The summer aerosol in the central Arctic 1991–2008: did it change or not?

In the course of global warming dramatic changes are taking place in the Arctic and boreal environments. However, physical aerosol data in from the central summer Arctic taken over the course of 18 yr from 1991 to 2008 do not show systematic year-to-year changes, albeit substantial interannual variations. Besides the limited extent of the data several causes may be responsible for these findings. The processes controlling concentrations and particle size distribution of the aerosol over the central Arctic perennial pack ice area, north of 80°, may not have changed substantially during this time. Environmental changes are still mainly effective in the marginal ice zone, the ice-free waters and continental rims and have not propagated significantly into the central Arctic yet where they could affect the local aerosol and its sources. The analysis of meteorological conditions of the four expedition summers reveal substantial variations which we see as main causes of the measured variations in aerosol parameters. With combined lognormal fits of the hourly number size distributions of the four expeditions representative mode parameters for the summer aerosol in the central Arctic have been calculated. The combined aerosol statistics discussed in the present paper provide comprehensive physical data on the summer aerosol in the central Arctic. These data are the only surface aerosol information from this region

The summer aerosol in the central Arctic 1991-2008: Did it change or not?

In the course of global warming dramatic changes are taking place in the Arctic and boreal environments. However, physical aerosol data in from the central summer Arctic taken over the course of 18 yr from 1991 to 2008 do not show systematic year-to-year changes, albeit substantial interannual variations. Besides the limited extent of the data several causes may be responsible for these findings. The processes controlling concentrations and particle size distribution of the aerosol over the central Arctic perennial pack ice area, north of 80°, may not have changed substantially during this time. Environmental changes are still mainly effective in the marginal ice zone, the ice-free waters and continental rims and have not propagated significantly into the central Arctic yet where they could affect the local aerosol and its sources. The analysis of meteorological conditions of the four expedition summers reveal substantial variations which we see as main causes of the measured variations in aerosol parameters. With combined lognormal fits of the hourly number size distributions of the four expeditions representative mode parameters for the summer aerosol in the central Arctic have been calculated. The combined aerosol statistics discussed in the present paper provide comprehensive physical data on the summer aerosol in the central Arctic. These data are the only surface aerosol information from this region

Out of Africa: High aerosol concentrations in the upper troposphere over Africa

International audienceIn the year 2000, six flights (three southbound and three northbound) of the CARIBIC project were conducted between Germany and two destinations in the southern hemisphere (Windhoek, Namibia and Cape Town, South Africa). In the present report, results on particle number concentrations are discussed in three size ranges (>4 nm, >12 nm, and >18 nm particle diameter) during the unique transequatorial Africa flights. The flights covered a total of about 80 h in May, July, and December. Thus, no claim can be made for long-term representativeness of the aerosol data. Nevertheless, they are the first upper systematic tropospheric transequatorial aerosol profiles over Africa. The average aerosol results show a broad maximum, roughly symmetrical to the equator, which compares well in latitudinal extent to a maximum of CO concentrations measured on the same flights. This export of continental surface aerosol to the upper troposphere will be dispersed on a global scale both with the easterly flow near the equator and with the westerlies in the adjacent subtropical regions. There was strong evidence of recent new particle formation before aerosol arrival at flight level, in particular during the time periods between 9:00 and 13:00 local time over Africa. Direct and indirect climate effects of the respective particulate matter remain to be investigated by future flights with the ongoing extension of the CARIBIC payload towards size-resolved measurements above 100 nm particle diameter. At the same time global chemical transport models and aerosol dynamics models need to be extended to be able to reproduce the CARIBIC findings over Africa

An overview of the ACE-2 clear sky column closure experiment (CLEARCOLUMN)

As 1 of 6 focused ACE-2 activities, a clear sky column closure experiment (CLEARCOLUMN) took place in June/July 1997 at the southwest corner of Portugal, in the Canary Islands, and over the eastern Atlantic Ocean surrounding and linking those sites. Overdetermined sets of volumetric, vertical profile and columnar aerosol data were taken from the sea surface to~5 km asl by samplers and sensors at land sites (20–3570 m asl), on a ship, and on 4 aircraft. In addition, 5 satellites measured upwelling radiances used to derive properties of the aerosol column. Measurements were made in a wide range of conditions and locations (e.g., the marine boundary layer with and without continental pollution, the free troposphere with and without African dust). Numerous tests of local and column closure, using unidisciplinary and multidisciplinary approaches, were conducted. This paper summarizes the methodological approach, the experiment sites and platforms, the types of measurements made on each, the types of analyses conducted, and selected key results, as a guide to the more complete results presented in other papers in this special issue and elsewhere. Example results include determinations of aerosol single scattering albedo by several techniques, measurements of hygroscopic effects on particle light scattering and size, and a wide range in the degree of agreement found in closure tests. In general, the smallest discrepancies were found in comparisons among (1) different techniques to measure an optical property of the ambient, unperturbed aerosol (e.g., optical depth, extinction, or backscatter by sunphotometer, lidar, and/or satellite) or (2) different techniques to measure an aerosol that had passed through a common sampling process (e.g., nephelometer and size spectrometer measurements with the same or similar inlets, humidities and temperatures). Typically, larger discrepancies were found between techniques that measure the ambient, unperturbed aerosol and those that must reconstruct the ambient aerosol by accounting for (a) processes that occur during sampling (e.g., aerodynamic selection, evaporation of water and other volatile material) or ( b) calibrations that depend on aerosol characteristics (e.g., sizedependent density or refractive index). A primary reason for the discrepancies in such cases is the lack of validated hygroscopic growth models covering the necessary range of particle sizes and compositions. Other common reasons include (1) using analysis or retrieval techniques that assume aerosol properties (e.g., density, single scattering albedo, shape) that do not apply in all cases and (2) using surface measurements to estimate column properties. Taken together, the ACE-2 CLEARCOLUMN data set provides a large collection of new information on the properties of the aerosol over the northeast Atlantic Ocean. CLEARCOLUMN studies have also pointed to improved techniques for analyzing current and future data sets (including satellite data sets) which will provide a more accurate and comprehensive description of the Atlantic–European–African aerosol. Thus they set the stage for an improved regional quantification of radiative forcing by anthropogenic aerosols

Out of Africa: High aerosol concentrations in the upper troposphere over Africa

In the year 2000, six flights (three southbound and three northbound) of the CARIBIC project were conducted between Germany and two destinations in the southern hemisphere (Windhoek, Namibia and Cape Town, South Africa). In the present report, results on particle number concentrations are discussed in three size ranges (>4 nm, >12 nm, and >18 nm particle diameter) during the unique transequatorial Africa flights. The flights covered a total of about 80 h in May, July, and December. Thus, no claim can be made for long-term representativeness of the aerosol data. Nevertheless, they are the first upper systematic tropospheric transequatorial aerosol profiles over Africa. The average aerosol results show a broad maximum, roughly symmetrical to the equator, which compares well in latitudinal extent to a maximum of CO concentrations measured on the same flights. This export of continental surface aerosol to the upper troposphere will be dispersed on a global scale both with the easterly flow near the equator and with the westerlies in the adjacent subtropical regions. There was strong evidence of recent new particle formation before aerosol arrival at flight level, in particular during the time periods between 9:00 and 13:00 local time over Africa. Direct and indirect climate effects of the respective particulate matter remain to be investigated by future flights with the ongoing extension of the CARIBIC payload towards size-resolved measurements above 100 nm particle diameter. At the same time global chemical transport models and aerosol dynamics models need to be extended to be able to reproduce the CARIBIC findings over Africa

Potential source regions and processes of aerosol in the summer Arctic

Sub-micrometer particle size distributions measured during four summer cruises of the Swedish icebreaker Oden 1991, 1996, 2001, and 2008 were combined with dimethyl sulfide gas data, back trajectories, and daily maps of pack ice cover in order to investigate source areas and aerosol formation processes of the boundary layer aerosol in the central Arctic. With a clustering algorithm, potential aerosol source areas were explored. Clustering of particle size distributions together with back trajectories delineated five potential source regions and three different aerosol types that covered most of the Arctic Basin: marine, newly formed and aged particles over the pack ice. Most of the pack ice area with < 15% of open water under the trajectories exhibited the aged aerosol type with only one major mode around 40 nm. For newly formed particles to occur, two conditions had to be fulfilled over the pack ice: the air had spent 10 days while traveling over ever more contiguous ice and had traveled over less than 30% open water during the last 5 days. Additionally, the air had experienced more open water (at least twice as much as in the cases of aged aerosol) during the last 4 days before arrival in heavy ice conditions at Oden. Thus we hypothesize that these two conditions were essential factors for the formation of ultrafine particles over the central Arctic pack ice. In a comparison the Oden data with summer size distribution data from Alert, Nunavut, and Mt. Zeppelin, Spitsbergen, we confirmed the Oden findings with respect to particle sources over the central Arctic. Future more frequent broken-ice or open water patches in summer will spur biological activity in surface water promoting the formation of biological particles. Thereby low clouds and fogs and subsequently the surface energy balance and ice melt may be affected

Size distribution and chemical composition of marine aerosols: A compilation and review

Some 30 years of physical and chemical marine aerosol data are reviewed to derive global-size distribution parameters and inorganic particle composition on a coarse 15°×15° grid. There are large gaps in geographical and seasonal coverage and chemical and physical aerosol characterisation. About 28% of the grid cells contain physical data while there are compositional data in some 60% of the cells. The size distribution data were parametrized in terms of 2 submicrometer log-normal distributions. The sparseness of the data did not allow zonal differentiation of the distributions. By segregating the chemical data according to the major aerosol sources, sea salt, dimethylsulfide, crustal material, combustion processes and other anthropogenic sources, much information on mass concentrations and contribution of natural and anthropogenic sources to the marine aerosol can be gleaned from the data base. There are significant meridional differences in the contributions of the different sources to the marine aerosol. Very clearly, we see though that the global marine surface atmosphere is polluted by anthropogenic sulfur. Only in the case of sulfur components did the coverage allow the presentation of very coarse seasonal distributions which reflect the spring blooms in the appropriate parts of the oceans. As an example of the potential value in comparing the marine aerosol data base to chemical transport models, global seasonal meridional MSA distributions were compared to modelled MSA distributions. The general good agreement in mass concentrations is encouraging while some latitudinal discrepancies warrant further investigations covering other aerosol components such as black carbon and metals

The atmospheric aerosol over Siberia, as seen from the 300 m ZOTTO tower

This report describes a unique setup for aerosol measurements at the new long-term Tall Tower monitoring facility near Zotino, Siberia (ZOTTO). Through two inlets at 50 and 300 m aerosol particle number size distributions are measured since September 2006 in the size range 15–835 nanometer dry diameter. Until the end of May 2007 total number (N300) concentrations at 300 m height ranged between 400 cm-3 (5%) and 4000 cm-3 (95%) with a median of 1200 cm-3, which is rather high for a nearly uninhabited boreal forest region during the low productivity period of the year. Fitting 1-h average distributions with a maximum of four lognormal functions yielded frequent ultrafine modes below 20 nm at 50 m height than at 300 m, whereas the latter height more frequently showed an aged nucleation mode near 30 nm. The positions of Aitken (≈80 nm) and accumulation modes (≈210 nm) were very similar at both inlet heights, the very sharp latter one being the most frequent of all modes. The encouraging first results let us expect exciting newfindings during the summer period with frequent forest fires and secondary particle sources from vegetation emissions

Marine nanogels as a source of atmospheric nanoparticles in the high Arctic

The high Arctic (north of 80°N) in summer is a region characterized by clean air and low abundances of preexisting particles. Marine colloidal nanogels i.e., assembled dissolved organic carbohydrate polymer networks have recently been confirmed to be present in both airborne particles and cloud water over the Arctic pack ice area. A novel route to atmospheric nanoparticles that appears to be operative in the high Arctic is suggested. It involves the injection of marine granular nanogels into the air from evaporating fog and cloud droplets, and is supported by observational and theoretical evidence obtained from a case study. Statistical analysis of the aerosol size distribution data recorded in the years 1991, 1996, 2001, and 2008 classified 75 nanoparticle events - covering 17% of the observed time period - as nanogel-type events, characterized by the spontaneous appearance of several distinct size bands below 200 nm diameter

Comparison of the mechanical solidity of soldered and differently laser welded test specimens from a Palladium based alloy before and after six months of chemical stress.

Titel   Inhaltsverzeichnis IV 1\. Einleitung 1 2\. Schrifttum 3 3\. Material und Methode 26 4\. Ergebnisse 14 5\. Diskussion 65 6\. Zusammenfassung 73 7\. Summary 75 8\. Literaturverzeichnis 77 9\. Anhang 87   Danksagung 108   Curriculum vitae 109In der vorliegenden Studie sollte ein Vergleich der mechanischen Festigkeit von gelöteten und verschiedenartig zusammen gelaserten Prüfkörpern aus einer Palladiumbasis-Legierung vor und nach sechsmonatiger chemischer Belastung vorgenommen werden. Im Vakuum-Druck-Guss-Verfahren sind 80 DIN- gerechte Prüfkörper aus der Palladiumbasis-Legierung BegoPal® 300 hergestellt worden. 3 der 10 Serien entstanden aus 5-mal vergossenem Altmetall, die restlichen aus reinem Neumetall. Nach visueller Überprüfung der Prüfkörper erfolgte das Trennen und Zusammenfügen für das jeweils zu testende Fügeverfahren. Serie 3 und 4 (beide aus Neumetall) wurden mit Hilfe von Flamme und Lot zusammengelötet, Serie 5 und 6 aus Neumetall wurden Stoß auf Stoß unter Verwendung eines Lasers sowie in Vorversuchen festgelegter Laserparameterkombinationen von 0,6 mm Fleckdurchmesser, einer Spannung von 310 V sowie einer Impulsdauer von 11,5 ms verschweißt. Die Serien 7 und 8 wurden genauso verschweißt wie Serie 5 und 6, sie bestanden jedoch aus Altmetall. Für die Serien 9 und 10 aus Neumetall, die wie alle übrigen Serien mittig getrennt, aber noch zusätzlich dachfirstartig abgeflacht wurden, wurde zum Zusammenfügen eine Lehre sowie Zulegematerial verwendet. Die Laserparameter wurden für diesen Fügevorgang nicht verändert. Von allen Serien erfolgte eine durch Mikrohärteeindruck nach VICKERS mit 10 Messpunkten festgelegte EDX-Analyse an der Fügezone, anschließend eine Einlagerung der Serien 4, 6 ,8 und 10 für 6 Monate in Kunstspeichel sowie ein erneuter EDX- Analyse-Vorgang nach chemischer Belastung. So wurden 100 EDX-Messwerte erstellt. Im Zugversuch nach DIN EN 10002: 1991 sind zunächst die ungefügten Serien 1 (Neumetall) und 2 (Altmetall), ohne chemische Belastung erfahren zu haben, auf ihre Zugfestigkeit überprüft worden. Es sind so Vergleichswerte für die zu testenden Fügemethoden erstellt worden. Mittelwertig ergaben sich Zugfestigkeitswerte von 829 MPa und 838 MPa für die Serien 1 und 2. Die gelöteten Serien erreichten davon 42 % (349 ± 64 MPa) bzw., nach Einlagerung in Kunstspeichel, 40 % der Zugfestigkeit der Serie 1. Alle gelöteten Prüfkörper rissen in der Lotnaht. Die Serien 5 und 6 aus Neumaterial erreichten sowohl vor als auch nach Einlagerung in Kunstspeichel mit 77 % - 82 % sehr gute Zugfestigkeitergebnisse. Ebenso die mit Zulegematerial gelaserten Prüfkörper, die 78 % vor und 69 % nach chemischer Belastung erreichen. Die lichtmikroskopischen Untersuchungen der im Zugversuch entstandenen Bruchflächen zeigten lunkerige Oberflächen der gelöteten Serien, jedoch keine Korrosionserscheinungen. Bei den gelaserten Prüfkörpern zeigten sich Gaslunker sowie teilweise unvollständig durchschweißte Zonen. Es konnten jedoch auch homogene Oberflächen gefunden werden. Die Zugfestigkeit wurde trotz Gaslunker im Vergleich zu homogenen Oberflächen nicht wesentlich erniedrigt. Alle gelaserten Prüfkörper rissen jedoch auch in der Fügezone. Die durchgeführte EDX-Analyse zeigte bei den gelaserten Prüfkörpern nach der Einlagerungszeit so gut wie keine Veränderung der Haftoxide an der Probenoberfläche. Die Elementverteilung auf den gelöteten Oberflächen wies schon vor chemischer Belastung erhebliche Unterschiede im Vergleich zu den ungefügten Prüfkörpern auf. Festgestellt werden konnte, dass keine der ausgewählten Fügemethoden unter den für gelötete Prüfkörper geforderten 350 MPa für Zugfestigkeit lag. In Bezug auf die Zugfestigkeit ist das Lasern, und hier vor allem das Stoß auf Stoß Lasern, dem Löten vorzuziehen, da auch bei unroutiniertem Gebrauch mit einem Laser höhere und nicht nur der Norm zu erfüllende Zugfestigkeitsergebnisse erzielt werden.The submitted study is about the comparison of the mechanical solidity of soldered and differently laser welded test specimens from a Palladium based alloy before and after six months of chemical stress. By vacuum-pressure- technique 80 DIN meeting test specimens have been produced from the Palladium alloy BegoPal® 300. 3 of the 10 series originated from five times cast reused metal, the remaining from pure new metal. After visual check of the test specimens, separating and linking took place for the respective method of fusion to tested. Series 3 and 4, both from metal, was soldered with the help of the flame and solder. Series 5 and 6 from new metal were welded together (butt joint) under application of a laser with in pilot tests found laser- parameter-combination of 0,6 mm diameters, tension of 310 V, and impulse- duration of 11,5 ms. The series 7 and 8 were equally treated like the 5 and 6 series, but consisted of reused metal however. The series 9 and 10 from new metal were cut symmetrical too, but also roof-ridge like, and a gauge was used as well as additional material for welding. The laser parameter were not changed for this fusion. All series were tested in the zone of fusion through an EDX-analysis, determined with micro-temper-stress-marks after Vickers with 10 measuring points. After the series 4, 6, 8, and 10 were stored for 6 month in artificial saliva, these series were again tested through EDX-analysis after this chemical stress. Altogether 100 EDX test results were established. First of all, a tension test after DIN EN 10002: 1991 was applied to the genuine series 1 (new metal) and 2 (reused metal) to establish a standard of comparison. The tension-resistance-factor for the series 1 and 2 reached an average of 829 MPa and 838 MPa. The soldered series achieved 42 % of these results (349 ± 64 MPa), respectively after treatment with artificial saliva 40 % of the results of the genuine series1. All soldered test specimens broke in the soldered seam. The series 5 and 6 (new metal) achieved not only before, but also after the treatment with artificial saliva very good tension-test results of 77 % - 82 %, as well as the additional material laser welded test specimens, which achieved 77 % before and 69% after chemical stress (artificial saliva). The light-microscopic examinations of the fracture- surface after the tests showed surfaces with shrinkholes on the soldered series, but no corrosion. The laser-welded series showed gas-shrinkholes and zones of incomplete welding. However, homogeneous surface could be found too. The resistance was not essentially lowered despite gas-shrinkholes in comparison to homogenous surfaces. All by laser welded test specimens broke, however, in the seam also. The applied EDX-analysis showed on the laser-welded specimens after the chemical treatment (artificial saliva) basically no change of the adhesive oxides on the surface. The element-distribution on the soldered surface showed considerably differences in comparison to the genuine test specimens already before the chemical treatment with artificial saliva. With reference to the tensile strength, the laser welding, and here above all the butt joint method, has to be preferred to soldering, under consideration that even the untrained use of laser welding results in higher and not only with standards complying tensile strength