Fragmentation and bond strength of airborne diesel soot agglomerates

Abstract

Background: The potential of diesel soot aerosol particles to break up into smaller units under mechanical stress was investigated by a direct impaction technique which measures the degree of fragmentation of individual agglomerates vs. impact energy. Diesel aerosol was generated by an idling diesel engine used for passenger vehicles. Both the aerosol emitted directly and aerosol that had undergone additional growth by Brownian coagulation ("aging") was investigated. Optionally a thermo-desoption technique at 280°C was used to remove all high-volatility and the majority of low-volatility HC adsorbates from the aerosol before aging.

Effect of Thermodenuding on the Structure of Nascent Flame Soot Aggregates

“…In a study on the fragmentation and bond strength of diesel soot, Rothenbacher et al [53] made a comparison between nascent soot treated with and without a TD as a function of impact velocity, and found no substantial change in the degree of fragmentation of nascent soot aggregates due to the thermodenuding. A low-pressure impactor was used to impart velocities of up to 300 m/s to the soot particles.…”

“…Chen et al [52] found that some polycyclic aromatic hydrocarbons, like phenanthrene and flouranthene, when present as a subnanometer layer on soot, behaved as subcooled liquid that weakened the bonds between the monomers, allowing them to slide and roll over each other and resulting in soot restructuring. Rothenbacher et al [53] provided evidence that thermodenuding might make a difference in the strength of the adhesive bonds between the monomers. For aged soot, they found a higher degree of fragmentation for thermodenuded particles (75% at 280 • C) than for untreated (not thermodenuded) particles (60%) when impacted at~200 m/s.…”

Deposition of fractal-like soot aggregates in the human respiratory tract

“…Moreover, if soot aggregates disintegrate upon contact with lung fluids (i.e. due to decreasing adhesion among the primary particles), penetration into the blood of individual soot spherules, small aggregates, or soluble matter adsorbed onto the aggregates is facilitated (Rothenbacher, Messerer, & Kasper, 2008;Torchilin, 2006). This penetration/absorption of individual spherules and toxic matter can induce the formation of reactive oxygen species and/or mediate chronic inflammatory response, resulting, among others, from overloading the immune system with excess activated sites.…”

Characterizing black carbon in rain and ice cores using coupled tangential flow filtration and transmission electron microscopy

“…Tests of bond strength between carbon spheres in BC show that aggregates are unlikely to fragment into smaller units (Rothenbacher et al, 2008). Hence, disaggregation from this method is unlikely.…”