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Cardiovascular Effects of Inhaled Ultrafine and Nanosized Particles

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IntroductionSources of UFPsMeasurement TechniquesTypical Physical and Chemical Particle CharacteristicsReferences

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... Fine and ultrafine particles (UFPs) are products of combustion and secondary atmospheric transformations, and ambient UFPs have multiple sources. Few emission inventories have been created for UFPs, but although constructed using different approaches, they all concluded that the highest contribution comes from emissions of industrial combustion processes and traffic-related emissions (Cass et al., 2000;Kuhlbusch and Asbach, 2011;Kulmala et al., 2011;Buonanno et al., 2009). In cement industries, dust is emitted from stockpiles, quarrying, transportation of raw materials, kiln operation, clinker cooling, and milling (Abdul-Wahab, 2006;European Commission, 2010;Gupta et al., 2012). ...
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Cement plants are responsible for particle and gaseous emissions into the atmosphere. With respect to particle emission, the greater part of is in the range from 0.05 to 5.0 µm in diameter. In the last years attention was paid to submicron particles, but there is a lack of available data on the emission from stationary sources. In this paper, concentration and size distribution of particles emitted from four cement kilns, in relationship to operational conditions (especially the use of alternative fuel to coal) of the clinker process are reported. Experimental campaigns were carried out by measuring particles concentration and size distribution at the stack of four cement plants through condensation particle counter (CPC) and scanning mobility particle sizer spectrometer (SMPS). Average total particle number concentrations were between 2000 and 4000 particles/cm(3), about 8-10 times lower that those found in the corresponding surrounding areas. As for size distribution, for all the investigated plants it is stable with a unimodal distribution (120-150 nm), independent from the fuel used. The study provides information on submicron particles emitted from cement kilns in different driving conditions. In particular, the total particle number is modest and considerably lower than that measured in ambient air, whereas the particle size distribution could be influenced by the operational conditions.
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Aerosol particles are ubiquitous in the Earth's atmosphere and are central to many environmental issues such as climate change, stratospheric ozone depletion and air quality. In urban environments, aerosol particles can affect human health through their inhalation. Atmospheric aerosols originate from naturally occurring processes, such as volcanic emissions, sea spray and mineral dust emissions, or from anthropogenic activity such as industry and combustion processes. Aerosols present pathways for reactions, transport, and deposition that would not occur in the gas phase alone. Understanding the ways in which aerosols behave, evolve, and exert these effects requires knowledge of their formation and removal mechanism, transport processes, as well as their physical and chemical characteristics. Motivated by climate change and adverse health effects of traffic-related air pollution, aerosol research has intensified over the past couple of decades, and recent scientific advances offer an improved understanding of the mechanisms and factors controlling the chemistry of atmospheric aerosols. Environmental Chemistry of Aerosols brings together the current state of knowledge of aerosol chemistry, with chapters written by international leaders in the field. It will serve as an authoritative and practical reference for scientists studying the Earth's atmosphere and as an educational and training resource for both postgraduate students and professional atmospheric scientists.
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During measurement campaigns at an urban background and a rural site, simultaneous measurements of particle size distributions using a scanning mobility particle sizer (SMPS)/aerodynamic particle sizer (APS) combination and Fuchs surface using an epiphaniometer have been made. The epiphaniometer was calibrated using sub-100 nm monodisperse aerosol and it was found that a calibration based upon particle electrical mobility diameters measured with a SMPS was consistent irrespective of the use of singlet particles of sodium chloride and ammonium sulphate or clusters of carbon. The field intercomparison of surface areas derived directly from the epiphaniometer and calculated from the size distributions determined by the SMPS/APS combination showed a good agreement of Fuchs surface estimates at both measurement sites. However, attempts to estimate a “geometric” surface area from the epiphaniometer data led to significant divergence from the estimates of the SMPS/APS combination when there was a significant fraction of coarser (>700 nm) particles contributing to the aerosol surface area.
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p within 2.4% error. The response of the EAD is almost proportional to diameter, D p .AP AS2000CE (Photoelectric Aerosol Sensor man- ufactured by EcoChem) gave both size and composition-dependent responses. For diesel particles produced at high engine loads, the response was nearly proportional to Fuchs surface area. However, at lighter engine loads, the response dropped sharply with decreas- ing D p. Light engine loads are associated with high fractions of volatile particles that may suppress the photoemission response. The secondary purpose of this study is to investigate the difference in charging rate between singlets (NaCl particles) and agglomer- ates (diesel particles) by using diffusion chargers. Agglomerates (diesel particles at engine load 75%) acquire more charge than singlets (NaCl particles) by 15 and 17% for LQ1-DC and EAD, respectively.
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The differential mobility chamber of Knutson and Whitby (1975a) is analyzed in terms of the mobility distribution function, and a new iterative scheme for converting the mobility distribution to a size distribution taking into account multiply charged aerosols is given. The scheme has been verified for trial size distributions and shown to converge rapidly to the correct distribution. A differential mobility chamber has been constructed and data obtained with the instrument demonstrate its utility in obtaining the size distribution of aerosols in the size range from 0.008 to 0.7 μm radius.
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The goal of continuous ambient participate monitoring has been realized through the use of tapered element oscillating microbalance technology. This technology measures particle mass inertially as the mass deposits on a filter. As such, it is a direct mass measurement and eliminates the mass uncertainties inherent in indirect methods represented by optical or beta adsorption instrumentation. A description of the tapered element oscillating microbalance PM-10 measurement technique is given. Tests have been conducted on tapered element oscillating microbalance PM-10 monitors both in the United States and Europe. Test results presented include comparisons to samplers designated as EPA reference methods.
The diffusion battery, an assembly of circular tubes or rectangular channels, is one of the best devices available for measuring the size and size distribution of submicron aerosols in the diameter range 0.002 to 0.2 micron. Experimental measurements on singly charged monodisperse aerosols from 0.01 to 0.1 micron are described using a condensation nucleus counter to measure the aerosol penetration through the stages of a set of portable diffusion batteries in series. Particle sizes in the range tested could be selected at will by adjusting the voltage of an electric mobility classifier. The fraction of aerosol of a given size passing through each battery stage was found to agree closely with the penetration calculated from molecular diffusion theory for that size. This shows that the theory is correct and confirms that the aerosol produced by the electric mobility classifier was monodisperse.
Article
Due to the lake of in-situ aerosol particle analysis systems, aerosol samples are taken and analyzed off-line. For detailed analysis of particle properties such as shape, morphology, and composition, off-line operating analytical tools like light microscopes, scanning electron microscopes (SEM), total reflection x-ray fluorescence (TXRF), and so on are used. The analysis must be performed on a representative sample of particles homogeneously deposited on a flat sample plate. This avoids sample preparation steps which may change the sample. In this paper we describe the design, construction, and evaluation of a continuous sampling device that deposits gasborne particles on an analytically suitable sample plate. The collection efficiency and the deposition pattern were optimized using a numerical model and experiments. It turned out that representative samples appropriate for further analysis can be taken in the particle size range from 0.03 mu m < Dp < 10 mu m. Additionally, the sampling efficiency was investigated for particles smaller than 0.03 mu m using electrical and non-electrical deposition mechanisms like diffusion and thermophoresis. The investigations performed demonstrate that the designed electrostatic precipitator (ESP) is a very useful tool for homogeneous particle deposition on analytically suitable flat sample plates and can be used as a back-up filter. Further, the ESP especially can be used in combination with a differential mobility analyzer (DMA) if detailed investigations of a narrow particle size range of a polydisperse aerosol are required.
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The properties and behavior of suspended particles (dust, smoke, clouds), and the physical principles underlying their behavior are covered. Applications such as filtration, respiratory deposition, sampling, and the production of test aerosols are discussed. Physical analysis rather than mathematical analysis is emphasized.
Article
Thermal precipitation is attractive for airborne particle collection because of the high collection efficiencies which may be attained and the convenient examination of the deposit. Most thermal precipitators, however, have very low sampling capacities or flow rates. To take fullest advantage of the desirable features of thermal precipitation, a new precipitator was designed and constructed. It operated continuously, and deposited particles upon a moving tape or substrate. Complete collection of particles resolvable with an electron microscope was attained in a 3‐in. diameter precipitating zone at a flow rate of 1 l∕min.
Article
We investigated the effect of particle pre-existing charges on unipolar charging. Particles carrying a defined number and polarity of pre-existing charges were used to study the unipolar charging process in a unipolar diffusion charger with positive ions. It was found that the particles initially carrying negative charges have almost the same amount of positive charges as the initially uncharged particles after passing the test charger; and the particles initially carrying more positive charges have more final charges. An analytical solution of a model for particle charge distribution of initially charged particles was provided for unipolar charging based on Fuchs' theory and the birth-and-death theory. The N ion t value used in this model was obtained by fitting the experimental data of average charge on particles for initially uncharged particles. The results from the analytical solution show very good agreements with experimental data regarding the relationship between the pre-existing charge and the final charge on particles (50–200 nm in this study). Experimental tests of the response of Nanoparticle Surface Area Monitor (NSAM) against initially charged particles demonstrated that NSAM could have a large response deviation (more than 20% in the tested charge level) depending on the particle size and the amount of pre-existing positive charges on particles. Modeling of NSAM response showed similar deviation and predicted that when pre-existing charge is high enough, the NSAM response can be as large as 5 and 9 times of the uncharged particle response for alveolar and tracheobronchial surface area concentration, respectively.
Article
Condensation of supersaturated vapors has been used for more than a century to grow small aerosol particles to sizes that can be detected optically. This paper discusses the history of instruments that use condensation to detect particles. I divide this history into two main sections. The first of these focuses on the development of expansion-type instruments including the ''dust counters'' in which John Aitken played the decisive role and ''photoelectric nucleus counters'' primarily by L. W. Pollak and coworkers. The second section deals with the development of steady-flow condensation nucleus counters (CNCs) in which Jean Bricard and coworkers played the decisive role. The importance of calibration methodologies is also pointed out. Refinements by instrumentation manufacturers and many aerosol scientists have led to the reliable, accurate instruments that are widely used today.
Article
We report on a new instrument developed for rapid automated on-line and continuous measurement of ambient aerosol bulk com- position.Thegeneralapproachisbasedonearlierdevices(Khlystov et al. 1995; Simon and Dasgupta 1995) in which ambient particles are mixed with saturated water vapor to produce droplets easily collected by inertial techniques. The resulting liquid stream is an- alyzed with an ion chromatograph to quantitatively measure the bulk aerosol ionic components. In this instrument, a modié ed ver- sion of a particle size magnié er (Okuyama et al. 1984) is employed to activate and grow particles comprising the é ne aerosol mass. A single jet inertialimpactor isused tocollect the droplets onto a ver- tical glass plate that is continually washed with a constant water diluent è ow of nominally 0.10 ml min¡ 1. The è ow is divided and then analyzed by a dual channel ion chromatograph. In its current form, 4.3 min integrated samples were measured every 7 min. The instrument provides bulk composition measurements with a detec- tion limit of approximately 0.1 πg m¡ 3 for chloride, nitrate, sul-
Article
A new water-based condensation particle counter (WCPC) is presented. The WCPC is a thermally diffusive, laminar flow instrument. Condensational enlargement is achieved through the introduction of a saturated airflow into a “growth tube” with wetted walls held at a temperature higher than that of the entering flow. An unsheathed, 1 L/min instrument utilizing this principle has been evaluated with various aerosols. The particle size detected with an efficiency of 50% is at or below 4.8 nm for particles sampled from vehicular emissions or ambient air, and for various laboratory-generated inorganic salts. The cut point is higher for the organic materials tested, ranging from 8 nm to 30 nm depending on the compound and purity level. An empirically determined dead-time correction factor is applied to the coincidence correction, which allows extension of the single-count mode to higher concentrations. The counting efficiencies for 80 nm oil and salt aerosols are equal, and above 97% for concentrations approaching 10 cm. When subject to a step-fucntion change in input concentration the time required to attain 90% of the final value, including a 0.5 s lag, is 1.3 s. The corresponding exponential time constant is 0.35 s. The WCPC evaluated here is marketed as the TSI Model 3785.
Article
Samples of atmospheric aerosols, collected with cascade impactors in the urban area of Vienna (Austria) and at a coastal site on the North Sea, were investigated for black carbon (BC) as the main component of absorbing material and for mass. The size distributions are structured. The BC distributions of these samples show a predominant mode, the accumulation aerosol, in the upper submicron size range, a less distinct finer mode attributable to fresh emissions from combustion sources, and a distinct coarse mode of unclear origin. It is important to note that some parameters of the accumulation aerosol are related statistically, indicating the evolution of the atmospheric accumulation aerosol.
Article
Abstraet--A new principle of sampling aerosol particles by means of steam injection with the consequent collection of grown droplets has been established. An air stream free of water-soluble gases is rapidly mixed with steam. The resulting supersaturation causes aerosol particles to grow into droplets. The droplets containing dissolved aerosol species are then collected by two cyclones in series. The solution collected in the cyclones is constantly pumped out and can be on-or off-line analysed by means of ion chromatography or flow injection analysis. On the basis of the new sampling principle a prototype of an aerosol sampler was designed which is capable of sampling particles quantitatively down to several nanometres in diameter. The mass sampling efficiency of the instrument was found to be 99%. The detection limit of the sampler for ammonium, sulphate, nitrate and chloride ions is below 0.7/~g m-a. By reduction of an already identified source of contamination, much lower detection limits can be achieved. During measurements the sampler proved to be stable, working without any assistance for extended periods of time. Comparison of the sampler with filter packs during measurements of ambient air aerosols showed that the sampler gives good results.
Article
Standard aerosol instruments to measure particle size distributions in the ultrafine size range are large and heavy. We built a small electrical diffusion battery, which can be carried in a backpack and thus makes size-resolved short-term personal aerosol exposition measurements possible. The instrument was designed for maximal measurable particle size range and long maintenance intervals. The optimum number of stages for the diffusion battery was found with a Monte-Carlo simulation. To assess the instrument's performance, we compared size distributions measured with the electrical diffusion battery to those obtained with standard aerosol instruments (the scanning mobility particle sizer and the fast mobility particle sizer of TSI Inc.). In general, the readings of the electrical diffusion battery and those of standard instruments agree well (to within 10–20%).
Article
An integrated collection and vaporization cell has been developed to provide automated, 10-min resolution monitoring of fine particle nitrate in the atmosphere. Particles are collected by a humidified impaction process and analyzed in place by flash vaporization and chemiluminescent detection of the evolved nitrogen oxides. Particle collection efficiency was measured between 95% and 100% for particles above 0.1 μm. Evaporative losses for ammonium nitrate were 2 ± 4%. Average nitrate values from the automated system were compared to traditional denuder filter measurements in three cities, with correlation coefficients of greater than 0.97 and regression slopes ranging from 0.96 to 1.06. The detection limit is governed by the field blank, which for the Los Angeles area was 0.4 μg/m3. The system operated unattended for days at a time, with data recovery of 97%.
Article
Atmospheric ultrafine particles (diameter < 0.1 μm) are under study by inhalation toxicologists to determine whether they pose a threat to public health, yet, little is known about the chemical composition of ultrafine particles in the atmosphere of cities. In the present work, the number concentration, size distribution, and chemical composition of atmospheric ultrafine particles is determined under wintertime conditions in Pasadena, CA, near Los Angeles. These experiments are conducted using a scanning dif ferential mobility analyzer, laser optical counter, and two micro-orifice impactors. Samples are analyzed to create a material balance on the chemical composition of the ultrafine particles. The number concentration of ultrafine particles in the size range 0.017 < dp < 0.1 μm, analyzed over 24-h periods, is found to be consistently in the range 1.3 × 104 ± 8.9 × 103 particles cm-3 air. Ultrafine particle mass concentrations are in the range 0.80−1.58 μg m-3. Organic compounds are the largest contributors to the ultrafine particle mass concentration. A small amount of sulfate is present in these particles, at concentrations too low to tell whether it exists as unneutralized sulfuric acid. Iron is the most prominent transition metal found in the ultrafine particles. These data may assist the health effects research community in constructing realistic animal or human exposure studies involving ultrafine particles.
Article
INTRODUCTION In recent years there has been an increased number of investigations to determine particle size distributions for the submicron regime. These distributions are frequently obtained using a differential mobility analyser (DMA). Raw data from the DMA can be converted into a size distribution if the bipolar charge distribution for the aerosol is known. Hence the size distribution will be representative only if the bipolar charge distribution is accurately described. Bipolar charge distributions measured by Hussin et al. (1983), Adachi et al. (1985) and Wiedensohler et al. (1986) for particles in air at room temperature support the diffusion charging theories proposed by Fuchs (1963) and Gunn (1956). Fuchs (1963) developed a model to describe the bipolar charging of submicron particles; the charging theory proposed by Gunn (1956) is only valid for particles with diameters greater than approx. 50 nm. An analytical solution is obtainable for the Gunn theory, while the Fuchs model must be solved numerically. To permit a rapid calculation of the bipolar charge distribution in the size range 1-1000 nm, an empirical expression is presented to approximate the distribution calculated from the Fuchs model. THEORY AND ANALYSIS For an aerosol in charge equilibrium, the fraction of particles carrying up to two elementary charges can be estimated using the proposed approximation derived from the Fuchs model. The fraction of particles with three or more elementary charge units can be calculated using the following expression: _ r In + + [N _2rceoDnkT, /CNI Z 1 e e2 f(N) = x/(4rdeoDpkT) "exp 22rceoDpkT , (1) e 2 where e = electronic charge, e0 = dielectric constant, Dp = particle diameter, k = Boltzmann's constant, T= temperature, N = number of elementary charge units on particle, c~ ± = ion concentration, and Z~ ± = ion mobility. Equation (1) was derived by Gunn (1956). The concentration for positive and negative ions is assumed to be equal. The ratio of ion mobilities, Z~+/Z~_, was taken by Wiedensohler et al. (1986) to be 0.875. The approximation was developed as follows. Fuchs theory was used to calculate the charge distribution for several particle sizes. The parameters and their sources are: (1) ion mobilities from Wiedensohler et al. (1986); (2) ion masses from Hussin et al; (1983), and (3) the correction of the ~t-parameters (collision probability of ions with the particle) following Hoppel and Frick (1986).
Article
The development of a condensation nucleus counter (CNC) for detecting ultrafine aerosol (UFA) particles (particle diameter 5 20 nm) is described here. This instrument is designed specifically for high-efficiency detection and counting of ultrafine particles. It is a modified version of the TSI model 3020 continuous flow, single-particle-counting condensation nucleus counter with sequential saturator and condenser. Design modifications incorporating aerosol sheathing techniques have minimized inlet sampling losses and optimized nucleus detection efficiency. Overall counting efficiency for the UFACNC is theoretically predicted including inlet sampling, nucleus activation, and droplet detection efficiencies. The theory was experimentally verified for low concentration, monodisperse NaCl aerosols in the 2 to 15 nm particle diameter range. The UFACNC has a counting efficiency of > 70% for particles down to 3.5 nm in diameter. Below this size counting efficiency drops sharply to zero at about 2.6 nm with 50% efficiency at about 3 nm.
Article
The application of mass spectrometric techniques to the real-time measurement and characterization of aerosols represents a significant advance in the field of atmospheric science. This review focuses on the aerosol mass spectrometer (AMS), an instrument designed and developed at Aerodyne Research, Inc. (ARI) that is the most widely used thermal vaporization AMS. The AMS uses aerodynamic lens inlet technology together with thermal vaporization and electron-impact mass spectrometry to measure the real-time non-refractory (NR) chemical speciation and mass loading as a function of particle size of fine aerosol particles with aerodynamic diameters between ∼50 and 1,000 nm. The original AMS utilizes a quadrupole mass spectrometer (Q) with electron impact (EI) ionization and produces ensemble average data of particle properties. Later versions employ time-of-flight (ToF) mass spectrometers and can produce full mass spectral data for single particles. This manuscript presents a detailed discussion of the strengths and limitations of the AMS measurement approach and reviews how the measurements are used to characterize particle properties. Results from selected laboratory experiments and field measurement campaigns are also presented to highlight the different applications of this instrument. Recent instrumental developments, such as the incorporation of softer ionization techniques (vacuum ultraviolet (VUV) photo-ionization, Li+ ion, and electron attachment) and high-resolution ToF mass spectrometers, that yield more detailed information about the organic aerosol component are also described. © 2007 Wiley Periodicals, Inc., Mass Spec Rev 26:185–222, 2007
Article
Nanoparticle Surface Area Monitor (NSAM, TSI model 3550 and Aerotrak 9000) is an instrument designed to measure airborne surface area concentrations that would deposit in the alveolar or tracheobronchial region of the lung. It was found that the instrument can only be reliably used for the size range of nanoparticles between 20and 100nm. The upper size range can be extended to 400nm, where the minimum in the deposition curves occurs. While the fraction below 20nm usually contributes only negligibly to the total surface area and is therefore not critical, a preseparator is needed to remove all particles above 400nm in cases where the size distribution extends into the larger size range. Besides limitations in the particle size range, potential implications of extreme concentrations up to the coagulation limit, particle material (density and composition) and particle morphology are discussed. While concentration does not seem to pose any major constraints, the effect of different agglomerate shapes still has to be further investigated. Particle material has a noticeable impact neither on particle charging in NSAM nor on the deposition curves within the aforementioned size range, but particle hygroscopicity can cause the lung deposition curves to change significantly which currently cannot be mimicked with the instrument. Besides limitations, possible extensions are also discussed. It was found that the tendencies of the particle deposition curves of a reference worker for alveolar, tracheobronchial, total and nasal depositions share the same tendencies in the 20–400nm size range and that their ratios are almost constant. This also seems to be the case for different individuals and under different breathing conditions. By means of appropriate calibration factors NSAM can be used to deliver the lung deposited surface area concentrations in all these regions, based on a single measurement.
Article
By the limiting sphere method the combination coefficients for gaseous ions and aerosol particles were calculated, allowing for the jump in ion concentration at the surface of the particles. Hence the stationary charge distribution on aerosol particles in a symmetrical bipolar ionic atmosphere was determined. The use of the Boltzmann equation for this purpose proposed by some authors is theoretically wrong asthis equation applies to equilibrium rather than to stationary states. In practice, the Boltzmann equation can be used for particles with radius 310–5 cm (under atmospheric pressure). Within this range the image forces and the jump in ion concentration may be neglected. The conditions of the applicability of the steady diffusion equations to the theory of the stationary charge distribution in aerosols are discussed.
Article
A new analytical instrument has been developed to give real‐time chemical composition and size data on individual aerosol particles. It separates the particles from the entraining gases by means of aerodynamic nozzles and differential pumping, so that they enter the high vacuum region as a collimated beam. Each arriving particle is flash vaporized, the vapor ionized, and the ions analyzed by a quadrupole mass spectrometer. The instrument has been tested with several inorganic and organic aerosols and has yielded mass spectral peaks corresponding to a series of fragment ions. The more stable compounds yielded the parent ion as well. Particles 0.9 μm in diameter are readily detected with signal‐to‐noise ratios of 12:1 on the dominant peak. On this basis, the small‐size sensitivity limit is well under 0.5 μm diameter and, with design improvements, can probably be extended to 0.1 μm or smaller.
Article
Electrical detection is used for the first time to achieve real-time operation of a low pressure cascade impactor. An instrument is developed using Berner type multijet low pressure impactor stages with minimum modification. The cut-sizes of the seven channel system range from 0.030 to 1.0 μm. A multichannel electrometer is constructed using low cost monolithic electrometer operational amplifiers. The zero-check technique is applied to achieve a lowest detectable current of 10 fA, less than a tenth of the input bias current of the operational amplifiers. The time resolution is 1 min in the lock-in mode and 1 s in the high concentration mode. The sensitivity and size resolution of the instrument are comparable to the corresponding values of the Electrical Aerosol Analyzer. The feasibility of the instrument in measuring submicron number size distribution has been tested by comparison measurements with a differential mobility analyzer. The results show quantitative agreement.
Article
A commercial semi-continuous elemental and organic carbon (ECOC) analyzer has been developed by Sunset Laboratory Inc. for the analysis of atmospheric particulate matter. The field deployable instrument is an alternative to off-line laboratory-based analysis of samples collected in the field. Although the Sunset Laboratory analyzer provides time-resolved particulate ECOC measurements using a methodology comparable to the laboratory-based NIOSH 5040 ECOC measurement, the performance of the semi-continuous ECOC analyzer has not been fully validated in the past.
Article
A new device is described, which allows continuous monitoring of aerosols of any kind. Air is continuously pumped through a closed chamber containing short-lived 211Pb atoms delivered by a 227Ac source. These atoms attach onto the aerosol particles. After transportation through a thin capillary to a filter and counting station the particles are detected by means of an α-detector for measuring the decay of 211Pb (via 211Bi). Due to the relatively short half-life of 211Pb, the system allows continuous monitoring of aerosols without changing or transporting the filter. The measured signal is proportional to the exposed Fuchs surface of the aerosol particles. In the case of environmental applications, the device is therefore most sensitive to particles contained in the accumulation mode. Due to its high sensitivity it also works well at the lowest particle concentrations of less than 100 ng m−3 with gas flow rates as low as 1 l min−1.