Terms Of Number Concentration Research Articles

Summertime fluorescent bioaerosol particles in the coastal megacity Tianjin, North China

Primary biological particles are an important subset of atmospheric aerosols. They have significant impacts on climate change and public health. Tianjin is a coastal megacity in the North China Plain, which is affected by both anthropogenic activities and marine air masses. To study the abundance and dynamic change of bioaerosols in Tianjin, fluorescent biological aerosol particles (FBAPs) in Tianjin were investigated by a wideband integrated bioaerosol sensor (WIBS-4A) in terms of number concentrations and size distributions in summer (11th –25th August 2018). Meanwhile, total suspended particles were collected and analyzed for chemical compounds to identify potential sources of bioaerosols. WIBS data showed that fluorescent biological particles exhibited two peaks at sunrise (~7:00) and in the evening (~20:00), which were probably caused by the enhancement of fungal spores and bacteria. Three rain events occurred during the observation period. Precipitation enhanced the abundance of biological particles, which were likely released from vegetation leaves, resuspended from soil surfaces, and/or carried by raindrops from high altitudes. The abundance of biological particles showed no significant correlation with Na+ (r = −0.17), indicating the air masses from marine areas carried limited biological particles compared to those from continental areas.

Aerosol depositional characteristics in piping assembly under varying flow conditions

In the event of a nuclear reactor accident, large amount of radioactivity in the form of fission products may get released to the piping assembly of primary heat transport system. These fission products mostly in the form of aerosol particles get deposited on the inner surface of the piping system due to various depositional processes. The removal processes in the complex piping system are controlled to a large extent by the thermal-hydraulic conditions like temperature, pressure and flow rates. These parameters generally vary with time and therefore must be carefully monitored to predict the aerosol behavior in the piping system. Experimental determination of the deposition fraction, interpretation of the role of controlling parameters and development/validation of theoretical models are key areas gaining constant attention among researchers. In the present work, experiments were conducted in a piping assembly consisting of bends and horizontal-vertical orientation at two different carrier gas flow rates. Deposition fractions in the test assembly were estimated and the role of different dynamical processes (thermophoresis, gravitation and bend impaction) was interpreted. The computational fluid dynamics modeling approach is used for theoretical simulation in this work. Aerosol behavior in terms of number concentration, particle size distribution, and particle deposition in the piping system was simulated with the computational fluid dynamics software ANSYS Fluent 16.0 and the results were compared with experimental measurements (wherever applicable).

Different metrics (number, surface area, and volume concentration) of urban particles with varying sizes in relation to fractional exhaled nitric oxide (FeNO).

There have been increasing concerns on potential health effects of ultrafine particles (UFP); but little is known as to what are the most biologically relevant metrics for these particles that make up very little mass concentration. We examined a range of particle metrics (number, surface area, active surface area, and volume concentration) in relation to fractional exhaled nitric oxide (FeNO), a well-established biomarker of pulmonary inflammation. We conducted a panel study in 17 non-asthmatic children who attended schools and resided near a monitoring site at which particles in the size range of 3-800 nm were measured using a TDMPS and particles in the size range of 0.5 to 10 µm were measured using an APS. Particles were classified by size into the nucleation, Aitken, accumulation, or coarse mode, respectively, for calculating mode-specific number, surface area, active surface area, and volume concentrations. Each participating child was measured for FeNO daily for 30 days. We used linear mixed-effects models to assess the associations between various particle metrics and FeNO. In terms of number concentration, ambient particles in the Aitken mode and in the accumulation mode were significantly and positively associated with FeNO; but particles in the nucleation mode were significantly and negatively associated with FeNO. Moreover, UFP as a lump sum of both nucleation-mode and Aikten-mode particles did not show a significant association with FeNO. In terms of surface area concentration, ambient particles only in the accumulation mode were significantly and positively associated with FeNO. In terms of volume concentration, ambient particles in both the accumulation mode and the coarse mode were significantly and positively associated with FeNO. Analyses of the relationships between FeNO and metrics for particles deposited in the respiratory tract generated consistent findings, showing a negative association for the number concentration of deposited particles (driven by nucleation-mode particles), a positive association for the surface area concentration of deposited particles (driven by accumulation-mode particles), and a positive association for the volume concentration of deposited particles (driven by accumulation-mode and coarse-mode particles). Particles contributing largely to the surface area concentration and/or the volume concentration of ambient particles or particles deposited in the respiratory tract had a significant positive association with pulmonary inflammation. Nucleation-mode particles, that have large number concentrations but contribute little to the surface area or volume concentration of ambient or deposited particles, had a significant negative association with FeNO. This may indicate a different biological process or may simply be due to the negative and strong correlation between nucleation-mode and accumulation-mode particles. Given that particles in different modes may have different biological actions, measuring UFP as a whole may not necessarily be useful from a biological effect standpoint.

Carboxylesterase Concentration in Mouse Exposed to Particulate Matters on Inhalation Exposure of Prallethrin and d-Phenothrin Mixture

CE enzyme applied critical hydrolysis of pyrethroid families such as prallethrin and d-phenothrin, this active ingredient was commonly contained in mosquito repellent (MR). The previous study found that MRs as particulate matters (PMs) were very hazardous for living organisms due to the characteristics of number and mass concentration. This study examined the CE concentration in Mus musculus exposed to PM on inhalation exposure of prallethrin and d-phenothrin mixture. The lower dose was a mixture of 0.000141 mg/L prallethrin and 0.104 mg/L d-phenothrin, while the higher dose was a mixture of 0.00141 mg/L prallethrin and 1.04 mg/L d-phenothrin. Prallethrin and d-phenothrin were dissolved in acetonitrile, then diluted several times to obtain the preferred concentration. The solution was inflated with air through a diffuser to generate PMs which inserted into the chamber contained mice. The experimental group was divided into three, namely: positive control (PC), and lower- and higher-dose treatment groups, with three replicates for each group. The results illustrate that lower and higher dose demonstrated major differences. The statistical analysis confirmed that CE concentration had significant differences between groups. The increase in pyrethroid concentration followed by the increase of CE concentration, It indicated that the increasing CE substrates would be followed by the increasing of protein synthesis including CE. PMs in terms of number concentration of the largest (particles/L) is 0.3 µm, followed by 0.5 µm, 1 µm, and 5 µm. Approximately 99.86 % of the mass concentration the breathing zone is contributed by respirable particles (fine and ultrafine particles). Even if ultrafine particles are the largest number concentration, they have no significant contributions to the mass. A very abundant of fine and ultrafine particles affects they were beyond detection limit instruments, thus, they have no significant relationship with CE concentration, even though number concentration is more prominent than the mass concentration in the toxicological field, due to the high surface area of ultrafine particles.

Method for Extraction and Quantification of Metal-Based Nanoparticles in Biological Media: Number-Based Biodistribution and Bioconcentration.

A multistep sample preparation method was developed to separate metal-based engineered nanoparticles (ENPs) from biological samples. The method was developed using spiked zebrafish tissues and standard titanium dioxide (TiO2) and cerium dioxide (CeO2) ENPs. Single-particle inductively coupled plasma mass spectrometry was used to quantify the separated particles in terms of number concentration. This method demonstrated mass recoveries of more than 90% and did not strikingly alter the median particles size. High number recoveries were calculated for CeO2 ENPs (>84%). Particle number recoveries were poor for TiO2 ENPs (<25%), which could be due to the interference of 48Ca with the measured isotope 48Ti. The method was verified using zebrafish exposed to CeO2 ENPs to test its applicability for nanotoxicokinetic investigations. Total mass of Ce and particle number concentration of CeO2 ENPs were measured in different tissues. Notably, the mass-based biodistribution of Ce in the tissues did not follow the number-based biodistribution of CeO2. Moreover, the calculated mass-based bioconcentration factors showed a different pattern in comparison to the number-based bioconcentration factors. Our findings suggest that considering mass as the sole dose-metric may not provide sufficient information to investigate toxicity and toxicokinetics of ENPs.

Nano-object Release During Machining of Polymer-Based Nanocomposites Depends on Process Factors and the Type of Nanofiller.

We tested the nanomaterial release from composites during two different mechanical treatment processes, automated drilling and manual sawing. Polyurethane (PU) polymer discs (1-cm thickness and 11-cm diameter) were created using different nanomaterial fillers: multiwall carbon nanotubes (MWCNT), carbon black (CB), silicon dioxide (SiO2), and an unfilled PU control. Drilling generated far more submicron range particles than sawing. In the drilling experiments, none of the tested nanofillers showed a significant influence on particle number concentrations or sizes, except for the PU/MWCNT samples, from which larger particles were released than from control samples. Higher drilling speed and larger drill bit size were associated with higher particle counts. Differences between composites were observed during sawing: PU/CB released higher number concentrations of micro-sized particles compared to reference samples. When sawing PU/SiO2 more nanoparticle agglomerates were observed. Furthermore, polymer fumes were released during sawing experiments, which was attributed to the process heat. For both drilling and sawing, the majority of the aerosolized particles were polymer matrix materials containing nanofillers (or protruding from their surface), as evidenced by electron microscopic analysis. Results suggest that: (i) processes associated with higher energy inputs are more likely to result in higher particle release in terms of number concentration; (ii) nanofillers may alter release processes; and (iii) other types of released particles, in particular polymer fumes from high-temperature processes, must also be considered in occupational exposure and risk assessments.

Effects of exhaust gas recirculation at various loads on diesel engine performance and exhaust particle size distribution using four blends with a research octane number of 70 and diesel

Partially premixed combustion using gasoline-like fuels on compression ignition engines shows great potentials to break the soot-nitrogen oxides trade off and reduce both emissions simultaneously. By simply adjusting the dilution strategies and injection events, the control of partially premixed combustion is relatively easier compared to other low-temperature combustion concepts. However despite these advantages, recent research shows this concept tends to emit ultra-fine particles. Most previous work on partially premixed combustion only focuses on the soot emissions while the particulate matter in terms of number concentration and size distribution are not well investigated. Ultra-fine particles are dangerous to human health and are getting increasing attentions. Thus the detailed particulate matter emission from partially premixed combustion needs to be further investigated. In this work four gasoline-like ternary fuel blends are designed and experimentally tested under partially premixed combustion. The test blends all share the same two base fuels and blended with different additives. The fuel composition is varied to have the same research octane number. Tests are conducted under different engine loads and dilution strategies since the temperature and oxygen concentration are the key factors in the formation and oxidation of soot. Standard diesel is also tested under the same conditions as a comparison. It is found that these blends are capable of running under partially premixed combustion at low and medium loads and they produce near zero soot emissions when using high exhaust gas recirculation rate. However, these blends do emit smaller particles than diesel under all test loads. Besides, blends with oxygen content yield less soot emissions and smaller particles compared to non-oxygen blends.

Characterization, mixing state, and evolution of urban single particles in Xi'an (China) during wintertime haze days

A Single Particle Aerosol Mass Spectrometer (SPAMS) was deployed in the urban area of Xi'an to investigate size-resolved chemical composition and mixing state of single particles during the heavy haze episode occurred from January 13 to January 27 in 2013. Nine major single particle types were resolved with ART-2a algorithm including biomass burning (BB), Potassium-Secondary (KSec), elemental and organic Carbon (ECOC), sodium-potassium-rich ECOC (NaKECOC), sodium-potassium-rich-secondary (NaKSec), EC, OC, and Dust. Daily PM2.5 mass concentration was 213±122μgm−3. ~96% of the ambient particles were carbonaceous and internally mixed with secondary species such as sulfate and nitrate. The major particle types were from combustion sources, including coal burning, biomass burning, and vehicle exhaust. Mixing state analysis suggests gas-to-particle conversion was an important mechanism forming organic species during the winter haze episode. The relative abundances of the aged particle types, such as KSec and NaKSec increased with the elevated RH when RH<80%. The fraction of aged particles in terms of number concentration was prominent during high levels of PM2.5 under stagnant air conditions. This study gained new knowledge on atmospheric aerosol formation and evolution in urban environment heavy winter haze condition.

In situ characterisation of physicochemical state and concentration of nanoparticles in soil ecotoxicity studies using environmental scanning electron microscopy

Environmental context Characterisation of nanoparticles in terms of number concentration and aggregation state is essential for interpreting data from toxicological tests. These parameters have never been measured in situ in tests carried out in soil matrices. Here, environmental scanning electron microscopy imaging is evaluated for particles in soil, and a method for determining the number concentrations by counting the particles in the images is developed. Abstract The interpretation of nanoparticle toxicity data in soils is currently impeded by the lack of methods capable of characterising particles in situ. To draw relevant and accurate conclusions it would be desirable to characterise particle sizes, agglomeration state and number concentrations. In this article, methodologies for imaging nanoparticles in soils are evaluated for conventional scanning electron microscopy (SEM) and environmental or variable pressure scanning electron microscopy (ESEM). A protocol for dispersing Au particles (~25 to ~450nm) into soil without causing aggregation was developed. The number of particles observed per imaged area of soil correlated linearly with concentration. To determine the number of particles per volume of soil it was also necessary to know how deep in the sample the particles can be visualised. The depth was estimated by both using the Kanaya Okayama model, and spiking the soil with dispersions of known number concentration. These concentrations were determined with a range of methods to ensure their accuracy. Because larger particles can be detected deeper in the matrix, such a calibration should be performed over a range of particle sizes.

Toward a comprehensive framework for nanomaterials: An interdisciplinary assessment of the current Environmental Health and Safety Regulation regarding the handling of carbon nanotubes

The United States has recently paid significant attention to potential environmental health and safety concerns surrounding nanomaterials. Still, there exist several policy barriers to constructing effective regulation. These policy barriers include public awareness and perception, an inadequate classification system, a deficient assessment process, and industry cooperation. While public perception and industry cooperation vary greatly by country and trade, our team finds that a critical failure in the assessment and classification processes is the insufficient testing framework for classifying environmental health and safety (EHS) risk. In large part, this is due to relative novelty of the field but is also a result of the wide variety of new and under researched variables relevant to the unique health risks posed by nanomaterials. One area we believe deserves more attention in the Environmental Protection Agency's (EPA) current approach for assessing the potential toxicity of airborne nanomaterials, specifically in regards to issues of agglomeration. To better understand the potential EHS risk associated with airborne agglomeration of nanoparticles, we examine carbon nanotubes (CNTs) a nanomaterial touted for use in several consumer technologies. The first section of this paper provides a summary of the recent approaches to EHS regulation of nanomaterials. In this section we target four main policy barriers that are hindering effective EHS regulation for the research sectors in the life cycle of nanomaterial development across several government agencies. The second section is a review of the toxicology literature on inhalation risk associated with CNTs. The third section outlines the series of aerosols tests we conducted to characterize common exposure mechanisms in terms of airborne nanotubes and to determine whether current exposure levels of carbon nanotubes are acceptable under existing industry regulation. We measure exposure levels in terms of number concentration (#/cm3) and mass concentration (mg/m3) for vertically aligned CNTs and dispersed single and multi-walled CNTs. We conclude that CNTs may pose an inhalation risk to people in a manufacturing or laboratory setting and that new OSHA exposure levels need to be set for nanomaterials to secure a safe working environment. Additionally, we believe that NIOSH needs to invest in CNT aerosol studies to better develop thorough chemical and physical test processes, understand the inhalation risks associated with nanomaterials, and build toward comprehensive framework for assessment and classification of EHS risks.

Activation of “synthetic ambient” aerosols – Relation to chemical composition of particles &lt;100 nm

Abstract Cloud condensation nuclei (CCN) are an important fraction of atmospheric aerosols because of their role in cloud formation. Experimental studies focus either on direct field measurements of complex ambient aerosols or laboratory investigations on well defined aerosols produced from single substances or substance mixtures. In this study, we focussed on the ultrafine aerosol because in terms of number concentration, the majority of the CCN are expected to have sizes in this range. A field study was performed from July 2007 to October 2008 to investigate the activation behaviour of the atmospheric aerosol in Vienna ( Burkart et al., 2011 ). Filter samples of the aerosol Giebl et al., 2002; Dusek et al., 2006b ) at a nominal supersaturation (SS) of 0.5%. Activation diameters d act ranged from 54.5 nm to 66 nm, were larger than d act of typical single inorganic salts and showed no seasonal pattern in contrast to the fraction of water soluble organic carbon (WSOC), which ranged from 44% in spring to 15% in winter. The average hygroscopicity parameter κ ( Petters and Kreidenweis, 2007 ) obtained from the activation curves ranged from 0.20 to 0.30 (average 0.24), which was significantly lower than κ chem calculated from the chemical composition (0.43 ± 0.07).

Modelling the chemically aged and mixed aerosols over the eastern central Atlantic Ocean – potential impacts

Abstract. Detailed information on the chemical and physical properties of aerosols is important for assessing their role in air quality and climate. This work explores the origin and fate of continental aerosols transported over the Central Atlantic Ocean, in terms of chemical composition, number and size distribution, using chemistry-transport models, satellite data and in situ measurements. We focus on August 2005, a period with intense hurricane and tropical storm activity over the Atlantic Ocean. A mixture of anthropogenic (sulphates, nitrates), natural (desert dust, sea salt) and chemically aged (sulphate and nitrate on dust) aerosols is found entering the hurricane genesis region, most likely interacting with clouds in the area. Results from our modelling study suggest rather small amounts of accumulation mode desert dust, sea salt and chemically aged dust aerosols in this Atlantic Ocean region. Aerosols of smaller size (Aitken mode) are more abundant in the area and in some occasions sulphates of anthropogenic origin and desert dust are of the same magnitude in terms of number concentrations. Typical aerosol number concentrations are derived for the vertical layers near shallow cloud formation regimes, indicating that the aerosol number concentration can reach several thousand particles per cubic centimetre. The vertical distribution of the aerosols shows that the desert dust particles are often transported near the top of the marine cloud layer as they enter into the region where deep convection is initiated. The anthropogenic sulphate aerosol can be transported within a thick layer and enter the cloud deck through multiple ways (from the top, the base of the cloud, and by entrainment). The sodium (sea salt related) aerosol is mostly found below the cloud base. The results of this work may provide insights relevant for studies that consider aerosol influences on cloud processes and storm development in the Central Atlantic region.

Analysis of the particulate emissions and combustion performance of a direct injection spark ignition engine using hydrogen and gasoline mixtures

Three different fractions (2%, 5%, and 10% of stoichiometric, or 2.38%, 5.92%, and 11.73% by energy fraction) of hydrogen were aspirated into a gasoline direct injection engine under two different load conditions. The base fuel was 65% iso-octane, and 35% toluene by volume fraction. Ignition sweeps were conducted for each operation point. The pressure traces were recorded for further analysis, and the particulate emission size distributions were measured using a Cambustion DMS500. The results indicated a more stable and faster combustion as more hydrogen was blended. Meanwhile, a substantial reduction in particulate emissions was found at the low load condition (more than 95% reduction either in terms of number concentration or mass concentration when blending 10% hydrogen). Some variation in the results occurred at the high load condition, but the particulate emissions were reduced in most cases, especially for nucleation mode particulate matter. Retarding the ignition timing generally reduced the particulate emissions. An engine model was constructed using the Ricardo WAVE package to assist in understanding the data. The simulation reported a higher residual gas fraction at low load, which explained the higher level of cycle-by-cycle variation at the low load.

Measurements of nanoparticle number concentrations and size distributions in contrasting aquatic environments using nanoparticle tracking analysis

Environmental context. Manufactured and unintentionally produced nanoparticles have been of environmental concern owing to potential harm to humans and ecosystems, but very little is known of the actual concentrations of these owing to limitations of available methods. In order to understand both the potential adverse effects and the underlying natural processes, improved measurement techniques are needed. Here, we explore the feasibility of a novel minimum perturbation method that relates the diffusive movement of nanoparticles in a light field to their size distributions. Abstract. A feasibility study of nanoparticle tracking analysis (NTA) for aquatic environmental samples is presented here. The method has certain virtues such as minimum perturbation of the samples, high sensitivity in terms of particle concentration, and provision of number-based size distributions for aquatic samples. NTA gave linear calibration curves in terms of number concentration and accurately reproduced size measurements of certified reference material nanoparticles. However, the accuracy of the size distributions obtained with this method exhibited a high dependence on set-up parameters and the concentrations were shown to be strongly correlated with the refractive index of the material under examination. Different detection cameras and different data acquisition modes were compared and evaluated. Also, the effect of filtration of the samples was assessed. The size distributions for the contrasting environmental samples were fairly reasonable compared with other studies but an underestimation of small sizes was observed, which can be explained by a material-dependent lower detection limit in terms of size. The number concentrations obtained for the natural nanoparticles ranged from 0.5 to 20 × 108 particles mL–1 and correlated well with conventional turbidity measurements.

Aerosol number fluxes over the Amazon rain forest during the wet season

Abstract. Number fluxes of particles with diameter larger than 10 nm were measured with the eddy covariance method over the Amazon rain forest during the wet season as part of the LBA (The Large Scale Biosphere Atmosphere Experiment in Amazonia) campaign 2008. The primary goal was to investigate whether sources or sinks dominate the aerosol number flux in the tropical rain forest-atmosphere system. During the measurement campaign, from 12 March to 18 May, 60% of the particle fluxes pointed downward, which is a similar fraction to what has been observed over boreal forests. The net deposition flux prevailed even in the absolute cleanest atmospheric conditions during the campaign and therefore cannot be explained only by deposition of anthropogenic particles. The particle transfer velocity vt increased with increasing friction velocity and the relation is described by the equation vt = 2.4×10−3×u* where u* is the friction velocity. Upward particle fluxes often appeared in the morning hours and seem to a large extent to be an effect of entrainment fluxes into a growing mixed layer rather than primary aerosol emission. In general, the number source of primary aerosol particles within the footprint area of the measurements was small, possibly because the measured particle number fluxes reflect mostly particles less than approximately 200 nm. This is an indication that the contribution of primary biogenic aerosol particles to the aerosol population in the Amazon boundary layer may be low in terms of number concentrations. However, the possibility of horizontal variations in primary aerosol emission over the Amazon rain forest cannot be ruled out.

Particle and nanoparticle characterization at the exhaust of internal combustion engines

The aim of this work is the characterization of the emissions of exhaust particles in terms of number size distribution and chemical—physical properties. Laser-induced incandescence and broadband ultraviolet—visible extinction and scattering spectroscopy were used at the exhaust of a common-rail diesel engine and of a port fuel injection (PFI) spark ignition (SI) engine. The optical results were compared with size distributions obtained with an electrical low-pressure impactor and a scanning mobility particle sizer. Moreover, the fundamental engine parameters and the particulate mass and gas concentrations were measured using conventional instrumentation. With respect to the diesel engine, the effect of the exhaust after-treatment was investigated. The exhaust gas recirculation influenced the particle size distribution in terms of number concentration owing to the formation of accumulation mode particles. The catalysed diesel particulate filter strongly reduced the particle number concentration in the loading phase. Effects on the chemical nature of the particles were observed during the filter regeneration phase. With respect to the PFI SI engine, high number concentrations of nanoparticles ( D&lt;50nm) were measured for all the engine operating conditions. The chemical nature of the nanoparticles was investigated.

Effects of Driving Conditions on Diesel Exhaust Particulates

Four driving conditions were examined to characterize how speeds and loads of a medium-duty diesel engine affect resultant diesel exhaust particulates (DEPs) in terms of number concentrations (≤400 nm), size distribution, persistent free radicals, elemental carbon (EC), and organic carbon (OC). At the medium engine load (60%), DEPs surged in number concentrations at around 40–70 nm, whereas DEPs from the full engine load (100%) showed a distinctive bimodal distribution with a large population of 30–50 nm and 100–400 nm. Under the full engine load, engine speeds insignificantly affected resultant DEP number concentrations. When the engine load decreased from 100% to the medium level (60%), DEPs of ultrafine size and 100–400 nm decreased at least 1.4 times (from 5.6 × 108 to 4 × 108 #/cm3) and more than 3 times (from 2.7 × 108 to 0.8 × 108 #/cm3), respectively. The same reduction in the engine load significantly decreased persistent free radicals in DEPs up to approximately 30 times (from 123 × 1016 to 4 × 1016 #spin/g). Decreasing the engine load from 100 to 60% also concurrently reduced both EC and OC in total DEPs around 2 times, from 27.3 to 13.9 mg/m3, and from 17.6 to 9.2 mg/m3, respectively. For DEPs smaller than 1 µm, under the full engine load, EC and OC consistently peaked at 170–330 nm under an engine speed of 1800 rpm or 94–170 nm under an engine speed of 3000 rpm, reflecting processes of nucleation, cluster-cluster agglomeration, and condensation. Decreasing the engine load from 100 to 60% reduced EC and OC in DEPs (smaller than 1 μm) at least 3 times (0.6 to 0.2 mg/m3) and 2 times (0.4 to 0.2 mg/m3), respectively. Taken together, decreasing the full engine load to a medium (60%) level effectively reduced the number concentrations (≤400 nm), persistent free radicals, EC, and OC of total DEPs, as well as the concentration of EC and OC in ultrafine and accumulation-mode DEPs.

전문가시스템을 이용한 석면 및 비석면의 분류 및 확인

Asbestos is the name of a group of minerals with long and thin fibers that originate naturally in the environment. Asbestos mainly affects lungs and the membrane that surrounds the lungs. In general, PCM (phase contrast microscopy) and PLM (polarized light microscopy) have been used to analyze asbestos fibers. However, these methods have often problems to over-estimate number concentration when counting real asbestos fibers. Moreover, there are many difficulties when separating and identifying various asbestos and non-asbestos fibers. In order to determine quantitative information on fibrous particles, source profiles for asbestos and non-asbestos fibers must be initially developed on the basis of their chemical compositions and physical parameters. In our study, a SEM/EDX was used to develop source profiles from known asbestos samples as reference samples. We could make the source profile matrix consisting of 6 types of asbestos fibers and 2 types of non-asbestos fibers by analyzing 380 fibers. Based on these profiles, a rule building expert system was developed by using the visual basic application (VBA). Various fibers were successfully classified by 2 simple rules in the EXCEL environment based on several visual steps such as inserting data, viewing results, and saving results. For a case study to test the expert system, samples from a construction materials and from various indoor environments such as a residental area, a preschool classroom, and an underground store were collected and analyzed. As a result of the survey, a total of 76 individual test fiber particles was well classified into 5 different types of particle classes; 9.3% of chrysotile, 15.4% of amosite, 0.8 of crocidolite, 4.2% of tremolite, 5.8% glass fiber, 21.1% of other fibers, and 43.5% of unknown fibers in terms of number concentration. Even though unknown portion was high, it will be decreased markedly when expanding fiber source profiles.

Measurements of Nanoparticles of Organic Carbon and Soot in Flames and Vehicle Exhausts

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.

Mass, surface area and number metrics in diesel occupational exposure assessment

While diesel aerosol exposure assessment has traditionally been based on the mass concentration metric, recent studies have suggested that particle number and surface area concentrations may be more health-relevant. In this study, we evaluated the exposures of three occupational groups-bus drivers, parking garage attendants, and bus mechanics-using the mass concentration of elemental carbon (EC) as well as surface area and number concentrations. These occupational groups are exposed to mixtures of diesel and gasoline exhaust on a regular basis in various ratios. The three groups had significantly different exposures to workshift TWA EC with the highest levels observed in the bus garage mechanics and the lowest levels in the parking ramp booth attendants. In terms of surface area, parking ramp attendants had significantly greater exposures than bus garage mechanics, who in turn had significantly greater exposures than bus drivers. In terms of number concentrations, the exposures of garage mechanics exceeded those of ramp booth attendants by a factor of 5-6. Depending on the exposure metric chosen, the three occupational groups had quite different exposure rankings. This illustrates the importance of the choice of exposure metric in epidemiological studies. If these three occupational groups were part of an epidemiological study, depending on the metric used, they may or may not be part of the same similarly exposed group (SEG). The exposure rankings (e.g., low, medium, or high) of the three groups also changes with the metric used. If the incorrect metric is used, significant misclassification errors may occur.