Repository of University of Nova Gorica

Search the repository
A+ | A- | Help | SLO | ENG

There are two search modes available: simple and advanced. The simple search mode searches by title, abstract, key words and full text. The advanced search mode offers several attributes and search operators to search with. This search method also allows the use of Boolean operators.

Help
Search in:
Options:
 


71 - 80 / 200
First pagePrevious page45678910111213Next pageLast page
71.
72.
Long-term brown carbon spectral characteristics in a Mediterranean city (Athens)
Eleni Liakakou, Dimitris G. Kaskaoutis, Georgios Grivas, Iasonas Stavroulas, M. Tsagkaraki, D. Paraskevopoulou, Aikaterini Bougiatioti, Umesh Chandra Dumka, Evangelos Gerasopoulos, Nikolaos Mihalopoulos, 2020, original scientific article

Abstract: This study analyses 4-years of continuous 7-λ Aethalometer (AE-33) measurements in an urban-background environment of Athens, to resolve the spectral absorption coefficients (babs) for black carbon (BC) and brown carbon (BrC). An important BrC contribution (23.7 ± 11.6%) to the total babs at 370 nm is estimated for the period May 2015–April 2019, characterized by a remarkable seasonality with winter maximum (33.5 ± 13.6%) and summer minimum (18.5 ± 8.1%), while at longer wavelengths the BrC contribution is significantly reduced (6.8 ± 3.6% at 660 nm). The wavelength dependence of the total babs gives an annual-mean AAE370-880 of 1.31, with higher values in winter night-time. The BrC absorption and its contribution to babs presents a large increase reaching up to 39.1 ± 13.6% during winter nights (370 nm), suggesting residential wood burning (RWB) emissions as a dominant source for BrC. This is supported by strong correlations of the BrC absorption with OC, EC, the fragment ion m/z 60 derived from ACSM and PMF-analyzed organic fractions related to biomass burning (e.g. BBOA). In contrast, BrC absorption decreases significantly during daytime as well as in the warm period, reaching to a minimum during the early-afternoon hours in all seasons due to photo-chemical degradation. Estimated secondary BrC absorption is practically evident only during winter night-time, implying the fast oxidation of BrC species from RWB emissions. Changes in mixing-layer height do not significantly affect the BrC absorption in winter, while they play a major role in summer.
Keywords: spectral aerosol absorption, brown carbon, wood burning, organic aerosols, chemical composition, Athens
Published in RUNG: 10.05.2024; Views: 275; Downloads: 1
URL Link to file

73.
Field evaluation of low-cost PM sensors (Purple Air PA-II) under variable urban air quality conditions, in Greece
Iasonas Stavroulas, Georgios Grivas, Panagiotis Michalopoulos, Eleni Liakakou, Aikaterini Bougiatioti, Panayiotis Kalkavouras, Kyriaki Maria Fameli, Nikolaos Hatzianastassiou, Nikolaos Mihalopoulos, Evangelos Gerasopoulos, 2020, original scientific article

Abstract: Recent advances in particle sensor technologies have led to an increased development and utilization of low-cost, compact, particulate matter (PM) monitors. These devices can be deployed in dense monitoring networks, enabling an improved characterization of the spatiotemporal variability in ambient levels and exposure. However, the reliability of their measurements is an important prerequisite, necessitating rigorous performance evaluation and calibration in comparison to reference-grade instrumentation. In this study, field evaluation of Purple Air PA-II devices (low-cost PM sensors) is performed in two urban environments and across three seasons in Greece, in comparison to different types of reference instruments. Measurements were conducted in Athens (the largest city in Greece with nearly four-million inhabitants) for five months spanning over the summer of 2019 and winter/spring of 2020 and in Ioannina, a medium-sized city in northwestern Greece (100,000 inhabitants) during winter/spring 2019–2020. The PM2.5 sensor output correlates strongly with reference measurements (R2 = 0.87 against a beta attenuation monitor and R2 = 0.98 against an optical reference-grade monitor). Deviations in the sensor-reference agreement are identified as mainly related to elevated coarse particle concentrations and high ambient relative humidity. Simple and multiple regression models are tested to compensate for these biases, drastically improving the sensor’s response. Large decreases in sensor error are observed after implementation of models, leading to mean absolute percentage errors of 0.18 and 0.12 for the Athens and Ioannina datasets, respectively. Overall, a quality-controlled and robustly evaluated low-cost network can be an integral component for air quality monitoring in a smart city. Case studies are presented along this line, where a network of PA-II devices is used to monitor the air quality deterioration during a peri-urban forest fire event affecting the area of Athens and during extreme wintertime smog events in Ioannina, related to wood burning for residential heating.
Keywords: particulate matter, PM2.5, air quality, low-cost sensors, optical particle counter
Published in RUNG: 10.05.2024; Views: 248; Downloads: 3
URL Link to file
This document has many files! More...

74.
Carbonaceous aerosols in contrasting atmospheric environments in Greek cities : evaluation of the EC-tracer methods for secondary organic carbon estimation
Dimitris G. Kaskaoutis, Georgios Grivas, Christina Theodosi, M. Tsagkaraki, D. Paraskevopoulou, Iasonas Stavroulas, Eleni Liakakou, Antonis Gkikas, Nikolaos Hatzianastassiou, Cheng Wu, 2020, original scientific article

Abstract: This study examines the carbonaceous-aerosol characteristics at three contrasting urban environments in Greece (Ioannina, Athens, and Heraklion), on the basis of 12 h sampling during winter (January to February 2013), aiming to explore the inter-site differences in atmospheric composition and carbonaceous-aerosol characteristics and sources. The winter-average organic carbon (OC) and elemental carbon (EC) concentrations in Ioannina were found to be 28.50 and 4.33 µg m−3, respectively, much higher than those in Heraklion (3.86 µg m−3 for OC and 2.29 µg m−3 for EC) and Athens (7.63 µg m−3 for OC and 2.44 µg m−3 for EC). The winter OC/EC ratio in Ioannina (6.53) was found to be almost three times that in Heraklion (2.03), indicating a larger impact of wood combustion, especially during the night, whereas in Heraklion, emissions from biomass burning were found to be less intense. Estimations of primary and secondary organic carbon (POC and SOC) using the EC-tracer method, and specifically its minimum R-squared (MRS) variant, revealed large differences between the sites, with a prevalence of POC (67–80%) in Ioannina and Athens and with a larger SOC fraction (53%) in Heraklion. SOC estimates were also obtained using the 5% and 25% percentiles of the OC/EC data to determine the (OC/EC)pri, leading to results contrasting to the MRS approach in Ioannina (70–74% for SOC). Although the MRS method provides generally more robust results, it may significantly underestimate SOC levels in environments highly burdened by biomass burning, as the fast-oxidized semi-volatile OC associated with combustion sources is classified in POC. Further analysis in Athens revealed that the difference in SOC estimates between the 5% percentile and MRS methods coincided with the semi-volatile oxygenated organic aerosol as quantified by aerosol mass spectrometry. Finally, the OC/Kbb+ ratio was used as tracer for decomposition of the POC into fossil-fuel and biomass-burning components, indicating the prevalence of biomass-burning POC, especially in Ioannina (77%).
Keywords: carbonaceous aerosols, inorganic species, POC-SOC estimation, biomass burning, MRS method, Greece
Published in RUNG: 10.05.2024; Views: 229; Downloads: 3
.pdf Full text (2,64 MB)
This document has many files! More...

75.
Online chemical characterization and sources of submicron aerosol in the major mediterranean port city of Piraeus, Greece
Iasonas Stavroulas, Georgios Grivas, Eleni Liakakou, Panayiotis Kalkavouras, Aikaterini Bougiatioti, Dimitris G. Kaskaoutis, Maria Lianou, Kyriaki Papoutsidaki, M. Tsagkaraki, Evangelos Gerasopoulos, Pavlos Zarmpas, Nikolaos Mihalopoulos, 2021, original scientific article

Abstract: Port cities are affected by a wide array of emissions, including those from the shipping, road transport, and residential sectors; therefore, the characterization and apportionment of such sources in a high temporal resolution is crucial. This study presents measurements of fine aerosol chemical composition in Piraeus, one of the largest European ports, during two monthly periods (winter vs. summer) in 2018–2019, using online instrumentation (Aerosol Chemical Speciation Monitor—ACSM, 7-λ aethalometer). PMF source apportionment was performed on the ACSM mass spectra to quantify organic aerosol (OA) components, while equivalent black carbon (BC) was decomposed to its fossil fuel combustion and biomass burning (BB) fractions. The combined traffic, shipping and, especially, residential emissions led to considerably elevated submicron aerosol levels (22.8 μg m−3) in winter, which frequently became episodic late at night under stagnant conditions. Carbonaceous compounds comprised the major portion of this submicron aerosol in winter, with mean OA and BC contributions of 61% (13.9 μg m−3) and 16% (3.7 μg m−3), respectively. The contribution of BB to BC concentrations was considerable and spatially uniform. OA related to BB emissions (fresh and processed) and hydrocarbon-like OA (from vehicular traffic and port-related fossil fuel emissions including shipping) accounted for 37% and 30% of OA, respectively. In summer, the average PM1 concentration was significantly lower (14.8 μg m−3) and less variable, especially for the components associated with secondary aerosols (such as OA and sulfate). The effect of the port sector was evident in summer and maintained BC concentrations at high levels (2.8 μg m−3), despite the absence of BB and improved atmospheric dispersion. Oxygenated components yielded over 70% of OA in summer, with the more oxidized secondary component of regional origin being dominant (41%) despite the intensity of local sources, in the Piraeus environment. In general, with respect to local sources that can be the target of mitigation policies, this work highlights the importance of port-related activities but also reveals the extensive wintertime impact of residential wood burning. While a separation of the BB source is feasible, more research is needed on how to disentangle the short-term effects of different fossil-fuel combustion sources.
Keywords: Athens, harbor, shipping emissions, PM1, chemical speciation, organic aerosol, black carbon, ACSM, aethalometer, PMF
Published in RUNG: 10.05.2024; Views: 235; Downloads: 2
URL Link to file
This document has many files! More...

76.
77.
In situ identification of aerosol types in Athens, Greece, based on long-term optical and on online chemical characterization
Dimitris G. Kaskaoutis, Georgios Grivas, Iasonas Stavroulas, Eleni Liakakou, Umesh Chandra Dumka, Konstantinos Dimitriou, Evangelos Gerasopoulos, Nikolaos Mihalopoulos, 2021, original scientific article

Abstract: Absorption Ångström Exponent (AAE) and Scattering Ångström Exponent (SAE) values, derived from aethalometer and nephelometer measurements during a period of 3 years at an urban background site in Athens, are combined for the first aerosol type classification using in situ measurements in the eastern Mediterranean. In addition, single scattering albedo (SSA) and its wavelength dependence (dSSA), as well as the chemical composition of fine aerosols and precursor gases from collocated measurements, are utilized to provide further insights on the optical-chemical characterization and related sources of seven identified aerosol types. Urban aerosols are mostly characterized as Black Carbon (BC)-dominated (76.3%), representing a background atmosphere where fossil-fuel combustion is dominant throughout the year, while 14.3% of the cases correspond to the mixed Brown Carbon (BrC)-BC type, with a higher frequency in winter. The BrC type is associated with the highest scattering and absorption coefficients during winter nights, representing the impact from residential wood-burning emissions. Dust mixed with urban pollution (1.2%) and large particles mixed with BC (5.3%) have a higher frequency in spring. Furthermore, aging processes and BC coating with organic and inorganic species with weak spectral absorption (AAE<1) account for 2.2%, with a differentiation between small and large particles. dSSA is recognized as a useful parameter for aerosol characterization, since fine aerosols are associated with negative dSSA values. The identified aerosol types are examined on a seasonal, monthly, hourly basis and by potential source areas, as well as in comparison with fine-aerosol chemical composition and apportioned organic aerosol source contributions, in an attempt to explore the linkage between optical, physical and chemical aerosol properties. Chemical analysis indicates high organic fraction (60–68%) for the BrC and BrC/BC, 20–30% larger compared to other types. The results are essential for parametrization in chemical transport models and for reducing the uncertainty in the assessment of aerosol radiative effects.
Keywords: aerosol types, classification, AAE, SAE, dSSA, chemical composition, sources, Athens
Published in RUNG: 10.05.2024; Views: 239; Downloads: 2
URL Link to file
This document has many files! More...

78.
79.
Absorption enhancement of black carbon particles in a Mediterranean city and countryside : effect of particulate matter chemistry, ageing and trend analysis
Jesús Yus-Díez, Marta Via, Andrés Alastuey, Angeliki Karanasiou, Maria Cruz Minguillon, Noemí Perez, Xavier Querol, Cristina Reche, Matic Ivančič, Martin Rigler, 2022, original scientific article

Abstract: Abstract. Black carbon (BC) is recognized as the most important warming agent among atmospheric aerosol particles. The absorption efficiency of pure BC is rather well-known, nevertheless the mixing of BC with other aerosol particles can enhance the BC light absorption efficiency, thus directly affecting Earth's radiative balance. The effects on climate of the BC absorption enhancement due to the mixing with these aerosols are not yet well constrained because these effects depend on the availability of material for mixing with BC, thus creating regional variations. Here we present the mass absorption cross-section (MAC) and absorption enhancement of BC particles (Eabs), at different wavelengths (from 370 to 880 nm for online measurements and at 637 nm for offline measurements) measured at two sites in the western Mediterranean, namely Barcelona (BCN; urban background) and Montseny (MSY; regional background). The Eabs values ranged between 1.24 and 1.51 at the urban station, depending on the season and wavelength used as well as on the pure BC MAC used as a reference. The largest contribution to Eabs was due to the internal mixing of BC particles with other aerosol compounds, on average between a 91 % and a 100 % at 370 and 880 nm, respectively. Additionally, 14.5 % and 4.6 % of the total enhancement at the short ultraviolet (UV) wavelength (370 nm) was due to externally mixed brown carbon (BrC) particles during the cold and the warm period, respectively. On average, at the MSY station, a higher Eabs value was observed (1.83 at 637 nm) compared to BCN (1.37 at 637 nm), which was associated with the higher fraction of organic aerosols (OA) available for BC coating at the regional station, as denoted by the higher organic carbon to elemental carbon (OC:EC) ratio observed at MSY compared to BCN. At both BCN and MSY, Eabs showed an exponential increase with the amount of non-refractory (NR) material available for coating (RNR-PM). The Eabs at 637 nm at the MSY regional station reached values up to 3 during episodes with high RNR-PM, whereas in BCN, Eabs kept values lower than 2 due to the lower relative amount of coating materials measured at BCN compared to MSY. The main sources of OA influencing Eabs throughout the year were hydrocarbon OA (HOA) and cooking-related OA (COA), i.e. primary OA (POA) from traffic and cooking emissions, respectively, at both 370 and 880 nm. At the short UV wavelength (370 nm), a strong contribution to Eabs from biomass burning OA (BBOA) and less oxidized oxygenated OA (LO-OOA) sources was observed in the colder period. Moreover, we found an increase of Eabs with the ageing state of the particles, especially during the colder period. This increase of Eabs with particle ageing was associated with a larger relative amount of secondary OA (SOA) compared to POA. The availability of a long dataset at both stations from offline measurements enabled a decade-long trend analysis of Eabs at 637 nm, that showed statistically significant (s.s.) positive trends of Eabs during the warmer months at the MSY station. This s.s. positive trend in MSY mirrored the observed increase of the OC:EC ratio over time. Moreover, in BCN during the COVID-19 lockdown period in spring 2020 we observed a sharp increase of Eabs due to the observed sharp increase of the OC:EC ratio. Our results show similar values of Eabs to those found in the literature for similar background stations.
Keywords: black carbomn, coating, organic aerosol, light absorption
Published in RUNG: 10.05.2024; Views: 260; Downloads: 2
.pdf Full text (2,74 MB)
This document has many files! More...

80.
Search done in 0.1 sec.
Back to top