Abstract |
The paper gives results of measurements of metal partitioning between the fine condensation aerosol and the larger particles produced during rapid heating of aqueous and organic solutions containing metal additives with widely varying volatilities in a laboratory-scale furnace operated over a range of temperatures (900-1500 K). A stream of monodisperse droplets (nominal diameter of 36 micrometers) was injected into an isothermal, laminar drop-tube reactor, quickly developing into a stream of droplets with heterogeneous size distribution due to droplet collision and coalescence. Gas was introduced to disperse the droplet stream, eliminating droplet interactions after 3 cm (2 ms) of flight. In the remaining 90% of reactor length, the droplets vaporized and burned, yielding inorganic particles of various sizes. Aqueous solutions containing nitrates of Cd, Pb, and Ni gave rise to particles with trimodal size distributions. Partitioning of the larger particles between residual and intermediate modes is suggestive of particle porosity variation. In addition, ultrafine particles, with submicron aerodynamic diameter, were formed, both by the anticipated vaporization pathway and by an unexpected explosive fragmentation mechanism. The fraction of submicron particles produced upon heating of a NiCl2 solution was higher than that formed by the heating of a Ni(NO3)2 solution. |