Carbonaceous nanoparticles in premixed flames: spectroscopic properties and size distributions

Epidemiological observations in industrialized cities are consistently finding that increased particle concentration, mainly generated by combustion, is correlated with a variety of detrimental health effects including increased daily mortality. While the toxicological mechanism for how particles affect human health is not yet known, recent studies show growing evidence that smaller size particles induce stronger health effects in both humans and animals, and that number concentration and surface area are possibly more important characteristics for health effects than mass and chemical composition. The strongest health effects are often observed for the smallest size particle measured (d=10-20 nm), which is unfortunately determined by limitations inherent in particle sizing instruments. Particles in the d= 2-4 nm size range are formed in combustion processes during the molecular growth process leading to soot inception. These particles are too small to be detected by current commercial particle sizing instruments, and as a result they have not yet been characterized for their toxicity. In this paper, we report two optical diagnostics for the spectroscopic characterization and size determination of carbonaceous nanoparticles formed in flames: the first one is the determination of the UV absorption spectra from 200 to 600 nm, obtained employing as light source a plasma produced by a laser breakdown. The second one is based on the time-resolved laser induced fluorescence and incandescence.