| 1. |
- Gustavsson, Eva, et al.
(författare)
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Evaluation of Aerodynamic Particle Sizer and Electrical Low-Pressure Impactor for Unimodal and Bimodal Mass-Weighted Size Distributions
- 2005
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Ingår i: Aerosol Science and Technology. - : Taylor and Francis Ltd. - 0278-6826 .- 1521-7388. ; 39:9, s. 871-887
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this study was to investigate the feasibility of the Aerodynamic Particle Sizer (APS) and the Electrical Low-Pressure Impactor (ELPI) to study mass weighted particle size distributions. Unimodal and bimodal liquid test aerosols were produced to a small chamber. Simultaneous measurements were performed with an APS 3320, an APS 3321, an ELPI and a Dekati Low-Pressure Impactor (DLPI) analyzed gravimetrically. ELPI current and mass responses were simulated for lognormal size distributions using a parameterization of the impactor kernel functions. In experiments with a single coarse mode, the mass ratio to the DLPI was between 0.75 and 1.15 for both APS models up to 5 µ m and for the ELPI up to 3 µ m. For larger sizes the ELPI and APS 3320 overestimated and the APS 3321 underestimated the concentration. In experiments with a single fine mode, submicrometer ELPI and DLPI results were in good agreement. However, in contrast to the DLPI all three spectrometers showed a significant mass fraction above 1 µ m. In experiments with a bimodal size distribution, the mass ratios were altered compared to single coarse mode experiments. Simulations showed that uncertainties in ELPI measurements of larger particles occur when concentrations of small particles are high. Several mechanisms that may bias ELPI and APS measurements are described. With knowledge of these, ELPI and APS 3321 can, under many circumstances give accurate time-resolved mass size distributions for particles smaller than 3 and 5 µm, respectively.
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| 2. |
- Khalizov, Alexei F., et al.
(författare)
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Formation of highly hygroscopic soot aerosols upon internal mixing with sulfuric acid vapor
- 2009
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Ingår i: Journal of Geophysical Research. - 2156-2202. ; 114
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Tidskriftsartikel (refereegranskat)abstract
- The hygroscopic properties of submicron soot particles during internal mixing with gaseous sulfuric acid have been investigated using a combined tandem differential mobility analyzer (TDMA) and differential mobility analyzer-aerosol particle mass analyzer (DMA-APM) technique. Fresh particles exhibit no change in mobility size and mass at subsaturated conditions, whereas particles exposed to gaseous sulfuric acid (10(9)-10(10) molecule cm(-3), 12 s contact time) experience significant mobility size and mass changes with increasing relative humidity (RH). The DMA-APM measurements reveal that particles of all sizes exposed to H2SO4 vapor gain mass with increasing RH because of absorption of water by sulfuric acid coating. However, on the basis of mobility size measurements using TDMA, upon humidification H2SO4-coated soot agglomerates display distinct hygroscopic growth patterns depending on their initial size and the mass fraction of condensed sulfuric acid. While small particles experience an increase in their mobility sizes, larger particles exhibit a marked shrinkage due to compaction. We suggest that determination of the hygroscopic properties of soot particles using a TDMA alone can be inconclusive. Restructuring of the soot agglomerates and filling of the voids that accompany the condensation of water-soluble materials and subsequent water absorption lead to little or no observable changes in particle mobility size at subsaturated RH even for particles that contain aqueous coatings. Extrapolation of our experimental results to the urban atmosphere indicates that initially hydrophobic soot particles acquire sufficient sulfate coating to become efficient CCN (cloud condensation nuclei) within a time period ranging from a few hours to a few days, dependent on the ambient H2SO4 level. The results imply that internal mixing with sulfuric acid through H2SO4 vapor condensation likely represents a common aging process for a variety of atmospheric aerosols. The variations in the size and hygroscopicity of soot particles during atmospheric processing influence their optical properties, cloud-forming potential, and human health effects.
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| 3. |
- Löndahl, Jakob, et al.
(författare)
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A set-up for field studies of respiratory tract deposition of fine and ultrafine particles in humans
- 2006
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Ingår i: Journal of Aerosol Science. - : Elsevier BV. - 0021-8502. ; 37:9, s. 1152-1163
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Tidskriftsartikel (refereegranskat)abstract
- Respiratory tract deposition data of ultrafine aerosol particles, hygroscopic particles and ambient particles in general are scarce. Measurements are associated with several difficulties. The objective of this work was to design a method for fast determination of highly size-resolved fine and ultrafine particle deposition, to be used on larger groups of human subjects in exposure studies and in typical ambient and indoor environments. The particle size distributions in dried samples of the inhaled and exhaled air are characterised with an electrical mobility spectrometer. A particle counter desmearing procedure reduces the spectrometer scan time. The precision and sensitivity of the method was tested for hygroscopic sodium chloride (NaCl) and hydrophobic Di-Ethyl-Hexyl-Sebacate (DEHS) aerosols in repeated identical experiments and experiments with different breathing frequencies on a single subject. The accuracy of the method was estimated by comparing results from three subjects with previous data obtained with monodisperse particles and with the well-established International Commission on Radiological Protection model (1994). Potential errors due to size shifts between the inhaled and exhaled samples and coagulation were simulated. The system has low losses in the studied particle size range (10-475 nm), typically 10% or less of the fraction deposited in the respiratory tract. Coagulation is noticeable at 10(5) cm(-3) but can be corrected for up to 5 x 10(5) cm(-3). The precision in the determined deposited fraction is 0.02-0.08. The method is sensitive enough to quantify differences between breathing patterns and differences between hygroscopic and hydrophobic aerosols. Our results for NaCl and DEHS are in agreement with the ICRP 66 model [International Commission on Radiological Protection. (1994). Human respiratory tract model for radiological protection (ICRP Publication 66). Oxford, UK: Elsevier Science], and also suggest that the relative humidity in the respiratory tract is close to 99.5%. A respiratory tract deposition measurement can be done in 15-30 min. Recommendations are given for field applications of the method. (C) 2005 Elsevier Ltd. All rights reserved.
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| 4. |
- Löndahl, Jakob, et al.
(författare)
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Deposition of biomass combustion aerosol particles in the human respiratory tract.
- 2008
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Ingår i: Inhalation Toxicology. - : Informa UK Limited. - 0895-8378 .- 1091-7691. ; 20:10, s. 923-933
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Tidskriftsartikel (refereegranskat)abstract
- Smoke from biomass combustion has been identified as a major environmental risk factor associated with adverse health effects globally. Deposition of the smoke particles in the lungs is a crucial factor for toxicological effects, but has not previously been studied experimentally. We investigated the size-dependent respiratory-tract deposition of aerosol particles from wood combustion in humans. Two combustion conditions were studied in a wood pellet burner: efficient ("complete") combustion and low-temperature (incomplete) combustion simulating "wood smoke." The size-dependent deposition fraction of 15-to 680-nm particles was measured for 10 healthy subjects with a novel setup. Both aerosols were extensively characterized with regard to chemical and physical particle properties. The deposition was additionally estimated with the ICRP model, modified for the determined aerosol properties, in order to validate the experiments and allow a generalization of the results. The measured total deposited fraction of particles from both efficient combustion and low-temperature combustion was 0.21-0.24 by number, surface, and mass. The deposition behavior can be explained by the size distributions of the particles and by their ability to grow by water uptake in the lungs, where the relative humidity is close to saturation. The experiments were in basic agreement with the model calculations. Our findings illustrate: (1) that particles from biomass combustion obtain a size in the respiratory tract at which the deposition probability is close to its minimum, (2) that particle water absorption has substantial impact on deposition, and (3) that deposition is markedly influenced by individual factors.
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| 5. |
- Löndahl, Jakob, et al.
(författare)
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Experimentally Determined Human Respiratory Tract Deposition of Airborne Particles at a Busy Street
- 2009
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Ingår i: Environmental Science & Technology. - : American Chemical Society (ACS). - 1520-5851 .- 0013-936X. ; 43:13, s. 4659-4664
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Tidskriftsartikel (refereegranskat)abstract
- Traffic is one of the major sources of harmful airborne particles worldwide. To relate exposure to adverse health effects it is important to determine the deposition probability of the inhaled particles in the human respiratory tract. The size-dependent deposition of 12-580 nm particles was measured with a novel setup in 9 healthy subjects breathing by mouth on the windward side of a busy street in Copenhagen, Denmark. The aerosol was characterized both at the curbside and, to obtain the background concentration, at rooftop level. Particle hygroscopicity, a key parameter affecting respiratory tract deposition, was also measured at the same time of exposure. The total deposition fraction of the curbside particles in the range 12-580 nm was 0.60 by number, 0.29 by surface area, and 0.23 by mass. The deposition fractions of the "traffic exhaust" contribution, calculated as the hydrophobic fraction of the curbside particles, was 0.68, 0.35, and 0.28 by number, surface area, and mass, respectively. The deposited amount of traffic exhaust particles was 16 times higher by number and 3 times higher by surface area compared to the deposition of residential biofuel combustion particles investigated previously (equal inhaled mass concentrations). This was because the traffic exhaust particles had both a higher deposition probability and a higher number and surface area concentration per unit mass. To validate the results, the respiratory tract deposition was estimated by using the well-established ICRP. model. Predictions were in agreement with experimental results when the effects of particle hygroscopicity were considered in the model.
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| 6. |
- Löndahl, Jakob, et al.
(författare)
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Size-Resolved Respiratory Tract Deposition of Fine and Ultrafine Hydrophobic and Hygroscopic Aerosol Particles during Rest and Exercise
- 2007
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Ingår i: Inhalation Toxicology. - : Informa UK Limited. - 0895-8378 .- 1091-7691. ; 19:2, s. 109-116
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Tidskriftsartikel (refereegranskat)abstract
- Airborne ultrafine particles (diameter <100 nm) are ubiquitous in the environment and have been associated with adverse health effects. The respiratory-tract deposition of these particles is fundamentally influenced by their hygroscopicity: their ability to grow by condensation of water in the humid respiratory system. Ambient particles are typically hygroscopic, to varying degrees. This article investigates the influence of hygroscopicity, exercise level, gender, and intersubject variability on size-dependent deposition of fine and ultrafine particles during spontaneous breathing. Using a novel and well-characterized setup, respiratory-tract deposition in the range 12-320 nm has been measured for 29 healthy adults (20 men, 9 women). Each subject completed four sessions: rest and light exercise on an ergometer bicycle while inhaling both hydrophobic (diethylhexylsebacate) and hygroscopic (NaCl) particles. The deposited fraction (DF) based on dry diameters was two to four times higher for the hydrophobic ultrafine particles than for the hygroscopic. The DF of hygroscopic ultrafine particles could be estimated by calculating their equilibrium size at 99.5% relative humidity. The differences in average DF due to exercise level and gender were essentially less than 0.03. However, the minute ventilation increased fourfold during exercise and was 18-46% higher for the men than for the women. Consequently the deposited dose of particles was fourfold higher during exercise and considerably increased for the male subjects. Some individuals consistently had a high DF in all four sessions. As an example, the results show that an average person exposed to 100-nm hydrophobic particles during exercise will receive a 16 times higher dose than a relaxed person exposed to an equal amount of hygroscopic (NaCl) particles.
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| 7. |
- Pagels, Joakim, et al.
(författare)
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Chemical composition and mass emission factors of candle smoke particles
- 2009
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Ingår i: Journal of Aerosol Science. - : Elsevier BV. - 0021-8502. ; 40:3, s. 193-208
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study is to investigate the physical and chemical properties of particle emissions from candle burning in indoor air. Two representative types of tapered candies were studied during steady burn, sooting burn and smouldering (upon extinction) under controlled conditions in a walk-in stainless steel chamber. Steady burn emits relatively high number emissions of ultrafine particles dominated by either phosphates or alkali nitrates. The likely source of these particles is flame retardant additives to the wick. Sooting burn in addition emits larger particles mainly consisting of agglomerated elemental carbon. This burning mode is associated with the highest mass emission factors. Particles emitted during smouldering upon extinction are dominated by organic matter. A mass closure was illustrated for the total mass concentration, the summed mass concentration from chemical analysis and the size-integrated mass concentration assessed from number distribution measurements using empirically determined effective densities for the three particle types. (C) 2008 Published by Elsevier Ltd.
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| 8. |
- Pagels, Joakim, et al.
(författare)
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Processing of Soot by Controlled Sulphuric Acid and Water Condensation - Mass and Mobility Relationship
- 2009
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Ingår i: Aerosol Science and Technology. - : Informa UK Limited. - 1521-7388 .- 0278-6826. ; 43:7, s. 629-640
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Tidskriftsartikel (refereegranskat)abstract
- The effects of atmospheric processing on soot particle morphology were studied in the laboratory using the Differential Mobility Analyzer-Aerosol Particle Mass Analyzer (DMA-APM) and the DMA-DMA (Tandem DMA) techniques. To simulate atmospheric processing, combustion soot agglomerates were altered by sulphuric acid vapor condensation, relative humidity (RH) cycling, and evaporation of the sulphuric acid and water by heating. Primary investigated properties were particle mobility size and mass. Secondary properties, derived from these, include effective density, fractal dimension, dynamic shape factor, and the mass fraction of condensed material. A transformation of the soot particles to more compact forms occurs as sulphuric acid and water condense onto fresh soot. The particle mass increases and initially the mobility diameter decreases, indicating restructuring of the soot core, likely due to surface tension forces. For a given soot source and condensing liquid, the degree of compaction depends strongly on the mass (or volume) fraction of condensed material. For water and sulphuric acid condensing on combustion soot, a mass increase of 2-3 times is needed for a transformation to spherical particles. In the limit of spherical particles without voids, the effective density then approaches the inherent material density, the fractal dimension approaches 3 and the dynamic shape factor approaches 1. Our results indicate that under typical atmospheric conditions, soot particles will be fully transformed to spherical droplets on a time scale of several hours. It is expected that the morphology changes and addition of soluble material to soot strongly affect the optical and hygroscopic properties of soot.
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| 9. |
- Persson, Ola, et al.
(författare)
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Air contaminants in a submarine equipped with air independent propulsion
- 2006
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Ingår i: Journal of Environmental Monitoring. - : Royal Society of Chemistry (RSC). - 1464-0325. ; 8:11, s. 1111-1121
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Tidskriftsartikel (refereegranskat)abstract
- The Swedish Navy has operated submarines equipped with air independent propulsion for two decades. This type of submarine can stay submerged for periods far longer than other nonnuclear submarines are capable of. The air quality during longer periods of submersion has so far not been thoroughly investigated. This study presents results for a number of air quality parameters obtained during more than one week of continuous submerged operation. The measured parameters are pressure, temperature, relative humidity, oxygen, carbon dioxide, hydrogen, formaldehyde and other volatile organic compounds, ozone, nitrogen dioxide, particulate matter and microbiological contaminants. The measurements of airborne particles demonstrate that air pollutants typically occur at a low baseline level due to high air exchange rates and efficient air-cleaning devices. However, short-lived peaks with comparatively high concentrations occur, several of the sources for these have been identified. The concentrations of the pollutants measured in this study do not indicate a build-up of hazardous compounds during eight days of submersion. It is reasonable to assume that a substantial build-up of the investigated contaminants is not likely if the submersion period is prolonged several times, which is the case for modern submarines equipped with air independent propulsion.
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| 10. |
- Saqnati, Mehri, et al.
(författare)
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Hygroscopic behaviour of aerosol particles emitted from biomass fired grate boilers
- 2005
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Ingår i: Aerosol Science and Technology. - : Taylor & Francis Group. - 0278-6826 .- 1521-7388. ; 39:91, s. 919-930
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Tidskriftsartikel (refereegranskat)abstract
- This study focuses on the hygroscopic properties of submicrometer aerosol particles emitted from two small-scale district heating combustion plants (1 and 1.5 MW) burning two types of biomass fuels (moist forest residue and pellets). The hygroscopic particle diameter growth factor (Gf ) was measured when taken from a dehydrated to a humidified state for particle diameters between 30– 350 nm (dry size) using a Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA). Particles of a certain dry size all showed similar diameter growth and the Gf at RH = 90% for 110/100 nm particles was 1.68 in the 1MWboiler, and 1.5 in the 1.5MWboiler. These growth factors are considerably higher in comparison to other combustion aerosol particles such as diesel exhaust, and are the result of the efficient combustion and the high concentration of alkali species in the fuel. The observed water uptake could be explained using the Zdanovski-Stokes-Robinson (ZSR) mixing rule and a chemical composition of potassium salts only, taken from ion chromatography analysis of filter and impactor samples (KCl, K2SO4, andK2CO3). Agglomerated particles collapsed and became more spherical when initially exposed to a moderately high relative humidity. When diluted with hot particle-free air, the fractallike structures remained intact until humidified in the H-TDMA. A method to estimate the fractal dimension of the agglomerated combustion aerosol and to convert the measured mobility diameter hygroscopic growth to the more useful property volume diameter growth is presented. The fractal dimension was estimated to be ∼2.5.
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