| 1. |
- Ahlm, Lars, et al.
(författare)
-
Modeling the thermodynamics and kinetics of sulfuric acid-dimethylamine-water nanoparticle growth in the CLOUD chamber
- 2016
-
Ingår i: Aerosol Science and Technology. - : Informa UK Limited. - 0278-6826 .- 1521-7388. ; 50:10, s. 1017-1032
-
Tidskriftsartikel (refereegranskat)abstract
- Dimethylamine (DMA) has a stabilizing effect on sulfuric acid (SA) clusters, and the SA and DMA molecules and clusters likely play important roles in both aerosol particle formation and growth in the atmosphere. We use the monodisperse particle growth model for acid-base chemistry in nanoparticle growth (MABNAG) together with direct and indirect observations from the CLOUD4 and CLOUD7 experiments in the cosmics leaving outdoor droplets (CLOUD) chamber at CERN to investigate the size and composition evolution of freshly formed particles consisting of SA, DMA, and water as they grow to 20nm in dry diameter. Hygroscopic growth factors are measured using a nano-hygroscopicity tandem differential mobility analyzer (nano-HTDMA), which combined with simulations of particle water uptake using the thermodynamic extended-aerosol inorganics model (E-AIM) constrain the chemical composition. MABNAG predicts a particle-phase ratio between DMA and SA molecules of 1.1-1.3 for a 2nm particle and DMA gas-phase mixing ratios between 3.5 and 80 pptv. These ratios agree well with observations by an atmospheric-pressure interface time-of-flight (APi-TOF) mass spectrometer. Simulations with MABNAG, direct observations of the composition of clusters <2nm, and indirect observations of the particle composition indicate that the acidity of the nucleated particles decreases as they grow from approximate to 1 to 20nm. However, MABNAG predicts less acidic particles than suggested by the indirect estimates at 10nm diameter using the nano-HTDMA measurements, and less acidic particles than observed by a thermal desorption chemical ionization mass spectrometer (TDCIMS) at 10-30nm. Possible explanations for these discrepancies are discussed.
|
|
| 2. |
- Alsved, Malin, et al.
(författare)
-
Exhaled respiratory particles during singing and talking
- 2020
-
Ingår i: Aerosol Science and Technology. - : Informa UK Limited. - 1521-7388 .- 0278-6826. ; 54:11, s. 245-1248
-
Tidskriftsartikel (refereegranskat)abstract
- Choir singing has been suspended in many countriesduring the Covid-19 pandemic due to incidental reportsof disease transmission. The mode of transmission has been attributed to exhaled droplets, but with the exception of a study on tuberculosis from1968, there is presently almost no scientific evidence ofincreased particle emissions from singing. A substantial number of studies have,however, investigated aerosols emitted from breathing,talking, coughing and sneezing. It has also been shown that justnormal breathing over time can generate more viablevirus aerosol than coughing, since the latter is a less fre-quent activity.Compared to talking, singing often involves continu-ous voicing, higher sound pressure, higher frequencies,deeper breaths, higher peak airflows and more articu-lated consonants. All these factors are likely to increaseexhaled emissions.The aim of this study was to investigate aerosol anddroplet emissions during singing, as compared to talking and breathing. We also examined the presence of SARS-CoV-2 in the air from breathing, talking and singing,and the efficacy of face masks to reduce emissions. In this study we defined aerosol particles as having a drysize in the range 0.5–10mm. Although debatable from anaerosol physics point of view, a cutoff diameter between5 and 10mm is normally used in medicine for classifica-tion of aerosol versus droplet route of transmission. Droplets are here defined as exhaled particles, frommicron size with no upper size limit, and measured dir-ectly at the mouth before complete evaporation, thuspartly in liquid phase.
|
|
| 3. |
- Alsved, Malin, et al.
(författare)
-
Natural sources and experimental generation of bioaerosols : Challenges and perspectives
- 2020
-
Ingår i: Aerosol Science and Technology. - : Informa UK Limited. - 0278-6826 .- 1521-7388. ; 54:5, s. 547-571
-
Forskningsöversikt (refereegranskat)abstract
- Experimental aerosol generation methods aim to represent natural processes; however, the complexity is not always captured and unforeseen variability may be introduced into the data. The current practices for natural and experimental aerosol generation techniques are reviewed here. Recommendations for best practice are presented, and include characterization of starting material and spray fluid, rational selection of appropriate aerosol generators, and physical and biological characterization of the output aerosol. Reporting of bioaerosol research should capture sufficient detail to aid data interpretation, reduce variation, and facilitate comparison between research laboratories. Finally, future directions and challenges in bioaerosol generation are discussed.
|
|
| 4. |
- Bogan, Michael J., et al.
(författare)
-
Aerosol Imaging with a Soft X-Ray Free Electron Laser
- 2010
-
Ingår i: Aerosol Science and Technology. - : Informa UK Limited. - 0278-6826 .- 1521-7388. ; 44:3, s. I-VI
-
Tidskriftsartikel (refereegranskat)abstract
- Lasers have long played a critical role in the advancement of aerosol science. A new regime of ultrafast laser technology has recently be realized, the world's first soft x-ray free electron laser. The Free electron LASer in Hamburg, FLASH, user facility produces a steady source of 10 femtosecond pulses of 7–32 nm x-rays with 1012 photons per pulse. The high brightness, short wavelength, and high repetition rate (> 500 pulses per second) of this laser offers unique capabilities for aerosol characterization. Here we use FLASH to perform the highest resolution imaging of single PM2.5 aerosol particles in flight to date. We resolve to 35 nm the morphology of fibrous and aggregated spherical carbonaceous nanoparticles that existed for less than two milliseconds in vacuum. Our result opens the possibility for high spatial- and time-resolved single particle aerosol dynamics studies, filling a critical technological need in aerosol science.
|
|
| 5. |
- Cha, Yingying, 1989-, et al.
(författare)
-
Effective density of airborne particles in a railway tunnel from field measurements of mobility and aerodynamic size distributions
- 2018
-
Ingår i: Aerosol Science and Technology. - : Taylor & Francis. - 0278-6826 .- 1521-7388. ; 52:8, s. 886-899
-
Tidskriftsartikel (refereegranskat)abstract
- The objective of this study is to investigate the particle effective density of aerosol measurements in a railway tunnel environment. Effective density can serve as a parameter when comparing and calibrating different aerosol measurements. It can also be used as a proxy parameter reflecting the source of particles. Effective density was determined using two different methods. Method one defined it by the ratio of mass concentration to apparent volume size distribution. Method two relied on a comparison of aerodynamic and mobility diameter size distribution measurements. The aerodynamic size range for method one was 0.006–10 µm, and for method two, it was 10–660 nm. Using the first method, a diurnal average value of about 1.87 g/cm3 was observed for the measurements with tapered element oscillating microbalance (TEOM) in tandem with aerodynamic particle sizer + scanning mobility particle sizer (SMPS), and 1.2 g/cm3 for the combination of TEOM with electrical low pressure impactor plus (ELPI+) in the presence of traffic. With method two, the effective density was 1.45 g/cm3 estimated from the size distribution measurements with ELPI + and fast mobility particle sizer (FMPS), and 1.35 g/cm3 from ELPI + in tandem with SMPS. With both calculation methods, the effective density varied for conditions with and without traffic, indicating different sources of particles. The proportion of particles with small sizes (10–660 nm) had a significant effect on the value of the effective density when no traffic was operating. The responses of different instruments to the railway particle measurements were also compared.
|
|
| 6. |
- Damour, T M, et al.
(författare)
-
Experimental evidence for evaporation/condensation nonuniform flow in a horizontal aerosol generator
- 2005
-
Ingår i: Aerosol Science and Technology. - : Informa UK Limited. - 1521-7388 .- 0278-6826. ; 39:5, s. 444-451
-
Tidskriftsartikel (refereegranskat)abstract
- The formation of deposition patterns in the cooling zone during operation of a horizontal evaporation/condensation nanoparticle generator was studied to obtain information about flow conditions during particle formation. Quartz reactor tubes were used together with a simple light attenuation measurement to characterize deposition as a function of axial location. Results for the onset and pattern of deposition for four different metals-indium, gallium, silver, and lead-were obtained, and size distributions for indium and gallium particle nanoparticles at different temperatures were measured. Distinct deposition bands could be observed resulting from vapor deposition, nanioparticle deposition, or a combination of both. The location or the bands varied with metal and evaporation temperature. Experimentally observed fluctuations in temperature, bimodal size distributions obtained at the highest furnace temperatures, as well as asymmetric deposition patterns suggested the How in the cooling portion of the generator is nonuniform, possibly as a result of buoyancy. These results are important for the design of nanoparticle generation systems, in that horizontal evaporation/condensation generators are often chosen on the basis of assumed simplicity with respect to flow, and this may not always be the case.
|
|
| 7. |
- Guo, Yong, et al.
(författare)
-
Deposition of droplets from the trachea or bronchus in the respiratory tract during exhalation : A steady-state numerical investigation
- 2020
-
Ingår i: Aerosol Science and Technology. - : Informa UK Limited. - 0278-6826 .- 1521-7388. ; 54:8, s. 869-879
-
Tidskriftsartikel (refereegranskat)abstract
- Respiratory droplets are bioaerosols that originate from the respiratory tract. Knowing their deposition characteristics during exhalation would facilitate the understanding of the source of large respiratory droplets and their importance in the spread of respiratory infectious diseases. In this study, computational fluid dynamics is used to simulate the motion and deposition of droplets released from either trachea or bronchi in a realistic reconstruction of the human respiratory tract. Influences of airflow structures and locations of droplet generation on droplet deposition are studied, and droplets with diameters between 1 and 50 mu m are examined. The deposition of droplets is found to be influenced mainly by the droplet diameter and the flow rate of exhalation. The number of droplets released from the trachea or bronchi that can escape into the environment decreases as the flow rate increases. When the flow rate is low (10 L/min), the critical diameter of droplets generated in the lower respiratory system that can escape into the air is approximately 12 mu m, but this diameter is approximately 5 mu m when the flow rate is medium (30 to 60 L/min) or large (90 L/min). The larynx is the dominant site of deposition for droplets smaller than the critical diameter, while trachea and bronchus are more important locations that account for the deposition of larger droplets. This study indicates that the lower respiratory tract is an important source of fine droplets (<5 mu m) in indoor environments, and larger droplets probably originate from the upper respiratory tract, which needs further investigation. Copyright
|
|
| 8. |
- Gustavsson, Eva, et al.
(författare)
-
Evaluation of Aerodynamic Particle Sizer and Electrical Low-Pressure Impactor for Unimodal and Bimodal Mass-Weighted Size Distributions
- 2005
-
Ingår i: Aerosol Science and Technology. - : Taylor and Francis Ltd. - 0278-6826 .- 1521-7388. ; 39:9, s. 871-887
-
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.
|
|
| 9. |
- Hallberg, R. T., et al.
(författare)
-
Hydrogen-assisted spark discharge generated metal nanoparticles to prevent oxide formation
- 2018
-
Ingår i: Aerosol Science and Technology. - : Informa UK Limited. - 0278-6826 .- 1521-7388. ; 52:3, s. 347-358
-
Tidskriftsartikel (refereegranskat)abstract
- There exists a demand for production of metal nanoparticles for today's emerging nanotechnology. Aerosol-generated metal nanoparticles can oxidize during particle formation due to impurities in the carrier gas. One method to produce unoxidized metal nanoparticles is to first generate metal oxides and then reduce them during sintering. Here, we propose to instead prevent oxidation by introducing the reducing agent already at particle formation. We show that by mixing 5% hydrogen into the nitrogen carrier gas, we can generate single crystalline metal nanoparticles by spark discharge from gold, cobalt, bismuth, and tin electrodes. The non-noble nanoparticles exhibit signs of surface oxidation likely formed post-deposition when exposed to air. Nanoparticles generated without hydrogen are found to be primarily polycrystalline and oxidized. To demonstrate the advantages of supplying the reducing agent at generation, we compare to nanoparticles that are generated in nitrogen and sintered in a hydrogen mixture. For bismuth and tin, the crystal quality of the particles after sintering is considerably higher when hydrogen is introduced at particle generation compared to at sintering, whereas for cobalt it is equally effective to only add hydrogen at sintering. We propose that hydrogen present at particle generation prevents the formation of oxide primary particles, thus improving the ability to sinter the nanoparticles to compact and single crystals of metal. This method is general and can be applied to other aerosol generation systems, to improve the generation of size-controlled nanoparticles of non-noble metals with a suitable reducing agent.
|
|
| 10. |
|
|
