Effect of lubricant on the formation of heavy-duty diesel exhaust nanoparticles

Effect of metallic lubricant additives on morphology, nanostructure, graphitization degree and oxidation reactivity of diesel particles

This paper investigates the impact of metallic lubricant additives on the morphology, nanostructure, graphitization degree, and oxidation reactivity of diesel exhaust particles. The experiments were conducted on a turbocharged heavy-duty diesel engine. Four typical lubricant oil additives, including Ca-based, Zn-based, Mo-based and ashless additives, were mixed into diesel at 0.5% and 1.0% by mass. Analytical characterization equipment used in this study includes a high resolution transmission electron microscopy (HRTEM), a Raman spectroscopy, and a Thermogravimetric analyzer (TGA). Results showed that the lubricant additives significantly changed the soot properties. Diesel fuels blended with ashless and Zn-based additives led to a more disordered nanostructure of diesel particles, thereby improving their oxidation reactivity. When Ca and Mo additives participated in combustion, the oxidation mass loss curve of soot particles shifted to a higher temperature range due to the combined effect of the physical and chemical characteristics of soot particles and the catalytic oxidation of metallic ash. Although Ca, Mo, and other metals in lubricant additives could promote the soot oxidation, the changes in the physicochemical properties of soot particles (including increased fringe length, reduced fringe tortuosity, and higher graphitization degree) rendered it more difficult to oxidize.

Responses of reconstituted human bronchial epithelia from normal and health-compromised donors to non-volatile particulate matter emissions from an aircraft turbofan engine

Health effects of particulate matter (PM) from aircraft engines have not been adequately studied since controlled laboratory studies reflecting realistic conditions regarding aerosols, target tissue, particle exposure and deposited particle dose are logistically challenging. Due to the important contributions of aircraft engine emissions to air pollution, we employed a unique experimental setup to deposit exhaust particles directly from an aircraft engine onto reconstituted human bronchial epithelia (HBE) at air-liquid interface under conditions similar to in vivo airways to mimic realistic human exposure. The toxicity of non-volatile PM (nvPM) from a CFM56-7B26 aircraft engine was evaluated under realistic engine conditions by sampling and exposing HBE derived from donors of normal and compromised health status to exhaust for 1 h followed by biomarker analysis 24 h post exposure. Particle deposition varied depending on the engine thrust levels with 85% thrust producing the highest nvPM mass and number emissions with estimated surface deposition of 3.17 × 10⁹ particles cm^-2 or 337.1 ng cm^-2. Transient increase in cytotoxicity was observed after exposure to nvPM in epithelia derived from a normal donor as well as a decrease in the secretion of interleukin 6 and monocyte chemotactic protein 1. Non-replicated multiple exposures of epithelia derived from a normal donor to nvPM primarily led to a pro-inflammatory response, while both cytotoxicity and oxidative stress induction remained unaffected. This raises concerns for the long-term implications of aircraft nvPM for human pulmonary health, especially in occupational settings.

Revisiting Total Particle Number Measurements for Vehicle Exhaust Regulations

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.

Uncertainty of laboratory and portable solid particle number systems for regulatory measurements of vehicle emissions

In the European Union's emissions regulations, limits for solid particles >23 nm are applicable for the type-approval and in use compliance of vehicles. Consequently, particle number (PN) systems are used very often for both research and development of engines and vehicles, both in the laboratory and on the road. The technical specifications of the laboratory and portable on-board systems are not the same resulting in different measurement uncertainties. Furthermore, particles, in contrast to gases, can be lost in the transfer lines making comparisons at different sampling locations difficult. Moreover, the size dependent counting efficiency of the systems can result in high discrepancies when the measured particle sizes are close to the decreasing steep part of the curves. The different sampling locations (tailpipe or dilution tunnel) and thermal pretreatments of the aerosol further enhance the differences. The studies on the measurement uncertainty are scarce, especially for the PN systems measuring from 10 nm that will be introduced in the future regulations. This study quantified the uncertainty sources of the PN systems: (i) due to the technical requirements and the calibrations, (ii) due to the unknown particle sizes during measurement, (iii) due to particle losses from the vehicle to the PN systems at the tailpipe or the dilution tunnel, (iv) other parameters needed for the calculation of the emissions, non-related to the PN systems, e.g. flow and distance. The expanded uncertainty of the 23 nm laboratory systems sampling from the dilution tunnel was estimated to be 32%, with 18% originating from the calibration procedures, while of those sampling from the tailpipe 34%. For the 23 nm portable systems measuring on-road the uncertainty was 39%. The values were 2-8% higher for the 10 nm systems.

Identification of engine oil-derived ash nanoparticles and ash formation process for a gasoline direct-injection engine

Engine oil-derived ash particles emitted from internal combustion (IC) engines are unwanted by-products, after oil is involved in in-cylinder combustion process. Since they typically come out together with particulate emissions, no detail has been reported about their early-stage particles other than agglomerated particles loaded on aftertreatment catalysts and filters. To better understand ash formation process during the combustion process, differently formulated engine oils were dosed into a fuel system of a gasoline direct injection (GDI) engine that produces low soot mass emissions at normal operating conditions to increase the chances to find stand-alone ash particles separated from soot aggregates in the sub-20-nm size range. In addition to them, ash/soot aggregates in the larger size range were examined using scanning transmission electron microscopy (STEM)-X-ray electron dispersive spectroscopy (XEDS) to present elemental information at different sizes of particles from various oil formulations. The STEM-XEDS results showed that regardless of formulated oil type and particle size, Ca, P and C were always contained, while Zn was occasionally found on relatively large particles, suggesting that these elements get together from an early stage of particle formation. The S, Ca and P K-edge X-ray absorption near edge structure (XANES) analyses were performed for bulk soot containing raw ash. The linear combination approach & cross-checking among XANES results proposed that Ca₅(OH)(PO₄)₂, Ca₃(PO₄)₂ and Zn₃(PO₄)₂ are potentially major chemical compounds in raw ash particles, when combined with the STEM-XEDS results. Despite many reports that CaSO₄ is a major ash chemical when ash found in DPF/GFP systems was examined, it was observed to be rarely present in raw ashes using the S K-edge XANES analysis, suggesting ash transformation.

Overview of Sources and Characteristics of Nanoparticles in Urban Traffic-Influenced Areas

Atmospheric nanoparticles can be formed either via nucleation in atmosphere or be directly emitted to the atmosphere. In urban areas, several combustion sources (engines, biomass burning, power generation plants) are directly emitting nanoparticles to the atmosphere and, in addition, the gaseous emissions from the same sources can participate to atmospheric nanoparticle formation. This article focuses on the sources and formation of nanoparticles in traffic-influenced environments and reviews current knowledge on composition and characteristics of these nanoparticles. In general, elevated number concentrations of nanoparticles are very typically observed in traffic-influenced environments. Traffic related nanoparticles can originate from combustion process or from non-exhaust related sources such as brake wear. Particles originating from combustion process can be divided to three different sources; 1) primary nanoparticles formed in high temperature, 2) delayed primary particles formed as gaseous compounds nucleate during the cooling and dilution process and 3) secondary nanoparticles formed from gaseous precursors via the atmospheric photochemistry. The nanoparticles observed in roadside environment are a complex mixture of particles from several sources affected by atmospheric processing, local co-pollutants and meteorology.

Characterization of particulate smoke and the potential chemical fingerprint of non-road construction equipment exhaust emission in China

Non-road construction equipment (NRCE) is an important source of atmospheric pollution in many developing and urbanizing countries such as China. However, NRCE source is frequently ignored and failed to be identified in the processing of the source apportionment for atmospheric pollution due to the little knowledge on its chemical fingerprint. In this study, seven types of NRCE are selected with the objectives of quantifying the emission factors of fine particulate matter (PM_2.5) (EF_PM) and exploring their potential chemical fingerprints. Our results show that the NRCE EF_PM in the working modes are ~2-3 times higher than those in idling modes, suggesting the important role of engine operating conditions in producing primary PM_2.5. As expected, carbonaceous aerosol is the dominant specie of PM_2.5, with a wide range of 64-95%. And, the ratio of organic carbon to elemental carbon displays a systematical decrease trend with the increase of engine rated powers. The analysis results show that NRCE PM_2.5 chemical compositions are highly correlated with the engine rated powers. In addition, we confirm that the ratio of vanadium and nickel can be used as a good tracer of NREC emission, which is distinct from other key combustion sources such as industry and ship emission. Taken together, this study reveals the emission characteristics of NRCE-related particles and urgently calls on that the NRCE source should be considered in the source apportionment models in the future.

Non-Volatile Particle Number Emission Measurements with Catalytic Strippers: A Review

Vehicle regulations include limits for non-volatile particle number emissions with sizes larger than 23 nm. The measurements are conducted with systems that remove the volatile particles by means of dilution and heating. Recently, the option of measuring from 10 nm was included in the Global Technical Regulation (GTR 15) as an additional option to the current >23 nm methodology. In order to avoid artefacts, i.e., measuring volatile particles that have nucleated downstream of the evaporation tube, a heated oxidation catalyst (i.e., catalytic stripper) is required. This review summarizes the studies with laboratory aerosols that assessed the volatile removal efficiency of evaporation tube and catalytic stripper-based systems using hydrocarbons, sulfuric acid, mixture of them, and ammonium sulfate. Special emphasis was given to distinguish between artefacts that happened in the 10–23 nm range or below. Furthermore, studies with vehicles’ aerosols that reported artefacts were collected to estimate critical concentration levels of volatiles. Maximum expected levels of volatiles for mopeds, motorcycles, light-duty and heavy-duty vehicles were also summarized. Both laboratory and vehicle studies confirmed the superiority of catalytic strippers in avoiding artefacts. Open issues that need attention are the sulfur storage capacity and the standardization of technical requirements for catalytic strippers.

Estimating Respirable Dust Exposure from Inhalable Dust Exposure

In the sector of occupational safety and health only a limited amount of studies are concerned with the conversion of inhalable to respirable dust. This conversion is of high importance for retrospective evaluations of exposure levels or of occupational diseases. For this reason a possibility to convert inhalable into respirable dust is discussed in this study. To determine conversion functions from inhalable to respirable dust fractions, 15 120 parallel measurements in the exposure database MEGA (maintained at the Institute for Occupational Safety and Health of the German Social Accident Insurance) are investigated by regression analysis. For this purpose, the whole data set is split into the influencing factors working activity and material. Inhalable dust is the most important predictor variable and shows an adjusted coefficient of determination of 0.585 (R2 adjusted to sample size). Further improvement of the model is gained, when the data set is split into six working activities and three material groups (e.g. high temperature processing, adj. R2 = 0.668). The combination of these two variables leads to a group of data concerned with high temperature processing with metal, which gives rise to a better description than the whole data set (adj. R2 = 0.706). Although it is not possible to refine these groups further systematically, seven improved groups are formed by trial and error, with adj. R2 between 0.733 and 0.835: soldering, casting (metalworking), welding, high temperature cutting, blasting, chiseling/embossing, and wire drawing. The conversion functions for the seven groups are appropriate candidates for data reconstruction and retrospective exposure assessment. However, this is restricted to a careful analysis of the working conditions. All conversion functions are power functions with exponents between 0.454 and 0.946. Thus, the present data do not support the assumption that respirable and inhalable dust are linearly correlated in general.

Effect of Alternative Liquid Fuels on the Exhaust Particle Size Distributions of a Medium-Speed Diesel Engine

We mainly aimed to determine how alternative liquid fuels affect the exhaust particle size distributions (PSD) emitted by a medium-speed diesel engine. The selected alternative fuels included: circulation-origin marine gas oil (MGO), the 26/74 vol. % blend of renewable naphtha and baseline low-sulfur marine light fuel oil (LFO), and kerosene. PSDs were measured by means of an engine exhaust particle sizer from the raw exhaust of a four-cylinder, turbocharged, intercooled engine. During the measurements, the engine was loaded by an alternator, the maximum power output being set at 600 kW(e) at a speed of 1000 rpm. The partial loads of 450, 300, 150 and 60 kW(e) were also used for measurements. At each load, the PSDs had a distinct peak between 20 and 100 nm regardless of fuel. Relative to the other fuels, circulation-origin MGO emitted the lowest particle numbers at several loads despite having the highest viscosity and highest density. Compared to baseline LFO and kerosene, MGO and the blend of renewable naphtha and LFO were more beneficial in terms of total particle number (TPN). Irrespective of the load or fuel, the TPN consisted mainly of particles detected above the 23 nm size category.

Diesel exhaust nanoparticles and their behaviour in the atmosphere

Diesel engine emissions are by far the largest source of nanoparticles in many urban atmospheres, in which they dominate the particle number count, and may present a significant threat to public health. This paper reviews knowledge of the composition and atmospheric properties of diesel exhaust particles, and exemplifies research in this field through a description of the FASTER project (Fundamental Studies of the Sources, Properties and Environmental Behaviour of Exhaust Nanoparticles from Road Vehicles) which studied the size distribution-and, in unprecedented detail, the chemical composition-of nanoparticles sampled from diesel engine exhaust. This information has been systematized and used to inform the development of computational modules that simulate the behaviour of the largely semi-volatile content of the nucleation mode particles, including consequent effects on the particle size distribution, under typical atmospheric conditions. Large-eddy model studies have informed a simpler characterization of flow around the urban built environment, and include aerosol processes. This modelling and engine-laboratory work have been complemented by laboratory measurements of vapour pressures, and the execution of two field measurement campaigns in London. The result is a more robust description of the dynamical behaviour on the sub-kilometre scale of diesel exhaust nanoparticles and their importance as an urban air pollutant.

Ultrafine particle emissions from modern Gasoline and Diesel vehicles: An electron microscopic perspective

Ultrafine (<100 nm) particles related to traffic are of high environmental and human health concern, as they are supposed to be more toxic than larger particles. In the present study transmission electron microscopy (TEM) is applied to obtain a concrete picture on the nature, morphology and chemical composition of non-volatile ultrafine particles in the exhaust of state-of-the-art, Euro 6b, Gasoline and Diesel vehicles. The particles were collected directly on TEM grids, at the tailpipe, downstream of the after-treatment system, during the entire duration of typical driving cycles on the chassis dynamometer. Based on TEM imaging coupled with Energy Dispersive X-ray (EDX) analysis, numerous ultrafine particles could be identified, imaged and analyzed chemically. Particles <10 nm were rarely detected. The ultrafine particles can be distinguished into the following types: soot, ash-bearing soot and ash. Ash consists of Ca, P, Mg, Zn, Fe, S, and minor Sn compounds. Most elements originate from lubricating oil additives; Sn and at least part of Fe are products of engine wear; minor W ± Si-bearing nearly spherical particles in Diesel exhaust derive from catalytic coating material. Ultrafine ash particles predominate over ultrafine soot or are nearly equal in amount, in contrast to emissions of larger sizes where soot is by far the prevalent particle type. This is probably due to the low ash amount per volume fraction in the total emissions, which does not favor formation of large ash agglomerates, opposite to soot, which is abundant and thus easily forms agglomerates of sizes larger than those of the ultrafine range. No significant differences of ultrafine particle characteristics were identified among the tested Gasoline and Diesel vehicles and driving cycles. The present TEM study gives information also on the imaging and chemical composition of the solid fraction of the unregulated sub-23 nm size category particles.

Traffic is a major source of atmospheric nanocluster aerosol

In densely populated areas, traffic is a significant source of atmospheric aerosol particles. Owing to their small size and complicated chemical and physical characteristics, atmospheric particles resulting from traffic emissions pose a significant risk to human health and also contribute to anthropogenic forcing of climate. Previous research has established that vehicles directly emit primary aerosol particles and also contribute to secondary aerosol particle formation by emitting aerosol precursors. Here, we extend the urban atmospheric aerosol characterization to cover nanocluster aerosol (NCA) particles and show that a major fraction of particles emitted by road transportation are in a previously unmeasured size range of 1.3-3.0 nm. For instance, in a semiurban roadside environment, the NCA represented 20-54% of the total particle concentration in ambient air. The observed NCA concentrations varied significantly depending on the traffic rate and wind direction. The emission factors of NCA for traffic were 2.4·1015 (kgfuel)-1 in a roadside environment, 2.6·1015 (kgfuel)-1 in a street canyon, and 2.9·1015 (kgfuel)-1 in an on-road study throughout Europe. Interestingly, these emissions were not associated with all vehicles. In engine laboratory experiments, the emission factor of exhaust NCA varied from a relatively low value of 1.6·1012 (kgfuel)-1 to a high value of 4.3·1015 (kgfuel)-1 These NCA emissions directly affect particle concentrations and human exposure to nanosized aerosol in urban areas, and potentially may act as nanosized condensation nuclei for the condensation of atmospheric low-volatile organic compounds.

Effect of lubricant sulfur on the morphology and elemental composition of diesel exhaust particles

This work investigates the effects of lubricant sulfur contents on the morphology, nanostructure, size distribution and elemental composition of diesel exhaust particle on a light-duty diesel engine. Three kinds of lubricant (LS-oil, MS-oil and HS-oil, all of which have different sulfur contents: 0.182%, 0.583% and 1.06%, respectively) were used in this study. The morphologies and nanostructures of exhaust particles were analyzed using high-resolution transmission electron microscopy (TEM). Size distributions of primary particles were determined through advanced image-processing software. Elemental compositions of exhaust particles were obtained through X-ray energy dispersive spectroscopy (EDS). Results show that as lubricant sulfur contents increase, the macroscopic structure of diesel exhaust particles turn from chain-like to a more complex agglomerate. The inner cores of the core-shell structure belonging to these primary particles change little; the shell thickness decreases, and the spacing of carbon layer gradually descends, and amorphous materials that attached onto outer carbon layer of primary particles increase. Size distributions of primary particles present a unimodal and normal distribution, and higher sulfur contents lead to larger size primary particles. The sulfur content in lubricants directly affects the chemical composition in the particles. The content of C (carbon) decreases as sulfur increases in the lubricants, while the contents of O (oxygen), S (sulfur) and trace elements (including S, Si (silicon), Fe (ferrum), P (phosphorus), Ca (calcium), Zn (zinc), Mg (magnesium), Cl (chlorine) and Ni (nickel)) all increase in particles.

Physical and Chemical Characterization of Real-World Particle Number and Mass Emissions from City Buses in Finland

Exhaust emissions of 23 individual city buses at Euro III, Euro IV and EEV (Enhanced Environmentally Friendly Vehicle) emission levels were measured by the chasing method under real-world conditions at a depot area and on the normal route of bus line 24 in Helsinki. The buses represented different technologies from the viewpoint of engines, exhaust after-treatment systems (ATS) and fuels. Some of the EEV buses were fueled by diesel, diesel-electric, ethanol (RED95) and compressed natural gas (CNG). At the depot area the emission factors were in the range of 0.3-21 × 10(14) # (kg fuel)(-1), 6-40 g (kg fuel)(-1), 0.004-0.88 g (kg fuel)(-1), 0.004-0.56 g (kg fuel)(-1), 0.01-1.2 g (kg fuel)(-1), for particle number (EFN), nitrogen oxides (EFNOx), black carbon (EFBC), organics (EFOrg), and particle mass (EFPM1), respectively. The highest particulate emissions were observed from the Euro III and Euro IV buses and the lowest from the ethanol and CNG-fueled buses, which emitted BC only during acceleration. The organics emitted from the CNG-fueled buses were clearly less oxidized compared to the other bus types. The bus line experiments showed that lowest emissions were obtained from the ethanol-fueled buses whereas large variation existed between individual buses of the same type indicating that the operating conditions by drivers had large effect on the emissions.

Effects of fresh lubricant oils on particle emissions emitted by a modern gasoline direct injection passenger car

Particle emissions from a modern turbocharged gasoline direct injection passenger car equipped with a three-way catalyst and an exhaust gas recirculation system were studied while the vehicle was running on low-sulfur gasoline and, consecutively, with five different lubrication oils. Exhaust particle number concentration, size distribution, and volatility were determined both at laboratory and on-road conditions. The results indicated that the choice of lubricant affected particle emissions both during the cold start and warm driving cycles. However, the contribution of engine oil depended on driving conditions being higher during acceleration and steady state driving than during deceleration. The highest emission factors were found with two oils that had the highest metal content. The results indicate that a 10% decrease in the Zn content of engine oils is linked with an 11-13% decrease to the nonvolatile particle number emissions in steady driving conditions and a 5% decrease over the New European Driving Cycle. The effect of lubricant on volatile particles was even higher, on the order of 20%.

Characterization of particulate matter emissions from a current technology natural gas engine

Experiments were conducted to characterize the particulate matter (PM)-size distribution, number concentration, and chemical composition emitted from transit buses powered by a USEPA 2010 compliant, stoichiometric heavy-duty natural gas engine equipped with a three-way catalyst (TWC). Results of the particle-size distribution showed a predominant nucleation mode centered close to 10 nm. PM mass in the size range of 6.04 to 25.5 nm correlated strongly with mass of lubrication-oil-derived elemental species detected in the gravimetric PM sample. Results from oil analysis indicated an elemental composition that was similar to that detected in the PM samples. The source of elemental species in the oil sample can be attributed to additives and engine wear. Chemical speciation of particulate matter (PM) showed that lubrication-oil-based additives and wear metals were a major fraction of the PM mass emitted from the buses. The results of the study indicate the possible existence of nanoparticles below 25 nm formed as a result of lubrication oil passage through the combustion chamber. Furthermore, the results of oxidative stress (OS) analysis on the PM samples indicated strong correlations with both the PM mass calculated in the nanoparticle-size bin and the mass of elemental species that can be linked to lubrication oil as the source.

Sulfur driven nucleation mode formation in diesel exhaust under transient driving conditions

Sulfur driven diesel exhaust nucleation particle formation processes were studied in an aerosol laboratory, on engine dynamometers, and on the road. All test engines were equipped with a combination of a diesel oxidation catalyst (DOC) and a partial diesel particulate filter (pDPF). At steady operating conditions, the formation of semivolatile nucleation particles directly depended on SO2 conversion in the catalyst. The nucleation particle emission was most significant after a rapid increase in engine load and exhaust gas temperature. Results indicate that the nucleation particle formation at transient driving conditions does not require compounds such as hydrocarbons or sulfated hydrocarbons, however, it cannot be explained only by the nucleation of sulfuric acid. A real-world exhaust study with a heavy duty diesel truck showed that the nucleation particle formation occurs even with ultralow sulfur diesel fuel, even at downhill driving conditions, and that nucleation particles can contribute 60% of total particle number emissions. In general, due to sulfur storage and release within the exhaust aftertreatment systems and transients in driving, emissions of nucleation particles can even be the dominant part of modern diesel vehicle exhaust particulate number emissions.

Vehicle engines produce exhaust nanoparticles even when not fueled

Vehicle engines produce submicrometer exhaust particles affecting air quality, especially in urban environments. In on-road exhaust studies with a heavy duty diesel vehicle and in laboratory studies with two gasoline-fueled passenger cars, we found that as much as 20-30% of the number of exhaust particles larger than 3 nm may be formed during engine braking conditions-that is, during decelerations and downhill driving while the engine is not fueled. Particles appeared at size ranges extending even below 7 nm and at high number concentrations. Their small size and nonvolatility, coupled with the observation that these particles contain lube-oil-derived metals zinc, phosphorus, and calcium, are suggestive of health risks at least similar to those of exhaust particles observed before. The particles' characteristics indicate that their emissions can be reduced using exhaust after-treatment devices, although these devices have not been mandated for all relevant vehicle types. Altogether, our findings enhance the understanding of the formation vehicle emissions and allow for improved protection of human health in proximity to traffic.

Metal particle emissions in the exhaust stream of diesel engines: an electron microscope study

Scanning electron microscopy and transmission electron microscopy were applied to investigate the morphology, mode of occurrence and chemical composition of metal particles (diesel ash) in the exhaust stream of a small truck outfitted with a typical after-treatment system (a diesel oxidation catalyst (DOC) and a downstream diesel particulate filter (DPF)). Ash consists of Ca-Zn-P-Mg-S-Na-Al-K-phases (lube-oil related), Fe, Cr, Ni, Sn, Pb, Sn (engine wear), and Pd (DOC coating). Soot agglomerates of variable sizes (<0.5-5 μm) are abundant upstream of the DPF and are ash-free or contain notably little attached ash. Post-DPF soot agglomerates are very few, typically large (>1-5 μm, exceptionally 13 μm), rarely <0.5 μm, and contain abundant ash carried mostly from inside the DPF. The ash that reaches the atmosphere also occurs as separate aggregates ca. 0.2-2 μm in size consisting of sintered primary phases, ca. 20-400 nm large. Insoluble particles of these sizes may harm the respiratory and cardiovascular systems. The DPF probably promotes breakout of large soot agglomerates (mostly ash-bearing) by favoring sintering. Noble metals detached from the DOC coating may reach the ambient air. Finally, very few agglomerates of Fe-oxide nanoparticles form newly from engine wear and escape into the atmosphere.

Effects of gaseous sulphuric acid on diesel exhaust nanoparticle formation and characteristics

Diesel exhaust gaseous sulphuric acid (GSA) concentrations and particle size distributions, concentrations, and volatility were studied at four driving conditions with a heavy duty diesel engine equipped with oxidative exhaust after-treatment. Low sulfur fuel and lubricant oil were used in the study. The concentration of the exhaust GSA was observed to vary depending on the engine driving history and load. The GSA affected the volatile particle fraction at high engine loads; higher GSA mole fraction was followed by an increase in volatile nucleation particle concentration and size as well as increase of size of particles possessing nonvolatile core. The GSA did not affect the number of nonvolatile particles. At low and medium loads, the exhaust GSA concentration was low and any GSA driven changes in particle population were not observed. Results show that during the exhaust cooling and dilution processes, besides critical in volatile nucleation particle formation, GSA can change the characteristics of all nucleation mode particles. Results show the dual nature of the nucleation mode particles so that the nucleation mode can include simultaneously volatile and nonvolatile particles, and fulfill the previous results for the nucleation mode formation, especially related to the role of GSA in formation processes.

Nanotoxicity: a growing need for study in the endocrine system

Nanomaterials (NMs) are engineered for commercial purposes such as semiconductors, building materials, cosmetics, and drug carriers, while natural nanoparticles (NPs) already exist in the environment. Due to their unique physicochemical properties, they may interact actively with biological systems. Some of these interactions might be detrimental to human health, and therefore studies on the potential 'nanotoxicity' of these materials in different organ systems are warranted. The purpose of developing the concept of nanotoxicity is to recognize and evaluate the hazards and risks of NMs and evaluate safety. This review will summarize and discuss recent reports derived from cell lines or animal models concerning the effects of NMs on, and their application in, the endocrine system of mammalian and other species. It will present an update on current studies of the effects of some typical NMs-such as metal-based NMs, carbon-based NMs, and dendrimers-on endocrine functions, in which some effects are adverse or unwanted and others are favorable or intended. Disruption of endocrine function is associated with adverse health outcomes including reproductive failure, metabolic syndrome, and some types of cancer. Further investigations are therefore required to obtain a thorough understanding of any potential risk of pathological endocrine disruption from products containing NMs. This review aims to provide impetus for further studies on the interactions of NMs with endocrine functions.

Functional interaction between charged nanoparticles and cardiac tissue: a new paradigm for cardiac arrhythmia?

AIM

To investigate the effect of surface charge of therapeutic nanoparticles on sarcolemmal ionic homeostasis and the initiation of arrhythmias.

MATERIALS & METHODS

Cultured neonatal rat myocytes were exposed to 50 nm-charged polystyrene latex nanoparticles and examined using a combination of hopping probe scanning ion conductance microscopy, optical recording of action potential characteristics and patch clamp.

RESULTS

Positively charged, amine-modified polystyrene latex nanoparticles showed cytotoxic effects and induced large-scale damage to cardiomyocyte membranes leading to calcium alternans and cell death. By contrast, negatively charged, carboxyl-modified polystyrene latex nanoparticles (NegNPs) were not overtly cytotoxic but triggered formation of 50-250-nm nanopores in the membrane. Cells exposed to NegNPs revealed pro-arrhythmic events, such as delayed afterdepolarizations, reduction in conduction velocity and pathological increment of action potential duration together with an increase in ionic current throughout the membrane, carried by the nanopores.

CONCLUSION

The utilization of charged nanoparticles is a novel concept for targeting cardiac excitability. However, this unique nanoscopic investigation reveals an altered electrophysiological substrate, which sensitized the heart cells towards arrhythmias.

Effect of nanoparticle-rich diesel exhaust on testosterone biosynthesis in adult male mice

The effect of nanoparticle-rich diesel exhaust (NR-DE) on the testicular function and factors related with the biosynthesis of testosterone gene expression were investigated in mice. Male C57BL/Jcl mice were exposed to clean air, low-dose NR-DE (Low NR-DE), high-dose NR-DE (High NR-DE) or filtered diesel exhaust (F-DE) for 8 weeks. We found that the mice exposed to High NR-DE had significantly higher testosterone levels than those in the control and F-DE groups. To determine the effects of NR-DE on testicular testosterone production, interstitial cells dissected from the male mice which were exposed to NR-DE, F-DE, or clean air for 8 weeks were incubated with or without human chorionic gonadotropin (hCG; 0.1 IU/mL) for 4 h. The concentrations of testosterone in the culture media were measured. The testosterone production was significantly increased in with or without hCG of High NR-DE exposed group, and significantly decreased in both with or without hCG of F-DE exposed groups. Moreover, several genes, which is associated with testicular cholesterol synthesis, HMG-CoA, LDL-R, SR-B1, PBR, and P450scc, P450 17α, and 17β-HSD were determined in the testis of adult male mice. The results showed High NR-DE exposure significantly increased the expression of these genes. Whereas, the levels in the F-DE exposure group returned to those in the control group, implicating that the nanoparticles in DE contribute to the observed reproductive toxicity. We conclude that enhancement of testosterone biosynthesis by NR-DE exposure may be regulated by increasing testicular enzymes of testosterone biosynthesis.

First online measurements of sulfuric acid gas in modern heavy-duty diesel engine exhaust: implications for nanoparticle formation

To mitigate the diesel particle pollution problem, diesel vehicles are fitted with modern exhaust after-treatment systems (ATS), which efficiently remove engine-generated primary particles (soot and ash) and gaseous hydrocarbons. Unfortunately, ATS can promote formation of low-vapor-pressure gases, which may undergo nucleation and condensation leading to formation of nucleation particles (NUP). The chemical nature and formation mechanism of these particles are only poorly explored. Using a novel mass spectrometric method, online measurements of low-vapor-pressure gases were performed for exhaust of a modern heavy-duty diesel engine operated with modern ATS and combusting low and ultralow sulfur fuels and also biofuel. It was observed that the gaseous sulfuric acid (GSA) concentration varied strongly, although engine operation was stable. However, the exhaust GSA was observed to be affected by fuel sulfur level, exhaust after-treatment, and driving conditions. Significant GSA concentrations were measured also when biofuel was used, indicating that GSA can be originated also from lubricant oil sulfur. Furthermore, accompanying NUP measurements and NUP model simulations were performed. We found that the exhaust GSA promotes NUP formation, but also organic (acidic) precursor gases can have a role. The model results indicate that that the measured GSA concentration alone is not high enough to grow the particles to the detected sizes.

Source characterization of PM10 and PM2.5 mass using a chemical mass balance model at urban roadside

The 24-h average ambient particulate matter (PM(10) and PM(2.5)) concentrations are sampled concurrently during November 2008-April 2009 at a busy roadside in Chennai City, India. The elemental (Ag, Al, As, B, Ba, Be, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, K, Li, Mg, Mn, Mo, Na, Ni, Pb, Rb, Se, Sr, Te, Tl, V and Zn) and ionic (Na(+), NH(4)(+), K(+), Ca(2+), Mg(2+), F(-), Cl(-), NO(2)(-), NO(3)(-) and SO(4)(2-)) composition of PM(10) and PM(2.5) are determined using an inductively coupled plasma-optical emission spectrometer (ICP-OES) and an ion chromatograph (IC), respectively. The emission inventory at the study area is also carried out to identify the likely PM emission sources. The U.S. EPA's-CMB (chemical mass balance) version 8.2 is applied to identify the source contribution of ambient PM(10) and PM(2.5) concentrations at the study area. Results indicated that diesel exhausts (43-52% in PM(10) and 44-65% in PM(2.5)) and gasoline exhausts (6-16% in PM(10) and 3-8% in PM(2.5)) are found to be the major source contributors at the study site followed by the paved road dusts (PM(10)=PM(2.5)=0.-2.3%), brake lining dusts (0.1% in PM(10) and 0.2% in PM(2.5)), brake pad wear dusts (0.1% in PM(10) and 0.01% in PM(2.5)), marine aerosols (PM(10)=PM(2.5)=0.1%) and cooking (~0.8% in PM(10) and ~1.5% in PM(2.5)).

Influence of real-world engine load conditions on nanoparticle emissions from a DPF and SCR equipped heavy-duty diesel engine

The experiments aimed at investigating the effect of real-world engine load conditions on nanoparticle emissions from a Diesel Particulate Filter and Selective Catalytic Reduction after-treatment system (DPF-SCR) equipped heavy-duty diesel engine. The results showed the emission of nucleation mode particles in the size range of 6-15 nm at conditions with high exhaust temperatures. A direct result of higher exhaust temperatures (over 380 °C) contributing to higher concentration of nucleation mode nanoparticles is presented in this study. The action of an SCR catalyst with urea injection was found to increase the particle number count by over an order of magnitude in comparison to DPF out particle concentrations. Engine operations resulting in exhaust temperatures below 380 °C did not contribute to significant nucleation mode nanoparticle concentrations. The study further suggests the fact that SCR-equipped engines operating within the Not-To-Exceed (NTE) zone over a critical exhaust temperature and under favorable ambient dilution conditions could contribute to high nanoparticle concentrations to the environment. Also, some of the high temperature modes resulted in DPF out accumulation mode (between 50 and 200 nm) particle concentrations an order of magnitude greater than typical background PM concentrations. This leads to the conclusion that sustained NTE operation could trigger high temperature passive regeneration which in turn would result in lower filtration efficiencies of the DPF that further contributes to the increased solid fraction of the PM number count.

Effects of biodiesel, engine load and diesel particulate filter on nonvolatile particle number size distributions in heavy-duty diesel engine exhaust

Diesel engine exhaust contains large numbers of submicrometer particles that degrade air quality and human health. This study examines the number emission characteristics of 10-1000 nm nonvolatile particles from a heavy-duty diesel engine, operating with various waste cooking oil biodiesel blends (B2, B10 and B20), engine loads (0%, 25%, 50% and 75%) and a diesel oxidation catalyst plus diesel particulate filter (DOC+DPF) under steady modes. For a given load, the total particle number concentrations (N(TOT)) decrease slightly, while the mode diameters show negligible changes with increasing biodiesel blends. For a given biodiesel blend, both the N(TOT) and mode diameters increase modestly with increasing load of above 25%. The N(TOT) at idle are highest and their size distributions are strongly affected by condensation and possible nucleation of semivolatile materials. Nonvolatile cores of diameters less than 16 nm are only observed at idle mode. The DOC+DPF shows remarkable filtration efficiency for both the core and soot particles, irrespective of the biodiesel blend and engine load under study. The N(TOT) post the DOC+DPF are comparable to typical ambient levels of ≈ 10(4)cm(-3). This implies that, without concurrent reductions of semivolatile materials, the formation of semivolatile nucleation mode particles post the after treatment is highly favored.

Effect of advanced aftertreatment for PM and NOx reduction on heavy-duty diesel engine ultrafine particle emissions

Four heavy-duty and medium-duty diesel vehicles were tested in six different aftertreament configurations using a chassis dynamometer to characterize the occurrence of nucleation (the conversion of exhaust gases to particles upon dilution). The aftertreatment included four different diesel particulate filters and two selective catalytic reduction (SCR) devices. All DPFs reduced the emissions of solid particles by several orders of magnitude, but in certain cases the occurrence of a volatile nucleation mode could increase total particle number emissions. The occurrence of a nucleation mode could be predicted based on the level of catalyst in the aftertreatment, the prevailing temperature in the aftertreatment, and the age of the aftertreatment. The particles measured during nucleation had a high fraction of sulfate, up to 62% of reconstructed mass. Additionally the catalyst reduced the toxicity measured in chemical and cellular assays suggesting a pathway for an inverse correlation between particle number and toxicity. The results have implications for exposure to and toxicity of diesel PM.

Characterization of dilution conditions for diesel nanoparticle inhalation studies

Diesel exhaust nanoparticles easily coagulate during transportation from the engine to the inhalation chamber, depending on concentrations and residence times. Although dilution is effective in suppressing coagulation growth of nanoparticles, volatile organic carbon (OC) evaporates as a result of dilution. Thus, the design of an inhalation facility to investigate the health effects of nanoparticle-rich exhaust is important. In this study, we determined the optimum dilution conditions in consideration of coagulation growth and evaporation of OC for inhalation studies of nanoparticle-rich diesel exhaust. We found that a short residence time prevented coagulation growth in the primary dilution tunnel after the primary dilution or before the diluted exhaust reached the inhalation chamber after the secondary dilution. However, due to the longer residence time in the inhalation chamber, the coagulation growth occurred in the inhalation chamber depending on secondary dilution ratio which controlled exposure dose (particle concentration in the inhalation chamber). We determined that the secondary dilution ratio for the high-concentration chamber should be around 4.5 times to prevent coagulation growth and to obtain the desired exposure dose. We also found that the loss of OC was relatively independent of the secondary dilution ratio when the secondary dilution ratio was more than 10 times because it seemed to reach a gas-particle equilibrium in the inhalation chamber. We therefore set the secondary dilution ratios for the middle- and low-concentration chambers to 13.5 and 40.5 times, respectively.

Effect of fuel and lube oil sulfur on the performance of a diesel exhaust gas continuously regenerating trap

The continuously regenerating trap (CRT) is a diesel exhaust emission control that removes nearly all diesel particulate matter on a mass basis, but under some circumstances oxidation of sulfur leads to the formation of nanoparticles. The objective of the four year study was to determine CRT performance under controlled, real-world, on-road conditions, and to develop quantitative relationships between fuel and lubrication oil sulfur concentration and particle number exhaust emissions. It was shown that nanoparticle emissions are minimized by the use of ultralow sulfur fuels and specially formulated low sulfur lubrication oil. Nanoparticle emissions increased with higher exhaust temperatures. Fuel and lubrication oil sulfur increased the particle concentration by, on average, 36 x 10(6) and 0.14 x 10(6) part/cm3 for each 1 ppm increase in sulfur. On the other hand there was a decrease in nanoparticle emissions by the CRT as the system aged.

[Health effects of nanoparticles and nanomaterials (II) methods for measurement of nanoparticles and their presence in the air]

The mass concentrations of airborne particles in the atmospheric, indoor, and industrial environments are regulated by air quality standards. Epidemiological studies show that there are significant positive correlations between particle mass concentrations and adverse health effects. In this context nanoparticles in the air, which are defined as particles with a diameter (Dp) of less than 50 nm or 100 nm for engineered ones, are gaining increasing attention despite a small contribution to the mass of total airborn particles. Contrary to the mass concentration the number concentrations of atmospheric nanoparticles are quite high in most cases. Moreover there is limited toxicological information on nanoparticles, although the deposition rate of nanoparticles in the respiratory region is known to be relatively high. Accordingly there are a lot of debates about what metric is best to depict the size distribution of nanoparticles, number, surface area, or mass. In this paper, we report methods for measurement of nanoparticles on the basis of those metrics. We also report sources of nanoparticle in the environment and occupational settings. The high number concentration of nanoparticles of 20-30 nm modal diameters have been documented at roadsides. Diesel-powered vehicles are major sources of those nanoparticles in the urban atmosphere. Engineered nanoparticles generate in some occupational settings in the handling processes such as bagging and cleaning with vacuum cleaners.

Hydrocarbon condensation in heavy-duty diesel exhaust

The semivolatile mass fraction of diesel exhaust particles was studied using size-resolved on-line techniques (DMA-ELPI; TDMA-ELPI). The average density of the semivolatile liquid on the particles was measured to be approximately 0.8 g/cm3. The measured size resolved values of mass transfer imply that condensation, or diffusion-limited mass transfer, plays a major role in driving the volatile matter to the diesel exhaust particles. The measured mass change values correspond to highly size dependent mass fractions for the semivolatile component, ranging from approximately 20-80%. Integrated over particle size distribution, the volatile mass fractions were 25 and 45% for the two load points studied. Calculation, based on the measured particle properties, indicates that only 10% volatile mass fraction could be explained by monolayer adsorption. The size resolved changes in particle effective density, fractal dimension, volatile mass fractions and mass are all in agreement with theoretical considerations of condensation.

Nucleation mode particles with a nonvolatile core in the exhaust of a heavy duty diesel vehicle

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.

Reduction of particulate matter emissions from diesel backup generators equipped with four different exhaust aftertreatment devices

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.

Effect of oxidation catalysts on diesel soot particles

The effect of a conventional oxidation catalyst and a novel particle oxidation catalyst (POC) on diesel particles is studied using identical methodology. Regulated particulate matter emission measurement is followed by analyzing soluble organic fraction. In addition, size distributions are measured using a partial flow sampling system with a thermodenuder as an option. A parallel ELPI-SMPS method is used to study the particle effective density and, further, the mass. Tests are conducted using a heavy duty diesel engine with a very low sulfur fuel. A decrease in particle mass was observed when using a catalyst. When using a conventional catalyst the decrease was attributed to the decrease of soluble organic fraction, while using POC the nonsoluble fraction was also found to decrease, by 8-38%. This observation is confirmed by particle number measurement, and POC was found to decrease the dry particle number concentration measured downstream of a thermodenuder by 13-28%. Further particle structure analysis indicated lower density values when using conventional catalyst or POC. The physical size of the particles was not changed noticeably over either catalyst--implying the soluble organic fraction was condensed onto the soot, filling the voids in the porous structure of soot agglomerates, when no catalyst is used.