First validation of GOME-2/MetOp Absorbing Aerosol Height using EARLINET lidar observations

he aim of this study is to investigate the potential of the Global Ozone Monitoring Experiment-2 (GOME-2) instruments, aboard the Meteorological Operational (MetOp)-A, MetOp-B and MetOp-C satellite programme platforms, to deliver accurate geometrical features of lofted aerosol layers. For this purpose, we use archived ground-based lidar data from stations available from the European Aerosol Research Lidar Network (EARLINET) database. The data are post-processed using the wavelet covariance transform (WCT) method in order to extract geometrical features such as the planetary boundary layer (PBL) height and the cloud boundaries. To obtain a significant number of collocated and coincident GOME-2 - EARLINET cases for the period between January 2007 and September 2019, 13 lidar stations, distributed over different European latitudes, contributed to this validation. For the 172 carefully screened collocations, the mean bias was found to be -0.18 ± 1.68 km, with a near-Gaussian distribution. On a station basis, and with a couple of exceptions where very few collocations were found, their mean biases fall in the ± 1 km range with an associated standard deviation between 0.5 and 1.5 km. Considering the differences, mainly due to the temporal collocation and the difference, between the satellite pixel size and the point view of the ground-based observations, these results can be quite promising and demonstrate that stable and extended aerosol layers as captured by the satellite sensors are verified by the ground-based data. We further present an in-depth analysis of a strong and long-lasting Saharan dust intrusion over the Iberian Peninsula. We show that, for this well-developed and spatially well-spread aerosol layer, most GOME-2 retrievals fall within 1 km of the exact temporally collocated lidar observation for the entire range of 0 to 150 km radii. This finding further testifies for the capabilities of the MetOp-borne instruments to sense the atmospheric aerosol layer heights.Horizon 2020 Framework Programme 654109, 87111

EARLINET evaluation of the CATS Level 2 aerosol backscatter coefficient product

We present the evaluation activity of the European Aerosol Research Lidar Network (EARLINET) for the quantitative assessment of the Level 2 aerosol backscatter coefficient product derived by the Cloud-Aerosol Transport System (CATS) aboard the International Space Station (ISS; Rodier et al., 2015). The study employs correlative CATS and EARLINET backscatter measurements within a 50km distance between the ground station and the ISS overpass and as close in time as possible, typically with the starting time or stopping time of the EARLINET performed measurement time window within 90min of the ISS overpass, for the period from February 2015 to September 2016. The results demonstrate the good agreement of the CATS Level 2 backscatter coefficient and EARLINET. Three ISS overpasses close to the EARLINET stations of Leipzig, Germany; Évora, Portugal; and Dushanbe, Tajikistan, are analyzed here to demonstrate the performance of the CATS lidar system under different conditions. The results show that under cloud-free, relative homogeneous aerosol conditions, CATS is in good agreement with EARLINET, independent of daytime and nighttime conditions. CATS low negative biases are observed, partially attributed to the deficiency of lidar systems to detect tenuous aerosol layers of backscatter signal below the minimum detection thresholds; these are biases which may lead to systematic deviations and slight underestimations of the total aerosol optical depth (AOD) in climate studies. In addition, CATS misclassification of aerosol layers as clouds, and vice versa, in cases of coexistent and/or adjacent aerosol and cloud features, occasionally leads to non-representative, unrealistic, and cloud-contaminated aerosol profiles. Regarding solar illumination conditions, low negative biases in CATS backscatter coefficient profiles, of the order of 6.1%, indicate the good nighttime performance of CATS. During daytime, a reduced signal-to-noise ratio by solar background illumination prevents retrievals of weakly scattering atmospheric layers that would otherwise be detectable during nighttime, leading to higher negative biases, of the order of 22.3%. © Author(s) 2019

EARLINET evaluation of the CATS Level 2 aerosol backscatter coefficient product

We present the evaluation activity of the European Aerosol Research Lidar Network (EARLINET) for the quantitative assessment of the Level 2 aerosol backscatter coefficient product derived by the Cloud-Aerosol Transport System (CATS) aboard the International Space Station (ISS; Rodier et al., 2015). The study employs correlative CATS EARLINET backscatter measurements within a 50 km distance between the ground station and the ISS overpass and as close in time as possible, typically with the starting time or stopping time of the EARLINET performed asurement time window within 90 min of the ISS overpass, for the period from February 2015 to September 2016

Κλιματολογία και ταξινόμηση των οπτικών και μικροφυσικών ιδιοτήτων των αιωρούμενων σωματιδίων με μεθόδους επίγειας τηλεπισκόπησης

The main topic of the thesis is the climatology and classification of the optical and microphysical properties of aerosols using ground-based remote sensing techniques. These techniques include mainly a lidar instrument and a sunphotometer. While the primary focus is on measurements performed at the Laboratory of Atmospheric Physics station in Thessaloniki, Greece, the thesis is also supplemented with public lidar data from the European Lidar Network (EARLINET) database. The analysis covers four main subjects. The maintenance and quality control procedures of a depolarization Raman lidar instrument located in the station of Thessaloniki, Greece, is presented first. Then, an extensive climatological analysis based on the aerosol optical and geometrical properties calculated from lidar and sunphotometer measurements of the station is performed. Aerosol microphysical properties obtained from combined lidar and sunphotometer measurements are applied in the evaluation of aerosol forecasts of an air quality model for Thessaloniki. Finally, some of the aforementioned lidar products, along with lidar data from the EARLINET database are applied for the validation of satellite products.Στη διατριβή αυτή μελετήθηκε η κλιματολογία και η ταξινόμηση των οπτικών και μικροφυσικών ιδιοτήτων των αιωρούμενων σωματιδίων με τη χρήση μεθόδων επίγειας τηλεπισκόπησης. Οι τεχνικές αυτές περιλαμβάνουν κατά βάση μία διάταξη lidar και ένα φωτόμετρο. Αν και η ανάλυση στο μεγαλύτερό της μέρος αφορά μετρήσεις του εργαστηρίου Φυσικής της Ατμόσφαιρας στην Θεσσαλονίκη, εντούτοις, στο πλαίσιο της διατριβής αξιοποιήθηκαν επίσης μετρήσεις του Ευρωπαϊκού δικτύου των lidar, European Lidar Network (EARLINET). Η ανάλυση συνοψίζεται σε τέσσερις κύριες θεματολογίες. Αρχικά, γίνεται παρουσίαση των διεργασιών συντήρησης και βελτιστοποίησης ενός συστήματος depolarization Raman lidar. Στη συνέχεια, περιγράφονται εκτενώς η μεθοδολογία και τα αποτελέσματα της κλιματολογικής ανάλυσης των μετρήσεων της χρονοσειράς του lidar και του φωτόμετρου στην περιοχή της Θεσσαλονίκης. Επιπρόσθετα, γίνεται υπολογισμός κάποιων μικροφυσικών ιδιοτήτων των αεροζόλ με τη συνδυαστική χρήση των δύο οργάνων και τα αποτελέσματα χρησιμοποιούνται για την αξιολόγηση ενός μοντέλου ποιότητας αέρα στην περιοχή της Θεσσαλονίκης. Τέλος, κάποια από τα προϊόντα τα οποία προέκυψαν από την ανάλυση, μαζί με μετρήσεις της βάσης δεδομένων του EARLINET αξιοποιήθηκαν στην αξιολόγηση δορυφορικών παρατηρήσεων

Columnar aerosol measurements in a continental southeastern Europe site: climatology and trends

Monitoring of aerosols and their temporal evolution is very important for climate and air quality studies. In this study, we present a climatology of aerosol optical and microphysical properties over a continental southeastern European area based on 9 years of observations from a Cimel sun-photometer operating at Magurele (Romania) in the framework of AErosol RObotic NETwork (AERONET). The site is characterized by high intra-annual and inter-annual variability of the total aerosol optical depth (AOD), which has two peaks, during March and August. For half year, from May to November, Magurele is affected by the transport of aerosols from the nearby city of Bucharest, since the dominant winds are from this direction. Thus, the predominant is the fine mode of aerosols. The high inter-annual and intra-annual variability of Angstrom exponent (440–870 nm) indicates the presence of aerosols of different sizes. Negative statistically significant trends at all AOD wavelengths, the order of 20–40% per decade, have been calculated for the 9-year period of study (2007–2016). These trends are mostly attributed to the reduction of the fine mode particles, showing that the implementation of the EU regulations for the decrease of particulate matter emissions in Bucharest has been beneficial

Deriving Aerosol Absorption Properties from Solar Ultraviolet Radiation Spectral Measurements at Thessaloniki, Greece

The gap in knowledge regarding the radiative effects of aerosols in the UV region of the solar spectrum is large, mainly due to the lack of systematic measurements of the aerosol single scattering albedo (SSA) and absorption optical depth (AAOD). In the present study, spectral UV measurements performed in Thessaloniki, Greece by a double monochromator Brewer spectrophotometer in the period 1998–2017 are used for the calculation of the aforementioned optical properties. The main uncertainty factors have been described and there is an effort to quantify the overall uncertainties in SSA and AAOD. Analysis of the results suggests that the absorption by aerosols is much stronger in the UV relative to the visible. SSA follows a clear annual pattern ranging from ~0.7 in winter to ~0.85 in summer at wavelengths 320–360 nm, while AAOD peaks in summer and winter. The average AAOD for 2009–2011 is ~50% above the 2003–2006 average, possibly due to increased emissions of absorbing aerosols related to the economic crisis and the metro-railway construction works in the city center

CONSISTENCY OF THE SINGLE CALCULUS CHAIN FOR CLIMATOLOGICAL STUDIES USING LONG-TERM MEASUREMENTS FROM THESSALONIKI LIDAR STATION

The long term analysis of 15 years of lidar data derived from a Raman lidar at Thessaloniki is presented here. All measurements have been processed with the latest version 4 of the EARLINET Single Calculus Chain algorithm and are compared with the results from the current operational retrieval algorithm. In this paper we investigate the consistency between the EARLINET database and SCC for the case of Thessaloniki and we identify the issues to be considered when switching from current operations to SCC

Evaluation of Aerosol Typing with Combination of Remote Sensing Techniques with In Situ Data during the PANACEA Campaigns in Thessaloniki Station, Greece

Two measurement campaigns were conducted at Thessaloniki, an urban station, (40.5°N, 22.9°E; 60 m) in the frame of the PANhellenic infrastructure for Atmospheric Composition and climatEchAnge (PANACEA) project. The first one covers the period from July to August 2019 and the second one from January to February An overview of the aerosol optical properties (columnar and height resolved), acquired with the remote sensing infrastructure of the Laboratory of Atmospheric Physics (LAP) of the Aristotle University of Thessaloniki (AUTH), as well as the additional instrumentation that participated during the PANACEA campaigns is presented. The majority of the detected layers (16 out of 40, ranged between 0.8 and 4.5 km) are classified as biomass burning aerosols, attributed to either city sources or long range transport. Concerning the other aerosol types, the Clean Continental cluster has an occurrence ratio of 23%, while dust layers and mixtures with urban particles transported to Thessaloniki are also identified. Our findings are discussed along with the surface information, i.e., the particulate matter (PM2.5 and PM10) concentrations and the black carbon (BC) concentration, separated into fossil fuel (BCff) and biomass/wood burning (BCwb) fractions. This is the first time that collocated in situ and remote sensing instruments are deployed in Thessaloniki in order to assess the presence of aerosols and the predominant aerosol type both in situ and at elevated heights. Overall, our study showed that the BCwb contribution to the BC values in Thessaloniki is quite low (11%), whilst the majority of the biomass burning layers identified with the lidar system, are also linked with enhanced BC contribution and high Fine Mode Fraction values

Consistency of the single calculus chain for climatological studies using long-term measurements from thessaloniki lidar station

The long term analysis of 15 years of lidar data derived from a Raman lidar at Thessaloniki is presented here. All measurements have been processed with the latest version 4 of the EARLINET Single Calculus Chain algorithm and are compared with the results from the current operational retrieval algorithm. In this paper we investigate the consistency between the EARLINET database and SCC for the case of Thessaloniki and we identify the issues to be considered when switching from current operations to SCC

Long term lidar measurements of aerosol properties over thessaloniki

In this study we present some first results on the potential of 15 years of lidar measurements over the lidar station of Thessaloniki to compile a climatology of the aerosol properties for the period 2001-2015. This is examined on a monthly, seasonal and annual basis. Both the profile structure and the columnar properties of the aerosol extinction and backscatter products are examined. The results are compared for consistency against co-located sunphotometer measurements