| 1. |
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| 2. |
- Asking, Lars, et al.
(författare)
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An electrostatic aerosol sampler
- 1988
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Ingår i: Journal of Aerosol Science. - : Elsevier BV. - 0021-8502. ; 19:7, s. 1023-1026
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Tidskriftsartikel (refereegranskat)
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| 3. |
- Berg, Olle H., et al.
(författare)
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Comparison of observed and modeled hygroscopic behavior of atmospheric particles
- 1998
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Ingår i: Contributions to Atmospheric Physics. - 0005-8173. ; 71:1, s. 47-64
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Forskningsöversikt (refereegranskat)abstract
- The hygroscopic behavior of sub-micrometer atmospheric aerosol particles was studied with a Tandem Differential Mobility Analyzer (TDMA) at a field site in the Po Valley, Italy. The measurements were done in a continental polluted aerosol during the CHEMDROP fog and haze field experiment at San Pietro di Capofiume in November 1994. In this study, hygroscopic diameter growth factors of individual particles were measured when taken from a dry state, to a relative humidity of 90 %. The aerosol consisted of two groups of particles with different hygroscopic properties, as also seen in an earlier field experiment at the same location in 1989 and at other continental sites. The present work is a closure study on the hygroscopic behavior of sub-micrometer aerosol particles and their mass. Ammonium sulfate was used to model the hygroscopic growth with a model based on thermodynamic data for non-ideal aqueous solutions at water vapor subsaturation. The study was made in two steps: The first step is a comparison between hygroscopic active aerosol volume fractions derived from TDMA measurements on individual particles integrated over the particle size distributions, and collected volume fractions of major ions sampled by size resolved cascade impactors. The model of hygroscopic growth was also used, in the second step, to calculate ambient sizes of individual aerosol particles. These sizes were then compared to the actual ambient sizes as measured by the Droplet Aerosol Analyzer. The result shows agreement, within the estimated errors, between the integrated hygroscopic active volume fractions and the collected volume fractions of inorganic salts, for five events out of six studied. A mass balance could also be obtained between the masses collected with the impactors and the integrated volume distributions, by attributing reasonable densities to the hygroscopically active and inactive fractions. The differences between the calculated and measured ambient sizes were within measurement errors, when Raoult's law was used to model the occasions with relative humidities larger than 95 %.
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| 4. |
- Cederfelt, Sven Inge, et al.
(författare)
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On the charge limit for crystallizing particles
- 1990
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Ingår i: Journal of Aerosol Science. - 0021-8502. ; 21:SUPPL. 1, s. 127-130
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Tidskriftsartikel (refereegranskat)abstract
- The electrical charge limit of crystallizing sodium chloride droplets has been studied. Moderately charged sodium chloride solution droplets were dried to highly charged residual particles. The charge limit was found to be near the Rayleigh charge limit for saturated sodium chloride droplets of the same size as the residual particle. The charge loss was not found to affect the particle size to a detectable degree.
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| 5. |
- Chen, Hao Yu, et al.
(författare)
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Association of FADS1/2 Locus Variants and Polyunsaturated Fatty Acids With Aortic Stenosis
- 2020
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Ingår i: JAMA cardiology. - : American Medical Association (AMA). - 2380-6583 .- 2380-6591. ; 5:6, s. 694-702
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Tidskriftsartikel (refereegranskat)abstract
- Importance: Aortic stenosis (AS) has no approved medical treatment. Identifying etiological pathways for AS could identify pharmacological targets.Objective: To identify novel genetic loci and pathways associated with AS.Design, Setting, and Participants: This genome-wide association study used a case-control design to evaluate 44 703 participants (3469 cases of AS) of self-reported European ancestry from the Genetic Epidemiology Research on Adult Health and Aging (GERA) cohort (from January 1, 1996, to December 31, 2015). Replication was performed in 7 other cohorts totaling 256 926 participants (5926 cases of AS), with additional analyses performed in 6942 participants from the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) Consortium. Follow-up biomarker analyses with aortic valve calcium (AVC) were also performed. Data were analyzed from May 1, 2017, to December 5, 2019.Exposures: Genetic variants (615 643 variants) and polyunsaturated fatty acids (ω-6 and ω-3) measured in blood samples.Main Outcomes and Measures: Aortic stenosis and aortic valve replacement defined by electronic health records, surgical records, or echocardiography and the presence of AVC measured by computed tomography.Results: The mean (SD) age of the 44 703 GERA participants was 69.7 (8.4) years, and 22 019 (49.3%) were men. The rs174547 variant at the FADS1/2 locus was associated with AS (odds ratio [OR] per C allele, 0.88; 95% CI, 0.83-0.93; P = 3.0 × 10-6), with genome-wide significance after meta-analysis with 7 replication cohorts totaling 312 118 individuals (9395 cases of AS) (OR, 0.91; 95% CI, 0.88-0.94; P = 2.5 × 10-8). A consistent association with AVC was also observed (OR, 0.91; 95% CI, 0.83-0.99; P = .03). A higher ratio of arachidonic acid to linoleic acid was associated with AVC (OR per SD of the natural logarithm, 1.19; 95% CI, 1.09-1.30; P = 6.6 × 10-5). In mendelian randomization, increased FADS1 liver expression and arachidonic acid were associated with AS (OR per unit of normalized expression, 1.31 [95% CI, 1.17-1.48; P = 7.4 × 10-6]; OR per 5-percentage point increase in arachidonic acid for AVC, 1.23 [95% CI, 1.01-1.49; P = .04]; OR per 5-percentage point increase in arachidonic acid for AS, 1.08 [95% CI, 1.04-1.13; P = 4.1 × 10-4]).Conclusions and Relevance: Variation at the FADS1/2 locus was associated with AS and AVC. Findings from biomarker measurements and mendelian randomization appear to link ω-6 fatty acid biosynthesis to AS, which may represent a therapeutic target.
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| 6. |
- Chen, H.Y., et al.
(författare)
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Dyslipidemia, inflammation, calcification, and adiposity in aortic stenosis: a genome-wide study
- 2023
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Ingår i: European Heart Journal. - : Oxford University Press. - 0195-668X .- 1522-9645. ; 44:21, s. 1927-1939
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Tidskriftsartikel (refereegranskat)abstract
- Aims Although highly heritable, the genetic etiology of calcific aortic stenosis (AS) remains incompletely understood. The aim of this study was to discover novel genetic contributors to AS and to integrate functional, expression, and cross-phenotype data to identify mechanisms of AS. Methods and results A genome-wide meta-analysis of 11.6 million variants in 10 cohorts involving 653 867 European ancestry participants (13 765 cases) was performed. Seventeen loci were associated with AS at P ≤ 5 × 10−8, of which 15 replicated in an independent cohort of 90 828 participants (7111 cases), including CELSR2–SORT1, NLRP6, and SMC2. A genetic risk score comprised of the index variants was associated with AS [odds ratio (OR) per standard deviation, 1.31; 95% confidence interval (CI), 1.26–1.35; P = 2.7 × 10−51] and aortic valve calcium (OR per standard deviation, 1.22; 95% CI, 1.08–1.37; P = 1.4 × 10−3), after adjustment for known risk factors. A phenome-wide association study indicated multiple associations with coronary artery disease, apolipoprotein B, and triglycerides. Mendelian randomization supported a causal role for apolipoprotein B-containing lipoprotein particles in AS (OR per g/L of apolipoprotein B, 3.85; 95% CI, 2.90–5.12; P = 2.1 × 10−20) and replicated previous findings of causality for lipoprotein(a) (OR per natural logarithm, 1.20; 95% CI, 1.17–1.23; P = 4.8 × 10−73) and body mass index (OR per kg/m2, 1.07; 95% CI, 1.05–1.9; P = 1.9 × 10−12). Colocalization analyses using the GTEx database identified a role for differential expression of the genes LPA, SORT1, ACTR2, NOTCH4, IL6R, and FADS. Conclusion Dyslipidemia, inflammation, calcification, and adiposity play important roles in the etiology of AS, implicating novel treatments and prevention strategies. © The Author(s) 2023. Published by Oxford University Press on behalf of the European Society of Cardiology.
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| 7. |
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| 8. |
- Friberg, Johan, et al.
(författare)
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Volcanic impact on the climate - The stratospheric aerosol load in the period 2006-2015
- 2018
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 18:15, s. 11149-11169
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Tidskriftsartikel (refereegranskat)abstract
- We present a study on the stratospheric aerosol load during 2006-2015, discuss the influence from volcanism and other sources, and reconstruct an aerosol optical depth (AOD) data set in a resolution of 1° latitudinally and 8 days timewise. The purpose is to include the "entire" stratosphere, from the tropopause to the almost particle-free altitudes of the midstratosphere. A dynamic tropopause of 1.5 PVU was used, since it enclosed almost all of the volcanic signals in the CALIOP data set. The data were successfully cleaned from polar stratospheric clouds using a temperature threshold of 195 K. Furthermore, a method was developed to correct data when the CALIOP laser beam was strongly attenuated by volcanic aerosol, preventing a negative bias in the AOD data set. Tropospheric influence, likely from upwelling dust, was found in the extratropical transition layer in spring. Eruptions of both extratropical and tropical volcanoes that injected aerosol into the stratosphere impacted the stratospheric aerosol load for up to a year if their clouds reached lower than 20 km altitude. Deeper-reaching tropical injections rose in the tropical pipe and impacted it for several years. Our AODs mostly compare well to other long-term studies of the stratospheric AOD. Over the years 2006-2015, volcanic eruptions increased the stratospheric AOD on average by ∼ 40 %. In absolute numbers the stratospheric AOD and radiative forcing amounted to 0.008 and -0.2 W m-2, respectively.
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| 9. |
- Fuzzi, Sandro, et al.
(författare)
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Overview of the Po valley fog experiment 1994 (CHEMDROP)
- 1998
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Ingår i: Contributions to Atmospheric Physics. - 0005-8173. ; 71:1, s. 3-19
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Forskningsöversikt (refereegranskat)abstract
- The paper presents an outline of the CHEMDROP field experiment, carried out in November 1994 at the field station of S. Pietro Capofiume in the Po Valley, Italy. The main objective of the project was to address the issue of the size-dependent chemical composition of fog droplets, by experimentally investigating the following processes, which are expected to affect (or be affected by) the chemical composition of fog droplets as a function of size: a) the connection of the size-dependent chemical composition of CCN to the size-dependent composition of fog droplets; b) the gas/liquid partitioning of the gaseous species NH3, SO2, HCHO, HNO3 in fog; c) the Fe(II)/Fe(III) redox cycle in fog water. Some general results and overall conclusions of the experiment are reported in this paper, while more specific scientific questions are discussed in other companion papers in this issue. CHEMDROP results show that several processes concur in determining the size-dependence of fog droplets chemical composition: nucleation scavenging of pre-existing CCN, fog dynamical evolution and gas/liquid exchange between interstitial air and fog droplets. Chemical transformations in the liquid phase can cause further changes in the chemical composition of the droplets. Only by taking into account the combination of all these processes, is it possible to explain the inhomogeneities in fog droplet chemical composition.
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| 10. |
- Hansson, Hans Christen, et al.
(författare)
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Long range aerosol transport in Southern Sweden : An example of multtvariate statistical evaluation methodology
- 1984
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Ingår i: Nuclear Inst. and Methods in Physics Research, B. - 0168-583X. ; 3:1-3, s. 483-488
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Tidskriftsartikel (refereegranskat)abstract
- The utilization of multivariate statistical techniques is discussed with emphasis on the rather new method SIMCA, when applied to multielemental data. The procedures of scaling and normalizing are described. The data base used is from a project studying long range aerosol transport to southern Sweden. SIMCA reveals low variability in fine mode elemental composition in southerly air masses being clearly different from the elemental compositions found in northerly air masses.
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| 11. |
- Heintzenberg, Jost, et al.
(författare)
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Characteristics of haze, mist and fog
- 1998
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Ingår i: Contributions to Atmospheric Physics. - 0005-8173. ; 71:1, s. 21-31
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Tidskriftsartikel (refereegranskat)abstract
- An aerosol and fog data set from a field experiment in November 1994 at San Pietro Capofiume, Northern Italy was analysed. With objective criteria developed from visibility measurements average aerosol characteristics in the dry and wet state were calculated for haze, mist and fog conditions which can be seen as representative for continental air masses in an industrialised region. Dry particle size distributions between three and 800 nm and ambient size distributions between and 50 μm were measured with a system consisting of the three size-segregating particle sensors differential mobility particle sizer, droplet aerosol analyser and FSSP. Systematic changes in particle properties were found for the transition from haze to fog that can be used to derive internally consistent optical aerosol properties. The analysis of the data set demonstrates that atmospheric sensors which have been developed for cloud and fog studies yield useful data for haze conditions.
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| 12. |
- Hermann, Markus, et al.
(författare)
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An optical particle size spectrometer for aircraft-borne measurements in IAGOS-CARIBIC
- 2016
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Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 9:5, s. 2179-2194
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Tidskriftsartikel (refereegranskat)abstract
- The particle number size distribution is an important parameter to characterize the atmospheric aerosol and its influence on the Earth's climate. Here we describe a new optical particle size spectrometer (OPSS) for measurements of the accumulation mode particle number size distribution in the tropopause region on board a passenger aircraft (IAGOS-CARIBIC observatory: In-service Aircraft for a Global Observing System - Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container). A modified KS93 particle sensor from RION Co., Ltd., together with a new airflow system and a dedicated data acquisition system, is the key component of the CARIBIC OPSS. The instrument records individual particle pulse signal curves in the particle size range 130-1110 nm diameter (for a particle refractive index of 1.47-i0.006) together with a time stamp and thus allows the post-flight choice of the time resolution and the size distribution bin width. The CARIBIC OPSS has a 50 % particle detection diameter of 152 nm and a maximum asymptotic counting efficiency of 98 %. The instrument's measurement performance shows no pressure dependency and no particle coincidence for free tropospheric conditions. The size response function of the CARIBIC OPSS was obtained by a polystyrene latex calibration in combination with model calculations. Particle number size distributions measured with the new OPSS in the lowermost stratosphere agreed within a factor of 2 in concentration with balloon-borne measurements over western North America. Since June 2010 the CARIBIC OPSS is deployed once per month in the IAGOS-CARIBIC observatory.
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| 13. |
- Knutas, Edmund
(författare)
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Mellan retorik och praktik. : En ämnesdidaktisk och läroplansteoretisk studie av svenskämnena och fyra gymnasielärares svenskundervisning efter gymnasiereformen 1994.
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Swedish as a school subject has long been debated in Sweden, and ideas concerning its content, role and function in school and society have varied greatly throughout the years. In 1994, there was an upper secondary school reform which resulted in a partial revision of the Swedish subject, including its introduction within a new course and grading system. The Swedish A and B courses became obligatory for all upper secondary students. Other courses in Swedish became largely optional. This study consists of two levels – a rhetorical and practical level. The rhetorical level deals with understandings and ideas of the Swedish subject and instruction as they are expressed in curricula and course syllabi, as well as with the understandings and ideas expressed by the four teachers in the study. In addition, the external and internal frame factors which underlie this rhetoric are considered. The practical level concerns the four teachers’ concrete Swedish instruction, i.e. the aims and goals, content and working methods which underlie their teaching, as well as the factors which influence, limit and facilitate it. The aim of the study is to attempt to describe, analyse and understand the role and function of the Swedish subject after the upper secondary school reform of 1994. What ideas do the four teachers express regarding the role and function of the Swedish subject in upper secondary school and society after 1994, and how should these ideas and reasons be interpreted and understood from a more comprehensive, general perspective? How do the teachers represent the Swedish subject in their teaching, i.e. how is their knowledge of subject didactics expressed? These are two central questions in the study. A third central question concerns notions of society and the good citizen implied in the chosen views of the Swedish subject. The study has two theoretical starting points: subject didactics and curriculum theory. Shulman’s concepts of pedagogical content knowledge and transformation are central to the subject didactics drawn upon here, while frame factor theory and Bernstein’s concepts of “classification” and “framing” are central to the curriculum-theoretical perspective. The perspective of subject didactics deals with the relation between teacher and content, while the curriculum-theoretical perspective deals with the relation between content, individual and society. This study shows that the teachers’ knowledge of subject didactics is vague. The teachers’ transformation of content in teaching resides to a high degree in an adaptation to the students; the focus is thus not on a transformation and content analysis of the Swedish subject. Further, the teachers have an instrumental approach to the steering documents. A common characteristic among the four teachers, and in Swedish instruction generally, is that a large degree of responsibility is placed on the individual student for their literary and language development. Collective meetings were very infrequent in the teaching of the four teachers in the study. This study discerns four teacher codes which reflect understandings and ideas of school and education, formed by previous and current material and sociocultural conditions and which the individual teacher has encountered, adopted and reshaped into his/her own. These four teacher codes can be described as closeness and hierarchy, tradition and renewal, vision and reality and the individual and the collective. The teacher codes reveal that the four teachers have relatively similar teaching strategies, whereas their teaching aims, goals and content diverge significantly. Viewed from the perspective of curriculum theory, it is evident that the teachers emphasise the individual student over the collective. It is a matter of developing one’s thought and personality and of fostering the students to be individual, active members of society. However, this active member of society does not appear to be aware and critically active, but rather a loyal and obedient member of society.
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| 14. |
- Kristiansson, Per, et al.
(författare)
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Photon-tagged nuclear reaction analysis for trace element determination
- 1997
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Ingår i: Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms. - 0168-583X. ; 132:1, s. 159-176
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Tidskriftsartikel (refereegranskat)abstract
- The new trace element measurement technique "photon-tagged Nuclear Reaction Analysis" (pNRA) is introduced and the experimental procedures are described in detail. The pNRA-technique is an ion-beam analytical technique intended for the determination of the abundance of the lightest elements, ranging from lithium to phosphorus. The technique is a complement to the PIXE technique. pNRA is a multiparameter technique, using fast coincidence criteria and high time resolution which identifies and measures the products of nuclear reactions from which the amount of an element in the irradiated target can be determined. A detection system suitable for use in pNRA analysis is described. Different aspects of experimental parameters, e.g. time resolution and γ-efficiency, are discussed and evaluated. Yield curves for all relevant light isotopes are presented for a proton beam energy between 3.5 and 3.75 MeV, and minimum detection limits (MDLs) are extracted for different environments. The results of the MDL measurements with pNRA_ are compared with the detection limits of other frequently used techniques such as proton-induced γ-emission (PIGE) and particle elastic scattering analysis (PESA), and are shown to match these other techniques very well.
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| 15. |
- Laj, Paolo, et al.
(författare)
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The size dependent composition of fog droplets
- 1998
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Ingår i: Contributions to Atmospheric Physics. - 0005-8173. ; 71:1, s. 115-130
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Tidskriftsartikel (refereegranskat)abstract
- The size dependency of fog droplet concentration and composition was studied using newly developed droplet impactors during the CHEMDROP campaign in the Po Valley (Italy). A strong size dependency of solute concentrations was measured during several fog episodes. The ionic strength of the droplet solutions varies as a function of droplet diameter, showing maximum values in the 9-19 μm diameter range. The solute concentration varies up to a factor of 10 among droplets of different diameter. Similarly, differences of up to 2 pH units are found among droplets of different diameter. The solute dependency of aerosol and droplets species from 0.1 μm to 50 μm is investigated. The monomodal behaviour of the solute concentration in droplets can be explained by both diffusional condensation of the aerosols serving as cloud condensation nuclei (CCN) and the air/liquid transfer of volatile species, in particular for HNO3 and NH3. The distribution of sulphur species is also size-dependent and is directly linked to the pH variations across the droplet spectrum, resulting in HMSA formation in small droplets and S(IV) oxidation large droplets.
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| 16. |
- Martinsson, Bengt G., et al.
(författare)
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A high-sensitivity method for hydrogen analysis in thin targets
- 1993
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Ingår i: Nuclear Inst. and Methods in Physics Research, B. - 0168-583X. ; 82:4, s. 589-599
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Tidskriftsartikel (refereegranskat)abstract
- A sensitive and fast method for hydrogen analysis has been developed. The method is based on a technique where a proton beam of a few MeV impinges on the target and the elastically scattered proton and the recoiling target hydrogen nucleus are detected in coincidence. The method makes use of the difference in time of flight and requires no energy determination. The system consists of two thin, large-area plastic scintillation detectors placed at angles of 45° relative to the beam direction on either side of the beam. Evaluations of the system showed that a stable coincidence yield with respect to position in the target plane and target displacement can be obtained provided that the geometry of the setup is carefully designed. The yield as a function of target thickness was almost linear for target thicknesses up to 2000 μg/cm2. It was also found that count rates up to 500000 s-1 in each branch may be used. The minimum detection limit for the hydrogen detection system was found to be of the order of a few pg/cm2 for a proton beam energy of 3.6 MeV.
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| 17. |
- MARTINSSON, BENGT G., et al.
(författare)
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A relative humidity processing method for the sampling of aerosol particles with low growth‐ability
- 1992
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Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 44:5, s. 632-644
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Tidskriftsartikel (refereegranskat)abstract
- A method for the fractionation of aerosol particles with respect to size and ability to grow with an increased relative humidity has been developed. The system consists of cascade impactors, diffusion driers, a humidifier and a temperature stabiliser. Diffusion driers were designed and the vapour penetration was modelled below 20%. A humidifier which can be operated with an output relative humidity above 95% was developed. Flow‐rates up to 51/min can be used and the relative humidity can be controlled within approximately 1%. The ability of the system to fractionate aerosol particles with respect to growth with relative humidity was investigated. The equivalent aerodynamic diameter growth factor for sodium chloride was determined to 2 at a relative humidity of 98%, in good agreement with theory. The growth is used to collect particles with no, or limited growth with increased relative humidity in separate fractions for chemical characterisation. This is obtained with an impactor stage operated at high relative humidity followed by a diffusion drier and an impactor stage with a factor of 1.4 lower cut‐off diameter operated at low relative humidity, where the particles with low growth‐ability are collected. The system was in operation during the EUROTRAC sub‐project Ground‐based Cloud Experiment (GCE) at Po Valley, supplying important information on the particle size related scavenging and the elemental composition of particles with a low growth‐ability.
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| 18. |
- Martinsson, Bengt G.
(författare)
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An external beam PIXE/PESA setup for characterization of fine aerosols
- 1987
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Ingår i: Nuclear Inst. and Methods in Physics Research, B. - 0168-583X. ; 22:1-3, s. 356-363
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Tidskriftsartikel (refereegranskat)abstract
- An external beam setup has been developed for the determination of elemental concentrations in fine aerosols (aerodynamic particle diameter less than about 2 μm). Carbon, nitrogen and oxygen are determined with particle elastic scattering analysis (PESA) and, simultaneously, elements heavier than silicon with PIXE at a proton energy of 3.58 MeV. Earlier work on aerosols with PESA and most PIXE work have been performed with the aerosol sample in high vacuum, which causes losses of certain compounds, e.g. several organic substances present in atmospheric aerosols. These losses are increased by the heating effect of the beam. The rate of mass loss of different aliphatic hydrocarbons has been investigated for different chamber gas pressures, chamber gas exchange rates and beam current densities. The external beam approach showed a considerable improvement compared with high vacuum analysis. The external beam setup is described in some detail with respect to geometry, electronics and the chamber gas-handling system.
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| 19. |
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| 20. |
- Martinsson, Bengt G., et al.
(författare)
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Droplet nucleation and growth in orographic clouds in relation to the aerosol population
- 1999
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Ingår i: Atmospheric Research. - 0169-8095. ; 50:3-4, s. 289-315
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Tidskriftsartikel (refereegranskat)abstract
- The formation and development of orographic clouds was studied in a field experiment comprising several measurement sites at a mountain ridge. The influence of the aerosol population present on the cloud microstructure was studied in relation to the dynamics in the cloud formation. Droplet nucleation scavenging was investigated by the introduction of a non-dimensional particle diameter related to the process, and it was found that the scavenging rose rapidly in a relatively narrow particle size interval. The size dependency of the scavenging could partly be explained by external mixture of the aerosol. The large particles in the cloud interstitial aerosol was found to be of a chemical nature which allows for only a very weak uptake of water, implying that the chemical composition of these particles rather than entrainment of dry air prevented the droplet nucleation. The aerosol particle number concentration was found to strongly influence the cloud microstructure. Droplet number concentrations up to approximately 2000 cm-3 were observed together with a substantially reduced effective droplet diameter. The observed effect of elevated particle number concentrations in orographic clouds was generalised to the climatologically more important stratiform clouds by the use of a cloud model. It was found that the microstructure of stratiform clouds was strongly dependent on the aerosol population present as well on the dynamics in the cloud formation.
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| 21. |
- Martinsson, Bengt G., et al.
(författare)
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Elemental composition of fog interstitial particle size fractions and hydrophobic fractions related to fog droplet nucleation scavenging
- 1992
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Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509. ; 44:5, s. 593-603
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Tidskriftsartikel (refereegranskat)abstract
- The cloud nucleation scavenging process was studied during a joint campaign of the EUROTRAC sub‐project Ground‐based Cloud Experiment. It was found that the particle size has a strong influence on the partitioning of particles between the cloud droplet and the interstitial aerosol reservoirs. A new aerosol sampling unit, the relative humidity processing system, was employed for the extraction of particles with a low growth‐ability with respect to increased relative humidity. The system supplied tracer elements on the particle growth‐ability. These elements could be used to identify a factor related to particle hygroscopic properties, which was in effect as a selector of cloud condensation nuclei.
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| 22. |
- Martinsson, Bengt G., et al.
(författare)
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Experimental cross sections for Bremsstrahlung production by the impact of MeV protons on low-Z targets
- 1990
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Ingår i: Nuclear Inst. and Methods in Physics Research, B. - 0168-583X. ; 47:4, s. 361-369
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Tidskriftsartikel (refereegranskat)abstract
- The production of continuously distributed X-rays by the impact of protons of 1.9-3.0 MeV for X-ray energies between 4 and 6.5 keV, and 1.9-2.65 MeV for X-ray energies between 1.7 and 4 keV has been investigated. Five different target types have been irradiated: polyethylene, polystyrene, carbon. KaptonTM and MylarTM. The results are presented as absolute cross sections for continuous X-ray production at the proton energy 2.55 MeV, and the proton energy dependence is presented in terms of linear and exponential functions in different regimes related to electron binding energy. The effect of electron escape was investigated. The data were modelled using the concept of effective electron escape depth.
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| 23. |
- Martinsson, Bengt G., et al.
(författare)
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Fine mode particulate sulphur in the tropopause region measured from intercontinental flights (CARIBIC)
- 2001
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Ingår i: Geophysical Research Letters. - 0094-8276. ; 28:7, s. 1175-1178
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Tidskriftsartikel (refereegranskat)abstract
- Here the first systematic study of the concentration of particulate sulphur in the upper troposphere and lower stratosphere is presented. The measurements were undertaken in the CARIBIC programme during intercontinental flights from a commercial aircraft, which was equipped with an aerosol inlet and a research payload in the cargo bay. Aerosol samples were collected and analysed for elemental composition. The data set comprises 21 flights between Germany and Male/Colombo in the Indian Ocean. The average fine mode, particulate sulphur concentration was 14 ng/m3 STP, which is low compared to remote areas at the Earth's surface. A pronounced dependence with latitude with elevated concentrations occurring within the densely industrialised northern hemispheric mid latitudes was observed, thus suggesting anthropogenic influence on the climate from sulphate particles in the tropopause region.
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| 24. |
- Martinsson, Bengt G., et al.
(författare)
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Five-satellite-sensor study of the rapid decline of wildfire smoke in the stratosphere
- 2022
-
Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 22:6, s. 3967-3984
-
Tidskriftsartikel (refereegranskat)abstract
- Smoke from western North American wildfires reached the stratosphere in large amounts in August 2017. Limb-oriented satellite-based sensors are commonly used for studies of wildfire aerosol injected into the stratosphere (OMPS-LP (Ozone Mapping and Profiler Suite Limb Profiler) and SAGE III/ISS (Stratospheric Aerosol and Gas Experiment III on the International Space Station)). We find that these methods are inadequate for studies of the first 1-2 months after such a strong fire event due to event termination ("saturation"). The nadir-viewing lidar CALIOP (Cloud-Aerosol LIdar with Orthogonal Polarization) is less affected due to shorter path in the smoke; furthermore, it provides a means to develop a method to correct for strong attenuation of the signal. After the initial phase, the aerosol optical depth (AOD) from OMPS-LP and CALIOP show very good agreement above the 380ĝK isentrope, whereas OMPS-LP tends to produce higher AOD than CALIOP in the lowermost stratosphere (LMS), probably due to reduced sensitivity at altitudes below 17ĝkm. Time series from CALIOP of attenuation-corrected stratospheric AOD of wildfire smoke show an exponential decline during the first month after the fire, which coincides with highly significant changes in the wildfire aerosol optical properties. The AOD decline is verified by the evolution of the smoke layer composition, comparing the aerosol scattering ratio (CALIOP) to the water vapor concentration from MLS (Microwave Limb Sounder). Initially the stratospheric wildfire smoke AOD is comparable with the most important volcanic eruptions during the last 25 years. Wildfire aerosol declines much faster, 80ĝ%-90ĝ% of the AOD is removed with a half-life of approximately 10ĝd. We hypothesize that this dramatic decline is caused by photolytic loss. This process is rarely observed in the atmosphere. However, in the stratosphere this process can be studied with practically no influence from wet deposition, in contrast to the troposphere where this is the main removal path of submicron aerosol particles. Despite the loss, the aerosol particles from wildfire smoke in the stratosphere are relevant for the climate.
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| 25. |
- Martinsson, Bengt G., et al.
(författare)
-
Formation and composition of the UTLS aerosol
- 2019
-
Ingår i: npj Climate and Atmospheric Science. - : Springer Science and Business Media LLC. - 2397-3722. ; 2:1
-
Tidskriftsartikel (refereegranskat)abstract
- Stratospheric aerosol has long been seen as a pure mixture of sulfuric acid and water. Recent measurements, however, found a considerable carbonaceous fraction extending at least 8 km into the stratosphere. This fraction affects the aerosol optical depth (AOD) and the radiative properties, and hence the radiative forcing and climate impact of the stratospheric aerosol. Here we present an investigation based on a decade (2005–2014) of airborne aerosol sampling at 9–12 km altitude in the tropics and the northern hemisphere (NH) aboard the IAGOS-CARIBIC passenger aircraft. We find that the chemical composition of tropospheric aerosol in the tropics differs markedly from that at NH midlatitudes, and, that the carbonaceous stratospheric aerosol is oxygen-poor compared to the tropospheric aerosol. Furthermore, the carbonaceous and sulfurous components of the aerosol in the lowermost stratosphere (LMS) show strong increases in concentration connected with springtime subsidence from overlying stratospheric layers. The LMS concentrations significantly exceed those in the troposphere, thus clearly indicating a stratospheric production of not only the well-established sulfurous aerosol, but also a considerable but less understood carbonaceous component.
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| 26. |
- Martinsson, Bengt G.
(författare)
-
Investigation of particle elastic scattering analysis as a complementary technique to pixe for aerosol characterization
- 1986
-
Ingår i: Nuclear Inst. and Methods in Physics Research, B. - 0168-583X. ; 15:1-6, s. 636-642
-
Tidskriftsartikel (refereegranskat)abstract
- The possibility of analysis by the detection of elastically scattered particles for carbon, nitrogen, oxygen and also hydrogen determination in the fine mode of aerosols has been investigated. The main objectives in this study have been to find suitable projectiles (protons or alpha particles) and projectile energy, in order to obtain separated peaks for the elements of interest and to achieve high analytical sensitivity and precision. Sensitive PIXE analysis should also be obtained on an aerosol substrate suitable for both methods. Relative scattering cross sections at an angle of 170° for protons (3.5-5.8 MeV) and alpha particles (8-9 MeV) on 12C, 14N and 16O have been investigated. Lower and upper energy limits are set by the demand for resolved peaks from C, N and O and the accelerator available, respectively. Protons were found to be the most suitable projectiles and for one proton energy, 3.58 MeV, fulfilling the requirements mentioned above, the possibility for H determination at laboratory scattering angles between 29° and 59° has been investigated. Some aerosol filters and foils have also been investigated at this proton energy in order to find a suitable aerosol substrate. The lowest detection limits were obtained for thin aluminum foils, yielding 15, 10 and 350 ng cm-2 for C, N and O, respectively, and PIXE detection limits comparable to those obtained with a Nuclepore® filter.
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| 27. |
- Martinsson, Bengt G., et al.
(författare)
-
Ion beam thermography - analysis of chemical compounds using ion beam techniques
- 1988
-
Ingår i: Nuclear Inst. and Methods in Physics Research, B. - 0168-583X. ; 34:2, s. 203-208
-
Tidskriftsartikel (refereegranskat)abstract
- The analytical technique of ion beam thermography (IBT) is reported for the first time. IBT is a technique for the determination of chemical compounds. This IBT setup combines the multielemental ion beam technique's particle-induced X-ray emission (PIXE) and particle elastic scattering analysis (PESA) with thermography. A large number of elements are monitored with PIXE (Z > 14) and PESA (hydrogen, carbon, nitrogen and oxygen). The thermographie treatment results in a thermogram for each element. The chemical compounds are inferred from these thermograms. This work describes the experimental setup. The capability of IBT is demonstrated on NH4C1, NH4NO3 and (NH4)2SO4.
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| 28. |
- Martinsson, Bengt G., et al.
(författare)
-
Particulate sulfur in the upper troposphere and lowermost stratosphere - Sources and climate forcing
- 2017
-
Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 17:18, s. 10937-10953
-
Tidskriftsartikel (refereegranskat)abstract
- This study is based on fine-mode aerosol samples collected in the upper troposphere (UT) and the lowermost stratosphere (LMS) of the Northern Hemisphere extratropics during monthly intercontinental flights at 8.8-12 km altitude of the IAGOS-CARIBIC platform in the time period 1999-2014. The samples were analyzed for a large number of chemical elements using the accelerator-based methods PIXE (particle-induced X-ray emission) and PESA (particle elastic scattering analysis). Here the particulate sulfur concentrations, obtained by PIXE analysis, are investigated. In addition, the satellite-borne lidar aboard CALIPSO is used to study the stratospheric aerosol load. A steep gradient in particulate sulfur concentration extends several kilometers into the LMS, as a result of increasing dilution towards the tropopause of stratospheric, particulate sulfur-rich air. The stratospheric air is diluted with tropospheric air, forming the extratropical transition layer (ExTL). Observed concentrations are related to the distance to the dynamical tropopause. A linear regression methodology handled seasonal variation and impact from volcanism. This was used to convert each data point into stand-alone estimates of a concentration profile and column concentration of particulate sulfur in a 3 km altitude band above the tropopause. We find distinct responses to volcanic eruptions, and that this layer in the LMS has a significant contribution to the stratospheric aerosol optical depth and thus to its radiative forcing. Further, the origin of UT particulate sulfur shows strong seasonal variation. We find that tropospheric sources dominate during the fall as a result of downward transport of the Asian tropopause aerosol layer (ATAL) formed in the Asian monsoon, whereas transport down from the Junge layer is the main source of UT particulate sulfur in the first half of the year. In this latter part of the year, the stratosphere is the clearly dominating source of particulate sulfur in the UT during times of volcanic influence and under background conditions.
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| 29. |
- Martinsson, Bengt G.
(författare)
-
Physical basis for a droplet aerosol analysing method
- 1996
-
Ingår i: Journal of Aerosol Science. - : Elsevier BV. - 0021-8502. ; 27:7, s. 997-1013
-
Tidskriftsartikel (refereegranskat)abstract
- A technique for the characterisation of droplet aerosols is presented and theoretically evaluated. The system, which finds applications for example in the experimental study of cloud formation and cloud water chemistry, relies on a four-step process. The droplet aerosol is electrically charged in a unipolar charging unit, followed by diffusion drying of the droplets, resulting in charged particles consisting of non-volatile matter (droplet residues). In the third step, the residual particles are classified by electrostatic spectrometry, and in the final step the residual particles are detected, collected or further characterised. The basic function in respect of the charging process and the particle interaction with water vapour is demonstrated by model calculations, which show that droplets which are activated in a thermodynamical sense can be separated from unactivated droplets. Different strategies for the application of the system are briefly outlined. By measuring two parameters, associated droplet size and residual particle size can be determined. Results from the first field measurement campaign of the resulting instrument are also briefly presented.
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| 30. |
- Martinsson, Bengt G., et al.
(författare)
-
Southern scandinavian aerosol composition and elemental size distribution characteristics dependence on air-mass history
- 1984
-
Ingår i: Atmospheric Environment. - 0004-6981. ; 18:10, s. 2167-2182
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of aerosol long range transport in southern Sweden was investigated from a data base consisting of simultaneous cascade impactor measurements at three sampling stations, two coastal and one inland rural location. The study focused on S and heavy metals determined by particle induced X-ray emission (PIXE) analysis. The influence of local emissions was minimized by eliminating samples which were strongly suspected to be contaminated. These were identified through size distribution alterations in combination with the concentration levels obtained. Based on air mass back trajectories the samples were classified into either a southern, a northern or an eastern sector or into one of the buffer sectors located in between the sectors mentioned above. Sector S elemental concentrations were generally one order of magnitude higher than those of sector N, while intermediate concentrations were found in the E sector. Intercomparisons of simultaneous fine mode elemental concentration measurements classified into sectors S and N, respectively, provides a method for calculating the sector S foreign contribution of the elemental concentrations in southern Sweden. These calculations, not based on emission data, result in a foreign contribution of the order of 50-90 % (lowest for components like V and Ni and highest for Ti, Mn and Zn) to the metal concentrations. The multivariate statistical method SIMCA revealed that the sector S aerosol elemental composition was dependent on particle size in the accumulation mode. Elements such as S and V (or Ni) normally assumed to originate mainly from the same sources (fossil fuel combustion) were clearly separated and instead S clustered with K, Mn and Zn. This indicates that the transformation processes are more important for the covariation of S with other elements than the source origin. Transformation of SO 2 in hygroscopic particles rich in K., Mn and Zn (compared with less hygroscopic particles rich in V and Ni) is a possible mechanism which would explain the results found.
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| 31. |
- Martinsson, Bengt G., et al.
(författare)
-
Validation of very high cloud droplet number concentrations in air masses transported thousands of kilometres over the ocean
- 2000
-
Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - 0280-6509. ; 52:2, s. 801-814
-
Tidskriftsartikel (refereegranskat)abstract
- The microstructure of orographic clouds related to the aerosol present was studied during the second Aerosol Characterisation Experiment (ACE-2). Very high cloud droplet number concentrations (almost 3000 cm -3 ) were observed. These high concentrations occurred when clouds formed on a hill slope at Tenerife in polluted air masses originating in Europe that had transported the order of 1000 km over the Atlantic Ocean. The validity of the measured droplet number concentrations was investigated by comparing with measurements of the aerosol upstream of the cloud and cloud interstitial aerosol. Guided by distributions of the ratios between the measurements, three criteria of typically 30% in maximum deviation were applied to the measurements to test their validity. Agreement was found for 88% of the cases. The validated data set spans droplet number concentrations of 150-3000 cm -3 . The updraught velocity during the cloud formation was estimated to 2.2 m s -1 by model calculations, which is typical of cumuliform clouds. The results of the present study are discussed in relation to cloud droplet number concentrations previously reported in the literature. The importance of promoting the mechanistic understanding of the aerosol/cloud interaction and the use of validation procedures of cloud microphysical parameters is stressed in relation to the assessment of the indirect climatic effect of aerosols.
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| 32. |
- Mentes, Besim, et al.
(författare)
-
Chemical speciation of aerosol samples by ion beam thermography
- 1996
-
Ingår i: Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms. - 0168-583X. ; 109-110, s. 511-518
-
Tidskriftsartikel (refereegranskat)abstract
- Ion beam thermography (IBT) is a technique for the determination of chemical compounds. The IBT setup combines the multielemental ion beam techniques PIXE, PESA, pNRA and cPESA with thermography. During thermography the temperature is gradually increased up to the order of 600 °C, causing vaporisation of chemical compounds at specific temperatures. The combination of methods display low detection limits over practically the whole periodic table, i.e. PIXE: Z > 13, PESA: C, N, O, pNRA: Li, Be, B, F, Na, Mg, cPESA: H. The analysis is undertaken with an external beam. The thermographic treatment results in a thermogram for each element i.e. the concentration as a function of the temperature of the sample. The chemical compounds are identified by the vaporisation temperature and the stoichiometric relations between the elements vaporised at that temperature. This work deals with technical improvements of the setup and evaluates the dependence on the rate of temperature increase of the vaporisation temperature of chemical compounds. An atmospheric aerosol sample was analysed to demonstrate the capabilities of this combination of IBA methods in atmospheric aerosol research. All major and several minor elements of the sample could be determined, the major inorganic compounds could be speciated and the carbonaceous constituents could be classified according to volatility.
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| 33. |
- Olabanji, Simon O., et al.
(författare)
-
Inner-shell ionization processes in low Z (Z ≤ 20) elements by proton bombardment
- 1987
-
Ingår i: Nuclear Inst. and Methods in Physics Research, B. - 0168-583X. ; 24-25:PART 1, s. 81-84
-
Tidskriftsartikel (refereegranskat)abstract
- K-shell X-ray ionization cross section from thin targets of P, S, Cl, K and Ca by proton impact in the energy range of 1.0-5.0 MeV are reported using a Si(Li) detector. Our experimental results are compared with previous very scanty available data and with ECPSSR theory. Data for P are reported for the first time. Results for S, Cl and K in this wide energy range are also new data. Our results show very good agreement with those of other authors and ECPSSR theory.
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| 34. |
- Sandvik, Oscar S., et al.
(författare)
-
Intercomparison of in-situ aircraft and satellite aerosol measurements in the stratosphere
- 2019
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- Aerosol composition and optical scattering from particles in the lowermost stratosphere (LMS) have been studied by comparing in-situ aerosol samples from the IAGOS-CARIBIC passenger aircraft with vertical profiles of aerosol backscattering obtained from the CALIOP lidar aboard the CALIPSO satellite. Concentrations of the dominating fractions of the stratospheric aerosol, being sulphur and carbon, have been obtained from post-flight analysis of IAGOS-CARIBIC aerosol samples. This information together with literature data on black carbon concentrations were used to calculate the aerosol backscattering which subsequently is compared with measurements by CALIOP. Vertical optical profiles were taken in an altitude range of several kilometres from and above the northern hemispheric extratropical tropopause for the years 2006-2014. We find that the two vastly different measurement platforms yield different aerosol backscattering, especially close to the tropopause where the influence from tropospheric aerosol is strong. The best agreement is found when the LMS is affected by volcanism, i.e., at elevated aerosol loadings. At background conditions, best agreement is obtained some distance (>2 km) above the tropopause in winter and spring, i.e., at likewise elevated aerosol loadings from subsiding aerosol-rich stratospheric air. This is to our knowledge the first time the CALIPSO lidar measurements have been compared to in-situ long-term aerosol measurements.
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| 35. |
- Sandvik, Oscar S., et al.
(författare)
-
Methodology to obtain highly resolved SO2 vertical profiles for representation of volcanic emissions in climate models
- 2021
-
Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 14:11, s. 7153-7165
-
Tidskriftsartikel (refereegranskat)abstract
- In this study we describe a methodology to create high-vertical-resolution SO2 profiles from volcanic emissions. We demonstrate the method's performance for the volcanic clouds following the eruption of Sarychev in June 2009. The resulting profiles are based on a combination of satellite SO2 and aerosol retrievals together with trajectory modelling. We use satellite-based measurements, namely lidar backscattering profiles from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite instrument, to create vertical profiles for SO2 swaths from the Atmospheric Infrared Sounder (AIRS) aboard the Aqua satellite. Vertical profiles are created by transporting the air containing volcanic aerosol seen in CALIOP observations using the FLEXible PARTicle dispersion model (FLEXPART) while preserving the high vertical resolution using the potential temperatures from the MERRA-2 (Modern-Era Retrospective analysis for Research and Application) meteorological data for the original CALIOP swaths. For the Sarychev eruption, air tracers from 75 CALIOP swaths within 9g d after the eruption are transported forwards and backwards and then combined at a point in time when AIRS swaths cover the complete volcanic SO2 cloud. Our method creates vertical distributions for column density observations of SO2 for individual AIRS swaths, using height information from multiple CALIOP swaths. The resulting dataset gives insight into the height distribution in the different sub-clouds of SO2 within the stratosphere. We have compiled a gridded high-vertical-resolution SO2 inventory that can be used in Earth system models, with a vertical resolution of 1g K in potential temperature, 61g g 56g m, or 1.8g g 2.9g mbar.
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| 36. |
- Schönherr, Christina, et al.
(författare)
-
Anaplastic Lymphoma Kinase (ALK) regulates initiation of transcription of MYCN in neuroblastoma cells
- 2012
-
Ingår i: Oncogene. - : Springer Science and Business Media LLC. - 0950-9232 .- 1476-5594. ; 31:50, s. 5193-5200
-
Tidskriftsartikel (refereegranskat)abstract
- Neuroblastoma is a neural crest-derived embryonal tumour of the postganglionic sympathetic nervous system and a disease with several different chromosomal gains and losses, which include MYCN-amplified neuroblastoma on chromosome 2, deletions of parts of the chromosomes 1p and 11q, gain of parts of 17q and triploidy. Recently, activating mutations of the ALK (Anaplastic Lymphoma Kinase) RTK (Receptor Tyrosine Kinase) gene have been described in neuroblastoma. A meta-analysis of neuroblastoma cases revealed that ALK mutations (49 of 709 cases) in relation to genomic subtype were most frequently observed in MYCN amplified tumours (8.9%), correlating with a poor clinical outcome. MYCN proteins target proliferation and apoptotic pathways, and have an important role in the progression of neuroblastoma. Here, we show that both wild-type and gain-of-function mutants in ALK are able to stimulate transcription at the MYCN promoter and initiate mRNA transcription of the MYCN gene in both neuronal and neuroblastoma cell lines. Further, this stimulation of MYCN gene transcription and de novo MYCN protein expression is abrogated by specific ALK inhibitors, such as crizotinib (PF-2341066), NVP-TAE684, and by small interfering RNA to ALK resulting in a decrease in proliferation rate. Finally, co-transfection of ALK gain-of-function mutations together with MYCN leads to an increase in transformation potential. Taken together, our results indicate that ALK signalling regulates initiation of transcription of the MYCN gene providing a possible explanation for the poor clinical outcome observed when MYCN is amplified together with activated ALK.
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| 37. |
- Siaw, Joachim T., et al.
(författare)
-
11q Deletion or ALK Activity Curbs DLG2 Expression to Maintain an Undifferentiated State in Neuroblastoma
- 2020
-
Ingår i: Cell Reports. - : Elsevier BV. - 2211-1247. ; 32:12
-
Tidskriftsartikel (refereegranskat)abstract
- High-risk neuroblastomas typically display an undifferentiated or poorly differentiated morphology. It is therefore vital to understand molecular mechanisms that block the differentiation process. We identify an important role for oncogenic ALK-ERK1/2-SP1 signaling in the maintenance of undifferentiated neural crest-derived progenitors through the repression of DLG2, a candidate tumor suppressor gene in neuroblastoma. DLG2 is expressed in the murine "bridge signature'' that represents the transcriptional transition state when neural crest cells or Schwann cell precursors differentiate to chromaffin cells of the adrenal gland. We show that the restoration of DLG2 expression spontaneously drives neuroblastoma cell differentiation, high-lighting the importance of DLG2 in this process. These findings are supported by genetic analyses of high-risk 11q deletion neuroblastomas, which identified genetic lesions in the DLG2 gene. Our data also suggest that further exploration of other bridge genes may help elucidate the mechanisms underlying the differentiation of NC-derived progenitors and their contribution to neuroblastomas.
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| 38. |
- Slemr, Franz, et al.
(författare)
-
Mercury distribution in the upper troposphere and lowermost stratosphere according to measurements by the IAGOS-CARIBIC observatory : 2014-2016
- 2018
-
Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 18:16, s. 12329-12343
-
Tidskriftsartikel (refereegranskat)abstract
- Mercury was measured onboard the IAGOS-CARIBIC passenger aircraft from May 2005 until February 2016 during near monthly sequences of mostly four intercontinental flights from Germany to destinations in North and South America, Africa and South and East Asia. Most of these mercury data were obtained using an internal default signal integration procedure of the Tekran instrument but since April 2014 more precise and accurate data were obtained using post-flight manual integration of the instrument raw signal. In this paper we use the latter data. Increased upper tropospheric total mercury (TM) concentrations due to large scale biomass burning were observed in the upper troposphere (UT) at the equator and southern latitudes during the flights to Latin America and South Africa in boreal autumn (SON) and boreal winter (DJF). TM concentrations in the lowermost stratosphere (LMS) decrease with altitude above the thermal tropopause but the gradient is less steep than reported before. Seasonal variation of the vertical TM distribution in the UT and LMS is similar to that of other trace gases with surface sources and stratospheric sinks. Speciation experiments suggest comparable TM and gaseous elementary mercury (GEM) concentrations at and below the tropopause leaving little space for Hg2+ (TM-thinsp;GEM) being the dominating component of TM here. In the stratosphere significant GEM concentrations were found to exist up to 4 km altitude above the thermal tropopause. Correlations with N2O as a reference tracer suggest stratospheric lifetimes of 72±37 and 74±27 years for TM and GEM, respectively, comparable to the stratospheric lifetime of COS. This coincidence, combined with pieces of evidence from us and other researchers, corroborates the hypothesis that Hg2+ formed by oxidation in the stratosphere attaches to sulfate particles formed mainly by oxidation of COS and is removed with them from the stratosphere by air mass exchange, gravitational sedimentation and cloud scavenging processes.
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| 39. |
- Swietlicki, Erik, et al.
(författare)
-
A closure study of sub-micrometer aerosol particle hygroscopic behaviour
- 1999
-
Ingår i: Atmospheric Research. - 0169-8095. ; 50:3-4, s. 205-240
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 40. |
- Swietlicki, Erik, et al.
(författare)
-
Hygroscopic properties of aerosol particles in the northeastern Atlantic during ACE-2
- 2000
-
Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 52:2, s. 201-227
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of the hygroscopic properties of sub-micrometer atmospheric aerosol particles were performed with hygroscopic tandem differential mobility analysers (H-TDMA) at 5 sites in the subtropical north-eastern Atlantic during the second Aerosol Characterization Experiment (ACE-2) from 16 June to 25 July 1997. Four of the sites were in the marine boundary layer and one was, at least occasionally, in the lower free troposphere. The hygroscopic diameter growth factors of individual aerosol particles in the dry particle diameter range 10-440 nm were generally measured for changes in relative humidity (RH) from <10% to 90%. In the marine boundary layer, growth factors at 90% RH were dependent on location, air mass type and particle size. The data was dominated by a unimodal growth distribution of more-hygroscopic particles, although a bimodal growth distribution including less-hygroscopic particles was observed at times, most often in the more polluted air masses. In clean marine air masses the more-hygroscopic growth factors ranged from about 1.6 to 1.8 with a consistent increase in growth factor with increasing particle size. There was also a tendency toward higher growth factors as sodium to sulphate molar ratio increased with increasing sea-salt contribution at higher wind speeds. During outbreaks of European pollution in the ACE-2 region, the growth factors of the largest particles were reduced, but only slightly. Growth factors at all sizes in both clean and polluted air masses were markedly lower at the Sagres, Portugal site due to more proximate continental influences. The frequency of occurrence of less-hygroscopic particles with a growth factor of ca. 1.15 was greatest during polluted conditions at Sagres. The free tropospheric 50 nm particles were predominately less-hygroscopic, with an intermediate growth factor of 1.4, but more-hygroscopic particles with growth factors of about 1.6 were also frequent. While these particles probably originate from within the marine boundary layer, the less-hygroscopic particles are probably more characteristic of lower free tropospheric air masses. For those occasions when measurements were made at 90% and an intermediate 60% or 70% RH, the growth factor G(RH) of the more-hygroscopic particles could be modelled empirically by a power law expression. For the ubiquitous more-hygroscopic particles, the expressions G(RH) = (1 - RH/100)-0.210 for 50 nm Aitken mode particles and G(RH) = (1 - RH/100)-0.233 for 166 nm accumulation mode particles are recommended for clean marine air masses in the north-eastern Atlantic within the range 0 < RH < 95%, and for wind speeds for which the local sea-salt production is small (< ca. 8 m s-1).
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| 41. |
- Swietlicki, Erik, et al.
(författare)
-
PIXE elemental characterization of air masses using a multivariate statistical technique
- 1987
-
Ingår i: Nuclear Inst. and Methods in Physics Research, B. - 0168-583X. ; 22:1-3, s. 264-269
-
Tidskriftsartikel (refereegranskat)abstract
- An example is given to show the possibility of using a multivariate statistical evaluation technique in order to extract more information from a multielemental PIXE data set. Four weeks of continuous sampling was carried out at a background air pollution monitoring station in Sweden. Samples were collected both in fine and coarse mode, with a cutoff at 2 μm. In the subsequent PIXE analysis of the samples, 12-16 elements were detected in the fine fraction and 9-12 elements in the coarse fraction. The fine fraction PIXE data was further analysed using the multivariate statistical programme package SIMCA, which combines a pattern recognition technique and principal component analysis. Based on 1000 mbar back trajectories for the sampling period, principal component class models were constructed for Easterly and North-Westerly air masses using 15 elements (S, K, Ca, Ti, V. Cr, Mn, Fe, Ni, Cu, Zn, Ga. As, Br and Pb). For these elements, mean concentration values and standard deviations for the two classes are given. A methodology is presented which excluded outliers and facilitated the calculation of classes with a restricted and definable data distribution representative of the elemental composition of the air masses originating from the two source regions.
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| 42. |
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| 43. |
- Vernier, J. -P., et al.
(författare)
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Increase in upper tropospheric and lower stratospheric aerosol levels and its potential connection with Asian pollution
- 2015
-
Ingår i: Journal of Geophysical Research: Atmospheres. - 2169-8996. ; 120:4, s. 1608-1619
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Tidskriftsartikel (refereegranskat)abstract
- Satellite observations have shown that the Asian Summer Monsoon strongly influences the upper troposphere and lower stratosphere (UTLS) aerosol morphology through its role in the formation of the Asian Tropopause Aerosol Layer (ATAL). Stratospheric Aerosol and Gas Experiment II solar occultation and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) lidar observations show that summertime UTLS Aerosol Optical Depth (AOD) between 13 and 18 km over Asia has increased by three times since the late 1990s. Here we present the first in situ balloon measurements of aerosol backscatter in the UTLS from Western China, which confirm high aerosol levels observed by CALIPSO since 2006. Aircraft in situ measurements suggest that aerosols at lower altitudes of the ATAL are largely composed of carbonaceous and sulfate materials (carbon/sulfur elemental ratio ranging from 2 to 10). Back trajectory analysis from Cloud-Aerosol Lidar with Orthogonal Polarization observations indicates that deep convection over the Indian subcontinent supplies the ATAL through the transport of pollution into the UTLS. Time series of deep convection occurrence, carbon monoxide, aerosol, temperature, and relative humidity suggest that secondary aerosol formation and growth in a cold, moist convective environment could play an important role in the formation of ATAL. Finally, radiative calculations show that the ATAL layer has exerted a short-term regional forcing at the top of the atmosphere of -0.1 W/m(2) in the past 18 years.
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| 44. |
- Wendish, Manfred, et al.
(författare)
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Drop size distribution and LWC in Po valley fog
- 1998
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Ingår i: Contributions to Atmospheric Physics. - 0005-8173. ; 71:1, s. 87-100
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Tidskriftsartikel (refereegranskat)abstract
- In this paper results are presented of ground-based fog microphysical measurements obtained during the CHEMDROP experiment in the Po Valley (Northern Italy) in November 1994. Altogether about 85 hours of drop microphysical data are analyzed. At the beginning of the experiment a comparison of some of the different microphysical instruments, operated during the experiment, was performed. It has revealed some differences between the Liquid Water Content LWC measured by Particle Volume Monitors (PVMs), and by several Forward Scattering Spectrometer Probes (FSSPs). Possible explanations for the discrepancies are discussed. The FSSP derived drop size distributions (number and mass) were parameterized in terms of log-normal distributions. The statistical analysis of the fittings has shown that the overwhelming majority of the drop mass size distributions was characterized by a bimodal shape. The most frequent values of the mode parameters (median diameter, geometric standard deviation) are given in Table 3 of this paper. An investigation of the temporal evolution of the drop size distribution revealed two typical phases of fog formation. In the first step both modes of the drop mass size distribution increase more or less uniform, whereas in the second phase the large drop mode drastically rises. Furthermore, the second phase is characterized by quasi-periodic oscillations in nearly all mode parameters of the drop size distribution with a period between ten and 15 minutes. In the last part of the paper the frequent occurrence of drizzle within the fog was studied by comparing the measurements with respective model calculations.
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| 45. |
- Yuskiewicz, Brett A., et al.
(författare)
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Changes in submicrometer particle distributions and light scattering during haze and fog events in a highly polluted environment
- 1998
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Ingår i: Contributions to Atmospheric Physics. - 0005-8173. ; 71:1, s. 33-45
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Tidskriftsartikel (refereegranskat)abstract
- The changes in submicrometer atmospheric particle size distributions measured with a Differential Mobility Particle Sizer (DMPS) system during a polluted fog experiment during November, 1994 are presented in this study. Results reveal three modes commonly evident in the size distribution (3 < DN < 843 nm) measurements; the ultrafine, Aitken and accumulation with respective geometric diameters, (Dgn), of 17, 110 and 400 nm. An additional mode, appears between the ultrafine and Aitken modes (Dgn = 52 nm) in approximately one quarter of the measurements and is linked to several industrial cities upwind of the measurement site. A stabile ultrafine mode appears consistently (84% of measurements) at 16-17 nm throughout the campaign, suggestive of a source, such as a highway in the near vicinity. During fog and haze periods number concentrations for particles less than 25 nm and greater than 400 nm decrease by 78 and 95%, respectively. These changes do not affect the aerosol scattering efficiency significantly. The overall aerosol mass scattering efficiency determined for the Po Valley region is 4.3 ± 0.6 m2 g-1. Closure is achieved for light extinction predicted from droplet distributions and measured with a transmissiometer in 37 of 39 cases during fog periods. Measured and calculated light extinction, bext, covary strongly with an R2 of 0.92.
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