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Opis: A significant fraction of atmospheric particles that serve as cloud condensation nuclei (CCN) are thought to originate from the condensational growth of new particle formation (NPF) from the gas phase. Here, 7 years of continuous aerosol and meteorological measurements (June 2008 to May 2015) at a remote background site of the eastern Mediterranean were recorded and analyzed to assess the impact of NPF (of 162 episodes identified) on CCN and cloud droplet number concentration (CDNC) formation in the region. A new metric is introduced to quantitatively determine the initiation and duration of the influence of NPF on the CCN spectrum. NPF days were found to increase CCN concentrations (from 0.10 % to 1.00 % supersaturation) between 29 % and 77 %. Enhanced CCN concentrations from NPF are mostly observed, as expected, under low preexisting particle concentrations and occur in the afternoon, relatively later in the winter and autumn than in the summer. Potential impacts of NPF on cloud formation were quantified by introducing the observed aerosol size distributions and chemical composition into an established cloud droplet parameterization. We find that the supersaturations that develop are very low (ranging between 0.03 % and 0.27 %) for typical boundary layer dynamics (σw ∼0.3 m s−1) and NPF is found to enhance CDNC by a modest 13 %. This considerable contrast between CCN and CDNC response is in part from the different supersaturation levels considered, but also because supersaturation drops from increasing CCN because of water vapor competition effects during the process of droplet formation. The low cloud supersaturation further delays the appearance of NPF impacts on CDNC to clouds formed in the late evening and nighttime – which has important implications for the extent and types of indirect effects induced by NPF events. An analysis based on CCN concentrations using prescribed supersaturation can provide very different, even misleading, conclusions and should therefore be avoided. The proposed approach here offers a simple, yet highly effective way for a more realistic impact assessment of NPF events on cloud formation.
Ključne besede: regional NPF, CCN, cloud droplets, Eastern Mediterranean, regional background
Objavljeno v RUNG: 13.05.2024; Ogledov: 208; Prenosov: 2
Celotno besedilo (3,07 MB)
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Opis: Atmospheric new particle formation (NPF) is an important source of submicron particles. In remote background environments where local sources are scarce such processes may impact significantly on climate-relevant parameters. On the other hand, in urban environments, newly-formed particles are adding up to submicron particles emitted from primary sources. As the exact mechanism which triggers NPF still remains elusive, so are the circumstances for simultaneous occurrence of such events in two different environments (urban vs. regional background). In this study, concurrent number size distribution measurements were conducted in the urban environment of Athens and at the regional background site of Finokalia, Crete, located 340 km away and spanning a 2-year period. It occurred that the relative frequency of NPF was similar at both sites (around 20%), with a higher frequency during spring and autumn at the urban site, while at the background site most events took place in August and December, during the studied period. There were 35 event days when NPF took place at both sites simultaneously, all associated with air masses originating from the Northern sector, indicating the presence of regional events in the extended geographical area and characterized by low condensation sink (CS). By comparing the common with the non-common class I NPF episodes, we conclude that the conditions applying when regional NPF events with growth are observed in the same day at the surface level of both areas, are: (i) lower CS, (ii) higher SO2 concentrations, (iii) lower RH, and finally (iv) lower formation and growth rates than those observed during the site-specific and more rapidly evolving NPF events.
Ključne besede: NPF, Athens, Eastern Mediterranean, particle number concentrations, size distributions, concurrent regional events
Objavljeno v RUNG: 10.05.2024; Ogledov: 181; Prenosov: 0
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Opis: This thesis represents a karstological study on the drainage of the Postojna Basin. It focuses on a multidisciplinary approach, based on fieldwork, computer analyses and dating. The northern study area has the highest: doline density of 108 dolines/km2, number of contact karst features (i.e. 9), and number of collapse dolines (i.e. 19). It has three catchments. The Lokva cuts into the flysch ridges and sinks in the Predjama Cave System at the lowest point of the basin (i.e. 474 m a.s.l.). Between 37 selected caves, 14 were longer than 150 m. The Predjama Cave System was developed in 3 levels and the Postojna Cave System was developed in 2 levels. The vertical passages connecting them are deepest in the Predjama cave, where the vadose zone is up to 250 m deep. By the favourable ponor steepheads and 140 m deep vadose passages, the Hrušica Plateau shows a major uplift phase. The Postojna Cave System, Risovec blind valley and 17 collapse dolines indicate significant past hydrological changes. First, Nanoščica formed the Risovec blind valley, followed by Otoška jama, Tartarus, Male jame, and Artificial tunnel toward E/NE, forming the Vodni dol. At the same time, the ponor of Pivka shifted in the Postojnska jama (at present “Stara jama”), flowing towards N, forming Jeršanove doline. The successive subsidence of the erosional base and the Postojna karst uplift redirected the Nanoščica in Pivka. Now they sink into active parts of the Postojna cave at 511 m a.s.l. The eastern study area has the Unroofed cave Kriva dolina as a former ponor of Pivka. At present the area has springs and favourable (sub)vertical passages. The southern study area has the highest variety of contact karst features (i.e. 5). The Prestranški ravnik represents an aquifer with ponors and springs. It is separated from the Slavinski ravnik, by a flysch belt. In the southern study area, 10 caves were longer than 150 m among 49 selected caves. The Loza Cave System, a case study in Slavinski ravnik, is developed in 3 epiphreatic levels that followed two phases of tectonic uplift with a successive formation of diversion routes through 30-40 m deep vadose passages. The oldest upper cave level has sediments from at least the Gilbert Chron with CW rotations. U-Th dates from speleothems prove vadose speleogenesis before the cave ceiling denudation and collapse from 210 ka to 550 ka (≤1.2 Ma). The middle cave level has epiphreatic sediments at least in the Gauss Chron (i.e. 2.59-3.59 Ma) and reveals 35-38° CCW rotations. The allogenic sediments in the lower cave level show Brunhes and Matuyama Chrons (i.e. <0.78-2.58 Ma). We generally discussed ponor steepheads that develop on steepest slopes on the thrust/fault contact, while blind valleys and border depressions develop on normal stratigraphic contact with mildest slopes. The speleogenesis was mainly driven by relatively quick tectonic uplift, followed by vadose speleogenesis, with intermediate speleogenesis in the epiphreatic zone. Speleogenesis and contact karst features follow the subsidence of the water table, evidenced by cave levels, and active and relict features. Allogenic sediments are followed by speleothems as shift of caves between hydrological zones. The sequence of events repeated 2-3 times. The main local source of allogenic sediments is in the Postojna Basin, represented by the erosion of flysch rocks and alluvium. The mineralogical composition between catchments is similar with no significant change. The regional compressional-tectonic regime has significantly influenced the changes in the drainage of the Postojna Basin during the last 7 Ma, with different uplifts and drop of the karst water table. The major uplift was reflected by the change in the Nanoščica course from the Slavinski ravnik to the Postojna karst from S to N, presumably between 3.59 Ma and >1.77 Ma and represented the last important general shift in the drainage of the Postojna Basin.
Ključne besede: karst, contact karst, regional tectonic uplift, cave levels, shift from epiphreatic to vadose speleogenesis, Loza Cave System, Postojna drainage basin
Objavljeno v RUNG: 05.12.2023; Ogledov: 779; Prenosov: 53
Celotno besedilo (29,89 MB)

Opis: In the summer of 2014 in situ and remote sensing instruments were deployed in Athens, in order to study the concentration, physical properties, and chemical composition of aerosols. In this manuscript we aim to combine the measurements of collocated in situ and remote sensing instruments by comparison and complementary use, in order to increase the accuracy of predictions concerning climate change and human health. We also develop a new method in order to select days when a direct comparison on in situ and remote sensing instruments is possible. On selected days that displayed significant turbulence up to approximately 1000 m above ground level (agl), we acquired the aerosol extinction or scattering coefficient by in situ instruments using three approaches. In the first approach the aerosol extinction coefficient was acquired by adding a Nephelometer scattering coefficient in ambient conditions and an Aethalometer absorption coefficient. The correlation between the in situ and remote sensing instruments was good (coefficient of determination equal to 0.69). In the second approach we acquired the aerosol refractive index by fitting dry Nephelometer and Aethalometer measurements with Mie algorithm calculations of the scattering and absorption coefficients for the size distribution up to a maximum diameter of 1000 nm obtained by in situ instruments. The correlation in this case was relatively good ( equal to 0.56). Our next step was to compare the extinction coefficient acquired by remote sensing instruments to the scattering coefficient calculated by Mie algorithm using the size distribution up to a maximum diameter of 1000 nm and the equivalent refractive index (), which is acquired by the comparison of the size distributions obtained by a Scanning Mobility Particle Sizer (SMPS) and an Optical Particle Counter (OPC). The agreement between the in situ and remote sensing instruments in this case was not satisfactory ( equal to 0.35). The last comparison for the selected days was between the aerosol extinction Ångström exponent acquired by in situ and remote sensing instruments. The correlation was not satisfactory ( equal to 0.4), probably due to differences in the number size distributions present in the air volumes measured by in situ and remote sensing instruments. We also present a day that a Saharan dust event occurred in Athens in order to demonstrate the information we obtain through the synergy of in situ and remote sensing instruments on how regional aerosol is added to local aerosol, especially during pollution events due to long range transport.
Ključne besede: Aerosol mixing in the vertical, In situ — Remote sensing comparison, Regional aerosol addition to local aerosol
Objavljeno v RUNG: 09.04.2020; Ogledov: 3000; Prenosov: 0
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Opis: This article discusses the literature of the national and linguistic minorities along the Slovene-Italian border area (Slovene and Friulian literature in Italy, Italian literature in Slovene Istria), comprised of the Friuli-Venezia Giulia region in Italy, and the Goriška and Coastal-Karst regions in neighbouring Slovenia. The discussion argues that a new methodological approach is needed to study these literatures, one that will upgrade the previous research (studying the literature's regional specifics, which stems from the authors' common living environment, regardless of their linguistic and national identity and the depiction of the foreign culture in minority literature), geared towards regional comparative literature The results of such studies would be useful to bolster the teaching material in literature classes in the given area.
Ključne besede: minority literature, regional comparative literature, literature didactic
Objavljeno v RUNG: 11.01.2018; Ogledov: 3704; Prenosov: 0
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