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| 2. |
- Ekström, Sanna, et al.
(författare)
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Biosurfactants as CCN : comparison between on-line and off-line measurements
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We are presenting the CCN properties for the bacterial compounds rhamnolipid and surfactin, which are extremely strong surfactants. Three organic:sodium chloride mixtures with mass percentages of 80:20, 50:50 and 20:80 were measured for each biosurfactant. Both on-line Cloud Condensation Nuclei Counter (CCNC) and off-line osmolality combined with surface tension measurements were performed to obtain two sets of critical supersaturations for various dry particle diameters. The critical supersaturations measured by the CCNC were systematically higher than the corresponding supersaturations derived from osmolality/surface tension measurements. A simple surface partitioning-adaption was applied to the off-line data and resulted in a correlation with the results from CCNC measurements for both mixtures with 20 wt% biosurfactant and the 50 wt% rhamnolipid mixture but not for the mixtures with 80 wt% biosurfactant and the 50 wt% surfactin mixture. An explanation can be unreliable CCNC results from the surfactin mixtures as we suspect poor dissolvement of the organic crystals. The choice of the assumed biosurfactant density also has an effect which should not be ignored. However, this indicate that the experimental method using osmolality and surface tension measurements together with a simple surface partitioning model can be used for strongly surfactant compounds as long as they do not dominate the particle mass. We also conclude that biosurfactants in mixed potential CCN particles can activate at relatively low supersaturation compared to other organic mixtures. Still, the critical supersaturation increases with increasing surfactant fraction.
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| 3. |
- Eriksson, Axel, et al.
(författare)
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Diesel soot aging in urban plumes within hours under cold dark and humid conditions
- 2017
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322.
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Tidskriftsartikel (refereegranskat)abstract
- Fresh and aged diesel soot particles have different impacts on climate and human health. While fresh diesel soot particles are highly aspherical and non-hygroscopic, aged particles are spherical and hygroscopic. Aging and its effect on water uptake also controls the dispersion of diesel soot in the atmosphere. Understanding the timescales on which diesel soot ages in the atmosphere is thus important, yet knowledge thereof is lacking. We show that under cold, dark and humid conditions the atmospheric transformation from fresh to aged soot occurs on a timescale of less than five hours. Under dry conditions in the laboratory, diesel soot transformation is much less efficient. While photochemistry drives soot aging, our data show it is not always a limiting factor. Field observations together with aerosol process model simulations show that the rapid ambient diesel soot aging in urban plumes is caused by coupled ammonium nitrate formation and water uptake.
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| 5. |
- Nordin, E. Z., et al.
(författare)
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Secondary organic aerosol formation from gasoline passenger vehicle emissions investigated in a smog chamber
- 2012
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Ingår i: Atmospheric Chemistry and Physics Discussions. - : Copernicus Publications. - 1680-7367 .- 1680-7375. ; 12:12, s. 31725-31765
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Tidskriftsartikel (refereegranskat)abstract
- Gasoline vehicles have elevated emissions of volatile organic compounds during cold starts and idling and have recently been pointed out as potentially the main source of anthropogenic secondary organic aerosol (SOA) in megacities. However, there is a lack of laboratory studies to systematically investigate SOA formation in real-world exhaust. In this study, SOA formation from pure aromatic precursors, idling and cold start gasoline exhaust from one Euro II, one Euro III and one Euro IV passenger vehicles were investigated using photo-oxidation experiments in a 6 m3 smog chamber. The experiments were carried out at atmospherically relevant organic aerosol mass concentrations. The characterization methods included a high resolution aerosol mass spectrometer and a proton transfer mass spectrometer. It was found that gasoline exhaust readily forms SOA with a signature aerosol mass spectrum similar to the oxidized organic aerosol that commonly dominates the organic aerosol mass spectra downwind urban areas. After 4 h aging the formed SOA was 1–2 orders of magnitude higher than the Primary OA emissions. The SOA mass spectrum from a relevant mixture of traditional light aromatic precursors gave f43 (mass fraction at m/z = 4 3) approximately two times higher than to the gasoline SOA. However O : C and H : C ratios were similar for the two cases. Classical C6–C9 light aromatic precursors were responsible for up to 60% of the formed SOA, which is significantly higher than for diesel exhaust. Important candidates for additional precursors are higher order aromatic compounds such as C10, C11 light aromatics, naphthalene and methyl-naphthalenes.
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| 9. |
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| 10. |
- Schmale, Julia, et al.
(författare)
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Collocated observations of cloud condensation nuclei, particle size distributions, and chemical composition
- 2017
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Ingår i: Scientific Data. - : Springer Science and Business Media LLC. - 2052-4463. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- Cloud condensation nuclei (CCN) number concentrations alongside with submicrometer particle number size distributions and particle chemical composition have been measured at atmospheric observatories of the Aerosols, Clouds, and Trace gases Research InfraStructure (ACTRIS) as well as other international sites over multiple years. Here, harmonized data records from 11 observatories are summarized, spanning 98,677 instrument hours for CCN data, 157,880 for particle number size distributions, and 70,817 for chemical composition data. The observatories represent nine different environments, e.g., Arctic, Atlantic, Pacific and Mediterranean maritime, boreal forest, or high alpine atmospheric conditions. This is a unique collection of aerosol particle properties most relevant for studying aerosol-cloud interactions which constitute the largest uncertainty in anthropogenic radiative forcing of the climate. The dataset is appropriate for comprehensive aerosol characterization (e.g., closure studies of CCN), model-measurement intercomparison and satellite retrieval method evaluation, among others. Data have been acquired and processed following international recommendations for quality assurance and have undergone multiple stages of quality assessment.
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| 11. |
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| 12. |
- Wittbom, Cerina
(författare)
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Black Death - Blue Skies - White Clouds : Water Vapour Uptake of Particles Produced from Traffic Exhaust and their Effect on Climate
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aerosol particles are everywhere in the air around us, regardless of whether you are in a busy city or in the serene Arctic. Airborne particles can be produced naturally or anthropogenically, and their properties changes during the time they spend in the atmosphere. Their sizes range from about 1 nm to 100 μm, and affect us in two ways; firstly, our health by deposition in the respiratory tract, and secondly via pertubation of the climate.The Earth’s climate is affected by the radiation balance, which is in turn affected by the presence of particles and the formation of cloud droplets. Cloud droplets form on pre-existing particles by condensation of watervapour. These particles, which act as seeds for the condensation of water, are called cloud condensation nuclei (CCN).The ability of particles to take up water vapour depends on their chemical and physical properties, and is described by particle hygroscopicity. The theoretical framework used in this work to calculate particle hygroscopicity was first introduced by Köhler in 1936, and has since then been developed to account for nonideal conditions. Particle hygroscopicity of fresh and aged traffic exhaust was investigated in laboratory measurements. The complete transformation of soot particles, from fresh emissions of hydrophobic, aspherical soot agglomerates to compacted soot particles coated with secondary organic aerosol (SOA), which are able to act as CCN, was captured for the first time. The SOA produced from traffic emissions showed differences in water vapour uptake, when measured in the subsaturated compared to supersaturated regimes. Theoretical analysis using modified Köhler theory, indicated that these measured differences could be explained by limitation of the solubility of the SOA that was condensed on the seed particles.Ambient measurements of particle hygroscopicity associated with traffic emissions were performed in urban and rural environments. The urban aerosol showed a clear diurnal variation as well as a dependence on air mass origin. The fraction of particles with low hygroscopicity and the fraction of fresh soot (from traffic) showed good agreement during the daytime. However, during the night-time the fraction of agglomerated soot decreased, probably as a result of soot emissions from further away having undergone ageing, and hence restructured to more dense particles, while the hygroscopicity was not notably improved. Furthermore, observations made by following air masses from the urban to the rural environments showed that soot particle restructuring and changes in their properties may occur much faster than previously thought (within 5 hours), due to particulate nitrate formation coupled to water vapour uptake.Finally, the impact of traffic exhausts on climate was synthetized by combining the results in this thesis with those from the literature. Soot particles lead mainly to global warming. Traffic emissions can also reduce visibility, as the ability to absorb and scatter light may increase with ageing and water vapour uptake. However, with further ageing and increased hygroscopicity, the particles produced by traffic can act as cloud condensation nuclei, thus contributing to cooling. The increased hygroscopicity (due to condensation of organic and inorganic material) will affect the atmospheric lifetime of the soot particles, which also influence climate change.
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| 13. |
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| 14. |
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| 15. |
- Wittbom, Cerina, et al.
(författare)
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Cloud droplet activity changes of soot aerosol upon smog chamber ageing
- 2014
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7324. ; 14:18, s. 9831-9854
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Tidskriftsartikel (refereegranskat)abstract
- Particles containing soot, or black carbon, are generally considered to contribute to global warming. However, large uncertainties remain in the net climate forcing resulting from anthropogenic emissions of black carbon (BC), to a large extent due to the fact that BC is co-emitted with gases and primary particles, both organic and inorganic, and subject to atmospheric ageing processes. In this study, diesel exhaust particles and particles from a flame soot generator spiked with light aromatic secondary organic aerosol (SOA) precursors were processed by UV radiation in a 6m3 Teflon chamber in the presence of NOx. The time-dependent changes of the soot nanoparticle properties were characterised using a Cloud Condensation Nuclei Counter, an Aerosol Particle Mass Analyzer and a Soot Particle Aerosol Mass Spectrometer. The results show that freshly emitted soot particles do not activate into cloud droplets at supersaturations <= 2 %, i. e. the BC core coated with primary organic aerosol (POA) from the exhaust is limited in hygroscopicity. Before the onset of UV radiation it is unlikely that any substantial SOA formation is taking place. An immediate change in cloud-activation properties occurs at the onset of UV exposure. This change in hygroscopicity is likely attributed to SOA formed from intermediate volatility organic compounds (IVOCs) in the diesel engine exhaust. The change of cloud condensation nuclei (CCN) properties at the onset of UV radiation implies that the lifetime of soot particles in the atmosphere is affected by the access to sunlight, which differs between latitudes. The ageing of soot particles progressively enhances their ability to act as cloud condensation nuclei, due to changes in: (I) organic fraction of the particle, (II) chemical properties of this fraction (e. g. primary or secondary organic aerosol), (III) particle size, and (IV) particle morphology. Applying kappa-K hler theory, using a kappa SOA value of 0.13 (derived from independent input parameters describing the organic material), showed good agreement with cloud droplet activation measurements for particles with a SOA mass fraction >= 0.12 (slightly aged particles). The activation properties are enhanced with only a slight increase in organic material coating the soot particles (SOA mass fraction < 0.12), however not as much as predicted by K hler theory. The discrepancy between theory and experiments during the early stages of ageing might be due to solubility limitations, unevenly distributed organic material or hindering particle morphology. The change in properties of soot nanoparticles upon photochemical processing clearly increases their hygroscopicity, which affects their behaviour both in the atmosphere and in the human respiratory system.
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| 16. |
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| 17. |
- Wittbom, Cerina
(författare)
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Cloud Droplet Forming Potential of Ageing Soot and Surfactant Particles : Laboratory research and Köhler modelling
- 2014. - LUTFD2 / (TFKF-3105) / 1 - 35/ 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aerosol particles affect Earth’s climate system by scattering and absorbing light. The perturbation of the climate system caused by a change in aerosol configuration due to anthropogenic emissions has recently improved. However, the radiation balance and hydrological cycle of Earth are also highly influenced by clouds: a small change in cloud configuration can have a large effect on the climate. Cloud droplets form on preexisting particles. For instance, the ability of black carbon (BC) particles when co-emitted with organic carbon (OC) to form cloud droplets are less well understood. A large fraction of the ambient organic aerosol is formed via oxidation of volatile organic compounds from both biogenic and anthropogenic sources. During atmospheric ageing, the properties of freshly emitted soot nanoparticles will change as volatile organics oxidize and interact with the primary soot emissions. As the particles undergo photochemical processing in the atmosphere they progressively become more hygroscopic and will thereby influence the climate due to their improved ability to act as cloud condensation nuclei (CCN) as well as affecting the human health by altering the uptake in the respiratory system. This work is part of the PhD work of the author of this report, with the aim to evaluate the ability of aerosol nanoparticles to form cloud droplets; of biogenic and anthropogenic origin. To gain better understanding of the cloud forming potential of organic compounds produced from living organisms as well as soot when co-emitted with organic compounds both laboratory research and Köhler modeling has been performed. Different biosurfactants was measured and compared with two different techniques in the first study. In the second study, soot from both a diesel vehicle and a flame soot generator was photochemically processed in a smog chamber, monitored with a comprehensive instrumental set-up. For both studies the measurement technique of the cloud activation properties was improved, gaining better resolution in data. The results in the first study show that the biosurfactants have good cloud forming abilities, however not as good as previously believed. There are discrepancies in the results from the two measurement techniques (on- and off-line), which partly can be explained by surface partitioning. In the second study, the freshly emitted soot particles neither showed any hygroscopic growth (at 90 % relative humidity) nor activated into cloud droplets (at a supersaturation of 2 %). As the emissions are photochemically processed the properties of the particles change and they become progressively more hygroscopic. The enhanced cloud forming abilities of the soot particles are due to changes in the organic fraction, both regarding quantity and quality, as well as a change in size and shape of the particles. Experimental and modeled (κ-Köhler theory) results show good agreement for particles with higher organic content, and with a κ-value of ~0.13. The κ-value derived from the chemical composition and the CCN measurements are consistent. Due to the morphology of the soot particles, predictions of the cloud droplet activity and hygroscopic growth cannot be performed using the measured mobility diameter. Instead, the volume equivalent diameter is a better size measure. This parameter has in this study successfully been estimated from the mobility diameter and the organic aerosol fraction of the particle.In summary, both the biosurfactants and aged anthropogenic particles show cloud droplet forming potential relevant in the ambient air, with the ability to affect the climate. The results from the anthropogenic experiment also imply that the sunlight affect the lifetime of soot in the atmosphere, due to changed cloud droplet activation as the UV radiation was turned on during experiments. Probably, the uptake in human lungs of larger particles increases as the soot particles age.
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