Correlation of chemical properties with optical and climatic parameters of particulate matter in the area of Athens

The objective of the present work is the investigation of the correlation between chemical composition and physico-optical parameters of aerosol, in order to comprehend their climatic role in a megacity that is located in the area of Eastern Mediterranean. Therefore, measurements of mass concentration, organic carbon, elemental carbon, main ions and (selectively) metal concentrations were applied on samples that were collected at 2 sites in Athens (urban and suburban). On a seasonal basis, summer EC is formed by dominant regional sources (53±12% of EC) while, in winter the prevailing result of local sources is highlighted (71±8% of EC). OC reaches 79±4% of total carbon and the estimated particulate organic matter (POM) constitutes 24±6% of the collected fine particles. The calculated mean concentration of water soluble organic carbon (WSOC) is 1.5±0.9 μg m-3 and the estimated ratio WSOC/OC is 63±7%, reflecting the presence of aged aerosol in the area. A detailed analysis of ionic mass fraction shows that nss-SO4-2 constitutes the major component while, NO3- and NH4+ contribute to a lesser extent. Chemical mass closure justifies on average 96±11% and 82±10% of measured aerosol mass, during dust events and in the absence of dust events, respectively. POM and ionic mass (IM) contribute mainly in the total particulate mass, followed by dust and water. The application of PMF3.0 model led to the identification of six factors, in descending order: secondary photochemistry, soil, fossil fuel combustion, traffic, biomass burning and sea salt. Furthermore, in the urban station, the relative contribution of local EC, IM and POM is 52-56% in winter, in contrast to the warmer period of the year, when only 11% of EC, IM and POM is local. Daily values of scattering coefficient give an average of 30.1±3.9 Μm-1 while, the mean value of absorption coefficient is 5.2±1.4 Μm-1. Scattering coefficient is significantly affected by fine particles and the included sulphate ions while, absorption coefficient is mainly affected by EC concentration. The mean single scattering albedo (SSA) value is estimated to be 0.87±0.11. Daily values of scattering coefficient that is measured by the nephelometer and is reconstructed on dry and ambient conditions (based on chemical parameters) present good correlation while, the seasonal variability of the scattering coefficient is satisfactorily represented by aerosol chemical composition. The water reception is estimated to contribute on average 46±13% to the reconstructed scattering coefficient. Finally, the effect of dust on absorption of radiation is studied and, its estimated contribution equals to 13%, during the whole studied period.Αντικείμενο της παρούσας διατριβής είναι η διερεύνηση των συσχετισμών μεταξύ της χημικής σύστασης και των φυσικό-οπτικών ιδιοτήτων των αερολυμάτων, προκειμένου να κατανοηθεί ο κλιματικός τους ρόλος σε μία μεγαλούπολη στην ευρύτερη περιοχή της Ανατολικής Μεσογείου. Ως εκ τούτου, πραγματοποιήθηκαν μετρήσεις των μαζών, του στοιχειακού άνθρακα, οργανικού άνθρακα, των ιόντων και των μετάλλων (επιλεκτικά), στα δείγματα που συλλέχθηκαν σε 2 σταθμούς της Αθήνας (αστικό και περιαστικό). Σε εποχική βάση, ο EC εκπέμπεται από κυρίαρχες περιοχικές πηγές (53±12% του EC) ενώ, κατά τη διάρκεια του χειμώνα, επισημαίνεται η σημαντικότητα των τοπικών πηγών (71±8% του EC). Ο OC φθάνει στο 79±4% του ολικού άνθρακα, και η εκτιμώμενη σωματιδιακή οργανική ύλη (ΡΟΜ) αποτελεί το 24±6% των συλλεχθέντων λεπτών αερολυμάτων. Η υπολογισμένη μέση συγκέντρωση του υδατοδιαλυτού οργανικού άνθρακα (WSOC) είναι 1.5±0.9 μg m-3 και ο εκτιμώμενος λόγος WSOC/OC είναι 63±7%, αντανακλώντας την παρουσία «γερασμένων» αερολυμάτων στην τοποθεσία. Η λεπτομερής ανάλυση του ιοντικού κλάσματος μάζας δείχνει ότι τα θειικά μη-θαλάσσιας προέλευσης (nss-SO4-2) αποτελούν τα κύρια συστατικά ενώ, τα νιτρικά (NO3-) και αμμώνια (NH4+) συνεισφέρουν σε μικρότερο ποσοστό. Το ισοζύγιο χημικής μάζας δικαιολογεί, κατά μέσο όρο, το 96±11% και το 82±10% της μετρούμενης μάζας των αερολυμάτων, κατά την διάρκεια των επεισοδίων σκόνης και απουσία σκόνης, αντίστοιχα. Στη συνολική σωματιδιακή μάζα των ΡΜ2.5 συνεισφέρουν, κατά κύριο λόγο, η οργανική σωματιδιακή ύλη και η ιοντική μάζα (ΙΜ) ενώ, ακολουθεί η σκόνη και το νερό. Η χρήση μοντέλου PMF οδήγησε στην ταυτοποίηση έξι πηγών αερολυμάτων, με σειρά φθίνουσας συνεισφοράς: δευτερογενής φωτοχημεία, έδαφος, χρήση ορυκτών καυσίμων, κυκλοφορία αυτοκινήτων, καύση βιομάζας και θαλάσσιο άλας. Επιπλέον, στον αστικό σταθμό, η σχετική συνεισφορά των τοπικών EC, IM και POM είναι 52-56% το χειμώνα, σε αντίθεση με τη θερμότερη περίοδο του χρόνου, οπότε μόνο το 11% των EC, IM και POM είναι τοπικό. Η μέση τιμή του συντελεστή σκέδασης είναι 30.1±3.9 Μm-1 ενώ, ο μέσος όρος για το συντελεστή απορρόφησης προέκυψε 5.2±1.4 Μm-1. Ο συντελεστής σκέδασης επηρεάζεται σημαντικά από τα λεπτά σωματίδια και από τα περιεχόμενα σε αυτά θειικά ιόντα, ενώ ο συντελεστής απορρόφησης εξαρτάται, κυρίως, από την συγκέντρωση του EC στα λεπτά σωματίδια. Η μέση τιμή της ανακλαστικότητας μεμονωμένης σκέδασης (SSA) εκτιμάται ότι είναι 0.87±0.11. Οι ημερήσιες τιμές του συντελεστή σκέδασης που έχει μετρηθεί από το νεφελόμετρο και αυτού που έχει ανακτηθεί, σύμφωνα με τη χημεία, σε συνθήκες περιβάλλοντος και σε ξηρές συνθήκες, παρουσιάζουν καλή συσχέτιση μεταξύ τους ενώ, φαίνεται ότι η εποχική μεταβλητότητα του συντελεστή σκέδασης μπορεί να αναπαραχθεί ικανοποιητικά μέσω της χημικής σύστασης των αερολυμάτων. Υπολογίζεται ότι η σχετική συνεισφορά της πρόσληψης νερού στον ανακτώμενο συντελεστή σκέδασης συνεισφέρει κατά μέσο όρο 46±13%. Τέλος, μελετάται η επίδραση της σκόνης στην απορρόφηση της ακτινοβολίας και η συνεισφορά της βρέθηκε ίση με 13% για το συνολικό μελετώμενο χρονικό διάστημα

Impact of COVID-19 Lockdown on Oxidative Potential of Particulate Matter: Case of Athens (Greece)

This work evaluates the aerosol oxidative potential (OP) and its changes from modified air pollution emissions during the COVID-19 lockdown period in 2020, with the intent of elucidating the contribution of aerosol sources and related components to aerosol OP. For this, daily particulate matter (PM) samples at an urban background site were collected and analyzed with a chemical (acellular) assay based on Dithiothreitol (DTT) during the COVID-19 restriction period in Athens (Greece). The obtained time-series of OP, PM2.5, organic matter (OM) and SO42− of the pre-, post- and lockdown periods were also compared to the data of the same time periods during the years 2017–2019. Even though all traffic-related emissions have been significantly reduced during the lockdown period (by 30%), there is no reduction in water-soluble OP, organics and sulfate concentrations of aerosol during 2020. The results reveal that the decrease in traffic was not sufficient to drive any measurable change on OP, suggesting that other sources—such as biomass burning and secondary aerosol from long-range transport, which remained unchanged during the COVID lockdown—are the main contributors to OP in Athens, Greece

High-Resolution Measurements of SO₂, HNO₃ and HCl at the Urban Environment of Athens, Greece: Levels, Variability and Gas to Particle Partitioning

High-resolution measurements of sulfur dioxide (SO2), nitric acid (HNO3), and hydrochloric acid (HCl) were conducted in Athens, Greece, from 2014 to 2016 via a wet rotating annular denuder system paired with an ion chromatograph. Decreased mean annual levels of SO2 and HNO3 (equal to 3.3 ± 4.8 μg m−3 and 0.7 ± 0.6 μg m−3, respectively) were observed relative to the past, whereas for HCl (mean of 0.4 μg m−3 ) no such comparison was possible as the past measurements are very scarce. Regional and local emission sources regulated the SO2 levels and contributed to both the December and the July maxima of 6.6 μg m−3 and 5.5 μg m−3, respectively. Similarly, the significant enhancement at noon and during the winter nighttime was due to transported SO2 and residential heating, respectively. The oxidation of NO2 by OH radicals and the heterogeneous reactions of HNO3 on sea salt seemed to drive the HNO3 and HCl formation, respectively, whereas nighttime biomass burning affected only the former by almost 50%. During summer, the sulfate anions dominated over the SO2, in contrast to the chloride and nitrate ions that prevailed during the winter and were linked to the aerosol acidity that influences their lifetime as well as their impact on ecosystems

High-Resolution Measurements of SO2, HNO3 and HCl at the Urban Environment of Athens, Greece: Levels, Variability and Gas to Particle Partitioning

High-resolution measurements of sulfur dioxide (SO2), nitric acid (HNO3), and hydrochloric acid (HCl) were conducted in Athens, Greece, from 2014 to 2016 via a wet rotating annular denuder system paired with an ion chromatograph. Decreased mean annual levels of SO2 and HNO3 (equal to 3.3 ± 4.8 μg m−3 and 0.7 ± 0.6 μg m−3, respectively) were observed relative to the past, whereas for HCl (mean of 0.4 μg m−3 ) no such comparison was possible as the past measurements are very scarce. Regional and local emission sources regulated the SO2 levels and contributed to both the December and the July maxima of 6.6 μg m−3 and 5.5 μg m−3, respectively. Similarly, the significant enhancement at noon and during the winter nighttime was due to transported SO2 and residential heating, respectively. The oxidation of NO2 by OH radicals and the heterogeneous reactions of HNO3 on sea salt seemed to drive the HNO3 and HCl formation, respectively, whereas nighttime biomass burning affected only the former by almost 50%. During summer, the sulfate anions dominated over the SO2, in contrast to the chloride and nitrate ions that prevailed during the winter and were linked to the aerosol acidity that influences their lifetime as well as their impact on ecosystems

Spatiotemporal Gradients of PAH Concentrations in Greek Cities and Associated Exposure Impacts

To study the spatiotemporal variability of particle-bound polycyclic aromatic hydrocarbons (PAHs) and assess their carcinogenic potential in six contrasting urban environments in Greece, a total of 305 filter samples were collected and analyzed. Sampling sites included a variety of urban background, traffic (Athens, Ioannina and Heraklion), rural (Xanthi) and near-port locations (Piraeus and Volos). When considering the sum of 16 U.S. EPA priority PAHs, as well as that of the six EU-proposed members, average concentrations observed across locations during summer varied moderately (0.4–2.2 ng m−3) and independently of the population of each site, with the highest values observed in the areas of Piraeus and Volos that are affected by port and industrial activities. Winter levels were significantly higher and more spatially variable compared to summer, with the seasonal enhancement ranging from 7 times in Piraeus to 98 times in Ioannina, indicating the large impact of PAH emissions from residential wood burning. Regarding benzo(a)pyrene (BaP), an IARC Group 1 carcinogen and the only EU-regulated PAH, the winter/summer ratios were 24–33 in Athens, Volos, Heraklion and Xanthi; 60 in Piraeus; and 480 in Ioannina, which is afflicted by severe wood-burning pollution events. An excellent correlation was observed between organic carbon (OC) and benzo(a)pyrene (BaP) during the cold period at all urban sites (r2 > 0.8) with stable BaP/OC slopes (0.09–0.14 × 10−3), highlighting the potential use of OC as a proxy for the estimation of BaP in winter conditions. The identified spatiotemporal contrasts, which were explored for the first time for PAHs at such a scale in the Eastern Mediterranean, provide important insights into sources and controlling atmospheric conditions and reveal large deviations in exposure risks among cities that raise the issue of environmental injustice on a national level

Carbonaceous Aerosols in Contrasting Atmospheric Environments in Greek Cities: Evaluation of the EC-tracer Methods for Secondary Organic Carbon Estimation

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%)

DIANA-TarBase v7.0: indexing more than half a million experimentally supported miRNA:mRNA interactions

microRNAs (miRNAs) are short non-coding RNA species, which act as potent gene expression regulators. Accurate identification of miRNA targets is crucial to understanding their function. Currently, hundreds of thousands of miRNA:gene interactions have been experimentally identified. However, this wealth of information is fragmented and hidden in thousands of manuscripts and raw next-generation sequencing data sets. DIANA-TarBase was initially released in 2006 and it was the first database aiming to catalog published experimentally validated miRNA:gene interactions. DIANA-TarBase v7.0 (http://www.microrna.gr/tarbase) aims to provide for the first time hundreds of thousands of high-quality manually curated experimentally validated miRNA:gene interactions, enhanced with detailed meta-data. DIANA-TarBase v7.0 enables users to easily identify positive or negative experimental results, the utilized experimental methodology, experimental conditions including cell/tissue type and treatment. The new interface provides also advanced information ranging from the binding site location, as identified experimentally as well as in silico, to the primer sequences used for cloning experiments. More than half a million miRNA:gene interactions have been curated from published experiments on 356 different cell types from 24 species, corresponding to 9- to 250-fold more entries than any other relevant database. DIANA-TarBase v7.0 is freely available

An interlaboratory comparison to quantify oxidative potential measurement in aerosol particles: challenges and recommendations for harmonisation

International audienceThis paper presents the findings from a collaborative interlaboratory comparison exercise designed to assess oxidative potential (OP) measurements conducted by 20 laboratories worldwide. This study represents an innovative effort as the first exercise specifically aimed at harmonising this type of OP assay, setting a new benchmark in the field. Over the last decade, there has been a noticeable increase in OP studies, with numerous research groups investigating the effects of exposure to air pollution particles through the evaluation of OP levels. However, the absence of standardised methods for OP measurements has resulted in variability in results across different groups, rendering meaningful comparisons challenging. To address this issue, this study engages in an international effort to compare OP measurements using a simplified method (with a dithiothreitol (DTT) assay). Here, we quantify the OP in liquid samples to focus on the protocol measurement itself, while future ILCs should aim to assess the full-chain process, including the sample extraction. We analyse the similarities and discrepancies observed in the results, identifying the critical parameters (such as the instrument used, the use of a simplified protocol, the delivery and analysis time) that could influence OP measurements, and provide recommendations for future studies and interlaboratory comparisons. Even if other crucial aspects, such as sampling PM methods, sample storage, extraction methods and conditions, and the evaluation of other OP assays, still need to be standardised. This collaborative approach enhances the robustness of the OP-DTT assay and paves the way for future studies to build on a unified framework. This pioneering work concludes that interlaboratory comparisons provide essential insights into the OP metric and are crucial to move toward the harmonisation of OP measurements