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The physicochemical properties of combustion particles that promote lung toxicity are not fully understood, hindered by the fact that combustion particles vary based on the fuel and combustion conditions. Real-world combustion-particle properties also continually change as new fuels are implemented, engines age, and engine technologies evolve. This work used laboratory-generated particles produced under controlled combustion conditions in an effort to understand the relationship between different particle properties and the activation of established toxicological outcomes in human lung cells (H441 and THP-1). Particles were generated from controlled combustion of two simple biofuel/diesel surrogates (methyl decanoate and dodecane/BD, and butanol and dodecane/AD) and compared to a widely studied reference diesel particle (NIST SRM2975/RD). BD, AD, and RD particles exhibited differences in size, surface area, extractable chemical mass, and the content of individual polycyclic aromatic hydrocarbons (PAHs). Some of these differences were directly associated with different effects on biological responses. BD particles had the greatest surface area, amount of extractable material and oxidizing potential. These particles and extracts induced cytochrome P450 1A1 and 1B1 enzyme mRNA in lung cells. AD particles and extracts had the greatest total PAH content and also caused CYP1A1 and 1B1 mRNA induction. The RD extract contained the highest relative concentration of 2-ring PAHs and stimulated the greatest level of interleukin-8 (IL-8) and tumor necrosis factor-alpha (TNFα) cytokine secretion. Finally, AD and RD were more potent activators of TRPA1 than BD, and while neither the TRPA1 antagonist HC-030031 nor the antioxidant N-acetylcysteine (NAC) affected CYP1A1 or 1B1 mRNA induction, both inhibitors reduced IL-8 secretion and mRNA induction. These results highlight that differences in fuel and combustion conditions affect the physicochemical properties of particles, and these differences, in turn, affect commonly studied biological/toxicological responses.

In this study, a two-stage burner was used to determine kinetic parameters of soot oxidation by molecular oxygen. The two-stage burner technique produced soot particles from different fuels in the first burner and then oxidized the particles under either fuel lean or rich conditions in the secondary burner. Methyl decanoate/n-dodecane (surrogate for biodiesel/diesel) and n-butanol/n-dodecane (alcohol/diesel) were studied and compared with previous results using pure m-xylene, pure ndodecane, and m-xylene/n-dodecane mixtures (surrogate for conventional jet fuel (JP-8)). Particle size distributions, determined using samples taken from the center line of the secondary burner and characterized by a scanning mobility particle sizer, were used to determine the experimental oxidation rates. The evolution of major gas-phase species was measured experimentally by an online GC, and kinetic modeling was used to predict the concentration of OH radicals. The results revealed two regions in the flame: (i) a region close to the burner surface with a high O 2 concentration and (ii) a region where OH was formed and the O 2 concentration dropped. A power-law form of the kinetic rate was fitted to the experimental oxidation rates in the first region of flames where oxidation via O 2 dominated close to the burner surface and OH was not yet formed. The fit yielded an activation energy between 120.3 and 149.3 kJ mol −1 with an average of 134.8 kJ mol −1 . The average of the pre-exponential factor, A, was found to be 1600 with an order in molecular oxygen of 0.76, resulting in a kinetic rate equation of W O 2 (g cm −2 s −1 ) = 1600 × T −0.5 exp[(−134.8 ± 14.5)/RT](P O 2 ) 0.76 . The method was applied to calculate the oxidation rate of soot over the effective experimental temperature range 1350−1750 K and O 2 partial pressures from 0.065 to 0.123 atm. A comparison of the proposed model with the rates obtained for soot samples derived from the same fuels but oxidized in a thermographimetric analyzer showed that the proposed model can be extended to temperatures as low as 750 K. The reaction rate depended on the fuel source and flame condition, and some rates were over 1 order of magnitude higher than rates obtained from Nagle and Strickland-Constable.