Elucidating the polycyclic aromatic hydrocarbons involved in soot inception

Abstract

Polycyclic aromatic hydrocarbons are the main precursors to soot particles in combustion systems. A lack of direct experimental evidence has led to controversial theoretical explanations for the transition from gas-phase species to organic soot clusters. This work focuses on sampling infant soot particles from well-defined flames followed by analysis using state-of-the-art mass spectrometry. We found that PAH molecules present in soot particles are all stabilomers. Kinetic Monte Carlo simulations and thermodynamic stability calculations further identify the detected PAHs as peri-condensed and without aliphatic chains. Van der Waals forces can easily link PAHs of such size and shape to form PAH dimers and larger clusters under the specified flame conditions. Our results provide direct experimental evidence that soot inception is initiated by a physical process under typical flame conditions. This work improves our understanding of aerosol particulates, which has implications for their environmental and climate change impacts.

Bridging the gap: viable reaction pathways from tetrahedrane to benzyne

“…Hydrocarbons are known to exist in the interstellar medium (ISM) 1,2 with polycyclic aromatic hydrocarbons (PAHs) potentially responsible for around a quarter of the carbon molecularly sequestered in the ISM. 3 Recent research confirms that PAHs are the primary precursors to soot particles, 4 showcasing that these molecules are broadly applicable and not just limited to astrochemistry. This narrative enriches our comprehension of PAHs and underscores their universal presence and significance, both in earthly and cosmic environments.…”

“…While such reactions are believed to play an important role in astrochemistry, their role in combustion chemistry cannot be neglected as these molecules and their derivatives are known to inflict harmful consequences towards the climate, environment, and overall human health. 4,61–65…”

Direct Observation of Covalently Bound Clusters in Resonantly Stabilized Radical Reactions and Implications for Carbonaceous Particle Growth

“…24 The mass growth of PAH and soot in the absence of hydrogen radicals suggests that these documented pathways may not be favorable in radical-deficient environments as many free radicals are required for the activation of stable PAH molecules in the HACA, HAVA, and PAC mechanisms. 25 In addition, distinct aromatics such as peri-condensed aromatic hydrocarbons, 26 cata-condensed and pentagonal-ring linked species, 27 and bridged aromatics linked by aliphatic chains 28 have been suggested in flames and soot. However, the existing mechanisms do not fully explain the formation behavior of PAHs in various environments.…”