Molecular Precursor of Soot and Quantification of the Associated Health Risk

Abstract

Particles generated in the combustion of organic materials are intrinsically toxic. Our work focuses on finding a way to quantify the health risk despite the complexity of the particles. First the current experimental research on the primary combustion aerosols is summarized. We take samples from various locations inside a laminar methane diffusion flame and freeze their physical and chemical state by rapid dilution with cold inert gas. Formation and growth of large molecules, mostly polycyclic aromatic hydrocarbons (PAH) is detected by mass spectroscopy and laser induced ionization. Fullerenes are also found. Particle size distribution are measured by standard aerosol techniques. To test the sampling, the flame is optionally seeded with palladium aerosol of known size distribution. We believe that the experiments on the model flame reveal some general principles of soot formation, in particular the fact that soot particles do not nucleate by agglomeration of large PAH. Photoemission is applied to study surface properties of soot particles from the flame. It is shown that the surface of the particles is covered with PAH. By heating the PAH can be removed and the properties of the carbon core are revealed. One can thereby distinguish a soot growth- from a soot burnout region in the flame. Time resolved desorption experiments of perylene (a PAH) from model aerosol particles are presented. It is shown that they follow a first order rate law. The photoelectric PAH sensor is introduced as a personal air quality monitor. The danger from inhaling combustion aerosol can be expressed in units of standard cigarettes.