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 to date, and 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; a highly paraffinic fuel, a South
African market fuel and a European reference fuel. Portable denuder samplers were used to collect the emissions and analysis was
done by thermal desorption-comprehensive 2D gas chromatography-time of flight mass spectrometry (TD-GC x GC-TofMS). The South
African market diesel had the greatest n-alkane emissions, with greater emissions observed in the earlier phases (low and medium
phase) of the WLTC test cycle. The total n-alkane emissions for this fuel ranged from 34.80 mg/km - 282.67 mg/km from the low to
the extra-high phase. The paraffinic diesel had the second highest n-alkane emissions with the total emissions ranging from 35.43
mg/km – 164.99 mg/km. The European reference diesel had the lowest n-alkane emissions amongst the three fuels, with the total
emissions ranging from 22.46 mg/km – 82.56 mg/km. Substituted alkyl-benzenes were also detected in the gas phase emissions from
each fuel, however only semi-quantitative analysis of these compounds was conducted. 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.
