Low-pressure Cascade Impactor Research Articles

Measurements of thorium–B ( [formula omitted]) in the outdoor environment and evaluation of equivalent dose

The activity size distribution of unattached as well as attached 212 Pb to aerosol particles was measured in the open air of El-Minia City, Egypt. The samples were collected using a wire screen diffusion battery technique and a low pressure cascade impactor. The mean activity median thermodynamic diameter (AMTD) of unattached 212 Pb was determined to be 1.4 nm with a relative mean geometric standard deviation ( σ g) of 1.55. A mean unattached fraction ( f p ) of 0.03±0.007 was obtained at a mean aerosol particle concentration of 32×10 3 cm −3. Sometimes the f p values were less than the detection limit of 0.008. The mean concentration of activity of 212 Pb was found to be 9.6±1.1 mBq m −3. The mean activity median aerodynamic diameter (AMAD) of the accumulation mode of attached 212 Pb was determined to be 360 nm with a mean ( σ g) of 2.7. The mean value of specific air activity concentration of 212 Pb associated with that mode was determined to be 303±12 mBq m −3. With a dosimetric model calculation (International Commission on Radiological Protection. Human respiratory tract model for radiological protection. Oxford: Pergamon Press, ICRP Publication 66, 1994) the total deposition fractions as well as total equivalent and effective dose have been evaluated considering the obtained parameters of the activity size distributions. At a total deposition fraction of about 97% for unattached activities the total equivalent and effective doses to the lung were determined to be about 0.18 and 0.02 μSv, respectively, while total equivalent and effective doses of about 0.45 and 0.05 μ Sv, respectively, were determined at a total deposition fraction of about 23% for the attached activities.

Multi-element analysis by inductively coupled plasma optical emission spectrometry of airborne particulate matter collected with a low-pressure cascade impactor.

A method was developed for the elemental analysis of size segregated particles ranging from 0.03 to 10 microns. Sampling and analysis problems are discussed in this paper. Particles were collected with a Dekati low-pressure cascade impactor. PTFE filters coated with oleic acid were used as substrate. Particles were microwave digested in closed vessels. The optimum digestion mixture was composed of HNO3 (1 mL), HF (50 microL) and H2O (1 mL). The optimal power setting and digestion time were studied in order to achieve an efficient digestion. A ca. 35 min microwave digestion cycle at a 650 W maximum power allowed complete digestion of the samples. Special emphasis was placed on the pressure in the closed vessels to avoid sample losses. Solution samples were analysed by inductively coupled plasma optical emission spectrometry using an ultrasonic nebuliser for 18 elements (Al, Ba, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, S, Sr, Ti, V, Zn). This procedure was tested with NIST Standard Reference Material 1648 Urban Particulate. Recoveries for certified elements ranged from 95 to 105% except for Al (90%). The influence of cascade impactor materials was investigated with 44 field samples. Strong artefacts due to contamination were shown for analysis at environmental concentrations of Al, Cr, Mn and Ni.

Activity Size Distributions of Short Lived Radon Progeny in Indoor Air

The activity size distributions of both unattached and attached fractions of short-lived radon progeny ( 218 Po, 214 Pb and 214 Bi) were measured in indoor air of El-Minia University, Egypt. The measurements were performed with a wire screen diffusion battery and a low pressure cascade impactor (Berner type). The results for parameters of derived distributions demonstrate that the distributions for the unattached 218 Po and 214 Pb are similar. The mean diffusion equivalent diameters (d e ) of 218 Po and 214 Pb were determined to be 1.73 and 1.69 nm with relative mean geometric standard deviations (σ g ) of 1.63 and 1.69. respectively. The distributions of the attached 214 Pb and 214 Bi are also similar. Most of the attached activities were associated with the aerosol particles of accumulation mode. The mean activity median aerodynamic diameters (AMAD) of this mode for 214 Pb and 214 Bi were determined to be 0.32 and 0.34 μm, respectively, with the same relative mean geometric standard deviation of 2.7, Based on the obtained results of radon progeny size distributions (unattached and attached), the deposition fractions in each airway generation of the human lung were evaluated by using a deposition model of Koblinker and Hofmann.

A closure study of sub-micrometer aerosol particle hygroscopic behaviour

The hygroscopic properties of sub-micrometer aerosol particles were studied in connection with a ground-based cloud experiment at Great Dun Fell, in northern England in 1995. Hygroscopic diameter growth factors were measured with a Tandem Differential Mobility Analyser (TDMA) for dry particle diameters between 35 and 265 nm at one of the sites upwind of the orographic cloud. An external mixture consisting of three groups of particles, each with different hygroscopic properties, was observed. These particle groups were denoted less-hygroscopic, more-hygroscopic and sea spray particles and had average diameter growth factors of 1.11–1.15, 1.38–1.69 and 2.08–2.21 respectively when taken from a dry state to a relative humidity of 90%. Average growth factors increased with dry particle size. A bimodal hygroscopic behaviour was observed for 74–87% of the cases depending on particle size. Parallel measurements of dry sub-micrometer particle number size distributions were performed with a Differential Mobility Particle Sizer (DMPS). The inorganic ion aerosol composition was determined by means of ion chromatography analysis of samples collected with Berner-type low pressure cascade impactors at ambient conditions. The number of ions collected on each impactor stage was predicted from the size distribution and hygroscopic growth data by means of a model of hygroscopic behaviour assuming that only the inorganic substances interacted with the ambient water vapour. The predicted ion number concentration was compared with the actual number of all positive and negative ions collected on the various impactor stages. For the impactor stage which collected particles with aerodynamic diameters between 0.17–0.53 μm at ambient relative humidity, and for which all pertinent data was available for the hygroscopic closure study, the predicted ion concentrations agreed with the measured values within the combined measurement and model uncertainties for all cases but one. For this impactor sampling occasion, the predicted ion concentration was significantly higher than the measured. The air mass in which this sample was taken had undergone extensive photochemical activity which had probably produced hygroscopically active material other than inorganic ions, such as organic oxygenated substances.

Electrical calibration method for cascade impactors

A new method for measuring collection characteristics of cascade impactors is described. The method is based on challenging the impactor with monodispersed charged particles and measuring electrical currents on all the impactor stages plus a backup filter. From the current values, collection efficiency at a certain particle diameter can be calculated simultaneously for each impactor stage. To test the method, monodispersed dioctyl sebacate particles were generated using an atomiser, evaporation/condensation generator and an electrostatic classifier. The particle collection characteristics of the six lowest stages of a Berner-type low-pressure cascade impactor were measured. Comparison measurements were made with a real-time stage efficiency measurement system for single impactor stages. The results of the two methods were in good agreement.

Temporal variation of 7Be and 210Pb size distributions in ambient aerosol

The size distributions of the cosmogenic 7Be and of the long-lived radon progeny 210Pb in ambient aerosols were measured continuously from December 1994 to the end of March 1996 in ground-level air at a semi-rural location in south Germany. Aerosol sampling was performed at a height of 4 m above ground with a low-pressure cascade impactor of the Berner type covering the size range from 0.06 to 16 μm and simultaneously with an high-volume sampler. Each sampling period was 10 d. Activities of 7Be and 210Pb were measured by gamma spectrometry and aerosol mass was determined gravimetrically. In all experiments the activity distributions of 7Be as well as of 210Pb were unimodal (log-normal) and associated with submicron aerosols of about 0.5–0.6 μm aerodynamic diameter. On average, the activity median diameters of 7Be (AMD: 0.57 μm) and of 210Pb (AMD: 0.53 μm) have been found to be significantly lower than the average mass median diameter (MMD: 0.675 μm) and higher or at most equal than the respective surface median diameter (SMD: 0.465 μm) of the aerosols: SMD⩽AMD Pb210<AMD Be7 <MMD. Variation of the atmospheric processes during the study period resulted in a variability of the activity median diameter between 0.44 to 0.74 μm for 7Be and from 0.28 to 0.74 μm for 210Pb. While in the winter months (October to April) a difference between the activity distributions of 210Pb (AMD: 0.595 μm) and 7Be (AMD: 0.59 μm) was not detectable, in summer, 210Pb was associated with significantly smaller aerosols (AMD: 0.43 μm) than 7Be (AMD: 0.52 μm). Comparing the activity median diameters observed in summer with those in winter, on average significantly lower diameters were found in summer pointing to shorter residence times in the summer months.

A New Device to Measure the Activity Size Distribution of Radon Progeny in a Low Level Environment

In order to easily measure the activity size distribution of radon progeny, a new instrument was developed that can determine their activity median diameter in a low level environment within 90 min. A four stage low-pressure cascade impactor was used. The particle size cut-off points were >2,100, 700, 210 and 70 nm, based on a particle density of 1 g cm(-3). A 300 metal wire screen diffusion collector facing with a silicon semiconductor detector was placed within the first air inlet in order to measure unattached radon progeny concentrations and also to prevent unattached progeny from entering the impactor. Silicon photodiodes, from which the ceramic windows were removed, were installed in each stage of the impactor. Alpha particles could be effectively detected with 46.2% efficiency as radon progeny were directly collected on the detecting surface of the photodiode. The surface of the photodiodes was coated with silicon grease to prevent particle bounce-off. An inline-type filter holder with a silicon semiconductor detector was connected at the exit of the impactor in order to collect the remaining radon progeny and to measure their concentrations. The instrument was used to concurrently measure the size distribution of radon progeny and the aerosol in the natural environment. The results indicated that the activity median diameter fell in between the median diameter of the aerosol derived from number statistics and that derived from surface-area statistics. A negative correlation was found between the unattached fraction (f(p)) and the activity median diameter.

Data Reduction on the Measurement of the Size Distribution of Atmospheric Aerosols by a Low-Pressure Cascade Impactor

Data Reduction on the Measurement of the Size Distribution of Atmospheric Aerosols by a Low-Pressure Cascade Impactor

A Field Study of Submicron Particles from the Combustion of Straw

ABSTRACT The evolution of small aerosol particles accompanying the combustion of straw for energy production is investigated. A sampling equipment specially designed for field measurements is described and characterized. The aerosol is studied by low-pressure cascade impactor and scanning mobility particle sizer, the particle morphology by transmission electron microscopy, and the chemical composition by energy dispersive x-ray analysis. The combustion gas contains 3–500 mg/Nm3 of submicron particles with a mean diameter of approximately 0.3 μm. The particles consist of almost pure potassium chloride and sulphate. The formation mechanism is analyzed by a theoretical simulation of the chemical reactions and the aerosol change during cooling of the flue gas. It is concluded that some sulphation of KC1 occurs in the gas phase although the sulphate concentration is much lower than predicted by an equilibrium assumption. The theoretical simulation proves that the fine mode particles can be formed by homogeneou...

Particle size-dependent concentrations of polycyclic aromatic hydrocarbons

Particle size-dependent concentrations of PAHs from outdoor air sampling were measured. Size-segregated samples were collected at the outskirts of Munich in October 1994. A five-stage high-volume cascade impactor (HVS, particle diameter DP < 10 µm, 810 l min–1) and two Berner-type low-pressure cascade impactors (LPI, 79 l min–1, six-stage, DP= 0.04–21 µm and 29 l min–1, nine-stage, DP= 0.06–16 µm) were used. Eleven PAHs were quantified by HPLC with fluorescence detection. The concentrations of lead, bromine, zinc, sulfur and iron were measured by PIXE analysis. Particle number-concentrations in the range DP= 0.01–1 µm were measured with a differential mobility analyser (DMA). The concentrations of the PAHs in particulate matter were in the range 0.8–3.8 ng m–3. The concentrations found in the LPI samples always were higher than those in the samples taken with the HVS. The differences were in the range 30–63%. The results for the two LPI were in good agreement. The size-dependent PAH concentrations were similar with all three samplers. With the HVS, about 60% of the PAHs were found on the back-up filter (DP < 0.66 µm). In the LPI samples 40% of the total PAHs were found on particles with DP= 0.13–0.50 µm. Lead, bromine, zinc and sulfur showed the same distribution as the PAHs whereas iron had its maximum concentration at DP= 2–4 µm. The measurements with the DMA gave unimodal distributions with the maximum in particle mass at DP= 0.22–0.28 µm.

Measurement of the Particle-Size Distributions of Semivolatile Organic Contaminants in the Atmosphere

A method using a Berner five-stage, low-pressure cascade impactor was developed to measure the particle-size distributions of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere. Possible sampling artifacts that may occur when sampling semivolatile organic chemicals with this low-pressure particle impactor(e.g., absorption of vapors onto sampler surfaces or volatilization of analytes from collected particles under reduced pressures within the impactor) were quantified for a variety of PAHs in the laboratory. At 20°C, these artifacts were insignificant for the collection of PAHs with vapor pressures less than 10 -8 atm. Several samples collected at a rural site (Egbert, Ontario) and an urban location (Chicago, IL) demonstrate the utility of the Berner impactor to collect PAHs under a variety of field conditions. At both the rural and urban locations, sufficient quantities of particles were collected in the five aerodynamic equivalent diameter size ranges (0.04-0.14, 0.14-0.49, 0.49-1.7, 1.7-6, and 6-21 μm) during 12 h to provide detectable levels of PAHs. PAHs were most often associated with particles less than 1.7 μm in both the rural and urban areas based on a limited number of observations (N= 5).

Mass measurements of aerosol at mace head, on the west coast of Ireland

Abstract Aerosol mass/size measurements have been carried out at the Mace Head research station, on the west coast of Ireland, for a period of over two years. Mass/size distributions were obtained in the size range 0.06–10 μm using Berner low-pressure cascade impactor systems. The distributions obtained reflect the different types of air mass which are encountered at Mace Head. Westerly winds are dominant at the site with the associated air masses being typically maritime. Unimodal mass/size distributions with the peak mass concentration occurring principally in the 2–4 μm size range were characteristic of these conditions. Continental air masses from Europe are typified by mass/size distributions which have peak values in the submicron size range. Distinct bimodal distributions were obtained when aerosols were collected from a mixture of air mass types. Overall, the mass concentration was found to vary between approximately 2 and 45 μg m−3 A wide variation in mass concentration values were measured at similar wind speeds. However, a trend towards higher mass concentrations at higher wind speeds was observed in the coarse mass fraction contribution (> 1 μm) from westerly maritime air masses at higher wind speeds. A drop-off in mass concentration was observed at wind speeds greater than approximately 11 m s−1 This is attributed to the cut-off characteristic of the PM10 inlet used with the impactor system. High mass concentrations during long term pollution events at Mace Head were also observed with the collected aerosol resident principally in the submicron size range during these conditions.

Distribution of polychlorinated dibenzo- p-dioxins and dibenzofurans in atmospheric particulate matter with respect to particle size

The occurrence of polychlorinated dibenzo- p-dioxins and dibenzofurans (PCDD/Fs) in different size fractions of atmospheric particulate matter was investigated using a five-stage multijet low pressure cascade impactor backed up by a glass fibre fibrer. Three runs were conducted during the summer at a rural location in Germany. Approximately 90% of the PCDD/Fs were found on particles with aerodynamic diameters < 1.35 μm. The PCDD/F homologue group patterns were very similar on all particle size fractions of a particular run, which indicates that the particle-mediated behaviour will be similar for all PCDD/Fs. The concentrations of PCDD/Fs on the smaller atmospheric particles lay at the lower end of the range in incinerator fly ash published in the literature.

Estimates of residence times of sulfate aerosols in ambient air

The aerodynamic size distribution of sulfates in ambient aerosol particles were measured using a high-resolution, submicron region low-pressure cascade impactor. In continental areas the mass (volume) distribution of sulfates determined by ion chromatography, was largely associated with submicron aerosols in the accumulation mode (0.1–2 μm) peaking in the 0.2–0.5 μm size range. The mass median aerodynamic diameter (MMAD) varied from 0.25 to 0.31 μm (mean 0.28 μm). The mean value of the geometric standard deviation σg was 2.06. In estimating lifetimes of sulfate aerosols, the residence times of 12 days applies to aerosols of ∼ 0.3 μm MMAD size.

An Online α-Impactor for Short-Lived Radon Daughters

A low-pressure cascade impactor was developed for continuous measurements of the size distributions of aerosol-attached radon and thoron decay products under environmental conditions. The emitted α-particles of the size fractionated activities are registered during air sampling with surface barrier detectors (active area = 2000 mm2) with an energy resolution < 6% (FWHM). The impactor consists of nine stages and back-up filters and operates at a flow rate of 5.1 m3 /h. The 50% cutoff diameters range between 65 and 15,530 nm. The detection limit for the short-lived radon daughters is ∼ 2 Bq/m3 for a sampling time of 1 h and a statistical error of 10%. To minimize energy losses of the ∼-particles and blow-off effects the sampling units are rotatable.

Atmospheric gas-particle partitioning of organic compounds: Comparison of sampling methods

A conventional glass-fiber filter, a low-pressure cascade impactor and an electrostatic precipitator, each combined with two gas traps, were used to establish the significance of sampling artifacts occurring during the investigation of atmospheric gas-particle partitioning. The absolute concentrations and the gas-particle partitioning of polychlorinated benzenes, pentachloroanisole, hexachlorocyclohexanes, PCBs, p,p′-DDE, p,p′-DDT and some PAHs were determined. The total amounts of substance collected in the impactor and the filter system were similar, whereas the levels of most compounds in the precipitator system differed due to substance alteration in the sampler. The electrostatic precipitator therefore does not seem to be a reliable device for such measurements. The comparison of gas-particle partitioning showed particle bound fractions of the organochlorine compounds to be systematically higher in the impactor-adsorbent combination than in the filter-adsorbent sampler. This was attributed to the particle aggregation in the impactor preventing the chemicals on particle surfaces from an exchange with the gas phase. However, these differences did not exceed a factor of two and were on average in the range of 36%. This indicates that sampling artifacts through the use of glass-fiber filter-adsorbent systems for investigations of atmospheric gas-particle partitioning are less drastic than discussed in the literature.

Electrical low pressure impactor

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.

Blood-containing aerosols generated by surgical techniques: a possible infectious hazard.

The aerosols generated in an operating room during surgery were simulated in the laboratory by using a variety of common surgical power tools. A Stryker bone saw, a Hall drill, and a Shea drill were used on bone, and a Bovie electrocautery was used in both the cutting and coagulation modes on tendon, all in the presence of a thin film of blood. A 10-stage, low-pressure cascade impactor was used to determine the particle size distribution of each aerosol, and Hemastix was used to assess the hemoglobin content of each particle size fraction. The same assessment was done for another series of blood aerosols that had previously shown the ability to infect human T-cell cultures. All of the tools tested produced blood-containing aerosol particles in the respirable size range (less than 5 microns). Because surgical masks offer little protection against such particles, personal sampling is indicated to define the risk of exposure to bloodborne pathogens by this route.

To the relevant diameter of aerosol particles in the 0.1 to 1 μM transition range

Modern techniques used for particle sizing in the 0.1 to 1 μm transition range are based on different kinds of forces acting upon the particles. In a spiral centrifuge or a low pressure cascade impactor particles are exposed to mechanical forces and can be classified according to their aerodynamic diameter down to about 0.08 resp. 0.03 μm. In a differential mobility analyzer (DMA) particles are separated by electrical forces up to particle diameters of about 1 μm. Submicron particles below about 0.4 μm are often measured in diffusion batteries where particles are classified according to their diffusion coefficient. The diameter derived from the electrical mobility and from the diffusion coefficient can be combined to a common mobility diameter which is only a function of the geometrical particle dimensions. When studying particle behaviour in aerosol systems one has to be cautious in all cases where the forces acting upon the particles during the experiments differ from those ones used for their size characterization. To demonstrate this problem number size distributions of atmospheric aerosols are considered and particle deposition studies in human lungs are reported.

Aerosols Created by Some Surgical Power Tools: Particle Size Distribution and Qualitative Hemoglobin Content

Abstract Prompted by concerns about exposure to blood and other body substances, the possible generation of blood-containing aerosols in orthopaedic surgical practice was investigated. Common surgical power tools were operated in the laboratory to simulate the aerosols typically generated in common orthopaedic procedures. A bone saw, a Hall drill, a Shea drill, and an electrocautery were used on bone or tendon while blood was slowly dripped over the operative surface. Particle size distribution was evaluated with a low-pressure cascade impactor, and the presence of hemoglobin in inspirable particles was evaluated with the aid of a midget impinger. Particle size distribution depended on the type of power tool used, but most of the particles collected were in the respirable range. Hemoglobin was detected in all samples. Personal sampling is indicated to determine whether inspirable blood aerosols are present in the surgeon's breathing zone during an operation.