwall carbon nanotubes prepared in a similar manner. Sample preparation consisted of pressing the nanopowders into pellet form, dispersing them in isopropanol, or dispersing them in Shipley S1818 photoresist to achieve better adhesion to the substrates. Turn-on fields, at room temperature, ranged from 3-6 V/mum for the pressed and isopropanol prepared samples and shifted to 10-18 V/mum for the photoresist dispersed samples. At 120 degreesC, the turn-on fields for the photoresist dispersed samples shifted to lower values. This very strong temperature dependence is explained by a resonant Fowler-Nordheim tunneling model. It assumes that a thin barrier layer forms at the elevated temperatures due to outgassing/sublimation events. The macroscopic current densities reached for these samples are about 1-2 mA/cm(2). (C) 2004 American Vacuum Society.