Dust Generator for Inhalation Studies with Limited Amounts of Archived Particulate Matter

A novel design for a dry-aerosol generator that efficiently produces a well-dispersed dust suspension using small quantities of a PM_2.5-enriched powder sample is described. The motivation to develop a highly efficient dry-aerosol particle generator was to facilitate collaborative projects that combine in vitro cell culture experiments and multiday inhalation exposures using a single batch of well-characterized particles. Premixing of the test particles with larger diameter glass beads permits delivery of aerosol concentrations from 100–1000 μ g/m³ to an exposure chamber using only milligram quantities of the test powder per hour. Examination of exposure chamber filter samples by scanning electron microscopy showed well-dispersed particles of the test powder free of glass spheres or fragments. Data are presented from experiments using coal fly ash as the test powder to illustrate the system performance.     

Generation of Radiolabeled Soot-Like Ultrafine Aerosols Suitable for Use in Human Inhalation Studies

We have developed a method for radiolabeling ultrafine carbon particle aggregates with technetium-99m. The carbon aggregate aerosol was chosen to mimic the physical properties of urban combustion or ''soot-like'' particulate. The radioisotope is a short lived (t_1/2 = 6.02 h) gamma emitter commonly used in human studies where scintigraphic methods are employed. Primary carbon parti cles, the aggregation of which is controlled by concentration and time, were produced by arcing between graphite electrodes under an argon atmosphere. Radiolabeling of particles was accomplished by applying a pertechnetate solution onto the tips of electrodes prior to arcing. The activity median diameter of experimental aerosols could be varied from 50 to 150 nm. The specific activity of aerosols increased with the amount of activity applied to the electrodes and decreased with time of generator operation. In-vitro leaching of the radioisotope from particles into solution was also measured. Leaching appeared to increase with the specific activity of the aerosol but was not affected by particle size.     

Development and Evaluation of a High-Volume Aerosol-into-Liquid Collector for Fine and Ultrafine Particulate Matter

This study presents a novel high-volume aerosol-into-liquid collector, developed to provide concentrated slurries of fine and/or ultrafine particulate matter (PM) to be used for unattended, in situ measurements of PM chemistry and toxicity. This system operates at 200 liters per minute (L/min) flow and utilizes the saturation–condensation, particle-to-droplet growth component of the versatile aerosol concentration enrichment system (VACES), growing fine or ultrafine PM to 3–4-μm droplets, in conjunction with a newly designed impactor, in which grown particles are collected gradually forming highly concentrated slurries. Laboratory evaluation results indicated an excellent overall system collection efficiency (over 90%) for both monodisperse and polydisperse particles in the range of 0.01 to 2 μm. Field evaluations illustrated that overall a very good agreement was obtained for most PM_2.5 species between the new aerosol collection system and the VACES/BioSampler tandem as well as filter samplers operating in parallel. Very good agreement between the new system and the VACES/BioSampler was also observed for reactive oxygen species (ROS) in ambient PM_2.5 samples, whereas lower ROS values were obtained from the water extracts of the filter, likely due to incomplete extraction of water insoluble redox active species collected on the filter substrate. Moreover, the field tests indicated that the new aerosol collection system could achieve continuous and unattended collection of concentrated suspensions for at least 2 to 3 days without any obvious shortcomings in its operation. Both laboratory and field evaluations of the high-volume aerosol-into-liquid collector suggest that this system is an effective technology for collection and characterization of ambient aerosols.

Copyright 2013 American Association for Aerosol Research     

Generation of Airborne Multi-Walled Carbon Nanotubes for Inhalation Studies

Recent studies suggest that inhaled or intratracheally instilled multi-walled carbon nanotubes (MWCNTs) cause adverse health effects depending on the fiber length. In the present study a simple batch particle generation system was developed to generate airborne MWCNTs for inhalational toxicology studies. The generation rate can be controlled by the amplitude of sieve shaker. Maximum concentration of respirable airborne MWCNTs was 1.2 mg m^–3 at a nose-exposure chamber supplied with air at flow rate of 30 L min^–1. We examined the performance of airborne MWCNT generation system and characterized properties of generated fibrous particles at mass concentrations of 0.4 mg m^–3 (particle number; ca. 1700 cm^–3). Monomodal shaped size distributions with peak located at electrical mobility diameter of 300 nm (in number) and aerodynamic diameter of 1–2 μm (in mass) were measured with a scanning mobility particle sizer and with a low-pressure impactor, respectively. Two hour particle generation reproducibility tests were conducted five times, in which stability and repeatability of particle size and total number concentration were within an acceptable range. Aerodynamically classified particle morphology was studied by TEM, dissociated fiber-like and agglomerated MWCNT particles were observed. The former contributes up to 38% to counted particles, and the average width and length of fiber were 80 nm and 3.7 μm, respectively, with an aerodynamic size for particle of 260–381 nm.     

Generation of Nanoparticles of Lubricating Motor Oil for Inhalation Studies

Recent studies suggest that most 20–30 nm nanoparticles measured at roadsides are composed mainly of organic carbon derived from lubricating motor oil. Therefore, a simple particle generation system has been developed for controlled production of 20–30 nm nanoparticles of lubricating motor oil for inhalation toxicology studies by means of vapor condensation without addition of nuclei. Quasi-monodisperse particles with a modal diameter located at 20 nm and total number concentrations above 10 ⁶ cm ^?3 were generated. Ten 2-h particle generation reproducibility tests were conducted, in which stability and repeatability of particle size and total number concentration were good. Organic carbon is a major component of oil particles, and organic analysis showed that the compositions of oil particles were not subjected to distillation of organic compounds through evaporation to condensation. Using the nose-exposure system connected to the particle generation system, toxicity of 20-nm particle organic compounds of lubricating motor oil can be assessed by inhalation studies of experimental animals.     

A High Volume Apparatus for the Condensational Growth of Ultrafine Particles for Inhalation Toxicological Studies

A high volume (2500 LPM) system for the condensational growth of ultrafine particles was developed and evaluated using indoor air as a test aerosol. The main features of this system are the following: (a) ultrafine particles grow condensationally to supermicron sizes using high purity deionized water as a condensing medium; (b) the supersaturation ratio is adjustable and can be precisely controlled; (c) the system can operate for a wide range of ambient air temperature and relative humidity conditions; and (d) a thermal dryer is used to return the condensationally grown particles back to their original size. Restoring the original ambient size distribution and preserving the composition of the ambient ultrafine particles is very important for inhalation studies. The system is fully automated and has computerized feedback controls. In addition, saturation of the aerosol with water vapor occurs at close to ambient temperatures to minimize particle losses of volatile components. Saturation of sample air is obtained using a direct steam-injecting, fully modulating electric humidifier. The sample air after saturation is drawn through the supersaturator, which is a refrigerant-to-air heat exchanger and is cooled down to obtain the desirable supersaturation ratio. Supersaturation ratios can be precisely adjusted, with the optimum operational level found to be in the range of 2 to 3. The performance of the system was evaluated as a function of critical operation parameters, including the supersaturation ratio as well as the saturation and supersaturation temperatures. A series of virtual and conventional impactors was used to characterize the condensational growth of ultrafine particles. This new high volume apparatus was shown to grow ambient ultrafine particles to supermicron sizes with a particle size growth of approximately 1.8 w m. Particle losses in the system were found to be minimal (about 10%). The thermal dryer was used successfully to restore the grown particles back to their original size distribution. Particle concentration, aerosol temperature, and residence time (aerosol flow) are key parameters shown to affect the performance of the thermal dryer was used successfully to restore the grown particles back to their original size distribution. Particle concentration, aerosol temperature, and residence time (aerosol flow) are key parameters shown to affect the performance of the thermal dryer.     

烃源岩有机质生烃过程中的粘土矿物催化作用研究进展

本文简要回顾了国内外对于粘土矿物对有机质生烃催化作用的研究进展,系统阐述了粘土矿物催化作用机理及粘土矿物催化作用的内在决定因素和外在环境因素,着重总结了粘土矿物催化作用对有机质生烃的影响,并就这一方向的研究作了展望。     

Polycyclic Aromatic Hydrocarbon Concentration and Acute Toxicity of Airborne Particulate Matter: Using Microtox as a Toxicity Screening Tool

The present study evaluated six solvent vehicles and assessed acute toxicity of airborne particles in a Microtox system. Acetone, acetonitrile, dimethyl sulfoxide (DMSO), ethanol, ethylene glycol, and methanol were chosen as carrier solvents and examined for their suitability in the Microtox bioassay at initial concentrations of 5.0, 2.5, 1.0, 0.25, and 0.08% (v/v) respectively. Air samples were collected using a high-volume sampler on the roof of a four-story building and at a traffic intersection in Tainan in southern Taiwan during 2000. Results show that DMSO, at solvent levels of not more than 2.5% (v/v), is a better and more suitable solvent vehicle for assessing the acute toxicity of airborne particles in Microtox. In addition, concentrations of airborne particulate polycyclic aromatic hydrocarbons (PAHs) varied seasonally, and generally decreased with increasing temperature (winter > fall > spring > summer). However, particulate PAH concentrations measured on the roof were much lower than those measured at the traffic intersection, by factors of about 1/43 to 1/10. Concentrations of airborne particulate PAHs showed good correlation with EC 50 values for particle-associated soluble organic fraction.     

A Rational Basis for National Ambient Air Standards for Particulate Matter

The aspiration of large particles (18–30.5 μm) in the human nose was studied to determine the inhalation efficiency as a function of particle size, and to evaluate the upper size cutoff for inhalable particles in still air. Under these conditions, the ability of a particle to be inhaled is dependent on the inhalation velocity entering the nose and the particle terminal settling velocity. Nasal inhalation of radiolabeled pollen and wood dust aerosols was measured in four subjects at normal resting breathing rates. The efficiency of nasal aspiration was found to decrease as the square of the particle size. The upper size cutoff for inhalability was estimated to be approximately 39 μm in still air.     

Federal Reference and Equivalent Methods for Measuring Fine Particulate Matter

In the national ambient air quality standards specified by the U.S. Environmental Protection Agency in the Code of Federal Regulations, new standards were established for particulate matter on July 18, 1997. The new particulate matter standards specify mass concentration as the indicator for fine particulate matter (aerodynamic diameter of 2.5     

Determination of Levoglucosan in Particulate Matter Reference Materials

Source identification is critical for the effective management of air pollution. The ratio of levoglucosan (1,6-anhydro- β -D-glucose) to organic carbon has been used to identify and quantify the contribution of biomass combustion to the organic carbon content in aerosols. Therefore, accurate levoglucosan measurements in particulate matter are important. This study determined levoglucosan concentrations in urban dust Standard Reference Materials (SRMs) 1649a and 1648 available from the National Institute of Standards and Technology (NIST) as well as two particulate matter samples with particle sizes nominally 2.5 μ m and smaller collected in Baltimore, MD. Levoglucosan was extracted using both pressurized fluid and Soxhlet techniques. Quantification was performed with gas chromatography/mass spectrometry (GC/MS) using a deuterated levoglucosan internal standard and two different GC columns. Levoglucosan concentrations were 81.1 μ g g^?1 with a standard deviation of 9.4 μ g g^?1 (n = 9) for SRM 1649a, 107 μ g g^?1 with a standard deviation of 18 μ g g ^?1 (n = 8) for SRM 1648, 225 μ g g^?1 (standard deviation of 41 μ g g^?1 n = 4) and 138 μ g g^?1 (standard deviation of 39 μ g g ^{? 1} n = 5) for the two fine particulate matter samples collected in Baltimore, MD.     

细颗粒物电凝并技术研究进展

雾霾的主要污染物是细颗粒物PM2.5,主要来自燃煤过程,传统除尘技术对PM2.5的捕获效率较低,通过电凝并技术使PM2.5凝聚成大颗粒,再通过传统除尘器脱除,可提高PM2.5的捕集效率。综述了国内外电凝并技术的研究进展,主要包括静电场中异极性荷电颗粒凝并、交变电场中同极性荷电颗粒凝并、交变电场中异极性荷电颗粒凝并;介绍了一种新型荷电凝并装置,细颗粒物与大颗粒之间运动与凝并的直接观测实验,为电凝并技术的实际应用和装备开发提供技术支撑。     

Development of a Reference Standard for Particulate Matter Mass in Ambient Air

Particulate matter (PM) in ambient air is composed of many chemical species of varying vapor pressures. A direct mass measurement of PM mass on filters is the basis of regulatory PM reference methods. The loss of semi-volatile PM mass collected on filters and filter sampling artifacts can produce nonquantifiable biases in reference method measurements depending on the thermodynamic history of the filter; therefore, a reference method cannot be considered a scientific reference standard. A new technique is introduced which has the potential to overcome the difficulties inherent in PM mass measurement and holds the promise of the measurement of PM mass as it exists in ambient air at ambient temperature. While comprehensive laboratory and field studies of the instrument and its components are needed to fully characterize the system, preliminary data have been obtained to provide a basic proof of concept for the technique.     

Characterization of Particulate Matter from Direct Injected Gasoline Engines

The reactivity and reaction kinetics of particulate matter (PM) from direct injected gasoline (GDI) engines has been studied by O₂ and NO₂ based temperature programmed and isothermal step-response experiments, and the PM nano-structure has been characterized using HRTEM. The reactivity of the PM samples collected in filters during on-road driving was found to increase in the following order: Printex U < diesel < gasoline PI ≈ gasoline DI < ethanol for O₂ based combustion. The activation energies for O₂ and NO₂ based oxidation of PM collected from a GDI engine in an engine bench set-up was estimated to 146 and 71 kJ/mol respectively, which is comparable to corresponding values reported for diesel and model soot. Similar nano-structure features (crystallites plane dimensions, curvature and relative orientation) as observed for diesel soot were observed for gasoline PM.     

Generation and Characterization of Ultrafine Chain Aggregate Aerosols

Continuously stable, well-characterized chain aggregate aerosol sources generated from a flame aerosol generator are described. To characterize the length of the chain aggregate, a new image processing software was developed to measure the length distribution of aggregates. This program measures the path length of the aggregate that has been skeletonized into one pixel in width while maintaining its length and shape. In order to generate monodisperse chain aggregate sources, a differential mobility analyzer was used to classify aggregates according to electrical mobility. A series of experiments were conducted to generate singly charged, monodisperse chain aggregate aerosol sources. The operational range of the system for generation of monodisperse chain aggregates is described. Single-mode chain aggregates with a geometric mean particle length between 1.50 and 3.20 μm and a length standard deviation around 1.3 were generated.     

Rice Straw Smoke Generation System for Controlled Human Inhalation Exposures

A unique burner system was designed for the purposes of exposing human subjects to rice straw smoke under highly controlled conditions. The system burns individual straws and has produced particle concentrations up to 900 w g m m 3 in a temperature- and humidity-controlled exposure chamber. Burner operation is fully automatic and programmable. Ignition is by radiant heating in a manner similar to the field. Particle concentration is controlled by the firing interval between straws and by the ratio of burner outlet flow mixing with the main purified air supplied to the exposure chamber. Steady-state particle concentrations are achieved within 5 min from start. Repeatability of particle concentration is excellent at the two exposure levels used, 200 and 500 w g m m 3 . Measurements of particle size distributions suggest that approximately 80% of mass is in the size fraction below 1 w m. Although particle concentrations are controlled at target levels with good precision, emission factors are higher than achieved with similar material in wind tunnel and field experiments. Further characterization of particulate matter is needed to determine if higher emission factors are associated with changes in particle composition and morphology that may influence exposure results.     

大气颗粒物PM2.5化学组分分析方法概述

大气细颗粒物PM2.5中化学组分的分析方法做了简要的介绍,PM2.5的化学组分主要包括水溶性离子、无机元素、有机碳和元素碳,并分析了各种方法的优缺点,以便于在研究中选取更简单有效的方法,并展望了PM2.5中组分的研究前景.