Atmosphere Of Athens Research Articles

«WHY ACADEMY?»: AT THE ORIGINS OF THE ACADEMY OF PLATO (TO THE 100th ANNIVERSARY OF THE NATIONAL ACADEMY OF SCIENCES OF UKRAINE)

The origins of Platoʼs school are connected with the Academy. Today, the question of why the glorious history of academies of «all time and all peoples» began in that suburb of Athens is very topical for Ukraine, especially in connection with the celebration of the 100th anniversary of its foundation.As a student of Socrates, Plato was under the powerful influence of his teacher. It was typical for Socrates to obtrude his transatlantic reasons (διατριβαὶ καὶ λόγοι) on citizens of Athens and not in a particular place. Most often he does this in agora (αγορά), in gymnasiums (γυμνάσιον) and in symposiums (συμπόσιον) this practice dates back to the Homeric epochs. The circle of listeners for Socrates is also a peculiar characteristic. Unlike the Sophists, he holds his conversation with anyone who wishes to hear him and who is willing to jointly seek the truth, not the success in life.His students later will depart, to a certain extent, from the behavioral practices of their teacher. First, most of them will strive for the formal formalization of their schools. And secondly, they all will strive to localize, bind to a well-defined place. Communication between the teacher and his followers, students could take place on the plein air. Traditionally, however, such a place was the γυμνάσιον, «die zweite Agora» (Peter Scholz) – a widespread form of leisure activities (ἡ σχολή) for citizens of ancient city-states. In the γυμνάσιον (but not only in the γυμνάσιον) there will be ἡ παιδεία – education of the citizen of the polis, of the whole civil society, in the end, of all ancient civilization.The possibility of Plato's philosophical studies at the Academy before meeting with Socrates can also be witnessed by the intellectual atmosphere of Athens at the time of Pericles, and the Academy itself. The olive grove, the altars, the γυμνάσιον, the road with the tombstones of the famous Athenians, since the archaic era formed a sacred, socially significant space in the Athenian policy, a diatribe (ἡ διατριβή) worthy of a true citizen, a center of intellectual, political, religious life. The archaeologically discovered wall of the Hipparchus (το Ἱππάρχου τειχίον) and ΟΡΟΣ ΤΕΣ ΗΕΚΑΔΕΜΕΙΑΣ marked its limits already in the 6th century B.C.Young Plato comes to the Academy, looking for himself in various spheres. He leaves it, meets Socrates, but would return after the execution of the teacher by the Athenian democracy and after several years of wandering in Hellas. Of course, he will not buy (or friends will not buy for him) a γυμνάσιον at the Academy. The sources say that Plato (or his friends for him) will acquire a place in the grove of the Academy. There, near the γυμνάσιον, «on the plein air» starts walk with students and everyone who wishes to hear already his διατριβαὶ καὶ λόγοι to become a participant in the dialogue aimed at releasing golden grains of truth from the dim twilight of the Cave.

Aerosol Activity and Hygroscopicity Combined with Lidar Data in the Urban Atmosphere of Athens, Greece in the Frame of the HYGRA_CD Campaign

Measurements of cloud condensation nuclei (CCN) concentrations between 0.2-1.0% supersaturation and aerosol size distribution were performed at an urban background site of Athens during HygrA-CD. The site is affected by local and long-range transported emissions as portrayed by the external mixing of the particles, as the larger ones appear to be more hygroscopic and more CCN-active than smaller ones. Activation fractions at all supersaturations exhibit a diurnal variability with minimum values around noon, which are considerably lower than unity. This reinforces the conclusion that the aerosol is mostly externally mixed between “fresher”, less hygroscopic components with more aged, CCN active constituents.

A microscopic and Synchrotron-based characterization of urban particulate matter (PM 10–PM 2.5 and PM 2.5) from Athens atmosphere, Greece

Urban particulate matter (PM 10–PM 2.5 and PM 2.5) from Athens (Greece) atmosphere, primarily investigated by SEM-EDS, was further studied in the FLUO and SUL-X beamlines of ANKA Synchrotron facility (KIT, Germany). The SR μ-XRF study showed both geological (e.g. Ca Ti, Ca K and Ca Sr K Rb) and anthropogenic particles exhibiting heavy metal combinations such as Fe Co, Fe Co Cu V and Zn V. It was also revealed that very hazardous metalloids and heavy metals, namely As and Pb, are concentrated in isolated respirable (PM 2.5) microparticles. It was attempted to investigate the oxidation state of As by means of μ-XANES. The As K-edge XANES spectrum of the sample shows a main peak at about 11.874 keV which matches adequately with the As(V) reference spectrum but part of the As seems to have a lower oxidation state (most probably As(III)). This is the first non-bulk study with regard to the partitioning and solid-state speciation of hazardous chemical elements in urban atmospheric microparticles from greater Athens area, rated as an alpha-world city with a population of ca. 4 million people.

Lead patination in the atmosphere of Athens, Greece

Pure metallic Pb foils were exposed to the atmosphere of Athens for different periods of time (up to 150 non-rainy days) in the summer of 2005. The interacted Pb surfaces were probed using the 12C(d,p) 13C reaction ( E d: 1100 keV) at the Tandem accelerator of the NCSR “DEMOKRITOS”. Laser-μRaman and SEM–EDS were also complementary applied. Using the above methodology we recorded surface carbon profiles and concentrations as a function of the exposure time, corresponding to the evolution of the carbonate layer formed onto Pb foils due to the interaction with atmospheric H 2O and CO 2. The C-containing surface layer was found to be stabilized after ∼120 days. Further investigation by means of laser-μRaman and SEM–EDS indicated that the patina initially consists of Pb-hydroxycarbonates (hydrocerussite) overgrowing Pb-oxides, whereas Pb-sulfates (anglesite) and possibly basic Pb-sulfates are formed at the end of the patination process. The crystal growth of Pb-sulfates, or most likely the transformation of hydroxycarbonates to sulfates, is attributed to the pollution of Athens atmosphere by SO 2.

Nitro polycyclic aromatic hydrocarbons in atmospheric particulate matter of Athens, Greece

Polycyclic aromatic hydrocarbons (PAHs) and nitro polycyclic aromatic hydrocarbons (N-PAHs) are chemical species of proven mutant and carcinogenic activity. In this study, the concentrations of seven different N-PAHs [2-nitronaphthalene (2N-NAP), 2-nitroflourene (2N-FLU), 2-nitroflouranthene (2N-FLA), 3-nitroflouranthene (3N-FLA), 1-nitropyrene (1N-PYR) and 2-nitropyrene (2N-PYR)] were determined in two fractions of atmospheric particulate matter from the atmosphere of Athens: coarse (2.4 μm≪10 μm ) and fine (<2.4 μm ). 3N-FLA was not detected, whereas 1N-PYR, mostly originating from emissions from burning fuel, showed the maximum observed concentrations for both fractions and for the whole experimental period (especially during winter). In addition, 2N-FLA, a secondary nitro-PAH produced by photochemical reactions, showed relatively high values. Analysis of statistical data for N-PAH concentrations, using clustering technique, showed that: (1) 1N-NAP, 2N-FLU and 1N-PYR are mainly produced by direct burning; and (2) photochemical reactions are the dominant sources of 2N-NAP, 2N-PYR and 2N-FLA.

Polycyclic aromatic hydrocarbons and their oxygenated derivatives in the urban atmosphere of Athens

Ambient samples of coarse and fine organic particulate matter collected from two urban sites in the city of Athens over one warm and one cold period have been solvent-extracted and quantitatively characterized by gas chromatography–mass spectrometry for their content of polycyclic aromatic hydrocarbons (PAHs) and oxidized PAHs (oxyPAHs). Variable concentrations were observed for the two distinct monthly periods representing a cold, dry period and a summer period, relating to strong local primary emissions and to lower emissions with more stable meteorological conditions, respectively. Additionally, gaseous concentrations of selected PAHs were calculated, revealing that the relative proportions between gaseous and particle phase of individual compounds may differ significantly between summer and late winter, reflecting changes in PAH emission sources and climate conditions. In fact almost all of ΣPAHs were attributed to combustion sources (82–92%), while more than half are considered as comprising of probable human carcinogens (47–62%). Traffic was confirmed as the major contributor of PAHs when appropriate diagnostic ratios and traffic marker compounds were used. This approach also led to the estimation of diesel versus petrol contribution to the atmospheric PAH burden, using the methylphenanthrene to phenanthrene ratio. The fourteen oxygenated polycyclic compounds that were quantified had greater concentrations in the colder period. Among these compounds 9,10-phenanthrenequinone, 1-pyrenecarboxaldehyde and 9H-fluoren-9-one had the highest concentrations.

Spectral investigation of the diffuse-to-direct solar beam irradiances ratio (UV–VIS) in the urban Athens atmosphere

This study explores the influence of air gaseous pollutants–aerosols and solar zenith angle (SZA) on the spectral diffuse-to-direct beam E dλ/E bλ irradiances ratio. It does so using ground-based spectroradiometric measurements taken over the Athens atmosphere during May 1995. It was found that the spectral E dλ/E bλ ratio decreases rapidly with increasing wavelength and regression curves of the form E dλ/E bλ = aλ−b fitted the experimental data. These curves are strongly modified by aerosols–air pollutants, aerosol optical properties, and SZA. The log–log plot of E dλ/E bλ versus λ reveals a significant departure from linearity, which is likely to be associated with aerosol physical properties and SZA effects. The effect of atmospheric turbidity, as expressed through the aerosol optical at 500 nm and SZA on the spectral E dλ/E bλ ratio, is investigated in detail for two discernible atmospheric conditions observed in the urban Athens atmosphere. The first case includes different atmospheric turbidity levels under the same SZA, while the second corresponds to different SZA values under the same turbidity levels. It was found that the correlation between E dλ/E bλ and spectral aerosol optical depth can be a useful tool in determining the aerosol optical properties and aerosol types composition.

The role of primary and secondary air pollutants in atmospheric pollution: Athens urban area as a case study

The question to what extent primary and secondary air pollutants are relevant to atmospheric pollution and their effects on human health and the quality of the environment can be answered in a straight-forward manner: atmospheric processes, including oxidation procedures, particle formation and equilibria, determine the fate of primary emissions and, in most cases, the secondary products of these processes are the more important ones concerning their effects on human health and the quality of the environment. The formation of secondary products represents the critical property determining the establishment of certain air standards, rather than the actually emitted substance, although there are notable exceptions. In this paper, a review concerning transformation of primary pollutants as studied in the atmosphere of Athens is used to enlighten matters that may need further attention by the responsible authorities and stakeholders for the control and reduction of atmospheric pollution.

The role of aerosol models of the SMARTS code in predicting the spectral direct-beam irradiance in an urban area

Measurements of the ground-level spectral distribution of the direct-beam solar irradiance between 300 and 1000 nm were made in Athens, Greece, in May 1995. Results obtained using simple model for the atmospheric radiative transfer of sunshine (SMARTS) (version 2.9.2) parametric model for the urban atmosphere of Athens are analyzed and compared to the ground-level experimental spectral solar irradiance measurements obtained by the passive pyrheliometric scanner (PPS) in three discrete bands, UV (320–400 nm), VIS (400–700 nm) and NIR (700–1000 nm). The study uses two different input parameters for the aerosol characterization: the aerosol optical depth at 500 nm, t α 0.5, and the Ångström turbidity coefficient, β. The results clearly show that the nine aerosol models implemented in the SMARTS code lead to quite different predictions of the direct-beam spectrum, strongly depended on the input parameter. In all cases the inadequacies between the measured and the modeled direct-beam spectra are lower and higher when the urban and maritime aerosol models are used, respectively.

A study of aerosol particle sizes in the atmosphere of Athens, Greece, retrieved from solar spectral measurements

This work aims at determining the aerosol particle radii in the atmosphere of Athens. Such a work is carried out in Athens for the first time. For this purpose, solar spectral direct-beam irradiance measurements were used in the spectral range 310–575 nm. To estimate the particle radius from aerosol optical depth retrieval, a minimization technique was employed based on the golden-section search of the difference between experimental and theoretical values of the aerosol optical depth. The necessary Mie computations were performed based on the algorithm LVEC. In this study, the mean particle radius of a given distribution was calculated every 30 min during cloudless days in the period November 1996 to September 1997. The largest particles were observed in the summer and the smallest during winter. The result was verified by the increased values of the aerosol optical depth and the turbidity factors calculated in the summer. The differences in the diurnal variation from season to season are attributed to the prevailing wind regime, pollutant emission and sink rates in the atmosphere of Athens.

The dependence of global and diffuse PAR radiation components on sky conditions at Athens, Greece

The interrelationship between broadband solar components, global ( R S) and diffuse ( R d) and the photosynthetic photon flux density components, global ( Q P) and diffuse ( Q Pd), is investigated using a 2-year data archive obtained at Athens, Greece. These data are used to determine temporal variability of the ratios ( Q P/ R S) and ( Q Pd/ R d) and their dependence on sky conditions. The seasonal variation of the ratios obtained from hourly data ranges from 2.006 ± 0.032 (winter) to 1.989 ± 0.028 μmol J −1 (summer) with an annual mean of 1.995 ± 0.032 μmol J −1 for ( Q P/ R S) and from 2.298 ± 0.27 (winter) to 2.538 ± 0.22 μmol J −1 (summer) with an annual mean of 2.434 ± 0.26 μmol J −1 for ( Q Pd/ R d). The hourly ratio ( Q P/ R S) increased from 1.982 ± 0.025 to 2.106 ± 0.029 μmol J −1 as sky conditions changed from clear to overcast; whereas the ratio ( Q Pd/ R d) decreased from 2.556 ± 0.27 to 2.422 ± 0.24 μmol J −1 as sky conditions changed from clear to overcast skies. The seasonal daily ratio patterns are presented and discussed through clearness index k t (the ratio of the global-to-extraterrestrial solar radiation). Finally, the relationship between the spectral diffuse fraction k dP (the ratio of diffuse PAR-to-global PAR radiation) and the clearness index k tP (the ratio of global PAR-to-extraterrestrial solar PAR) is established for the Athens atmosphere.

Extreme Nitrogen Oxide and Ozone Concentrations in Athens Atmosphere in Relation to Meteorological Conditions

In the present study, we investigate the variation of NOx)(NO + NO2) and O3 concentrations and the relation between the extreme events (episodes) of NOx and O3 concentrations and the relevant meteorological conditions in the urban atmosphere of the Athens basin. Hourly data of NO, NO2 and O3 concentrations from 10 representative monitoring sites located in the Athens basin were used, covering the 10-year time period from 1994 to 2003. The results of our analysis show that the concentrations of air pollutants differ significantly from one monitoring site to another, due to the location and proximity of each station to the emission sources. For each site, there are also significant differences in NOx and O3 concentrations from day to day, as well as from month to month and/or from season to season. The annual and seasonal variations show higher NO values in winter and lower in summer. On the contrary, NO2 and O3 values are higher in summer (photochemical production of O3) and lower in winter. These differences are attributed, to a large extent, to the prevailing synoptic and meteorological conditions, the most important between them being the wind direction and speed as well as the atmospheric pressure. Our analysis of the identified 179 extreme NOx air pollution events shows that most of them took place under anticyclonic conditions, associated with calm or weak winds (speed <2.5 ms(-1)) of mostly southern to southwestern directions, as well as with low air temperatures and intense stable surface atmospheric conditions. There exists a significant decreasing tendency in NOx air pollution episodic events over the 10-year study period, resulting in very few to none events in the period from 2000 to 2003. As far as it concerns the extreme O3 concentrations, 34 air pollution events were identified, occurring under high air temperatures, variable weak winds and intense solar irradiation. The trends of O3 concentrations are stronger in suburban sites than in urban ones.

On the characterization of aerosols using the Ångström exponent in the Athens area

Ground-based spectroradiometric measurements were taken in the atmosphere of Athens during May 1995 in order to investigate various atmospheric conditions. This study focuses on the Ångström exponent α, which is the slope of the logarithm of the aerosol optical depth (AOD) versus the logarithm of the wavelength, ln λ, and is commonly used to characterize the wavelength dependence of AOD and to provide some basic information on the aerosol size distribution. Using the Volz method, Ångström exponent values, α, were derived in five narrow spectral bands, 340–380, 380–440, 440–500, 500–670 and 670–870 nm. Also using both Volz and least-squares fit methods α values were derived for the whole spectrum 340-870 nm.The results show that α depends strongly on the wavelength interval used due to the curvature of the lnAOD versus ln λ line. Using the spectral dependence of the Ångström exponent and the relationship between α computed in different spectral bands with AOD, an attempt to investigate on the aerosol types is made. The results obtained are rather contradictory and the determination of a dominant aerosol type in the Athens area is not clear. Nevertheless, in the most cases the anthropogenic aerosols seem to be the dominant type with rather significant contributions of coarse-mode particles due to particle growing or due to mixing processes with other aerosol types.

Chemical characterisation of single airborne particles in Athens (Greece) by ATOFMS

A TSI Model 3800 aerosol time-of-flight mass spectrometer (ATOFMS) was deployed for single-particle analysis to Athens (Greece) during August 2003. It has revealed particle types not previously reported in urban air, as well as adding appreciably to the knowledge of aerosol in the Athens atmosphere. Sampling was carried out on a minor road in the city centre and the mass spectra of 166,603 particles were recorded, with 128,290 presenting both positive and negative spectra. The ART-2a neural network algorithm was applied and five main classes of particle were characterised: sea salt, dust, carbon, inorganic and K-rich, with sub-classes within each. Dust (with five sub-classes) was the main class, accounting for up to 49.5% of the particles characterised. Oxygenated organic particles feature heavily in the dataset and some are internally mixed with nitrate and sulphate. Most of the carbon-containing particles appeared to be a secondary product of atmospheric chemistry and one specific class (C-SEC_2) peaked every night at 22:00, when temperature and RH values favoured condensation. The secondary particles showed clear internal mixing of organic and inorganic constituents in contrast to their common theoretical treatment as external mixtures. The apparent semi-volatility of one class was striking. Compared with measurements in northern Europe, the abundance of relatively coarse dust particles and of secondary organic particles is notable. The particle classes derived from analysis of the ATOFMS data were compared with published data on the composition of aerosol in Athens. The latter is largely restricted to major water-soluble ions, and the two measurement techniques proved to be highly complementary.

Comparison between experimental data and modeling estimates of aerosol optical depth over Athens, Greece

Ground-based spectroradiometric measurements taken in the atmosphere of Athens during May 1995 have been used to investigate various atmospheric parameters. From the direct-beam irradiance measurements the spectral aerosol optical depths as well as the Ångström parameters are derived using the least-squares method applied to measured spectral irradiance data. In this way the errors associated with the turbidity coefficient, β, are found to be 0.0029 on average and with the wavelength exponent, α, 0.031. In this paper, a comparative study between the aerosol optical depth derived by the spectral direct-beam irradiance measurements and those estimated through the Ångström's formula is made. The correlation coefficient between the measured and computed optical depth is higher than 0.93 in most cases, while their greatest differences take place at the shorter wavelengths. A further analysis of the above differences at 500 and 1000 nm shows very low values, especially at 500 nm, indicating the accuracy of the fitting. The differences at 1000 nm are much higher due to uncertainties in the water-vapor optical depth determination. The errors in Ångström parameters as well as in the Ångström's formula fitting to the derived spectral aerosol optical depth depend strongly on atmospheric turbidity, reaching to higher values under low atmospheric turbidity conditions.

Spectral aerosol optical depth and Angstrom parameters in the polluted Athens atmosphere

Using ground-based spectral solar extinction data taken in the Athens atmosphere during a field survey, experimental and modeled aerosol optical depths AOD have been retrieved. The Angstrom parameters α and β were derived through spectral extinction curves determined from a log–log plot fit in four spectral intervals, e.g. UV, VIS, UV-VIS and VIS-NIR. The results reveal that exponent α derived in the shorter wavebands, is correlated with β; in the VIS-NIR range the correlation is weaker, however. It has also found that α does not depend on the Angstrom law fits, while β does. Retrieved experimental AOD obtained at longer wavelengths exhibits a daily pattern similar to turbidity β; by contrast, AOD at shorter wavelengths follows the temporal variation of α.

Application of SPCTRAL2 parametric model in estimating spectral solar irradiances over polluted Athens atmosphere

Results obtained using SPCTRAL2 parametric model for the polluted urban atmosphere of Athens, Greece, were analysed and compared with ground level experimental spectral solar irradiance measurements and spectrally integrated solar irradiances in two discrete narrow bands, ultraviolet and visible. For the aerosol characterization, the aerosol optical depth evaluated at 500 nm was used as the basic input parameter. The algorithm used seems to reproduce the experimental solar spectral irradiances adequately depending on the aerosol model used. The results obtained have been explained through mean bias and root mean square statistical deviations and the resultant influence of the aerosol volume spectra.

Source identification of trace elements emitted into Athens atmosphere

The source identification of trace elements emitted into Athens (Greece) atmospheric environment has been studied by the Enrichment Factor (EF) and by Principal Component Analysis (PCA). The prevailing wind direction is related to EF data in order to identify the possible pathways of trace elements, in the Athens basin. As gas pollutants and trace elements could be emitted from the same source, the possible relation between these two groups is studied by PCA and correlation relations. According to EF data, the trace elements Fe, Sm, Th, Co, Sc, Cr and K have a crustal origin while the elements Zn, As, Sb, Ag, Br result of anthropogenic pollution. The study of the prevailing wind direction showed that the existing geophysical channel in the northern area of Athens basin could be a pathway for the entrance of Fe, La, Sm, Th, Co, Cr, Na and Ag into Athens atmosphere. On the contrary, the sea breeze could be a potential cleaner of the atmosphere from the same elements. Six source factors were resolved by PCA for all the Athens area explaining the 90% of the total variance. They could nominated as soil dust, central heating, movement of cars, car tires, car break abrasion and sea breeze. After the application of PCA and the linear regression model, the concentration of atmospheric ozone shows to have a positive significant correlation with Na and Zn and a negative significant correlation with As, Br, Ce, Co, Cr, Fe, La, Sb, Sc, Sm. A possible explanation of the mechanism for the decrease of atmospheric ozone concentration in relation to trace metals is given according to the existing literature data.

Characterization of lead, cadmium, arsenic and nickel in PM 2.5 particles in the Athens atmosphere, Greece

Concentrations of Pb, Cd, As and Ni in PM 2.5 particles were measured in samples collected, using low volume PM 2.5 samplers (Harvard Impactor system, HI) at two sites in Athens basin; Patission Street in Athens city center and Rentis, a semi-urban and industrial area, during March 1995–March 1996. Sample analysis for Pb, Cd, Ni and As was accomplished by electrothermal atomic absorption spectrometry after total digestion. Annual geometric mean values in 183 PM 2.5 particles samples were found to be: Pb: 143 ng m −3; Cd: 0.34 ng m −3; Ni: 4.55 ng m −3; As: 0.79 ng m −3. The geographical and temporal distribution patterns were investigated. Pb exhibited higher values during the winter period. For the other elements no significant seasonal variation was observed. Wind direction, air temperature and relative humidity affected element concentrations. Principal component analysis was applied on the data to enable source apportionment of toxic elements in PM 2.5 particles. It was found that Pb, As and Ni have common sources, which could be vehicles emissions/oil combustion and resuspended road dust. Cd and a portion of As originate from industrial activities.

Correlation of trace element content in air particulates with solar meteorological data in the atmosphere of Athens

In this paper, the relation between the trace element content in air particulates and solar meteorological data in the atmospheric environment of Athens, Greece, was studied. For this purpose, Sm, Br, As, Na, K, La, Ce, Cr, Ag, Sc, Fe, Zn, Co, Sb, Th were determined by INAA in respirable aerosols collected during winter 1993-1994. The results showed that the average cloudiness, sunshine, and the total solar radiation (sun and sky) on a horizontal surface, (3 variables) have no relation with trace element variation. However, diffuse solar radiation (sun and sky) on a horizontal surface seems to have statistically significant relationship with some of the trace element variation. It forms a single component with some trace elements after the application of the factor analysis. The increase of the same solar variable in the Athens City center, is one of the factors which cannot permit the emission of trace elements in the atmospheric environment from dust soil and car tires.