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Filtration and coagulation efficiency of sub-10 nm combustion-generated particles
Abstract
Particle size distributions are measured at the exhaust of a passenger-car diesel engine burning a Sulphur-free diesel oil. Different operating conditions of loads and engine speed, representative of low-loads are analyzed. Particles with sizes ranging from few nanometers up 1 µm are generated during diesel combustion. Operating conditions strongly affect the size distribution of the particles but overall they maintain a bimodality with a first mode, identified as nucleation mode, in the form of sub-10 nm particles, and a second mode in the form of soot particles and agglomerates. The lower is the engine load, the lower the emission of mass concentration of particulate matter but the higher the emission of particle numbers. Measurements performed in not-firing conditions confirmed that particles are generated during combustion more than by lube oil or mechanical friction. Filter efficiency with regard to the different particle sizes is evaluated by measuring particle size distributions before and after a diesel particulate filter. Results show that sub-10 nm particles are not sufficiently removed by the filter. Filter capture is almost complete for particles with sizes greater than 10 nm but the collection efficiency decreases to values of the order of 40–50% for sub-10 nm particles. This is of concern particularly when using fuels or operating conditions that produce a huge number of sub-10 nm particles not removed by the filter and hence emitted from the engine. The objective of the study is not to measure the filtration efficiency of a specific after-treatment system but to give a general warning on the capability of current particulate filters in removing sub-10 nm particles.
... Third, in the current simulation the collision efficiency is A = 1 , which should be the upper limit. Nonetheless, many studies have pointed out that collision efficiency is size dependent [32,[73][74][75] . The predicted PSDs are very sensitive to the collision efficiency as discussed in Section 5.2.1 , it is very likely that this oversimplified collision efficiency model would cause part of the discrepancy between the simulated and experimental PSDs. ...
... It is worth mentioning that the collision efficiency A increases with H p . Since the mean particle size increases with H p , Fig. 13 suggests that the collision efficiency increases with particle size, which is consistent with other studies [32,[73][74][75] . For instance, an experiment conducted by Sirignano and D'Anna [74] suggests that sub-10 nm nano-particles can have a sticking efficiency more than one order of magnitude lower than unity. ...
... For instance, an experiment conducted by Sirignano and D'Anna [74] suggests that sub-10 nm nano-particles can have a sticking efficiency more than one order of magnitude lower than unity. In a more recent study, Sirignano and D'Anna [75] attributed the size-dependent sticking efficiency to the drastic drop of van der Waals interactions between small nanoparticles, which can become lower than the kinetic energy of particles at flame temperature. At H p = 0 . ...
Numerical simulation of soot formation in a laminar premixed burner-stabilised benchmark ethylene stagnation flame was performed with a new detailed population balance model employing a two-step simulation methodology. In this model, soot particles are represented as aggregates composed of overlapping primary particles, where each primary particle is composed of a number of polycyclic aromatic hydrocarbons (PAHs). Coordinates of primary particles are tracked, which enables simulation of particle morphology and provides more quantities that are directly comparable to experimental observations. Parametric sensitivity study on the computed particle size distributions (PSDs) shows that the rate of production of pyrene and the collision efficiency have the most significant effect on the computed PSDs. Sensitivity of aggregate morphology to the sintering rate is studied by analysing the simulated primary particle size distributions (PPSDs) and transmission electron microscopy (TEM) images. The capability of the new model to predict PSDs in a premixed stagnation flame is investigated. Excellent agreement between the computed and measured PSDs is obtained for large burner-stagnation plate separation ( ≥ 0.7 cm) and for particles with mobility diameter larger than 6 nm, demonstrating the ability of this new model to describe the coagulation process of aggregate particles.
... The modes depend, among others, on the engine, fuel, combustion strategy, and aftertreatment devices [15,[170][171][172]. Recently, in addition to the combustion process related solid particles, nanoparticles during braking (motoring) have been reported, even when no fuel injection and combustion process take place in the cylinder [173][174][175]. Engine and aftertreatment wear particles can also been found [176]. ...
... Recently, in addition to the combustion process related solid particles, nanoparticles during braking (motoring) have been reported, even when no fuel injection and combustion process take place in the cylinder [173][174][175]. Engine and aftertreatment wear particles can also been found [176]. ...
Road transport significantly contributes to air pollution in cities. Emission regulations have led to significantly reduced emissions in modern vehicles. Particle emissions are controlled by a particulate matter (PM) mass and a solid particle number (SPN) limit. There are concerns that the SPN limit does not effectively control all relevant particulate species and there are instances of semi-volatile particle emissions that are order of magnitudes higher than the SPN emission levels. This overview discusses whether a new metric (total particles, i.e., solids and volatiles) should be introduced for the effective regulation of vehicle emissions. Initially, it summarizes recent findings on the contribution of road transport to particle number concentration levels in cities. Then, both solid and total particle emission levels from modern vehicles are presented and the adverse health effects of solid and volatile particles are briefly discussed. Finally, the open issues regarding an appropriate methodology (sampling and instrumentation) in order to achieve representative and reproducible results are summarized. The main finding of this overview is that, even though total particle sampling and quantification is feasible, details for its realization in a regulatory context are lacking. It is important to define the methodology details (sampling and dilution, measurement instrumentation, relevant sizes, etc.) and conduct inter-laboratory exercises to determine the reproducibility of a proposed method. It is also necessary to monitor the vehicle emissions according to the new method to understand current and possible future levels. With better understanding of the instances of formation of nucleation mode particles it will be possible to identify its culprits (e.g., fuel, lubricant, combustion, or aftertreatment operation). Then the appropriate solutions can be enforced and the right decisions can be taken on the need for new regulatory initiatives, for example the addition of total particles in the tailpipe, decrease of specific organic precursors, better control of inorganic precursors (e.g., NH3, SOx), or revision of fuel and lubricant specifications.
... The low interaction energy between incipient nanoparticles was confirmed with atomic force microscopy (AFM) studies showing the van der Waals interactions of these particles are decreased compared with primary soot particles [162]. Preliminary work shows that aftertreatment systems are only able to remove 40-50% of particles below 10 nm [223]. Another issue to consider is that fuels which are known to decrease the mass of soot emissions can increase the number of nanoparticles formed, for example biodiesel [219,224]. ...
... Another approach is to consider aftertreatment systems. As mentioned in Section 2.2, many of the smallest nanoparticles are not filtered by aftertreatment systems [223] due to their low coagulation efficiencies [37]. Recent efforts to remove these nanoparticles with activated carbon or fibre filters need to be more extensively explored [225]. ...
The route by which gas-phase molecules in hydrocarbon flames form condensed-phase carbonaceous nanoparticles (incipient soot) is reviewed. These products of incomplete combustion are introduced as particulates and materials revealing both their useful applications and unwanted impacts as pollutants. Significant advances in experimental techniques in the last decade have allowed the gas phase precursors and the transformation from molecules to nanoparticles to be directly observed. These measurements combined with computational techniques allow for various mechanisms known to date to be compared and explored. Questions remain surrounding the various mechanisms that lead to nanoparticle formation. Mechanisms combining physical and chemical routes, so-called physically stabilised soot inception, are highlighted as a possible “middle way”.
... PM is responsible for a range of human health concerns, especially the fine PM (PM 2.5 ) (Manojkumar and Srimuruganandam 2021). Based on sufficient evidence of carcinogenicity, the International Agency for Research on Cancer (IARC) classifies PM as Class I (carcinogenic to humans) (Sirignano and D'Anna 2018). PM is capable of causing lung diseases such as pulmonary fibrosis (Sun et al. 2020a), asthma, and chronic obstructive pulmonary disease through an inflammatory response, which has attracted increasing attention in recent years. ...
With the global emphasis on environmental protection and the proposal of the climate goal of “carbon neutrality,” countries around the world are calling for reductions in carbon dioxide, nitrogen oxide, and particulate matter pollution. These pollutants have severe impacts on human lives and should be effectively controlled. Engine exhaust is the most serious pollution source, and diesel engine is an important contributor to particulate matter. Diesel particulate filter (DPF) technology has proven to be an effective technology for soot control at the present and in the future. Firstly, the exacerbating effect of particulate matter on human infectious disease viruses is discussed. Then, the latest developments in the influence of key factors on DPF performance are reviewed at different observation scales (wall, channel, and entire filter). In addition, current soot catalytic oxidant schemes are presented in the review, and the significance of catalyst activity and soot oxidation kinetic models are highlighted. Finally, the areas that need further research are determined, which has important guiding significance for future research. Current catalytic technologies are focused on stable materials with high mobility of oxidizing substances and low cost. The challenge of DPF optimization design is to accurately calculate the balance between soot and ash load, DPF regeneration control strategy, and exhaust heat management strategy.
... Sirignano & D'Anna (2013) reported that the coagulation efficiency of soot particles decreases with increasing temperature. The low coagulation efficiency for 25 small particles colliding at high temperatures was ascribed to the high kinetic energy of particles (center of mass translational kinetic energy) due to Brownian motion, which caused thermal rebound effects prevailing over adhesion mechanisms due to van der Waals forces (D'Alessio et al., 2005;Sirignano & D'Anna, 2013;Wang & Kasper, 1991;Sirignano & D'Anna, 2018). coagulation of electrically neutral aerosol particles, where coagulation effi- ...
In this work, we studied the coagulation process of two PAH clusters with diameter ∼2 nm using reactive molecular dynamics (MD) simulations. To describe the coagulation process quantitatively, the distance between the center of mass (COM) of the two PAH clusters, as well as the inter-cluster potential energy and kinetic energy of the COM of the clusters were calculated. Head-on coagulation efficiencies (η) of two PAH clusters at typical flame temperatures where soot inception is most likely to occur, i.e., 1500 K—2000 K, were determined based on hundreds of MD simulated trajectories. Our simulation results showed that η decreases with increasing temperature, which is mainly due to the increased kinetic energy of atoms within the PAH clusters at higher temperature. In addition, introduction of surface σ-radical site fraction in the range of 0.01 to 0.1 can only moderately improve η by ∼10% by forming carbon–carbon bonds between the two coagulating clusters, which suggests η of incipient soot nanoparticles with surface σ-radicals in high temperature flame regions is very low even if with reactive coagulation taken into consideration.
... In particular, PM with a diameter of ≤ 2.5 µm potential threats both for human health and for the atmospheric environment (Dockery, 2009;Xie et al., 2016). New and rigorous ambient air quality standards have been devised and have necessitating novel and effective methods (Noh et al., 2001;Peukert and Wadenpohl, 2001;Sheng and Shen, 2017;Sobczyk et al., 2017;Chang et al., 2018;Sirignano and Danna, 2018) to remove fine particles from air to meet these standards. ...
Background
iodiesel is promoted as a sustainable replacement for commercial diesel. Biodiesel fuel and exhaust properties change depending on the base feedstock oil/fat used during creation. The aims of this study were, for the first time, to compare the exhaust exposure health impacts of a wide range of biodiesels made from different feedstocks and relate these effects with the corresponding exhaust characteristics.
Method
Primary airway epithelial cells were exposed to diluted exhaust from an engine running on conventional diesel and biodiesel made from Soy, Canola, Waste Cooking Oil, Tallow, Palm and Cottonseed. Exhaust properties and cellular viability and mediator release were analysed post exposure.
Results
The exhaust physico-chemistry of Tallow biodiesel was the most different to diesel as well as the most toxic, with exposure resulting in significantly decreased cellular viability (95.8±6.5%) and increased release of several immune mediators including IL-6 (+223.11±368.83 pg/mL) and IL-8 (+1516.17±2908.79 pg/mL) above Air controls. In contrast Canola biodiesel was the least toxic with exposure only increasing TNF-α (4.91±8.61).
Conclusion
This study, which investigated the toxic effects for the largest range of biodiesels, shows that exposure to different exhausts results in a spectrum of toxic effects in vitro when combusted under identical conditions.
A detailed experimental characterization of the particle emissions of a EURO 5 light-duty Diesel engine, equipped with a wall flow Diesel Particulate Filter (DPF), is presented. Particle Size Distributions (PSDs) in the range from 4.5 up to 160 nm have been measured at the engine exhaust by means of a Scanning Mobility Particle Sizer, during both DPF accumulation and regeneration phase. During accumulation, the size-dependent DPF removal efficiency has been evaluated by PSDs measurements at both inlet and outlet of the filter. The maximum efficiency was found in the range 10-40 nm. Nevertheless, the DPF ensures a strong reduction in the emissions for the sub-23 nm nanoparticles too, with an efficiency between 91–95%. Unless for the warm-up phase, the engine operating conditions do not have a great impact on the particles emitted due to the high DPF removal efficiency. The measurements carried out during the regeneration phase evidenced that particle emissions strongly depend on DPF temperature. Actually, once the soot burnout temperature is reached, soot oxidation starts and a great amount of particles in terms of PN is released. Overall, PSDs showed an increase in particle number concentration up to two order of magnitude with respect to the emissions measured during the accumulation phase.
Particles in gas always tend to move upward and be collected on cold surfaces. This behavior, which has resulted from the interaction of several mechanisms, including Brownian diffusion, inertial impaction, interception, thermophoresis, and diffusiophoresis, is complex. These mechanisms have been previously investigated profoundly. However, a systematic summary is scarce, and inconsistent statements and misunderstandings about these mechanisms are observed in previous works. To understand the behavior of particle collection on cold surfaces well, the status of these mechanisms has been reviewed, and a mechanism coordinator chart has been established in this paper. Meanwhile, the discrimination of diffusiophoresis in different fields has been analyzed. The research status of the behavior of particle collection on cold surfaces in three types of scenarios has been introduced. Finally, future research directions concerning this topic have been suggested.
Combustion and pollutant emission characteristics of diesel/gasoline/iso-butanol mixtures have been investigated in a low temperature combustion diesel engine at an engine speed of 1800 rpm and load of 3 bar brake mean effective pressure. The test fuels were denoted as D100 (diesel), DG (70% diesel + 30% gasoline, on a mass basis), DGB (70% diesel + 15% gasoline + 15% iso-butanol) and DB (70% diesel + 30% iso-butanol). The result reveals that blend fuels have longer ignition timing periods, delayed CA50 and higher brake thermal efficiencies than D100. Meanwhile, blend fuels have higher maximum pressure rise rates if the exhaust gas recirculation (EGR) rate is less than 14.2%, but an opposite trend is found as the EGR rate was increased sequentially. At a fixed EGR rate, blend fuels have lower CO emissions, large sized particle numbers and particle diameters, but higher HC and NOx emissions. An interesting result is that blend fuels have more nucleation mode and accumulation mode particle numbers at small EGR rate (≤14.2%), but it shows opposite change trends when the EGR rate higher than 14.2%. Furthermore, iso-butanol has a better effect than gasoline in reducing NOx and particulate matter emissions along with high levels of EGR. However, it is worth to noticed that diesel/iso-butanol has the highest number concentration of sub-10 nm particles.
A series of membranes, made from polystyrene microfibers and with different morphologies, were fabricated via electrospinning method in this study. In addition, not only porous fibers but also beaded fibers were obtained by adjusting the experimental temperature in a reasonable and appropriate way. Assisted by a high-speed camera, the images of jet behaviors at different experimental temperatures were captured for the purpose of in-depth and comprehensive understanding of formation mechanism of different fiber morphologies. Mono-disperse sodium chloride aerosol particles with different sizes and cigarette smoke were used, for the attainment of the objective of evaluation on the filtration performance of fabricated membranes. The experimental results showed that straight fiber with narrow pores on its surface can be obtained at 20°C spinning temperature because of the rapid jet motion and solvent evaporation, and also, beaded fibers can be fabricated in the situation of spinning temperature higher than 25°C due to the sudden change of surface tension resulted from the fast solvent evaporation. The porous straight fibers exhibited excellent filtration performance to cigarette smoke and aerosol containing particles of all sizes (99.76%, 99.92%, and 99.99% filtration efficiency for particles with sizes of 0.3 µm, 0.5 µm, and 1 µm, respectively).
Combustion and pollutant emissions from a high pressure common-rail diesel engine using ternary diesel/gasoline/iso-butanol blends were investigated experimentally in order to improve combustion process and farther decrease emissions of diesel/gasoline blends. The experiments were carried out at five injection timings under medium engine load. Four fuels were tested in this work, D100 (pure diesel) was tested for baseline comparison, the other three fuels were DG (30% gasoline in diesel fuel by mass), DGB (15% gasoline and 15% iso-butanol in diesel fuel) and DB (30% iso-butanol in diesel fuel). Experimental results indicate that DG, DGB and DB delayed the ignition timing periods and shortened the combustion durations, resulting in higher levels of premixed combustion and maximum pressure rise rates (MPRRs). Meanwhile, DGB and DB showed higher brake thermal efficiencies (BTEs) than DG and D100. It was also found that adding gasoline and iso-butanol, substantial decrease in carbon monoxide (CO) emissions, particulate diameters, nucleation mode (NM) and accumulation mode (AM) particle numbers were achieved, but the emissions of unburned hydrocarbons (HC) and nitrogen oxides (NOx) were increased slightly. DGB and DB produced better NOx-particulate matter (PM) trade-off than DG and D100 in combination with retarded injection timing. Furthermore, PM emitted from blend fuels showed higher ratios of sub-10 nm particle number concentrations, the sequence is D100 < DG < DGB < DB, which may be more harmful to human health.
Gasoline compression ignition (GCI) combustion is a promising solution to address increasingly stringent efficiency and emissions regulations imposed on the internal combustion engine. However, the high resistance to auto-ignition of modern market gasoline makes low load compression ignition operation difficult. The most comprehensive work focused on low load GCI operation has been performed on multi-cylinder research engines where it is difficult to decouple effects of the combustion event from air-handling and system level parameters (e.g., intake pressurization and exhaust gas recirculation (EGR)). Further, most research has focused on technology applications (e.g., use of variable valve actuation or supercharging) rather than fundamental effects, making identification of influential factors difficult. Accordingly, there is a need for detailed investigations focused on isolating the critical parameters that can be used to enable low load GCI operation. A full factorial parametric study was completed to isolate the effects of intake temperature, EGR rate, and fuel reactivity on low load performance. A minimum intake pressure metric was used to compare these parameters. This allowed for combustion phasing and load to be held constant while isolating the experiment from fuel injection effects. The effort showed that increasing intake temperature yields a linear reduction in the minimum intake pressure required for stable operation. Adding a small amount of diesel fuel to gasoline improved combustion stability with minimal need for energy addition through intake pressurization. The minimum intake pressure requirement also showed very good correlation with the measured research octane number of the fuel. However, increasing the fuel reactivity with diesel fuel, caused NOx emissions to increase. Response model analysis was used to determine the intake conditions required to maintain NOx levels that may not require lean NOx after treatment. The combination of diesel fuel blending and EGR allowed NOx levels to be reduced to near zero values with the minimum intake pressurization required. A detailed investigation into the effects of EGR showed that, for a given fuel, there is a maximum EGR rate that allows for stable operation, which effectively constrains the minimum NOx prior to aftertreatment.
Historically, regulators of diesel emissions have formulated their legislation in gravimetric terms (i.e., in g/km or g/kWh). This quantitative approach, while arguably valid for gaseous emissions such as NOx, does not appreciate the complexity of particulate matter. More recently, much research, along with new legislation, views particulate matter in a more qualitative way and focuses on such metric as the total particle count and size distribution. While the trade-off in gravimetric particular matter and NOx is well known as the “diesel dilemma” this study, for the first time, demonstrates that there is also a trade-off in particulate size modes (accumulation-nucleation). To this end, a wide range of fuel properties and engine operating conditions are tested on a dedicated heavy-duty test rig. The main message that can be drawn from the results is that the optima for both the classical and newly presented accumulation-nucleation trade-off appear to be concurrent in nature. This implies that when the position on the curve of any given data point is known for one trade-off, the associated location on the other can be qualitatively predicted. Given the breadth of the operation conditions and fuel properties tested in this study, it would appear that this concurrence, which could help guide engine calibrators and aftertreatment specialists, is quite robust indeed.
A solid particle number limit was applied to the European legislation for diesel vehicles in 2011. Extension to gasoline direct injection vehicles raised concerns because many studies found particles below the lower size limit of the method (23 nm). Here we investigated experimentally the feasibility of lowering this size. A nano Condensation Nucleus Counter system (nCNC) (d50% = 1.3 nm) was used in parallel with Condensation Particle Counters (CPCs) (d50% = 3 nm, 10 nm and 23 nm) at various sampling systems based on ejector or rotating disk diluters and having thermal pre-treatment systems consisting of evaporation tubes or catalytic strippers. An Engine Exhaust Particle Sizer (EEPS) measured the particle size distributions. Depending on the losses and thermal pre-treatment of the sampling system, differences of up to 150% could be seen on the final detected particle concentrations when including the particles smaller than 23 nm in diameter. A volatile artefact as particles with diameters below 10 nm was at times observed during the cold start measurements of a 2-stroke moped. The diesel vehicles equipped with the Diesel Particulate Filter (DPF) had a low solid sub-23 nm particles fraction (<20%), the gasoline with direct injection vehicles had higher (35–50%), the gasoline vehicles with port fuel injection and the two mopeds (two and four-stroke) had the majority of particles below 23 nm. The size distributions peaked at 60–80 nm for the DPF equipped vehicles, at 40–90 nm for the gasoline vehicles with a separate nucleation mode peak at approximately 10 nm sometimes. Mopeds peaked at sizes below 50 nm when their aerosol was thermally pre-treated.
Although mass emissions of combustion-generated particulate matter have been substantially reduced by new combustion technology, there is still a great concern about the emissions of huge numbers of sub-10 nm particles with insignificant mass. These particles have up to orders of magnitude higher surface area to mass ratios compared to larger particles, have surfaces covered with adsorbed volatile and semi-volatile organic species or even are constituted by such species. Currently there is only very little information available on exposure and related health effects specific for smaller particles and first evidences for long-term health effects has only been recently published. However, the fact that these nanoparticles are not easily measured at the exhausts and in the atmosphere and that their biological activity is obscure does not mean that we can overlook them. There is an urgent need to develop i) reliable methods to measure sub-10 nm particles at the exhaust and in the atmosphere and ii) a robust correlation between the chemical structure of the molecules making up combustion-generated nanoparticles and health burden of new combustion technologies. Our attention has to turn to this new class of combustion-generated nanoparticles, which might be the future major constituents of air pollution.
Interaction forces acting between combustion-generated carbon particles were studied by using atomic force microscopy (AFM). To this aim, carbon nanoparticles were produced in fuel-rich ethylene/air laminar premixed flames with different equivalent ratios Φ, and analyzed at a fixed residence time in the flame. Particles were collected on mica substrates by means of a thermophoretic sampling system and then analyzed by AFM. A characterization of particle dimension and morphology were performed operating AFM in semicontact mode, showing that the shape of the particles collected on a sampling plate is never spherical. Increasing the flame-equivalent ratio, particle shape moves from an almost atomically thick object to thicker compounds, indicating the transformation from particles made of small, defective graphene-like sheets to particles containing stacked aromatic layers. Attractive and adhesive forces between a titanium nitride probe and sampled particles were calculated from force–distance curves acquired in AFM force spectroscopy mode. Assuming that van der Walls forces are the main contribution to attractive forces, the measurement of attractive forces allowed the evaluation of the Hamaker constant for the carbon particles as a function of the flame-equivalent ratio. The comparison of the measured Hamaker constants with the values for benzene and HOPG, suggests a continuous increase of the aromatic domains and the three-dimensional order within the particles when the flame-equivalent ratio increases.Copyright 2015 American Association for Aerosol Research
This paper reviews the particle emissions formed during the combustion process in spark ignition and diesel engine. Proposed legislation in Europe and California will impose a particle number requirement for GDI (gasoline direct injection) vehicles and will introduce the Euro 6 and LEV-III emission standards. More careful optimization for reducing particulate emission on engine hardware, fuel system, and control strategy to reduce particulate emissions will be required during cold start and warm-up phases. Because The diesel combustion inherently produces significant amounts of PM as a result of incomplete combustion around individual fuel droplets in the combustion zone, much attention has been paid to reducing particle emissions through electronic engine control, high pressure injection systems, combustion chamber design, and exhaust after-treatment technologies. In this paper, recent research and development trends to reduce the particle emissions from internal combustion engines are summarized, with a focus on PMP activity in EU, CARB and SAE papers and including both state-of-the-art light-duty vehicles and heavy-duty engines.
In 2011, the European Commission introduced a limit for nonvolatile particle number (PN) emissions >23 nm from light-duty (LD) vehicles and the stated intent is to implement similar legislation for on-road heavy-duty (HD) engines at the next legislative stage. This paper reviews the recent literature regarding the operation-dependent emission of PN from LD vehicles and HD engines, and the measurement procedure used for regulatory purposes. The repeatability of the PN method is of the order of 5% and higher scatter of the results can easily be explained by the effect of the vehicles or the aftertreatment devices on the PN emissions (e.g., the fill state of the diesel particulate filters). Reproducibility remains an issue since it may exceed 30%. These high-variability levels are mainly associated with calibration uncertainties of the PN instruments. Correlation measurements between the full-flow dilution tunnels (constant-volume samplers, CVS) and the proportional partial-flow dilution systems (PFDS) showed agreement within 15% for the PN method down to 1 × 10 p/kWh. At lower concentrations, the PN background of the CVS and/or the PFDS can result in larger inconsistencies. The filter-based particulate matter (PM) mass and the PN emissions correlate well down to 1–2 mg/km for LD vehicles and to 2–3 mg/kWh for HD applications. The correlation improves when only elemental carbon mass is considered: it is relatively good down to 0.1–0.3 mg/km or mg/kWh.Copyright 2012 American Association for Aerosol Research
Although humans have been exposed to airborne nanosized particles (NSPs; < 100 nm) throughout their evolutionary stages, such exposure has increased dramatically over the last century due to anthropogenic sources. The rapidly developing field of nanotechnology is likely to become yet another source through inhalation, ingestion, skin uptake, and injection of engineered nanomaterials. Information about safety and potential hazards is urgently needed. Results of older biokinetic studies with NSPs and newer epidemiologic and toxicologic studies with airborne ultrafine particles can be viewed as the basis for the expanding field of nanotoxicology, which can be defined as safety evaluation of engineered nanostructures and nanodevices. Collectively, some emerging concepts of nanotoxicology can be identified from the results of these studies. When inhaled, specific sizes of NSPs are efficiently deposited by diffusional mechanisms in all regions of the respiratory tract. The small size facilitates uptake into cells and transcytosis across epithelial and endothelial cells into the blood and lymph circulation to reach potentially sensitive target sites such as bone marrow, lymph nodes, spleen, and heart. Access to the central nervous system and ganglia via translocation along axons and dendrites of neurons has also been observed. NSPs penetrating the skin distribute via uptake into lymphatic channels. Endocytosis and biokinetics are largely dependent on NSP surface chemistry (coating) and in vivo surface modifications. The greater surface area per mass compared with larger-sized particles of the same chemistry renders NSPs more active biologically. This activity includes a potential for inflammatory and pro-oxidant, but also antioxidant, activity, which can explain early findings showing mixed results in terms of toxicity of NSPs to environmentally relevant species. Evidence of mitochondrial distribution and oxidative stress response after NSP endocytosis points to a need for basic research on their interactions with subcellular structures. Additional considerations for assessing safety of engineered NSPs include careful selections of appropriate and relevant doses/concentrations, the likelihood of increased effects in a compromised organism, and also the benefits of possible desirable effects. An interdisciplinary team approach (e.g., toxicology, materials science, medicine, molecular biology, and bioinformatics, to name a few) is mandatory for nanotoxicology research to arrive at an appropriate risk assessment.
The link between elevated concentrations of ambient particulate matter (PM) and increased mortality has been investigated in numerous studies. Here we analyzed the role of different particle size fractions with respect to total and cardio-respiratory mortality in Erfurt, Germany, between 1995 and 2001. Number concentrations (NC) of PM were measured using an aerosol spectrometer consisting of a Differential Mobility Particle Sizer and a Laser Aerosol Spectrometer to characterize particles between 0.01 and 0.5 and between 0.1 and 2.5 microm, respectively. We derived daily means of particle NC for ultrafine (0.01-0.1 microm) and for fine particles (0.01-2.5 microm). Assuming spherical particles of a constant density, we estimated the mass concentrations (MC) of particles in these size ranges. Concurrently, data on daily total and cardio-respiratory death counts were obtained from local health authorities. The data were analyzed using Poisson Generalized Additive Models adjusting for trend, seasonality, influenza epidemics, day of the week, and meteorology using smooth functions or indicator variables. We found statistically significant associations between elevated ultrafine particle (UFP; diameter: 0.01-0.1 microm) NC and total as well as cardio-respiratory mortality, each with a 4 days lag. The relative mortality risk (RR) for a 9748 cm(-3) increase in UFP NC was RR=1.029 and its 95% confidence interval (CI)=1.003-1.055 for total mortality. For cardio-respiratory mortality we found: RR=1.031, 95% CI: 1.003-1.060. No association between fine particle MC and mortality was found. This study shows that UFP, representing fresh combustion particles, may be an important component of urban air pollution associated with health effects.
Particulate matter, especially ultrafine particles (UFPs), may cause health effects through generation of oxidative stress, with resulting damage to DNA and other macromolecules.
We investigated oxidative damage to DNA and related repair capacity in peripheral blood mononuclear cells (PBMCs) during controlled exposure to urban air particles with assignment of number concentration (NC) to four size modes with average diameters of 12, 23, 57, and 212 nm.
Twenty-nine healthy adults participated in a randomized, two-factor cross-over study with or without biking exercise for 180 min and with exposure to particles (NC 6169-15362/cm(3)) or filtered air (NC 91-542/cm(3)) for 24 hr.
The levels of DNA strand breaks (SBs), oxidized purines as formamidopyrimidine DNA glycolase (FPG) sites, and activity of 7,8-dihydro-8-oxoguanine-DNA glycosylase (OGG1) in PBMCs were measured by the Comet assay. mRNA levels of OGG1, nucleoside diphosphate linked moiety X-type motif 1 (NUDT1), and heme oxygenase-1 (HO1) were determined by real-time reverse transcriptase-polymerase chain reaction.
Exposure to UFPs for 6 and 24 hr significantly increased the levels of SBs and FPG sites, with a further insignificant increase after physical exercise. The OGG1 activity and expression of OGG1, NUDT1, and HO1 were unaltered. There was a significant dose-response relationship between NC and DNA damage, with the 57-nm mode as the major contributor to effects. Concomitant exposure to ozone, nitrogen oxides, and carbon monoxide had no influence.
Our results indicate that UFPs, especially the 57-nm soot fraction from vehicle emissions, causes systemic oxidative stress with damage to DNA and no apparent compensatory up-regulation of DNA repair within 24 hr.
Laser-induced incandescence (LII) measurements were conducted to explore the ability of LII to detect small soot particles of less than 10 nm in two sooting flat premixed flames of n-butane: a so-called nucleation flame obtained at a threshold equivalence ratio Φ = 1.75, in which the incipient soot particles undergo only minor soot surface growth along the flame, and a more sooting flame at Φ = 1.95. Size measurements were obtained by modeling the time-resolved LII signals detected using 1064 nm laser excitation. Spectrally-resolved LII signals collected in the nucleation flame display a similar blackbody-like behavior as mature soot. Soot particle temperature was determined from spectrally-resolved detection. LII modeling was conducted using parameters either relevant to those of mature soot or derived from fitting the modeled results to the experimental LII data. Particle size measurements were also carried out using (1) ex situ analysis by helium-ion microscopy (HIM) of particles sampled thermophoretically and (2) online size distribution analysis of microprobe-sampled particles using a 1 nm-SMPS. The size distributions of the incipient soot particles, found in the nucleation flame and in the early soot region of the Φ = 1.95 flame, derived from time-resolved LII signals are in good agreement with HIM and 1 nm-SMPS measurements and are in the range of 2–4 nm. The thermal and optical properties of incipient soot were found to be not radically different from those of mature soot commonly used in LII modeling. This explains the ability of incipient soot particles to produce continuous thermal emissions in the visible spectrum. This study demonstrates that LII is a promising in situ optical particle sizing technique that is capable of detecting incipient soot as small as about 2.5 nm and potentially 2 nm and resolving small changes in soot sizes below 10 nm.
© 2017 American Association for Aerosol Research
This paper presents both in-situ and ex-situ measurements of nanostructures (also loosely referred to as nanoparticles) in laminar flames with the purpose of providing an understanding of their evolution to soot. Two laminar flame burners are studied covering a range of C/O ratios and hence different sooting propensities. Ex-situ measurements, utilizing soot sampling and analysis using differential mobility analyzers, are performed to yield information on the particle size distribution (PSD). A broad range of in-situ measurement techniques are employed including laser-induced fluorescence (LIF), laser-induced incandescence (LII), and elastic laser scattering. In-situ measurements completed at the University of Sydney, utilise fast response photomultiplier tubes to monitor time-resolved emission signals simultaneously in four different spectral regions, whilst measurements performed at the University of Naples Federico II are spectrally resolved. The temporal lifetimes of the LIF signals are found to be much longer than that expected for molecules at the same temperature, yet much shorter and spectrally different than that of soot particles. The laser based measurements, combined with the PSD results, suggest that LIF is able to track nanostructures as condensed phase matter with sizes in the order of few nanometers and with internal structures exhibiting the spectroscopic behavior of small PAHs. Conversely, LII is more suited for the detection of solid state particles which are larger in size and have a more aromatic character. It is found that close to the burner exit plane in the early regions of the flames LIF is measured both in the visible and ultraviolet (UV) bands, but not LII, implying the existence of nanostructures rather than soot. Further downstream, these nanostructures continue to exist but now in the presence of soot as is evident by the persistence of the LIF–UV and LIF–visible in conjunction with LII and laser scattering. Collectively, these findings confirm the hybrid nature of nanostructures that dominate the early evolution of soot.
In this work, particle inception and early growth stages were investigated in an ethylene/air premixed flame by the evolution of the particle size and structure with flame residence time. Particle size distribution was measured by a scanning mobility particle seizer and chemical–physical investigation was carried out by Raman microspectroscopy, UV–visible light absorption and cyclic voltammetry.
From early inception of particles, just downstream the flame front, to the formation of primary soot particles, in the post-oxidation flame zone, particles participate in a series of chemical and physical reactions that strongly modify their nanostructure and physicochemical properties, resulting in different optical and electronic characteristics. The results presented in this study show that the evolution from a mono-modal to a bi-modal size distribution is associated to a particle graphitization process consisting of a slight increase of the in plane average size of the polyaromatic units within the particles, La, and on the formation of stacks of polyaromatic planes. These outcomes suggest that in our flame conditions particle coagulation/coalescence has a major role in the initial soot formation, affecting both physical and chemical particle properties.
Soot structural details were elicited through a detailed analysis of the main first-order Raman peaks measured at different excitation wavelengths (457, 514 and 633 nm) on soot produced in premixed fuel-rich flames of different hydrocarbon fuels (namely, methane, ethylene and benzene) burning in similar temperature conditions. Information on the distribution of the aromatic clusters size and on the configuration of the sp2 bonds was obtained. In particular the analysis of the main spectral parameters, namely the G and D band position and widths as well as the I(D)/I(G) ratio, elucidates that the sp2-bonded phase featuring soot particles resulted to be mainly organized in clusters of nanometric size with some presence of sp2 olefinic chains. The Raman spectral analysis allowed to follow even small soot structural differences deriving from the effect of fuel molecule identity and soot aging. In the framework of soot formation and growth process, graphitization, intended as increase of in-plane layer length (as derived from the I(D)/I(G) ratio), was found to generally occur to a very low extent as soot is formed. On the other hand, the widening of the main Raman bands was observed and indicated as signature of the disorder increase likely due to the coagulation of PAH of diverse size and shape, possibly interconnected by odd-numbered and/or sp3 bonds causing the warping and puckering during the aromatic layers growth.
Coagulation of combustion-generated particles has been investigated in low and intermediate temperature regimes in a tubular reactor with a residence time of 1.65 s. Particles, generated by premixed ethylene/air flames with equivalence ratios above the soot threshold limit, are fed to a tubular reactor, which can be operated at temperatures up to 650 K. A wide range of equivalence ratios are used to generate particles with different characteristics. The evolution of the particle size distributions has been evaluated by a differential mobility analyzer with high sensitivity in the 2–100 nm size range. The effect of the reactor temperature on coagulation has been systematically studied. Particles exhibit different coagulation efficiencies at the different temperatures. At room temperature, 2–4 nm particles fed to the reactor coagulate forming particles as large as 10–20 nm, whereas at higher temperatures the size distribution of the particles does not change with respect to that measured at the inlet of the reactor. This behavior suggests a very ineffective coagulation efficiency at higher temperatures for small nanoparticles. Larger particles do not exhibit this high sensitivity to temperature, substantially maintaining very high coagulation efficiencies. These considerations have been confirmed by numerical simulations conducted both with constant and size-dependent coagulation efficiency. The numerical results confirm that also at low and intermediate temperature regimes, the use of a size-dependent coagulation efficiency is mandatory to match the evolution of the particles during coagulation. On the other hand, the simple model of coagulation based on the van der Waals interactions between particles in the framework of gas kinetic collision theory is in slightly disagreement with the experimental results for very small particles, suggesting that more advanced modeling based on quantum mechanism and molecular dynamics are necessary to correctly reproduce the experimental data.
Theoretical studies have shown that in severe operating conditions, valve train friction losses are significant and have an adverse effect on fuel efficiency. However, recent studies have shown that existing valve train friction models do not reliably predict friction in boundary and mixed lubrication conditions and are not sensitive to lubricant chemistry. In these conditions, the friction losses depend on the tribological performance of tribofilms formed as a result of surface-lubricant additive interactions. In this study, key tribological parameters were extracted from a direct acting tappet type Ford Zetec SE (Sigma) valve train, and controlled experiments were performed in a block-on-ring tribometer under conditions representative of boundary lubrication in a cam and follower contact. Friction was recorded for the tribofilms formed by molybdenum dithiocarbamate (MoDTC), zinc dialkyldithiophosphate (ZDDP), detergent (calcium sulfonate), and dispersant (polyisobutylene succinimide) additives in an ester-containing synthetic polyalphaolefin (PAO) base oil on AISI E52100 steel components. A multiple linear regression technique was used to obtain a friction model in boundary lubrication from the friction data taken from the block-on-ring tribometer tests. The model was developed empirically as a function of the ZDDP, MoDTC, detergent, and dispersant concentration in the oil and the temperature and sliding speed. The resulting friction model is sensitive to lubricant chemistry in boundary lubrication. The tribofilm friction model showed sensitivity to the ZDDP-MoDTC, MoDTC-dispersant, MoDTC-speed, ZDDP-temperature, detergent-temperature, and detergent-speed interactions. Friction decreases with an increase in the temperature for all ZDDP/MoDTC ratios, and oils containing detergent and dispersant showed high friction due to antagonistic interactions between MoDTC-detergent and MoDTC-dispersant additive combinations. [DOI:10.1115/1.4004880]
Diesel particulate filter (DPF) technology has proven performance and reliability. However, the addition of a DPF adds significant cost and packaging constraints leading some manufacturers to design engines that reduce particulate matter in-cylinder. Such engines utilize high fuel injection pressure, moderate exhaust gas recirculation and modified injection timing to mitigate soot formation. This study examines such an engine designed to meet US EPA Interim Tier 4 standards for off-highway applications without a DPF. The engine was operated at four steady state modes and aerosol measurements were made using a two-stage, ejector dilution system with a scanning mobility particle sizer (SMPS) equipped with a catalytic stripper (CS) to differentiate semi-volatile versus solid components in the exhaust. Gaseous emissions were measured using an FTIR analyzer and particulate matter mass emissions were estimated using SMPS data and an assumed particle density function. Though the tested engine is predicted to largely meet current US particle mass standards it has significantly higher particle number emissions compared to the Euro 6 solid particle number emissions standard. Our work suggests that engine out solid particle mass would have to be reduced to extremely low levels, much lower than current standards, in order to meet the number standard without DPF aftertreatment.
Although the preponderance of current data points to semivolatile diesel nuclei particles composed of sulfuric acid and heavy hydrocarbons, the question remains as to what extent, if any, they contain solid cores. We present evidence here of a "solid" particle nucleation mode that accompanies normal soot emissions in the case of two modern light-duty diesel vehicles run with ultralow sulfur fuel. This mode is most prominent at idle, but also appears at speeds below approximately 30 mph, and is highly sensitive to the level of exhaust gas recirculation (EGR). The nuclei particles are examined for their volatility and electrical charge. In stark contrast to "conventional" nuclei particles, they remain nonvolatile to >400 degrees C and exhibit a bipolar charge with a Boltzmann temperature of 580 degrees C. Their nonvolatile nature rules out sulfate and heavy hydrocarbons as primary constituents, and their electrical charge requires formation in a high-temperature environment capable of generating bipolar ions. This suggests that "solid" nuclei particles form during combustion but remain distinct from soot particles, analogous to what has been found recently in flames. As concerns about potential emissions of nonvolatile nanoparticles have already surfaced, an important conclusion of this study is that diesel particulate filters remove the "solid" nucleation mode with an efficiency comparable to soot
While nuclei particles are found in vehicle emissions in low mass concentration, they are being studied since their number concentration may be high and they may contribute to the surface composition of larger particles and health effects associated with pollution. In this work, we obtain information on where particles emitted by an engine were formed/grown. This is done by comparing the measured particle charge fraction distributions to those calculated with Boltzmann theory for the different temperatures relevant to the combustion chamber, exhaust and sampling systems. We have applied this method to analyze the exhaust of a gasoline direct injection engine. Solid core particles with a size of 1–5 nm may be formed at high temperature in the combustion chamber and semivolatile species condense on their surface as the exhaust cools in the tail pipe, in low dilution conditions. Off-line measurements, using Surface Enhanced Raman Spectroscopy (SERS) show that the sampled particles have SERS spectra with typical D and G bands of disordered amorphous carbon similar to those measured for flame-generated nanoparticles.
Diesel engines offer higher fuel efficiency, but produce more exhaust particulate than conventional gasoline engines. Diesel particulate filters are presently the most efficient means to reduce these emissions. These filters typically trap particles in two basic modes: at the beginning of the exposure cycle the particles are captured in the filter holes, and at longer times the particles form a “cake” on which particles are trapped. Eventually the “cake” is removed by oxidation and the cycle is repeated. We have investigated the properties and behavior of two commonly used filters: silicon carbide (SiC) and cordierite (DuraTrap® RC) by exposing them to nearly-spherical ammonium sulfate particles. We show that the transition from deep bed filtration to “cake” filtration can easily be identified by recording the change in pressure across the filters as a function of exposure. We investigated the performance of these filters as a function of flow rate and particle size and found that the filters have the highest filtration efficiencies for particles smaller than ∼80nm and larger than ∼200nm. A comparison between the experimental data and a simulation using incompressible lattice-Boltzmann model shows good qualitative agreement, but the model over-predicts the filter's trapping efficiency.
The size distribution of the nanoparticles formed in premixed ethylene–air flames and collected thermophoretically on mica cleaved substrates is obtained by atomic force microscopy (AFM). The distribution function extends from 1 to about 5nm in non-sooting flames and in the soot pre-inception region of the richer flames, while it becomes bimodal and larger particles are formed in the soot inception region of the slightly sooting flames. The distribution is compared with the size distribution of nano-sized organic carbon (NOC) and soot particles, obtained by “in situ” multi-wavelength extinction and light scattering methods. The deposition efficiency is estimated from the differences between these two size distribution functions as a function of the equivalent diameter of the nanoparticles. Furthermore, the coagulation coefficient of particles in flame is obtained from the temporal evolution of the number concentration of the nanoparticles inside the flames. NOC particles, which are rapidly produced in locally rich combustion regions, have peculiar properties since their sticking coefficient both for coagulation and adhesion result to be orders of magnitudes lower than that expected by larger aerosols, like soot particles. The experimental results are interpreted by modelling the van der Waals interactions of the nanoparticles in terms of Lennard-Jones potentials and in the framework of the gas kinetic theory. The estimated adhesion and coagulation efficiencies are in good agreement with those calculated from AFM and optical data. The very low efficiency values observed for the smaller particles could be ascribed to the high energy of these particles due to their Brownian motion, which causes thermal rebound effects prevailing over adhesion mechanisms due to van der Waals forces.
Particle size distribution functions (PSDFs) of incipient soot formed in laminar premixed 24.2% ethylene–37.9% oxygen-diluent (nitrogen and/or argon) flames with an equivalence ratio of 1.92 were studied by online sampling and scanning mobility particle sizer. Two series of flames were studied to quantify the effect of flame temperature on the characteristics of PSDFs. In the first series, the variation of the flame temperature was accomplished by varying the cold gas velocity. Temperature in the second series of flames was manipulated by the diluent composition from argon to nitrogen. The results show that for flames with the maximum temperature (Tmax) around 1800 K the soot PSDFs were distinctively bimodal. As the flame temperature was increased to ∼1850 K, bimodality faded away. The distribution was unimodal for Tmax > 1900 K. The variation of the characteristics of the PSDF as a function of the flame temperature is consistent with the theoretical explanation that bimodality is the result of competition between persistent particle nucleation and particle–particle coagulation in low-temperature flames.
A nano differential mobility analyzer (DMA) is used to measure both the size and electrical charge distributions of soot particles generated during rich premixed combustion. The size distributions are bimodal. One mode peaks at diameters below the 3 nm lower limit of the nano DMA and falls off nearly exponentially with increasing particle diameter. The intensity of this mode persists with increasing height above the burner suggesting that it represents the continued formation of new particles. The second mode is lognormal in shape. Its intensity decreases and the mean diameter increases with increasing height above the burner due to coagulation and surface growth as the particles rise in the flame. The DMA measurements show that a substantial fraction of the soot particles are electrically charged in the flame, predominantly with a single charge per particle and with essentially equal numbers of positive and negative particles. These charged particles belong solely to the upper mode, whereas the lower mode remains charge neutral, suggesting that ions do not act as soot nuclei. Following soot inception, the fraction of charged particles quickly increases with height above the burner and stabilizes at ∼30% of the upper mode for each polarity.
Over the last two decades, our understanding of soot formation has evolved from an empirical, phenomenological description to an age of quantitative modeling for at least small fuel compounds. In this paper, we review the current state of knowledge of the fundamental sooting processes, including the chemistry of soot precursors, particle nucleation and mass/size growth. The discussion shows that though much progress has been made, critical gaps remain in many areas of our knowledge. We propose the roles of certain aromatic radicals resulting from localized π electron structures in particle nucleation and subsequent mass growth. The existence of these free radicals provides a rational explanation for the strong binding forces needed for forming initial clusters of polycyclic aromatic hydrocarbons. They may also explain a range of currently unexplained sooting phenomena, including the large amount of aliphatics observed in nascent soot formed in laminar premixed flames and the mass growth of soot in the absence of gas-phase H atoms. While the above suggestions are inspired, to an extent, by recent theoretical findings from the materials research community, this paper also demonstrates that the knowledge garnered through our longstanding interest in soot formation may well be carried over to flame synthesis of functional nanomaterials for clean and renewable energy applications. In particular, work on flame-synthesized thin films of nanocrystalline titania illustrates how our combustion knowledge might be useful for developing advanced yet inexpensive thin-film solar cells and chemical sensors for detecting gaseous air pollutants.
Most of the particle number emitted by engines is in the nanoparticle range, Dp<50 nm, while most of the mass is in the accumulation mode, nm, range. Nanoparticles are typically hydrocarbons or sulfate and form by nucleation during dilution and cooling of the exhaust, while accumulation mode particles are mainly carbonaceous soot agglomerates formed directly by combustion. Emission standards on diesel engines have led to dramatic reductions in particle mass emitted. However, a new HEI study shows that some low-emission diesel engines emit much higher concentrations of nanoparticles than older designs and other low-emission designs. Many recent studies suggest that at similar mass concentrations; nanometer size particles are more dangerous than micron size particles. This has raised questions about whether nanoparticle (number based) emission standards should be imposed. Unlike mass, number is not conserved. It may change dramatically by nucleation and coagulation during dilution and sampling, making it very difficult to design a standard. Furthermore, if nanoparticles are a problem, spark ignition engines may also have to be controlled.
A field-aged, passive diesel particulate filter (DPF) used in a school bus retrofit program was evaluated for emissions of particle mass and number concentration before, during, and after regeneration. For the particle mass measurements, filter samples were collected for gravimetric analysis with a partial flow sampling system, which sampled proportionally to the exhaust flow. A condensation particle counter and scanning mobility particle sizer measured total number concentration and number-size distributions, respectively. The results of the evaluation show that the number concentration emissions decreased as the DPF became loaded with soot. However, after soot removal by regeneration, the number concentration emissions were approximately 20 times greater, which suggests the importance of the soot layer in helping to trap particles. Contrary to the number concentration results, particle mass emissions decreased from 6 +/- 1 mg/hp-hr before regeneration to 3 +/- 2 mg/hp-hr after regeneration. This indicates that nanoparticles with diameters less than 50 nm may have been emitted after regeneration because these particles contribute little to the total mass. Overall, average particle emission reductions of 95% by mass and 10,000-fold by number concentration after 4 yr of use provided evidence of the durability of a field-aged DPF. In contrast to previous reports for new DPFs in which elevated number concentrations occurred during the first 200 sec of a transient cycle, the number concentration emissions were elevated during the second half of the heavy-duty Federal Test Procedure (FTP) when high speed was sustained. This information is relevant for the analysis of mechanisms by which particles are emitted from field-aged DPFs.
Diesel particulate matter (PM) reduction efficiencies for backup generators (BUGs) (> 300 kW) equipped with a diesel oxidation catalyst (DOC), DOC+fuel-borne catalyst additive combination (DOC+FBC), passive diesel particulate filter (DPF), and an active DPF were measured. Overall, the DOC and DOC+FBC technologies were found to be effective in reducing mainly organic carbon (OC) emissions (56-77%) while both DPFs showed excellent performance in reducing both elemental carbon (EC) and OC emissions (> 90%). These findings demonstrate the potential for applying DOCs to older engines where PM is dominated by the OC fraction. In most modern engine applications, where the PM consists of mainly EC, the DOC will be largely ineffective. Alternatively, passive and active DPFs are expected to be efficient for most engine technologies. Measurements of particle size distributions provided evidence of the high temperature formation of sulfate nanoparticles across the control technologies despite the use of ultralow sulfur diesel. Changes in the particle size distribution and the organic fraction of PM indicate that the OC component of PM is primarily found in the smaller sized particles.
Exposure to particulate matter is associated with risk of cardiovascular events, possibly through endothelial dysfunction, and indoor air may be most important.
We investigated effects of controlled exposure to indoor air particles on microvascular function (MVF) as the primary endpoint and biomarkers of inflammation and oxidative stress as secondary endpoints in a healthy elderly population.
A total of 21 nonsmoking couples participated in a randomized, double-blind, crossover study with two consecutive 48-hour exposures to either particle-filtered or nonfiltered air (2,533-4,058 and 7,718-12,988 particles/cm(3), respectively) in their homes.
MVF was assessed noninvasively by measuring digital peripheral artery tone after arm ischemia. Secondary endpoints included hemoglobin, red blood cells, platelet count, coagulation factors, P-selectin, plasma amyloid A, C-reactive protein, fibrinogen, IL-6, tumor necrosis factor-alpha, protein oxidation measured as 2-aminoadipic semialdehyde in plasma, urinary 8-iso-prostaglandin F(2alpha), and blood pressure. Indoor air filtration significantly improved MVF by 8.1% (95% confidence interval, 0.4-16.3%), and the particulate matter (diameter < 2.5 mum) mass of the indoor particles was more important than the total number concentration (10-700 nm) for these effects. MVF was significantly associated with personal exposure to iron, potassium, copper, zinc, arsenic, and lead in the fine fraction. After Bonferroni correction, none of the secondary biomarkers changed significantly.
Reduction of particle exposure by filtration of recirculated indoor air for only 48 hours improved MVF in healthy elderly citizens, suggesting that this may be a feasible way of reducing the risk of cardiovascular disease.
The characteristics of the nucleation mode particles of a Euro IV heavy-duty diesel vehicle exhaust were studied. The NOx and PM emissions of the vehicle were controlled through the use of cooled EGR and high-pressure fuel injection techniques; no exhaust gas after-treatment was used. Particle measurements were performed in vehicle laboratory and on road. Nucleation mode dominated the particle number size distribution in all the tested driving conditions. According to the on-road measurements, the nucleation mode was already formed after 0.7 s residence time in the atmosphere and no significant changes were observed for longer residence times. The nucleation mode was insensitive to the fuel sulfur content, dilution air temperature, and relative humidity. An increase in the dilution ratio decreased the size of the nucleation mode particles. This behavior was observed to be linked to the total hydrocarbon concentration in the diluted sample. In volatility measurements, the nucleation mode particles were observed to have a nonvolatile core with volatile species condensed on it. The results indicate that the nucleation mode particles have a nonvolatile core formed before the dilution process. The core particles have grown because of the condensation of semivolatile material, mainly hydrocarbons, during the dilution.
We measured the size distribution and UV extinction spectra of carbonaceous nanoparticles present in the size range of 1-100 nm in the exhausts of 2004 model gasoline and diesel powered vehicles and compared the results with those obtained in premixed flames. In addition to soot particles, nanoparticles of organic carbon (NOC) were measured in the emissions of these test vehicles in significant number and mass concentrations. The number and mass concentration of NOC was higher than soot in gasoline vehicle emissions. In diesel emissions, NOC had a higher number concentration than soot in terms of number concentration, but in terms of mass concentration, soot was higher than NOC. The size (1-3 nm) and extinction spectra in the UV-visible (strong in the UV and transparent in the visible) of macromolecules/nanoparticles collected in water samples from the vehicles are similar to those measured in laboratory hydrocarbon-air flames, suggesting that these nanoparticles are formed in hydrocarbon combustion reactions. We advance the hypothesis that NOC in vehicle emissions are produced by high-temperature combustion processes and not by low-temperature condensation processes.
Combustion-formed nanoparticles
D'Anna A. Combustion-formed nanoparticles. Proc Combust Inst 2009;32:593-613.