Many uncertainties exist regarding the chemical composition of semi-volatile and intermediate volatility organic compounds (S/IVOCs), as traditional gas chromatographic methods are unable to separate them adequately. Air samples were collected at four sites in central London and were analysed using thermal desorption coupled to comprehensive gas chromatography time-of-flight mass spectrometry (GC×GC-ToF-MS).
Main S/IVOC groups identified and quantified include C13-C36 alkanes (linear and branched alkanes), C12-C25 monocyclic alkanes, C13-C27 bicyclic alkanes and C10-C24 monocyclic aromatics in the gas phase and particle phase. Diagnostic ratios of n-alkanes as well as correlation analysis of S/IVOCs and traffic tracers suggest traffic is a major contributor with a minor contribution from other sources. The distribution of hydrocarbons is similar in background and roadside air, indicating the importance of road traffic as a source of hydrocarbons in the urban atmosphere of London. Emission factors estimated in this study are broadly similar to those measured elsewhere in the world, despite differences in traffic fleet composition. Gas-particle partitioning of n-alkanes is discussed and compared between sites. The S/IVOC concentrations identified contribute to a small fraction of the total OH reactivity and SOA formation in background London