Comparative sampling of gas phase volatile and semi-volatile organic fuel emissions from a combustion aerosol standard system

Abstract

The incomplete combustion of fossil fuels generates hazardous gaseous compounds which have been linked to various adverse environmental and human health effects worldwide. Cleaner alternatives such as gas-to-liquid (GTL) and biofuels such rapeseed oil methyl ester (RME) have therefore been investigated. In this study, a Combustion Aerosol Standard (CAST) was used to generate a diluted, consistent and relatively stable source of fuel emissions from the combustion of diesel, GTL and RME, respectively. Gas phase sampling was carried out by removing particulates using a filter upstream of three different samplers: i) a commercialised activated charcoal sampler; ii) a validated polydimethylsiloxane (PDMS) sampler; and iii) a novel graphene wool (GW) sampler. The latter two were thermally desorbed, whilst the charcoal sampler was solvent extracted. All three samplers were analysed for trace levels of selected volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs) by means of gas chromatography–mass spectrometry (GC–MS).

The GW sampler outperformed the PDMS and activated charcoal samplers as the GW sampled the most compounds and had a lower variability in VOC and SVOC (selected polycyclic aromatic hydrocarbon and n-alkane) concentrations sampled, especially in the case of the n-alkanes (average %RSDs of the GW, PDMS and activated charcoal samplers were found to be 23.8%, 43.1% and 52.9%, respectively). The activated charcoal sampler was found to be unsuitable in this study due to the low number of detected compounds, as well as high benzene and toluene backgrounds of the sorbent. Combustion of diesel was found to emit a total VOC and SVOC concentration 4–5 times that of GTL and RME, respectively, based on GW sampler analyses. This study therefore further supports GTL and RME as cleaner fuel alternatives to petroleum derived diesel.