Particle Number Distribution Research Articles

Emission Characterization and Efficiency Measurements of High-Efficiency Wood Boilers

Detailed gaseous and particle emissions along with thermal efficiency measurements were made on three mid-sized high-efficiency wood boilers with thermal output capacities of 150 kW (514 000 Btu h–1) (n = 2) and 500 kW (1.7 mmBtu h–1) (n = 1). Wood chips and commercial wood pellets were used as fuel. Continuous emissions of CO, NOx, SO2, fine particle mass (PM2.5), and ultrafine particle number distributions were determined using a dilution tunnel sampling system. PM2.5 and semivolatile organic compound characterization was performed. Low concentrations of CO, organic carbon (OC), and elemental carbon (EC) during steady-state boiler operation indicated good combustion conditions. Fine particle mass from wood pellets was predominantly K+ and SO42–, with <8% OC and <2% EC. Inorganic emissions (PM2.5, NOx, and SO2) were found to depend upon fuel quality, which indicates the need for wood pellet fuel standards in the U.S. Cd, Pb, Ti, Rb, and Zn were found to be enriched in PM2.5, which is of concern for human health. Levoglucosan was a predominant organic compound found for all fuels, ranging from 38 to 82 μg/MJ. Total particle and semivolatile polycyclic aromatic hydrocarbon (PAH) emissions were relatively low (19.4–92.8 μg/MJ). The thermal efficiencies of the wood pellet boilers determined using the provisional American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) standard 155p ranged between 70 and 86% for the 150 kW boiler tested and between 75 and 91% for the 500 kW boiler. The use of ASHRAE 155p allowed for the determination of the linear relationship between the energy input and the energy output over the range of energy outputs rather than only determining the efficiency at minimum and full load as is the current standard practice. Boiler capacity had no significant effect on efficiency; however, the operating conditions, such as fuel feed rate, outlet water temperature, and building demand, did affect the results.

Tracheobronchial and alveolar dose of submicrometer particles for different population age groups in Italy

Exposure to ultrafine particles (diameter less than 100 nm) is an important topic in epidemiological and toxicological studies. This study used the average particle number size distribution data obtained from our measurement survey in major microenvironments, together with the people activity pattern data obtained from the Italian Human Activity Pattern Survey to estimate the tracheobronchial and alveolar dose of submicrometer particles for different population age groups in Italy. We developed a numerical methodology based on Monte Carlo method, in order to estimate the best combination from a probabilistic point of view. More than 10 6 different cases were analyzed according to a purpose built sub-routine and our results showed that the daily alveolar particle number and surface area deposited for all of the age groups considered was equal to 1.5 × 10 11 particles and 2.5 × 10 15 μm 2 , respectively, varying slightly for males and females living in Northern or Southern Italy. In terms of tracheobronchial deposition, the corresponding values for daily particle number and surface area for all age groups was equal to 6.5 × 10 10 particles and 9.9 × 10 14 μm 2 , respectively. Overall, the highest contributions were found to come from indoor cooking (female), working time (male) and transportation (i.e. traffic derived particles) (children). ► We estimate particle number and surface area deposition for different age groups and lifestyles through an indirect approach. ► Particle number distribution range for each microenvironment was obtained from our measurement survey data. ► Deposition increases as a function age group, with the maximum value observed for 41–65 years old. ► Major contributions arise from indoor cooking and eating times (female), working time (male) and transportation (children).

Comprehensive characterization of ambient nanoparticles collected near an industrial science park: Particle size distributions and relationships with environmental factors

We investigated the characteristics of ambient particles and their relationships with various environmental factors, including gaseous pollutants (CH 4, non-methane hydrocarbons (NMHC), total hydrocarbons (THC), NO x, CO, SO 2), meteorological parameters (humidity, temperature), and time (day/night, workday/weekend). We used an electrical low-pressure cascade impactor to measure the number and size distributions of ambient particles (0.007–10 μm) that were collected approximately 1 km northwest of Hsinchu Science Park in Taiwan between February and May 2007. The number concentrations of particles were enhanced through photochemical reactions during the day. In addition, high traffic flow during workdays increased the formation of particulates. Except for SO 2, all of the gaseous pollutants we studied (CH 4, NMHC, THC, NO x, CO) correlated positively with the total number concentrations of ambient particles during daytime, indicating that they might contribute to the particulate burden. The poorer relationship between the SO 2 level and the total number concentration of particles suggests that SO 2 might participate indirectly in the nucleation process during particle formation, The high enrichment factors for Zn, Pb, Cu, and Mn, which mostly comprised the ultrafine particles (diameter: < 0.1 μm) and fine particles (diameter: 0.1–1 μm), presumably arose from emissions from traffic and high technology factories. Heterogeneous reactions on solid particles might play a role in the removal of SOx and NO x from the atmosphere. Sulfides and nitrides can further react with these local pollutants, forming specific Cu-containing compounds: CuO (39%), CuSO 4 (34%), and Cu(NO 3) 2 (27%), within the ambient particles in this industrial area.

Ground-fixed and on-board measurements of nanoparticles in the wake of a moving vehicle

An integrated experimental methodology has been applied to measure number and size distributions of particles in the 5-560nm size range in the wake of a diesel car running at different speeds. Measurements were made at both ground-fixed (0.10 and 0.25m above the ground level) and on-board (in 12 different sampling locations behind the moving car) measurement configurations using a fast response differential mobility spectrometer (Cambustion DMS50) with a sampling frequency up to 10Hz. Results from both the experimental campaigns were analysed to understand the dynamics, dispersion and transport of nanoparticle emissions in the wake of a moving vehicle. Temporal changes in results were divided into three main stages (pre-evolution, evolution and post-evolution) after the release of exhaust emissions from the tailpipe. Evolution stage is of most interest where all the changes to particle number and size distribution occurred. Up to four evolution sub-stages were observed, each showing distinct evolution patterns of particle size distributions, depending on the particular experimental run. In agreement with previous studies, dilution was found to be the dominant process throughout all the evolution stages. The first evolution sub-stage was common to all the measurements, and consisted of an initial particle number concentrations and distributions change due to rapid (less than 1s) nucleation followed by a rapid increase of accumulation mode particle number concentrations. After this first sub-stage the presence of vehicle wake with recirculating particles and the possible influence of other transformation processes lead to complex interactions. Results from the two experimental datasets clearly confirm the presence of two separate groups of particles: (i) new particles, which are freshly emitted and come directly from the tailpipe and (ii) relatively aged particles, which are entrained within the recirculation vortices of the vehicle wake and reside there for a longer time. The two groups have different characteristics and interact with each other. This interaction has often been overlooked in past studies about local scale dispersion of nanoparticle from moving vehicles.

A study of airborne wear particles generated from organic railway brake pads and brake discs

Brake pads on wheel-mounted disc brakes are often used in rail transport due to their good thermal properties and robustness. During braking, both the disc and the pads are worn. This wear process generates particles that may become airborne and thus affect human health. The long term purpose of ‘Airborne particles in Rail transport’ project is to gain knowledge on the wear mechanisms in order to find means of controlling the number and size distribution of airborne particles. In this regard, a series of full-scale field tests and laboratory tests with a pin-on-disc machine have been conducted. The morphology and the matter of particles, along with their size distribution and concentration, have been studied. The validity of results from the pin-on-disc simulation has been verified by the field test results. Results show an ultra-fine peak for particles with a diameter size around 100 nm in diameter, a dominant fine peak for particles with a size of around 350 nm in diameter, and a coarse peak with a size of 3–7 μm in diameter. Materials such as iron, copper, aluminum, chromium, cobalt, antimony, and zinc have been detected in the nano-sized particles.

Dynamics and dispersion modelling of nanoparticles from road traffic in the urban atmospheric environment—A review

Reducing exposure to atmospheric nanoparticles in urban areas is important for protecting public health. Developing new or improving the capabilities of existing dispersion models will help to design effective mitigation strategies for nanoparticle rich environments. The aims of this review are to summarise current practices of nanoparticle dispersion modelling at five local scales (i.e. vehicle wake, street canyons, neighbourhood, city and road tunnels), together with highlighting associated challenges, research gaps and priorities. The review begins with a synthesis of available information about the flow and mixing characteristics in urban environments which is followed by a brief discussion on dispersion modelling of nanoparticles. Further sections cover the effects of transformation processes in dispersion modelling of nanoparticles, and a critical discussion on associated structural and parametric uncertainties in modelling. The article concludes with a comprehensive summary of current knowledge and future research required on the topic areas covered. Appropriate treatment of transformation processes (i.e. nucleation, coagulation, deposition and condensation) in existing dispersion models is essential for extending the applicability of gaseous dispersion models to nanoparticles. Some modelling studies that consider the particles down to 1 nm size indicate importance of coagulation and condensation processes on street-scale modelling whereas others neglecting either sub-10 nm particles or Van der Waals forces along with fractal geometry suggest to discard these processes due to negligible effects on particle number and size distributions. Further, it is important to consider those transformation processes e.g. at city scale or in road tunnels because of the much longer residence time or much higher concentration levels compared to the street scale processes. Structural and parametric uncertainties affect the modelled results considerably. In particular, parametric uncertainty in the form of particle number emission factors appears to be the most significant due to considerably large variations in their estimates. A consistent approach to the use of emission factors, appropriate treatment of transformation processes in particle dispersion models and the evaluation of model performance against measured data are essential for producing reliable modelled results.

Safe uses of Hill's model: an exact comparison with the Adair-Klotz model

BackgroundThe Hill function and the related Hill model are used frequently to study processes in the living cell. There are very few studies investigating the situations in which the model can be safely used. For example, it has been shown, at the mean field level, that the dose response curve obtained from a Hill model agrees well with the dose response curves obtained from a more complicated Adair-Klotz model, provided that the parameters of the Adair-Klotz model describe strongly cooperative binding. However, it has not been established whether such findings can be extended to other properties and non-mean field (stochastic) versions of the same, or other, models.ResultsIn this work a rather generic quantitative framework for approaching such a problem is suggested. The main idea is to focus on comparing the particle number distribution functions for Hill's and Adair-Klotz's models instead of investigating a particular property (e.g. the dose response curve). The approach is valid for any model that can be mathematically related to the Hill model. The Adair-Klotz model is used to illustrate the technique. One main and two auxiliary similarity measures were introduced to compare the distributions in a quantitative way. Both time dependent and the equilibrium properties of the similarity measures were studied.ConclusionsA strongly cooperative Adair-Klotz model can be replaced by a suitable Hill model in such a way that any property computed from the two models, even the one describing stochastic features, is approximately the same. The quantitative analysis showed that boundaries of the regions in the parameter space where the models behave in the same way exhibit a rather rich structure.

An Evaluation of Particle Size Distributions and Particle Number-Based Reductions from Various PM Emission Control Technologies

An Evaluation of Particle Size Distributions and Particle Number-Based Reductions from Various PM Emission Control Technologies

Development and Evaluation of On-Board Measurement System for Nanoparticle Emissions from Diesel Engine

This work has focused on the development and evaluation of an experimental set-up to measure in real time and with on-board equipments the particle emissions of diesel vehicle minimizing the uncertainties associated to dilution ratio, the length of the transfer line and the sampling point in the engine exhaust pipe. Its suitability has been verified by ensuring the repeatability of the results in dynamometer tests reproducing standard circuits, as well as in closed circuits and in real urban traffic in Madrid, Spain. The experience derived from this work has been very useful, contributing to the advance in the measurement of particle number and size distribution in real time using on-board equipment and bringing us closer to understanding the relationship between the physical characteristics of the particles emitted by a diesel engine and its operation in real urban traffic conditions. The proposed on-board system has provided very satisfactory results.

Number-conserving master equation theory for a dilute Bose-Einstein condensate

We describe the transition of $N$ weakly interacting atoms into a Bose-Einstein condensate within a number-conserving quantum master equation theory. Based on the separation of time scales for condensate formation and noncondensate thermalization, we derive a master equation for the condensate subsystem in the presence of the noncondensate environment under the inclusion of all two-body interaction processes. We numerically monitor the condensate particle number distribution during condensate formation, and derive a condition under which the unique equilibrium steady state of a dilute, weakly interacting Bose-Einstein condensate is given by a Gibbs-Boltzmann thermal state of $N$ noninteracting atoms.

Effect of Engine Load on Size and Number Distribution of Particulate Matter Emitted from a Direct Injection Compression Ignition Engine

Particle size and number distribution from an engine tailpipe has a direct bearing on the residence time of the particles in the atmosphere and their toxicity. This study presents the number concentration and size distributions of nano-particles emitted from naturally aspirated, water cooled, single cylinder, diesel fuelled direct injection compression ignition (DICI) engine. The engine exhaust particle sizer (EEPS) was used for measurement of number, surface area and mass distributions of soot particles. It measures particle sizes ranging from 5.6 to 560 nm. Reading the size distribution 10 times per second allows for the measurement of transient emissions of soot particles. The experiments were conducted at a constant engine speed (1500 rpm) with varying engine load. It was found that (a) number and size distribution, (b) surface area and size distribution, and (c) mass and size distribution of soot particles varies significantly with the engine load. The width of the emitted particle size distribution increases with increasing engine load.

Onboard, Real-World Second-by-Second Particle Number Emissions from 2010 Hybrid and Comparable Conventional Vehicles

Despite hybrid-electric vehicles becoming more prominent in the on-road light-duty vehicle fleet, few studies have evaluated their real-world particle emissions. Hot-stabilized tailpipe particle number concentrations, emission rates, and number distributions emitted from two 2010 Toyota Camry vehicles—one hybrid and one conventional—were quantified during city driving in Burlington, Vermont, at ambient temperatures between −5°C and 9°C with the University of Vermont total onboard tailpipe emissions measurement system. Across replicate real-world runs, the average total cumulative particle number (3- to 3,000-nm particle diameter) emission rates measured for the hybrid vehicle were two times higher than that of the conventional vehicle, despite the hybrid vehicle's internal combustion engine being off 16% to 57% of the run duration. Average second-by-second number distributions for the conventional vehicle had three particle modes (10, 50, and 400 nm), whereas the broader hybrid vehicle distributions had two distinct modes (50 and 400 nm) with shoulders at 10 and 20 nm. These distributions changed little over the route for a given vehicle type. The unexpected higher particle number emission rates from the hybrid, and possibly the differences in number distributions, may be explained by an observed pattern of internal combustion engine restarts under stop-and-go driving that resulted in extreme particle emission rates up to 3.5 × 1010 (number per second) at every engine restart. The hybrid restart behavior resulted in high particle number emissions localized primarily at intersections. More detailed study is needed on different hybrid vehicle designs to determine the broader significance of the observed particle emission patterns.

Nucleation of Nanosized Particles (3–100 nm) From Ozone and D-Limonene Reaction

O-29A6-5 Background/Aims: Indoor aerosol particles have been shown to contribute to building occupants' health issues, such as asthma or airway irritation. Currently, a considerable effort has been devoted to understand how health effects associated with aerosol exposure, especially with nano-sized particles. Nevertheless, until recently, there was little information regarding freshly nucleated particles with diameters less than 10 nm due to instrumentation limitation. Methods: Taking advantage of the latest Scanning Mobility Particle Sizer (SMPS) technology (Model 3936, TSI), which provides real-time particle number and size distribution in the range from 3 to 100 nm, this study characterizes the chemistry of D-limonene reacting with ozone as a source of indoor nucleated particles. A series of experiments were conducted in a 4-L glass chamber with various reactant concentrations (2–4 ppbv for Limonene and 3–20 ppbv for ozone). The study also looked at the effects of cyclohexane, used to suppress the influence of OH radicals produced from limonene and ozone reaction, on particle size. Results: The study results show a significant effect of reactant levels on particle mass and size. Higher ozone concentration led to an increase in particle number. However, higher limonene levels led to a considerable increase in mass while particle number remained the same. One possible reason for that effect is excess limonene partitioning on to newly formed particles. In addition, more small new particles were formed with the presence of cyclohexane. The formation of nano-sized particles as low as 4.0 nm was observed with the mode growth rate of 10 to 15 nm per 2.5-minute scan during the first 10 to 15 min after limonene was introduced. Conclusion: The experimental results indicate that at lower levels of limonene and ozone, even smaller particles would be formed with a higher chance of nucleation (3 to −0 nm).

The possibilities for measurement and characterization of diesel engine fine particles: A review

This review paper considers possible instrumentation for diesel engine fine particles exhaust emission evaluation. The modern diesel engines have extremely low particles emission almost at the level of measurement error of existing gravimetric measurement method. Since coarse particles are eliminated by new engine technologies, fine particles, with very negative effects on human health, dominate in the emission of current diesel engine. Therefore, it is necessary not only to measure mass of emitted particles but also to investigate other important particle characteristics as: particles number, particle size, particle number and mass distribution, particle active surface, particle composition etc. Therefore, existing measurement technologies used in aerosol science can be used also to study diesel engine particles properties. This most common instrumentation in aerosol technique is shortly reviewed in the paper with special attention on candidate instruments included in EU program on portable emissions measurement systems (PEMS).

Correlation between airborne particle concentrations in seven industrial plants and estimated respiratory tract deposition by number, mass and elemental composition

The number and mass distribution of airborne particles were recorded in several industrial plants. From the data obtained, particle deposition was estimated in three regions of the respiratory tract using the ICRP grand average deposition model based on Hinds' (1999) parameterization. The median diameter was 30–70 nm (number distributions), and >4 μm (mass distributions) near most work activities, resulting in linear relationships between the deposited number/mass concentrations and the number/mass concentrations in the air. Welding and laser cutting produced particles in the 200–500-nm range; total deposition was small, not in accordance with the linear relationship observed for the other work activities. The elemental content varied between particle sizes in some workplaces, causing different elements to deposit in different respiratory regions. Iron was the most abundant element in the particles in many of the workplaces; in an iron foundry, however, Fe was most abundant only in the micron-sized particles whereas the nanoparticles mainly comprised Pb and Sb.

A danger of low copy numbers for inferring incorrect cooperativity degree

BackgroundA dose-response curve depicts the fraction of bound proteins as a function of unbound ligands. Dose-response curves are used to measure the cooperativity degree of a ligand binding process. Frequently, the Hill function is used to fit the experimental data. The Hill function is parameterized by the value of the dissociation constant and the Hill coefficient, which describes the cooperativity degree. The use of Hill's model and the Hill function has been heavily criticised in this context, predominantly the assumption that all ligands bind at once, which resulted in further refinements of the model. In this work, the validity of the Hill function has been studied from an entirely different point of view. In the limit of low copy numbers the dynamics of the system becomes noisy. The goal was to asses the validity of the Hill function in this limit, and to see in what ways the effects of the fluctuations change the form of the dose-response curves.ResultsDose-response curves were computed taking into account effects of fluctuations. The effects of fluctuations were described at the lowest order (the second moment of the particle number distribution) by using the previously developed Pair Approach Reaction Noise EStimator (PARNES) method. The stationary state of the system is described by nine equations with nine unknowns. To obtain fluctuation-corrected dose-response curves the equations have been investigated numerically.ConclusionsThe Hill function cannot describe dose-response curves in a low particle limit. First, dose-response curves are not solely parameterized by the dissociation constant and the Hill coefficient. In general, the shape of a dose-response curve depends on the variables that describe how an experiment (ensemble) is designed. Second, dose-response curves are multi-valued in a rather non-trivial way.

Particle number and size distribution characteristics from diesel- and liquefied-natural-gas-fuelled buses for various emission certification modes in the Republic of Korea

This study was primarily focused on the experimental comparison of the particle emission characteristics of diesel and liquefied-natural-gas (LNG) fuels for heavy-duty vehicles. Particulate matter from various heavy-duty engines and vehicles were analysed with a golden particle measurement system recommended by the Particle Measurement Program. This system consists of a constant-volume sampler, a particle number counter, and particle number diluters. To verify the particle number and size distribution characteristics of diesel-fuelled engines and buses, including LNG fuel, various dynamic operation modes, such as the European Transient Cycle (ETC) mode, the European Stabilized Cycle (ESC) mode, and the National Institute of Environmental Research mode, uniquely developed in Korea, were evaluated. The formation of the particles depended closely upon the vehicle speed and the load conditions of each mode. In particular, the particle number sharply increased for fast-transient-acceleration and high-load operation within a heavy-duty engine. The partial diesel particulate filter efficiency was evaluated under the ETC and ESC modes using both engine and vehicle dynamometers.

Thermalization in a Coherently Driven Ensemble of Two-Level Systems

We investigate the coherent quantum time evolution of a driven mesoscopic chain of two-level systems that interact via the vanderWaals interaction in their excited state. The Hamiltonian is the sum of a classical lattice gas Hamiltonian and an off-diagonal driving term without classical counterpart. Starting from a product state we observe-beyond a certain interaction strength-thermalization of the system with respect to observables of the classical lattice gas. This transition can be studied experimentally with Rydberg atoms, ions, or polar molecules. We suggest how to experimentally determine the temperature of the thermal state which should allow for thermometry of the internal degrees of freedom of cold Rydberg gases whose external dynamics is frozen.

Monitoring of sources and atmospheric processes controlling air quality in an urban Mediterranean environment

Different monitoring parameters (PM mass concentrations, number–size distribution, black carbon, gaseous pollutants, and chemical composition, among others) are currently used in air quality studies. Urban aerosols are the result of several sources and atmospheric processes, which suggests that a single monitoring technique is insufficient to quantitatively evaluate all of them. This study assesses the suitability of a number of monitoring techniques (PM mass concentrations, number and size distribution of ultra-fine particles, levels of gaseous pollutants, and a complete chemical characterization of PM 10 and PM 2.5) by examining the response of those techniques to the different emission sources and/or atmospheric processes affecting an urban Mediterranean area (Barcelona, NE Spain). The results of this work reveal that the PM mass, the number concentration and the chemical composition give different, but complementary, information. Whereas the mineral matter, a key atmospheric aerosol component across the Mediterranean, is not properly quantitatively assessed by measuring sub-micrometric particles, the monitoring of the number concentration is indispensable to interpret the origin of specific aerosol episodes. Furthermore, the chemical composition yields very relevant information to deduce the causes of specific pollution episodes. The number concentration of ultra-fine particles in urban areas is strongly dependent upon vehicle exhaust emissions, which may cause adverse health impacts. Moreover, urban Mediterranean environments are favourable to produce nucleation-mode particles (<20 nm) with photochemical origin. In those cases, these particles are expected to be of high solubility and consequently their toxicity may differ from that of traffic-generated ultra-fine particles. Thus, the use of a single monitoring parameter to evaluate the health effects seems to be not enough.

Study of indoor air pollution from household fuels in Gaborone, Botswana

This study monitored indoor air concentrations of CO and particulate matter of size range 0.3–5.0 μm in 30 households representing different income groups from July to September 2007. Selected members of the households were interviewed to assess health effects resulting from the fuel used. Fuels that produced more particles, especially those having the smallest diameters (0.3–0.5 μm), were found in the low income group household. People from these households reported more health effects when compared with those in the medium and high groups. The fuels that emitted most particles produced more than 10 times more particulate matter than the least emitting fuels. The particle number distributions for the different fuels studied were investigated and the corresponding surface area and volume distributions derived. Both the surface area and volume distributions were found to be bimodal with peaks around 0.5 μm and 2.0 μm.