Synthesis of an ultrafine iron and soot aerosol for the evaluation of particle toxicity

A diffusion flame system was used to generate an aerosol of soot and iron o xide. The primary fuel was ethylene. Iron was introduced by passing ethylen e over liquid iron pentacarbonyl. The aerosol emission from the flame was d iluted by secondary air to a level that could be used in animal exposure st udies. The system was designed to operate at a constant soot production rat e while the iron loading was varied from 0 to 50 mug m(-3) in the diluted p ostflame gases. The impact of the iron on soot production was counteracted by the addition of acetylene to the fuel. Particles were collected on carbo n grids and were examined via transmission electron microscopy. Electron en ergy loss spectroscopy was employed to characterize the aerosol. A differen tial mobility analyzer was used to measure the size distribution of the aer osol. The iron particles were typically 40 urn in diameter and often appear ed in isolation from the soot aerosol, suggesting that either they were not formed concurrently with the soot or they remained after oxidation of the surrounding soot. Samples collected from within the flame, and downstream o f the flame, indicated that the iron may have been present as very small pa rticles comingled with the soot. The iron particles apparently melted and c oalesced as they passed through the high temperature flame tip. Crystalliza tion of the iron proceeded as the postflame gases cooled by mixing with ext ernal air. The flame system was shown to be capable of consistently produci ng steady concentrations of soot and iron for delivery to animals, without the confounding presence of toxic gaseous compounds.