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Reactive Oxidative Species and Speciated Particulate Light-Duty Engine Emissions from Diesel and Biodiesel Fuel Blends
journal contribution
posted on 2017-06-28, 00:00 authored by Britt A. Holmén, Benjamin Rukavina, John Kasumba, Naomi K. FukagawaIt
is well established that particulate matter (PM) continues to
be a major air pollutant challenge for human health globally, and
vehicle exhaust PM emissions have been linked to many adverse health
effects. However, the relative toxicity of biodiesel emissions compared
to petroleum diesel remains unclear. Given the legislated mandates
to increase biodiesel fuel use in response to energy security and
climate concerns, in this study we examined the relationships between
biodiesel fuel blend, exhaust particle oxidative potential (OP), and
PM composition. Mechanistically, there is a growing consensus that
the formation of reactive oxygen species (ROS) due to PM exposure
leads to subsequent oxidative stress and inflammation at the cellular
level. Here, dithiothreitol (DTT) assays were performed on impinger
samples of PM obtained from light-duty diesel engine transient cycle
emission tests with two biodiesel feedstocks, soybean (SOY) and waste
vegetable oil (WVO), blended with ultralow sulfur petrodiesel at five
different volume percentages of biodiesel, Bxx (B0,
B10, B20, B50, and B100). The DTT activity per mass of PM sampled
generally decreased as the percent biodiesel increased in the fuel,
for both feedstocks. Mean DTT PM activity (±1 std dev) for SOY
decreased from 20.9 ± 4.2 to 13.6 ± 3.8 nmol/min/mgPM for B0 and B100, respectively, and from 22.6 ± 4.5
to 8.5 ± 2.8 nmol/min/mgPM for the WVO feedstock.
Results indicate biodiesel blend PM may be less toxic per unit PM
mass emitted by 50–80%, depending on feedstock. By comparison
of feedstocks, statistically significantly lower OP for WVO, only
for blends B50 and B100, suggests different combustion products between
feedstocks only for the more highly oxygenated biodiesel blends used
in this study. The organic composition of WVO exhaust particles measured
by GC-MS showed positive correlations between DTT PM activity and
particle-phase polycyclic aromatic hydrocarbons (PAHs), n-alkanes, aromatic aldehydes, aromatic ketones, and quinones, but
not aliphatic aldehydes. The results of this study point to the importance
of aromatic polar organic combustion products to the redox cycling
potential of PM derived from biodiesel fuel combustion. Of the redox-active
metals (Fe, Cu, and Zn), only Zn showed positive correlation with
OP. The decreasing trend in WVO OP points to recent improvements in
waste oil biodiesel fuel production technology that may have beneficial
effects on exhaust emissions toxicity. Here, WVO feedstock preprocessing
steps to remove free fatty acids and the relatively high (2000 ppm)
fuel antioxidant concentration may partially explain the decreasing
trend of OP with increasing Bxx. Future biodiesel
emissions studies should combine PM toxicity assays with detailed
fuel, lubrication oil, and exhaust particle composition to better
elucidate compositional factors contributing to toxicity and identify
alternative biodiesel fuel blend compositions that minimize biological
response from exposure to exhaust PM. This may be possible using fuel
additives beyond antioxidants. Future studies should also quantify
the sensitivity of biologic responses to blends commonly used in real-world
engines (B0 to B20) given the variability observed in this study at
low blend ratios.
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exhaust particle oxidativeWVO exhaust particlescombustion productsbiodiesel fuel combustionPAHvehicle exhaust PM emissionsultralow sulfur petrodieselair pollutant challengefuel antioxidant concentrationbiodiesel fuel blendbiodiesel blend PMunit PM masswaste vegetable oilB 0B xxblends B 50exhaust particle compositionROSfuture biodiesel emissions studiesGC-MSalternative biodiesel fuel blend compositionsreactive oxygen speciesWVO OP pointsWVO feedstock preprocessing stepsReactive Oxidative Speciesincrease biodiesel fuel useDTT PM activityoxygenated biodiesel blendsPM toxicity assaysSpeciated Particulate Light-Duty Engine EmissionsBiodiesel Fuel Blendscycle emission testsexhaust emissions toxicitywaste oil biodiesel fuel production technology
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