On-flight intercomparison of three miniature aerosol absorption sensors using unmanned aerial systems (UASs)

The present study investigates and compares the ground and in-flight performance of three miniaturized aerosol absorption sensors integrated on board small-sized Unmanned Aerial Systems (UASs). These sensors were evaluated during two contrasted field campaigns performed at an urban site, impacted mainly by local traffic and domestic wood burning sources (Athens, Greece), and at a remote regional background site, impacted by long-range transported sources including dust (Cyprus Atmospheric Observatory, Agia Marina Xyliatou, Cyprus). The miniaturized sensors were first intercompared at the ground-level against two commercially available instruments used as a reference. The measured signal of the miniaturized sensors was converted into the absorption coefficient and equivalent black carbon concentration (eBC). When applicable, signal saturation corrections were applied, following the suggestions of the manufacturers. The aerosol absorption sensors exhibited similar behavior against the reference instruments during the two campaigns, despite the diversity of the aerosol origin, chemical composition, sources, and concentration levels. The deviation from the reference during both campaigns concerning (eBC) mass was less than 8 %, while for the absorption coefficient it was at least 15 %. This indicates that those sensors that report black carbon mass are tuned and corrected to measure eBC more accurately than the absorption coefficient. The overall potential use of miniature aerosol absorption sensors on board small UASs is also illustrated. UAS-based absorption measurements were used to investigate the vertical distribution of eBC over Athens up to 1 km above sea level during January 2016, exceeding the top of the planetary boundary layer (PBL). Our results reveal a heterogeneous boundary layer concentration of absorbing aerosol within the PBL intensified in the early morning hours due to the concurrent peak traffic emissions at ground-level and the fast development of the boundary layer. After the full development of the PBL, homogenous concentrations are observed from 100 m a.g.l. to the PBL top

Aerosol absorption profiling from the synergy of lidar and sun-photometry : The ACTRIS-2 campaigns in Germany, Greece and Cyprus

© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/).Aerosol absorption profiling is crucial for radiative transfer calculations and climate modelling. Here, we utilize the synergy of lidar with sun-photometer measurements to derive the absorption coefficient and single scattering albedo profiles during the ACTRIS-2 campaigns held in Germany, Greece and Cyprus. The remote sensing techniques are compared with in situ measurements in order to harmonize and validate the different methodologies and reduce the absorption profiling uncertainties.Peer reviewe

Recommendations for reporting equivalent black carbon (eBC) mass concentrations based on long-term pan-European in-situ observations

A reliable determination of equivalent black carbon (eBC) mass concentrations derived from filter absorption photometers (FAPs) measurements depends on the appropriate quantification of the mass absorption cross-section (MAC) for converting the absorption coefficient (babs) to eBC. This study investigates the spatial–temporal variability of the MAC obtained from simultaneous elemental carbon (EC) and babs measurements performed at 22 sites. We compared different methodologies for retrieving eBC integrating different options for calculating MAC including: locally derived, median value calculated from 22 sites, and site-specific rolling MAC. The eBC concentrations that underwent correction using these methods were identified as LeBC (local MAC), MeBC (median MAC), and ReBC (Rolling MAC) respectively. Pronounced differences (up to more than 50 %) were observed between eBC as directly provided by FAPs (NeBC; Nominal instrumental MAC) and ReBC due to the differences observed between the experimental and nominal MAC values. The median MAC was 7.8 ± 3.4 m2 g-1 from 12 aethalometers at 880 nm, and 10.6 ± 4.7 m2 g-1 from 10 MAAPs at 637 nm. The experimental MAC showed significant site and seasonal dependencies, with heterogeneous patterns between summer and winter in different regions. In addition, long-term trend analysis revealed statistically significant (s.s.) decreasing trends in EC. Interestingly, we showed that the corresponding corrected eBC trends are not independent of the way eBC is calculated due to the variability of MAC. NeBC and EC decreasing trends were consistent at sites with no significant trend in experimental MAC. Conversely, where MAC showed s.s. trend, the NeBC and EC trends were not consistent while ReBC concentration followed the same pattern as EC. These results underscore the importance of accounting for MAC variations when deriving eBC measurements from FAPs and emphasize the necessity of incorporating EC observations to constrain the uncertainty associated with eBC.</p

Non methane hydrocarbons above the Eastern Mediterranean. Factors controlling their levels and contribution to the oxidative capacity of the atmosphere

The present work focuses on the study of light non methane hydrocarbons (NMHCs) in the Eastern Mediterranean. In the frame of this work a gas chromatograph equipped with flame ionization detector and a preconcentration unit was applied at a natural marine site from September 2003 to February 2006. NMHCs depicts a distinct seasonal cycle characterized by winter maximum and summer minimum due to photochemistry. Isoprene is an exception to this seasonal pattern as it presents a summer maximum which is due to photosynthetic induced production. Photochemistry also controls the diurnal variability of NMHCs as most of the species present a mid-day minimum. Isoprene is again an exception, as maximum occurs during mid-day due to enhanced photosynthetic production. Apart chemistry hydrocarbons level (especially the long-lived compounds >1 day ) is also determined by meteorology, namely air masses origin and wind speed. On the other hand due its extremely short lifetime (35min1 ημέρα) δίνοντας έμφαση στον ρόλο της προέλευσης και ταχύτητας των αερίων μαζών. Το ισοπρένιο λόγω του μικρού χρόνου ζωής (35min<τ<3.5h) δεν υφίσταται μεταφορά με αποτέλεσμα το επίπεδό του να αποδίδεται σε τοπικές πηγές με τις χερσαίες να υπερβαίνουν τις θαλάσσιες κατά έναν παράγοντα ως και 3 παρά την υψηλή θαλάσσια ροή ισοπρενίου η οποία εκτιμάται στα 108 - 6x109 molecules cm-2 s-1. Λαμβάνοντας υπόψη την εποχική και ημερήσια διακύμανση των NMHCs υπολογίζεται η ατμοσφαιρική συγκέντρωση ατόμων Cl και των ριζών ΟΗ αντίστοιχα. Για τα άτομα Cl, η μέση ετήσια τιμή εκτιμάται στα 2.7x103 άτομα/cm3 . Για τις ρίζες ΟΗ τα ημερήσια επίπεδα που εκτιμώνται από την μεταβλητότητα των NMHCs είναι 3.5x106 molecules/cm3, τιμή που συγκλίνει τα 3.8x106 molecules/cm3 των αποτελεσμάτων προσομοιώσεων μοντέλου κουτιού. Όσο αφορά στην επίδραση των NMHCs στο επίπεδο των ατμοσφαιρικών οξειδωτικών και φωτοχημικών προϊόντων καθοριστική κρίνεται η παρουσία του ισοπρενίου σε σχέση με τους άλλους υδρογονάνθρακες. Η παρουσία του έχει σαν αποτέλεσμα την μείωση NO3 και ΟΗ κατά 25% και 26% αντίστοιχα, ενώ ταυτόχρονα αυξάνει το επίπεδο των RΟx κατά 300-400%

Production of higher alcohols by catalytic conversion of bio-derived synthesis gas

The thermochemical conversion of biomass to synthesis gas (Η2/CO) through gasification, followed by catalytic conversion of syngas, could produce significant amounts of ethanol. Syngas originated from biomass can be also converted to methanol plus higher alcohols that can also be blended in gasoline. Carbon monoxide hydrogenation reaction towards higher alcohols is studied today under harsh operating conditions, due to the low yields and poor catalyst selectivity and no commercial process exists today. The key for a viable industrial application of this process is the development of a highly active and selective catalytic material, able to activate and convert carbon monoxide to higher alcohols at low temperature and pressure conditions and also exhibits satisfactory stability under typical syngas impurities. The purpose of the present thesis is the optimization of the higher alcohols (C2+) yield using the mildest possible conditions. Apart from that, the most promising materials are utilized for the synthesis of higher alcohols from a syngas with comparable composition to the synthesis gas produced from biomass gasification.More specifically, several catalytic systems, quite efficient for the production of higher alcohols from syngas, were developed and investigated, at mild reaction conditions (250 – 320°C and 40 – 60 bar), while mechanistic studies, as well as detailed investigation of the structural and physicochemical properties of the materials with respect to their catalytic performance, led to fundamental insight in the mechanistic pathway of the catalytic reaction and the nature of the active sites. The main part of the research was focused on two types of catalytic materials: copper based and molybdenum based catalysts.Hydrogenation of CO over K promoted Cu-based catalysts produced alcohols, with methanol being the major carbon oxygenated product. Mechanistic studies by means of in situ IR spectroscopy, showed that the non dissociative adsorption of CO on the surface of partially oxidized copper sites, Cu+, induces the formation of methanol. Accordingly, the present of Cu+ sites suggests that CO adsorbs mainly molecularly on the reference catalyst, forming a methanol indermediate that is further hydrogenated towards methanol. Zn substitution by Mn leads to increased Cu atoms electron density, resulting in the presence of both Cu+ and metallic Cu sites which may suggest that CO adsorbs in both non dissociative and dissociative forms. Molecularly adsorbed CO moves to anadsorbed CHx alkyl group to form ethanol and higher alcohols. Transition metal promotion in a series of K/Mo2C catalysts led to the development of the optimum catalytic materials of the present study. All transition metals increased the selectivity for higher alcohols compared to the reference material. Nickel had the most favorable effect, as it caused electron transfer from Ni to Mo atoms. We postulate that mixed Ni–Mo carbidic phase serves as the active centre for non-dissociative CO chemisorption and leads, in combination with dissociative CO adsorption on the Mo2C sites, to higher alcohol formation.Stability testing of the optimum Ni/K/Mo2C catalyst for 400h time on stream, demonstrated considerable deactivation, with an activity decrease of 25% during the first 150h, ascribed to carbon deposition and catalyst aggregation. Selectivity did not vary significantly with time on stream.Η θερμοχημική μετατροπή της βιομάζας προς αέριο σύνθεσης (Η2/CO), ακολουθούμενη από την καταλυτική μετατροπή του αερίου, αποτελεί μια εναλλακτική διεργασία παραγωγής αιθανόλης. Το αέριο σύνθεσης μπορεί να μετατραπεί επιπλέον και σε άλλες αλκοόλες που χρησιμοποιούνται ως καύσιμα, π.χ. μεθανόλη, βουτανόλη και ανώτερες αλκοόλες. Οι μέχρι σήμερα τυπικές συνθήκες λειτουργίας που εξετάζονται για τη σύνθεση των ανώτερων αλκοολών από αέριο σύνθεσης είναι ιδιαίτερα δραστικές, λόγω της χαμηλής απόδοσης των εξεταζόμενων καταλυτικών υλικών. Η βιομηχανική εφαρμογή μια τέτοιας διεργασίας απαιτεί την ανάπτυξη κατάλληλου καταλυτικού συστήματος το οποίο θα είναι ενεργό σε ήπιες συνθήκες αλλά και σταθερό παρουσία τυπικών προσμίξεων που μπορεί να περιέχονται στο αέριο σύνθεσης προερχόμενο από βιομάζα. Ως στόχος, λοιπόν, της παρούσας διατριβής τέθηκε η βελτιστοποίηση της απόδοσης σε ανώτερες (C2+) αλκοόλες σε όσο το δυνατόν πιο ήπιες συνθήκες θερμοκρασίας και πίεσης αλλά και η μελέτη της σταθερότητας των βέλτιστων καταλυτικών υλικών σε συνθήκες που προσομοιάζουν τις βιομηχανικές. Συγκεκριμένα, αναπτύχθηκαν και μελετήθηκαν καταλυτικά υλικά με ικανοποιητική απόδοση στην αντίδραση υδρογόνωσης του μονοξειδίου του άνθρακα προς ανώτερες αλκοόλες, σε χαμηλές θερμοκρασίες (250 – 320°C) και μέτριες πιέσεις (40 – 60 bar), ενώ μελέτη του μηχανισμού, καθώς και λεπτομερής διερεύνηση των δομικών και φυσικοχημικών χαρακτηριστικών των καταλυτών σε σχέση με την απόδοσή τους στην αντίδραση, οδήγησαν στην εξαγωγή σημαντικών πληροφοριών για τον τρόπο που λειτουργούν τα υλικά και τη φύση των ενεργών κέντρων της αντίδρασης. Η έρευνα που διεξήχθη επικεντρώθηκε στη μελέτη δύο μεγάλων κατηγοριών καταλυτικών υλικών: καταλύτες βασισμένους σε χαλκό και καταλύτες βασισμένους σε μολυβδαίνιο. Η μελέτη καταλυτικών υλικών βασισμένων σε χαλκό και ενισχυμένων με κάλιο έδειξε ότι οι καταλύτες αυτοί είναι ικανοποιητικά ενεργοί και εκλεκτικοί για την αντίδραση της υδρογόνωσης του μονοξειδίου του άνθρακα προς αλκοόλες, με κύριο οξυγονούχο προϊόν να αποτελεί η μεθανόλη. Διερεύνηση του μηχανισμού με τη μέθοδο της in situ υπέρυθρης φασματοσκοπίας έδειξε πως ο σχηματισμός μεθανόλης λαμβάνει χώρα μέσω της μη διασπαστικής ρόφησης του CO σε κέντρα Cu+, τα οποία διατηρούνται παρουσία του ψευδαργύρου και είναι ο κύριος μηχανισμός που λαμβάνει χώρα παρουσία του καταλύτη αναφοράς. Η αντικατάσταση του Zn από Mn διαφοροποιεί ηλεκτρονιακά τα ενεργά κέντρα του χαλκού, δημιουργώντας στην επιφάνεια τόσο κέντρα μοριακής ρόφησης του CO (σε Cu+), όσο και κέντρα διασπαστικής ρόφησης του CO προς C και Ο (σε μεταλλικό Cu), τα οποία υδρογονώνονται προς υδρογανθρακικά είδη. Tο μοριακό CO προστίθεται στα υδρογονανθρακικά είδη οδηγώντας στον σχηματισμό ανώτερων αλκοολών. Η ενίσχυση του K/Mo2C με μέταλλα μετάπτωσης επηρεάζει τόσο τα φυσικοχημικά χαρακτηριστικά όσο και την καταλυτική συμπεριφορά των καρβιδίων. Η προσθήκη του νικελίου είχε την πιο αξιοσημείωτη επίδραση, προκαλώντας διαφοροποίηση της ηλεκτρονιακής κατάστασης των κέντρων Μο, τα οποία σε συνδυασμό με το Ni αποτελούν τα ενεργά κέντρα για τη μοριακή, παρά για τη διασπαστική, ρόφηση του CO οδηγώντας σε αυξημένη παραγωγή ανώτερων αλκοολών. Στο πείραμα σταθερότητας, διάρκειας 400h, ο καταλύτης Ni/K/Mo2C, παρουσίασε μια σταθερή απενεργοποίηση κατά 25% για τις πρώτες 150 h λειτουργίας του, κυρίως λόγω εναπόθεσης άνθρακα στην καταλυτική επιφάνεια και δημιουργίας συσσωματωμάτων. Η εκλεκτικότητα στα διάφορα προϊόντα δεν βρέθηκε να μεταβάλλεται σημαντικά με το χρόνο

Non-methane hydrocarbon variability in Athens during wintertime: the role of traffic and heating

International audienceNon-methane hydrocarbons (NMHCs) play an important role in atmospheric chemistry, contributing to ozone and secondary organic aerosol formation. They can also serve as tracers for various emission sources such as traffic, solvents, heating and vegetation. The current work presents, for the first time to our knowledge, time-resolved data of NMHCs, from two to six carbon atoms, for a period of 5 months (mid-October 2015 to mid-February 2016) in the "greater Athens area" (GAA), Greece. The measured NMHC levels are among the highest reported in the literature for the Mediterranean area during winter months, and the majority of the compounds demonstrate a remarkable day-today variability. Their levels increase by up to factor of 4 from autumn (October-November) to winter (December-February). Mi-croscale meteorological conditions, especially wind speed in combination with the planetary boundary layer (PBL) height, seem to contribute significantly to the variability of NMHC levels, with an increase of up to a factor of 10 under low wind speed (< 3 m s −1) conditions; this reflects the impact of local sources rather than long-range transport. All NMHCs demonstrated a pronounced bimodal, diurnal pattern with a morning peak followed by a second peak before midnight. The amplitude of both peaks gradually increased towards winter, in comparison to autumn, by a factor of 3 to 6 and closely followed that of carbon monoxide (CO), which indicates a contribution from sources other than traffic, e.g., domestic heating (fuel or wood burning). By comparing the NMHC diurnal variability with that of black carbon (BC), its fractions associated with wood burning (BC wb) and fossil fuel combustion (BC ff), and with source profiles we conclude that the morning peak is attributed to traffic while the night peak is mainly attributed to heating. With respect to the night peak, the selected tracers and source profiles clearly indicate a contribution from both traffic and domestic heating (fos-sil fuel and wood burning). NMHCs slopes versus BC wb are similar when compared with those versus BC ff (slight difference for ethylene), which indicates that NMHCs are most likely equally produced by wood and oil fossil fuel burning

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 &plusmn; 4.8 &mu;g m&minus;3 and 0.7 &plusmn; 0.6 &mu;g m&minus;3, respectively) were observed relative to the past, whereas for HCl (mean of 0.4 &mu;g m&minus;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 &mu;g m&minus;3 and 5.5 &mu;g m&minus;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

Vertical Profiling of Fresh Biomass Burning Aerosol Optical Properties over the Greek Urban City of Ioannina, during the PANACEA Winter Campaign

Vertical profiling of aerosol particles was performed during the PANhellenic infrastructure for Atmospheric Composition and climatE chAnge (PANACEA) winter campaign (10 January 2020–7 February 2020) over the city of Ioannina, Greece (39.65° N, 20.85° E, 500 m a.s.l.). The middle-sized city of Ioannina suffers from wintertime air pollution episodes due to biomass burning (BB) domestic heating activities. The lidar technique was applied during the PANACEA winter campaign on Ioannina city, to fill the gap of knowledge of the spatio-temporal evolution of the vertical mixing of the particles occurring during these winter-time air pollution episodes. During this campaign the mobile single-wavelength (532 nm) depolarization Aerosol lIdAr System (AIAS) was used to measure the spatio-temporal evolution of the aerosols’ vertical profiles within the Planetary Boundary Layer (PBL) and the lower free troposphere (LFT; up to 4 km height a.s.l.). AIAS performed almost continuous lidar measurements from morning to late evening hours (typically from 07:00 to 19:00 UTC), under cloud-free conditions, to provide the vertical profiles of the aerosol backscatter coefficient (baer) and the particle linear depolarization ratio (PLDR), both at 532 nm. In this study we emphasized on the vertical profiling of very fresh (~hours) biomass burning (BB) particles originating from local domestic heating activities in the area. In total, 33 out of 34 aerosol layers in the lower free troposphere were characterized as fresh biomass burning ones of local origin, showing a mean particle linear depolarization value of 0.04 ± 0.02 with a range of 0.01 to 0.09 (532 nm) in a height region 1.21–2.23 km a.s.l. To corroborate our findings, we used in situ data, particulate matter (PM) concentrations (PM2.5) from a particulate sensor located close to our station, and the total black carbon (BC) concentrations along with the respective contribution of the fossil fuel (BCff) and biomass/wood burning (BCwb) from the Aethalometer. The PM2.5 mass concentrations ranged from 5.6 to 175.7 μg/m3, while the wood burning emissions from residential heating were increasing during the evening hours, with decreasing temperatures. The BCwb concentrations ranged from 0.5 to 17.5 μg/m3, with an extremely high mean contribution of BCwb equal to 85.4%, which in some cases during night-time reached up to 100% during the studied period