Abstract
Exhaust emissions from diesel vehicles have recently been receiving global attention, due to potential human health effects associated with exposure to emitted pollutants. In addition, a link has recently been established between unburnt hydrocarbon (HC) emissions from diesel engines and photochemical smog. Despite being present at very low concentrations in the exhaust, these HCs may act as precursors in the formation of photochemical smog pollution. While short-chain HCs are easier to characterise and have been successfully reduced in many developed cities, longer chain HCs, most likely arising from diesel exhaust emissions, have been poorly quantified and to date, a limited range of HCs from this source has been studied. In this study, transient cycle tests were conducted to collect exhaust emissions from a Euro 3 compliant, 1.6 L test engine fuelled with three diesel fuels (SAM10, PAR10, and EUR10), using portable denuder samplers which were analysed by thermal desorption-comprehensive 2D gas chromatography-time of flight mass spectrometry (TD-GC x GC-TofMS). The SAM10 diesel had the greatest n-alkane emissions with greater emissions observed in the earlier phases (low and medium phase) of the WLTC test cycle. PAR10 diesel had the second highest n-alkane emissions and EUR10 had the lowest n-alkane emissions amongst the three fuels. Substituted alkyl-benzenes were also detected in the gas phase emissions from each fuel. The results showed that long-chain HCs were present at easily detectable concentrations in diesel engine exhaust emissions, which is critical in understanding their contribution to photochemical ozone and informing appropriate mitigation and management strategies.
Highlights
Exhaust fumes from vehicular emissions are one of the biggest contributors to pollution of the ambient atmosphere, which could be of great concern for South Africa’s agricultural sector and in urban environments
The results show a decrease in emissions from the low phase to the extrahigh phase, which can be attributed to oxidation of gaseous hydrocarbon emissions by the diesel oxidation catalyst (DOC) during high engine temperatures
semi-volatile organic compounds (SVOCs) exhaust emissions from a diesel engine used in lightduty passenger vehicles were characterised for three fuels
Summary
Exhaust fumes from vehicular emissions are one of the biggest contributors to pollution of the ambient atmosphere, which could be of great concern for South Africa’s agricultural sector and in urban environments. The most significant pollutants from vehicular emissions include nitrogen oxides (NOx) and HCs which are key precursors to photochemical smog formation Whilst both diesel and petrol engines contribute to NOx emissions, until recently the latter was thought to be the primary source of HC emissions in the atmosphere. Such high volume samplers are robust and easy to use in the field, they exhibit inherent limitations due to the sampling configuration and high volumetric flow rate (Forbes and Rohwer, 2015) Another commonly used sampling method, when conducting engine tests, is collection of dilute exhaust emissions into Tedlar® bags from a constant volume sampler (CVS) and subsequent analysis of emissions by gas chromatographymass spectrometry (GC-MS). It consists of four characteristic speed phases (low, medium, high and extra high), and emissions from each phase were collected onto separate samplers
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