Factors determining the primary particle size of flame-generated inorganic aerosols

Abstract

The growth by coalescence of recently nucleated submicrometer ash primary particles was experimentally investigated by examining the products of combustion of both coals and synthetic chars in a laboratory study. Coalescence of submicrometer ash particles, which occurs by either solid state diffusion or viscous flow, was found to be a function of gas temperature and particle temperature, as indicated by the increase in ash particle size with increases in gas temperature and char combustion temperature. The chemical composition of the ash particles was also found to affect the final primary ash particle size, as demonstrated by the difference in primary particle sizes obtained from combustion of a variety of synthetic chars, each doped with a single mineral additive. The addition of sodium to a silicon system was seen to greatly increase the size of the submicrometer primary particles, by decreasing the viscosity and therefore permitting coalescence at lower temperatures. Trace impurities greatly affected the results for solid phase systems, as evidenced by the experimental results and theoretical predictions of particle coalescence behavior for calcium oxide particles that contained less than 1% impurity.