Study finds biodiesel blend reduces total particle mass in emissions but may have greater adverse health effect per mass than diesel
Findings from a study by researchers from the Department of Medicine and the School of Engineering at the University of Vermont suggest that the addition of biodiesel to diesel fuels will reduce the total particle mass of PM emissions—but that the biodiesel blend particles may contribute to greater biological effects per mass than B0, leading to potentially greater health risks.
As reported in a paper published in the ACS journal Environmental Science & Technology, the team first characterized exhaust particles produced by combustion of pure petrodiesel (B0) and B20 (20% soy biodiesel/ 80% B0) fuels using the same engine and running conditions, and then conducted experiments in two human cell lines representing bronchial epithelial cells and macrophages as well as in female mice. (Studies in cells alone do not necessarily reflect the integrated response of a whole animal, they noted.)
In the experiments, they used a 4-cylinder, 1.9-liter Volkswagen light-duty diesel engine and Klam dynamometer running at various throttle and brake settings over a 9-mode steady-state cycle to enable triplicate time-resolved measurement of particle number distributions with a scanning mobility particle sizer.
They found that total particulate gravimetric mass collected over the engine test cycle was more than 2 times higher for B0 than for B20 fuel. Particle number distributions aggregated over one example drive cycle indicate a unimodal B0 distribution centered at 51 nm, but a B20 distribution with a smaller diameter mode at 32.2 nm and a shoulder that corresponded to the B0 peak at ∼51 nm. The formation of smaller nanoparticles for B20 compared to the baseline B0 agrees with recent literature, they noted.
Surface areas computed from the number distributions showed that total integrated surface area of B20 particles was 2 times higher than that for B0 particles. The team determined that these smaller B20 particles formed during all but one operating mode.
The B0 particles were chiefly nonpolar and included n-alkanes, alkenes and 16 identified Polycyclic aromatic hydrocarbons (PAHs), representing ∼68% of the identified mass. About 46% of the B0 PM comprised polar compounds—chiefly esters, ketones and acids—also in agreement with earlier studies.
The most significant compositional difference between the exhaust PM from combustion of the 2 fuels was the ratio of polar to non-polar species: 46% assigned polar for B0 vs 68% polar compounds for the B20 fuel. We are unaware of previous studies reporting this type of comparison of the exhaust PM. However, our results are qualitatively consistent with previous work reporting lower elemental-to-organic carbon (EC/OC) ratio of biodiesel vs petrodiesel exhaust PM. Biodiesel PM contains a higher proportion of water-soluble organic carbon relative to petrodiesel PM. Addition of 20% soy biodiesel to B0 reduced the total PAH mass concentration by a factor of 2 for the 16 PAHs quantified with authentic standards. Benzo(a)pyrene, an IARC Class I carcinogen, was 2 times higher in B0 exhaust compared to B20, a result consistent with one previous study on rapeseed B30.—Fukagawa et al.
In vitro and in vivo responses to PM. Biological assays (inflammatory mediators, oxidative stress biomarkers) demonstrated that particulate matter (PM) generated by combustion of the two fuels induced different responses in in vitro and in vivo models.
They found that concentrations of inflammatory mediators (Interleukin-6, IL-6; Interferon-gamma-induced Protein 10, IP-10; Granulocyte-stimulating factor, G-CSF) in the medium of B20-treated cells and in bronchoalveolar lavage fluid of mice exposed to B20 were ∼20−30% higher than in B0-treated cells.
Together, in vitro and in vivo cytokine/chemokine data demonstrate an induction of inflammation as a consequence of exposure to the same mass concentrations of PM from B20 and B0 combustion with a higher response to B20 than B0, implying that acute exposure to biodiesel exhaust may be associated with more significant health outcomes. To determine the possible mechanism for the responses to PM, indices of oxidative stress and antioxidant defense were assessed.
...Taken together with the findings on particle characterization, it appears that the greater inflammatory responses and ROS [reactive oxygen species] production seen in cells and animals treated with B20 compared to B0 may be linked to the large polar component in B20 exhaust.
...although B20 produced less particle mass than B0, the relative smaller size but higher surface area, more polar components and FAME of B20 particles may contribute to greater biological effects per mass than B0, leading to potentially greater health risks.—Fukagawa et al.
Naomi K. Fukagawa, Muyao Li, Matthew E. Poynter, Brian C. Palmer, Erin Parker, John Kasumba, and Britt A. Holmén (2013) “Soy Biodiesel and Petrodiesel Emissions Differ in Size, Chemical Composition and Stimulation of Inflammatory Responses in Cells and Animals”, Environmental Science & Technology doi: 10.1021/es403146c