Influence of oxygen content of the certain types of biodiesels on particulate oxidative potential.

Oxidative potential (OP) is related to the organic phase, specifically to its oxygenated organic fraction (OOA). Furthermore, the oxygen content of fuel molecules has significant influence on particulate OP. Thus, this study aimed to explore the actual dependency of the OOA and ROS to the oxygen content of the fuel. In order to reach the goal, different biodiesels blends, with various ranges of oxygen content; have been employed. The compact time of flight aerosol mass spectrometer (c-ToF AMS) enabled better identification of OOA. ROS monitored by using two assays: DTT and BPEA-nit. Despite emitting lower mass, both assays agreed that oxygen content of a biodiesel is directly correlated with its OOA, and highly related to its OP. Hence, the more oxygen included in the considered biodiesels, the higher the OP of PM emissions. This highlights the importance of taking oxygen content into account while assessing emissions from new fuel types, which is relevant from a health effects standpoint.

Influence of fuel molecular structure on the volatility and oxidative potential of biodiesel particulate matter.

We have studied the effect of chemical composition of biodiesel fuel on the physical (volatility) and chemical (reactive oxygenated species concentration) properties of nano particles emitted from a modern common-rail diesel engine. Particle emissions from the combustion of four biodiesels with controlled chemical compositions and different varying unsaturation degrees and carbon-chain lengths, together with a commercial diesel, were tested and compared in terms of volatility of particles and the amount of reactive oxygenated species carried by particles. Different blends of biodiesel and petro diesel were tested at several engine loads and speeds. We have observed that more saturated fuels with shorter carbon chain lengths result in lower particle mass but produce particles that are more volatile and also have higher levels of Reactive Oxygen Species. This highlights the importance of taking into account metrics that are relevant from the health effects point of view when assessing emissions from new fuel types.

Molecular orientational order of nitroxide radicals in liquid crystalline media.

The orientational distribution of a set of stable nitroxide radicals in aligned liquid crystals 5CB (nematic) and 8CB (smectic A) was studied in detail by numerical simulation of EPR spectra. The order parameters up to the 10th rank were measured. The directions of the principal orientation axes of the radicals were determined. It was shown that the ordering of the probe molecules is controlled by their interaction with the matrix molecules more than the inherent geometry of the probes themselves. The rigid fused phenanthrene-based (A5) and 2-azaphenalene (A4) nitroxides as well as the rigid core elongated C11 and 5α-cholestane (CLS) nitroxides were found to be most sensitive to the orientation of the liquid crystal matrixes.

Influence of oxygenated organic aerosols (OOAs) on the oxidative potential of diesel and biodiesel particulate matter.

Generally, the magnitude of pollutant emissions from diesel engines running on biodiesel fuel is ultimately coupled to the structure of the fuel's constituent molecules. Previous studies demonstrated the relationship between the organic fraction of particulate matter (PM) and its oxidative potential. Herein, emissions from a diesel engine running on different biofuels were analyzed in more detail to explore the role that different organic fractions play in the measured oxidative potential. In this work, a more detailed chemical analysis of biofuel PM was undertaken using a compact time of flight aerosol mass spectrometer (c-ToF AMS). This enabled a better identification of the different organic fractions that contribute to the overall measured oxidative potentials. The concentration of reactive oxygen species (ROS) was measured using a profluorescent nitroxide molecular probe 9-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-ethynyl)-10-(phenylethynyl)anthracene (BPEAnit). Therefore, the oxidative potential of the PM, measured through the ROS content, although proportional to the total organic content in certain cases, shows a much higher correlation with the oxygenated organic fraction as measured by the c-ToF AMS. This highlights the importance of knowing the surface chemistry of particles for assessing their health impacts. It also sheds light onto new aspects of particulate emissions that should be taken into account when establishing relevant metrics for assessing health implications of replacing diesel with alternative fuels.

Physicochemical characterization of particulate emissions from a compression ignition engine: the influence of biodiesel feedstock.

This study undertook a physicochemical characterization of particle emissions from a single compression ignition engine operated at one test mode with 3 biodiesel fuels made from 3 different feedstocks (i.e., soy, tallow, and canola) at 4 different blend percentages (20%, 40%, 60%, and 80%) to gain insights into their particle-related health effects. Particle physical properties were inferred by measuring particle number size distributions both with and without heating within a thermodenuder (TD) and also by measuring particulate matter (PM) emission factors with an aerodynamic diameter less than 10 µm (PM(10)). The chemical properties of particulates were investigated by measuring particle and vapor phase Polycyclic Aromatic Hydrocarbons (PAHs) and also Reactive Oxygen Species (ROS) concentrations. The particle number size distributions showed strong dependency on feedstock and blend percentage with some fuel types showing increased particle number emissions, while others showed particle number reductions. In addition, the median particle diameter decreased as the blend percentage was increased. Particle and vapor phase PAHs were generally reduced with biodiesel, with the results being relatively independent of the blend percentage. The ROS concentrations increased monotonically with biodiesel blend percentage but did not exhibit strong feedstock variability. Furthermore, the ROS concentrations correlated quite well with the organic volume percentage of particles - a quantity which increased with increasing blend percentage. At higher blend percentages, the particle surface area was significantly reduced, but the particles were internally mixed with a greater organic volume percentage (containing ROS) which has implications for using surface area as a regulatory metric for diesel particulate matter (DPM) emissions.

Physicochemical characterization of particulate emissions from a compression ignition engine employing two injection technologies and three fuels.

Alternative fuels and injection technologies are a necessary component of particulate emission reduction strategies for compression ignition engines. Consequently, this study undertakes a physicochemical characterization of diesel particulate matter (DPM) for engines equipped with alternative injection technologies (direct injection and common rail) and alternative fuels (ultra low sulfur diesel, a 20% biodiesel blend, and a synthetic diesel). Particle physical properties were addressed by measuring particle number size distributions, and particle chemical properties were addressed by measuring polycyclic aromatic hydrocarbons (PAHs) and reactive oxygen species (ROS). Particle volatility was determined by passing the polydisperse size distribution through a thermodenuder set to 300 °C. The results from this study, conducted over a four point test cycle, showed that both fuel type and injection technology have an impact on particle emissions, but injection technology was the more important factor. Significant particle number emission (54%-84%) reductions were achieved at half load operation (1% increase-43% decrease at full load) with the common rail injection system; however, the particles had a significantly higher PAH fraction (by a factor of 2 to 4) and ROS concentrations (by a factor of 6 to 16) both expressed on a test-cycle averaged basis. The results of this study have significant implications for the health effects of DPM emissions from both direct injection and common rail engines utilizing various alternative fuels.

Oxidative potential of logwood and pellet burning particles assessed by a novel profluorescent nitroxide probe.

This study reports the potential toxicological impact of particles produced during biomass combustion by an automatic pellet boiler and a traditional logwood stove under various combustion conditions using a novel profluorescent nitroxide probe, BPEAnit. This probe is weakly fluorescent but yields strong fluorescence emission upon radical trapping or redox activity. Samples were collected by bubbling aerosol through an impinger containing BPEAnit solution, followed by fluorescence measurement. The fluorescence of BPEAnit was measured for particles produced during various combustion phases: at the beginning of burning (cold start), stable combustion after refilling with the fuel (warm start), and poor burning conditions. For particles produced by the logwood stove under cold-start conditions, significantly higher amounts of reactive species per unit of particulate mass were observed compared to emissions produced during a warm start. In addition, sampling of logwood burning emissions after passing through a thermodenuder at 250 degrees C resulted in an 80-100% reduction of the fluorescence signal of the BPEAnit probe, indicating that the majority of reactive species were semivolatile. Moreover, the amount of reactive species showed a strong correlation with the amount of particulate organic material. This indicates the importance of semivolatile organics in particle-related toxicity. Particle emissions from the pellet boiler, although of similar mass concentration, were not observed to lead to an increase in fluorescence signal during any of the combustion phases.

The vibrational group frequency of the N-O* stretching band of nitroxide stable free radicals.

The group frequency of the N-O radical stretching vibration has received scant attention in the literature. The few existing treatments of the vibrational spectroscopy of nitroxides are incomplete at best and potentially misleading to workers in the field. To close this gap in the available knowledge, the existing literature on the vibrational spectra of nitroxide stable free radicals is critically reviewed with particular reference to the wavenumber position of the N-O* stretching vibration, nu(N-O*). Poor evidentiary bases for the assignment nu(N-O) were found in many instances. Ab initio Density Field Theory calculations using a model chemistry of UB3LYP at the 6-311++G(d,p) level were performed to obtain a theoretical band position of nu(N-O) for comparison with the published data. Large discrepancies between the theoretical and experimental values were found for the radical 3-carbamoyl-2,2,5,5-tetramethyl-3-pyrrolin-1-yloxyl, which currently sets the lower limit of the accepted wavenumber range of nu(N-O*), as well as for the nitronyl and iminyl nitroxides. The wavenumber position of nu(N-O*) was found to occur in the range 1450-1420cm(-1) for 5-membered cyclic nitroxides and 1395-1340cm(-1) for 6-membered cyclic and acyclic nitroxides. In nitronyl nitroxides, the symmetric stretching vibration occurs in the region 1470cm(-1), but coupling to other modes makes specific band assignments problematic for the nitronyl nitroxide group.

The vibrational spectrum of the stable free radical 1,1,3,3-tetramethylisoindolin-2-yloxyl.

Solid and solution IR and Raman spectra of a stable nitroxide radical, 1,1,3,3-tetramethylisoindolin-2-yloxyl (TMIO), are reported and compared to ab initio density functional theory calculations of the vibrational frequencies to obtain unequivocal band assignments, in particular of the NO stretching frequency, nu(NO). The band position was found to be at 1431 cm(-1) for the solid, which is well outside the previously published range of 1310-1380 cm(-1) for nitroxide radicals. This apparently anomalous peak position was confirmed by undertaking isotopic substitution studies through the preparation and recording of vibrational spectra of tetrakis(trideuteriomethyl)isoindolin-2-yloxyl ([2H12]-TMIO) and [2H12,15N]-TMIO analogues. Solution spectra of TMIO in methanol and CCl4 are assessed for possible solvent-dependent spin density distribution effects in the NO bond.

Electrospray ionization mass spectrometry of stable nitroxide free radicals and two isoindoline nitroxide dimers.

Electrospray ionization (ESI) mass spectra were recorded for a range of substituted isoindoline nitroxides, two isoindoline nitroxide dimers and two piperidinyl nitroxides. In all cases the dominant molecular species arise from oxidation rather than protonation, an unusual process in ESI. Fragment ion spectroscopy was used to establish fragmentation mechanisms for the nitroxides under ESI conditions.

Reaction of substituted anthracenes and a butadiene with nitric oxide: product formation determined by EPR spectroscopy.

When nitric oxide (NO), generated from nitric acid and copper, was reacted with a series of 9,10-substituted anthracenes, only 9,10-dimethylanthracene gave EPR detectable nitroxide radicals, although the expected bicyclic nitroxide arising from cheletropic NO addition across the 9,10-positions was not observed. Purity of the NO is crucial as the presence of higher oxides of nitrogen leads to radicals by hydrogen abstraction which are trapped by NO and the resultant nitroso compounds produce stable nitroxides detectable by EPR. In contrast the acyclic system, 3,4-diphenyl-2,5-dimethyl-2,4-hexadiene gives rise to an EPR spectrum consistent with cheletropic NO addition, although higher oxides of nitrogen again mediate the formation of different nitroxides.