Abstract
Abstract. Airborne particles and vapours, like many other environmental samples including water, soils and sediments, contain complex mixtures of hydrocarbons, often deriving from crude oil either before or after fractionation into fuels, lubricants and feedstocks. Comprehensive 2D gas chromatography time-of-flight mass spectrometry (GC × GC-ToF-MS), offers a very powerful technique that separates and identifies many compounds in complicated hydrocarbon mixtures. However, quantification and identification of individual constituents at high ionization energies would require hundreds of expensive (when available) standards for calibration. Although the precise chemical structure of hydrocarbons does matter for their environmental impact and fate, strong similarities can be expected for compounds having very similar chemical structures and carbon numbers. There is, therefore, a clear benefit in an analytical technique which is specific enough to separate different classes of compounds and to distinguish homologous series while avoiding the need to handle each isomer individually. Varying EI (electron impact) ionization mass spectrometry significantly enhances the identification of individual isomers and homologous compound groups, which we refer to as “isomer sets”. Advances are reported in mapping and quantifying isomer sets of hydrocarbons (≥ C12) in diesel fuel, lubricating oil and diesel exhaust emissions. By using this analysis we report mass closures of ca. 90 and 75 % for diesel fuel and lubricating oil, and identify 85 and 75 % of the total ion current for gas- and particulate-phase diesel exhaust emissions.
Highlights
Crude oil contains a highly complex mixture of chemical constituents, mainly hydrocarbons (C4–C55) (Riazi, 2005)
Previous research has used a limited range of tracer compounds, or homologous series, for the quantification of emissions, considering representative species that can be distinguished from the bulk of the mass, typically involving analysis of the n-alkanes, polycyclic aromatic hydrocarbons (PAHs), hopanes and steranes (Schauer et al, 1999, 2002), each of which represent only a small fraction of the total mass or number of compounds emitted and might lead to an underestimation of the importance of lubricating oil as a source of secondary organic aerosol (SOA) (Brandenberger et al, 2005; Fujita et al, 2007)
Compounds identified within the diesel fuel included n-alkanes, branched alkanes, n-alkyl cycloalkanes, branched monocyclic alkanes, C1–C12 substituted bicyclic alkanes, C1–C4 substituted tetralins and indanes, C3–C12 substituted monocyclic aromatics, C1–C3 substituted biphenyls/acenaphthenes, C1–C4 substituted bicyclic aromatics, C1–C2 substituted fluorenes (FLU), C1–C2 substituted phenanthrene/anthracenes (PHE/ANT) and unsubstituted PAHs
Summary
Crude oil contains a highly complex mixture of chemical constituents, mainly hydrocarbons (C4–C55) (Riazi, 2005). Previous research has used a limited range of tracer compounds, or homologous series, for the quantification of emissions, considering representative species that can be distinguished from the bulk of the mass, typically involving analysis of the n-alkanes, polycyclic aromatic hydrocarbons (PAHs), hopanes and steranes (Schauer et al, 1999, 2002), each of which represent only a small fraction of the total mass or number of compounds emitted and might lead to an underestimation of the importance of lubricating oil as a source of SOA (Brandenberger et al, 2005; Fujita et al, 2007). GoodmanRendall et al (2016) used GC-MS with cold electron impact (EI) ionization, resolving detailed molecular components of diesel fuel Their results showed that the most important factors in determining SOA yields were carbon number, the presence (or absence) of a ring moiety and the degree of substitution; and precise information of branching and degrees of unsaturation was of secondary importance. Two dimensional gas chromatography timeof-flight-mass spectrometry (GC × GC-ToF-MS) (Adahchour et al, 2008; Alam et al, 2013; Alam and Harrison, 2016) was combined with an innovative quantification methodology based on total ion current (TIC) signal response to provide identification and quantification for the compound classes within typical diesel fuel, engine lubricant and engine emissions (gas and particulate phases), providing a nearcomplete mass closure for diesel fuel and engine lubricant and analyses of diesel engine exhaust composition
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