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• Soot inception causes a discontinuity in the properties of flame-generated matter. • The physical-chemical properties of incipient soot are unique. • Incipient soot acts as sink for large aromatics. • The structure of incipient soot is closely related to amorphous carbon. The transformation of molecular precursors in the gas phase into nanoparticles in the condensed phase (soot inception) during combustion has not yet been fully understood. While several hypotheses on soot inception are currently being examined, their validation requires detailed knowledge of the physical–chemical properties of the matter first formed in the condensed phase (incipient soot). However, characterizing short–lived species in a reactive environment at high temperature is inherently difficult. In this work, we propose a multi–analytical approach to indirectly characterize chemical composition and structure of incipient soot obtained in controlled laboratory conditions. The results are explained in light of recent developments on the characterization of the optical and magnetic properties of incipient soot, and used to build a phenomenological model of soot inception. The acquired information is key to support the hypothesis selection and to understand the reactivity of combustion byproducts and thus their impact on health and the environment. [ABSTRACT FROM AUTHOR] more...

[Display omitted] • Catalytic stripper: volatile phase remover in particle emission measurement systems. • Gas phase, polydisperse and size-selected particle chemical characterization. • Laser desorption/laser ionization/mass spectrometry/statistical data processing. • Lowest-size (10–32 nm) nanoparticles carry the highest surface organic fraction. • Excellent agreement with real-time in-situ aerodynamic-mass-mobility measurements. This work combines laser desorption/ionization mass spectrometry (L2MS) and advanced statistical techniques to reveal the impact of a catalytic stripper (CS) on the chemical composition (at the molecular level) of a gasoline direct injection engine exhaust, and follow the evolution of size-dependent chemical characteristics over the whole particles size range (10–560 nm). The gas phase and polydisperse particles making up the exhaust are separated and sampled on distinct substrates using an original homebuilt two-filter system, while size-selected particles are collected using a cascade impactor and separated into 13 different size bins (smallest diameters 10–18 nm). We demonstrate that a fine molecular-level characterization of the exhaust particulate matter is necessary to assess the effect of the CS, especially for the smallest ultra-fine particles carrying the largest volatile fraction. [ABSTRACT FROM AUTHOR] more...

• Exchange kinetic in CH 4 -hydrates using CO 2 or CO 2 -N 2 gas. • Impact of the initial CH 4 -hydrate system properties on the kinetic. • Structure, cage occupancy and phase composition monitored by Raman spectroscopy. • Quantitative and qualitative estimates of factors influencing the kinetic. Recovering methane from natural gas hydrate deposits using carbon dioxide injection is currently of great environmental and energetic interest as it shows potential for producing an energy resource while mitigating CO 2 emissions through CO 2 sequestration. This work investigates the exchange kinetic between CH 4 and CO 2 (or CO 2 -N 2 (v)) in synthetic hydrates, with an emphasis on the impact of CH 4 hydrate formation conditions (e.g. driving force Δ p) on the subsequent exchange reactions. Different driving forces Δ p are utilized and show that the exchange kinetic is improved by a factor of ~3 when the exchange is performed with low Δ p CH 4 hydrates, for which there is a higher relative amount of free H 2 O(liq) (277 K); the kinetic is further improved when stirring is applied. Isobaric CH 4 hydrates exhibit a fast primary hydrate dissociation and CH 4 release, followed by a slower exchange kinetic, possibly limited by solid-state exchange diffusion or secondary CO 2 -rich hydrate formation within the stability field of CH 4 hydrates. Upon exposure to a mixed CO 2 -N 2 (v) gas stream, secondary hydrate production is governed by the effective Δ p remaining after dissolution of the gas mixture, and results in an even slower exchange reaction rate. These results may help optimizing recovery processes in field trial experiments, where both hydrates and liquid water coexist, and aid in predicting the risk of geo-hazards induced by unstable secondary hydrate formation. Furthermore, the exchange kinetic dependencies highlighted here are important as they affect the overall energy efficiency and energy cost of CH 4 recovery processes in gas hydrate field trials. [ABSTRACT FROM AUTHOR] more...