This paper introduces the generalization of reverse-phase HPLC fundamentals to normal-phase liquid chromatography, hydrophilic interaction chromatography (HILIC) and Automated Solid Phase Extraction (A-SPE).

In the current study, the chemical characterization of polycyclic aromatic hydrocarbons (PAHs) adsorbed on soot from premixed flames of synthetic paraffinic kerosene (SPK), conventional kerosene (Jet A-1), and Jet A-1/synthetic biofuel blends was carried out. Jet A-1 and SPK liquid fuels were analyzed with NMR to provide supporting information on their chemical composition. The analytical procedure used to characterize PAHs fraction in soot samples includes the following: (i) filtration of the soot samples diluted into n-hexane through PTFE filters, (ii) automated solid-phase extraction (A-SPE) for fractioning and cleaning-up the soot extracts, and (iii) chromatographic analysis of every fraction by reverse high-performance liquid chromatography (RPLC) with photodiode array (PDA) detection. Application of the aforementioned methodology allowed the identification of 78 compounds including indene, toluene, and 76 PAHs. Moreover, the relative abundance of fivemembered-ring PAHs and alkyl PAHs was evaluated, and 19 PAHs (16 EPA PAHs, 1-methylnaphthalene, 2-methylnaphthalene, and coronene) were quantified. The PAH characterization should contribute to improve our understanding of atmospheric reactivity of soot and other environmental aspects of aromatic compounds adsorbed on soot.

The heterogeneous reactions between trace gases and aerosol surfaces have been widely studied over the past decades, revealing the crucial role of these reactions in atmospheric chemistry. However, existing knowledge on the reactivity of mixed aerosols is limited, even though they have been observed in field measurements. In the current study, the heterogeneous interaction of NO2 with solid surfaces of Al2O3 covered with kerosene soot was investigated under dark conditions and in the presence of UV light. Experiments were performed at 293 K using a low-pressure flow-tube reactor coupled with a quadrupole mass spectrometer. The steady-state uptake coefficient, γ(ss), and the distribution of the gas-phase products were determined as functions of the Al2O3 mass; soot mass; NO2 concentration, varied in the range of (0.2-10) × 10(12) molecules cm(-3); photon flux; and relative humidity, ranging from 0.0032% to 32%. On Al2O3/soot surfaces, the reaction rate was substantially increased, and the formation of HONO was favored compared with that on individual pure soot and pure Al2O3 surfaces. Uptake of NO2 was enhanced in the presence of H2O under both dark and UV irradiation conditions, and the following empirical expressions were obtained: γ(ss,BET,dark) = (7.3 ± 0.9) × 10(-7) + (3.2 ± 0.5) × 10(-8) × RH and γ(ss,BET,UV) = (1.4 ± 0.2) × 10(-6) + (4.0 ± 0.9) × 10(-8) × RH. Specific experiments, with solid sample preheating and doping with polycyclic aromatic hydrocarbons (PAHs), showed that UV-absorbing organic compounds significantly affect the chemical reactivity of the mixed mineral/soot surfaces. A mechanistic scheme is proposed, in which Al2O3 can either collect electrons, initiating a sequence of redox reactions, or prevent the charge-recombination process, extending the lifetime of the excited state and enhancing the reactivity of the organics. Finally, the atmospheric implications of the observed results are briefly discussed.