Nikolaos Siomos

Modification of local urban aerosol properties by long-range transport of biomass burning aerosol

During August 2016, a quasi-stationary high-pressure system spreading over Central and North-Eastern Europe, caused weather conditions that allowed for 24/7 observations of aerosol optical properties by using a complex multi-wavelength PollyXT lidar system with Raman, polarization and water vapour capabilities, based at the European Aerosol Research Lidar Network (EARLINET network) urban site in Warsaw, Poland. During 24–30 August 2016, the lidar-derived products (boundary layer height, aerosol optical depth, Angstrom exponent, lidar ratio, depolarization ratio) were analysed in terms of air mass transport (HYSPLIT model), aerosol load (CAMS data) and type (NAAPS model) and confronted with active and passive remote sensing at the ground level (PolandAOD, AERONET, WIOS-AQ networks) and aboard satellites (SEVIRI, MODIS, CATS sensors). Optical properties for less than a day-old fresh biomass burning aerosol, advected into Warsaw’s boundary layer from over Ukraine, were compared with the properties of long-range transported 3–5 day-old aged biomass burning aerosol detected in the free troposphere over Warsaw. Analyses of temporal changes of aerosol properties within the boundary layer, revealed an increase of aerosol optical depth and Angstrom exponent accompanied by an increase of surface PM10 and PM2.5. Intrusions of advected biomass burning particles into the urban boundary layer seem to affect not only the optical properties observed but also the top height of the boundary layer, by moderating its increase.

A sensitivity study of the LIdar-Radiometer Inversion Code (LIRIC) using selected cases from Thessaloniki, Greece database

ABSTRACT We investigate the uncertainty introduced to the optical and microphysical properties estimated with the lidar radiometer inversion code (LIRIC) by user-defined input parameters based on measurements carried out with a multi-wavelength Raman lidar and a sun photometer located at Thessaloniki, Greece (40.6° N, 22.9° E, 60 m above sea level). The sensitivity study involves three tests. We first evaluate the selection of the regularization parameters needed for the algorithm to initialize the iteration process. The latter two tests consider the impact of the boundary limits at the top/bottom (upper/lower limit) of the signal to the derived concentration profiles. The aforementioned tests were applied to two different cases, a Saharan dust event and a continental pollution case. We concluded that the largest uncertainties are introduced when varying the lower limit (more than 35%) regardless of the aerosol type or mode (fine/coarse). Varying the regularization parameters resulted in an uncertainty of 20%, and the selection of upper limit led to discrepancies of less than 3%. In conclusion, this sensitivity study indicates that future LIRIC users should apply an overlap function to the lidar signals before applying the methodology for minimizing the uncertainties in the near range.

Are EARLINET and AERONET climatologies consistent? The caseof Thessaloniki, Greece

In this study we investigate the climatological behavior of the aerosol optical properties over Thessaloniki during the years 2003–2017. For this purpose, measurements of two independent instruments, a lidar and a sunphotometer, were used. These two instruments represent two individual networks, the European Lidar Aerosol Network (EARLINET) and the Aerosol Robotic Network (AERONET). They include different measurement schedules. Fourteen years of lidar and sunphotometer measurements were analyzed, independently of each other, in order to obtain the annual cycles and trends of various optical and geometrical aerosol properties in the boundary layer, in the free troposphere, and for the whole atmospheric column. The analysis resulted in consistent statistically significant and decreasing trends of aerosol optical depth (AOD) at 355 nm of −23.2 and −22.3 % per decade in the study period over Thessaloniki for the EARLINET and the AERONET datasets, respectively. Therefore, the analysis indicates that the EARLINET sampling schedule can be quite effective in producing data that can be applied to long-term climatological studies. It is also shown that the observed decreasing trend is mainly attributed to changes in the aerosol load inside the boundary layer. Seasonal profiles of the most dominant aerosol mixture types observed over Thessaloniki have been generated from the lidar data. The higher values of the vertically resolved extinction coefficient at 355 nm appear in summer, while the lower ones appear in winter. The dust component is more dominant in the free troposphere than in the boundary layer during summer. The biomass burning layers tend to arrive in the free troposphere during spring and summer. This kind of information can be quite useful for applications that require a priori aerosol profiles. For instance, they can be utilized in models that require aerosol climatological data as input, in the development of algorithms for satellite products, and also in passive remote-sensing techniques that require knowledge of the aerosol vertical distribution.

Long-Term Comparison of Lidar Derived Aerosol Optical Depth Between Two Operational Algorithms and Sun Photometer Measurements for Thessaloniki, Greece

Results of a multi-year comparison of the aerosol optical depth, derived by two operational algorithms based on lidar measurements with a Raman/elastic backscatter lidar in Thessaloniki, Greece and ground-based sun photometer observations are presented. Measurements from the European Aerosol Research Lidar Network (EARLINET) database processed with the operational algorithm of Aristotle University of Thessaloniki (AUTH) for the period 2001–2007, have been reprocessed with the Single Calculus Chain (SCC) algorithm. The SCC algorithm was developed within the EARLINET to provide high quality, standardized aerosol optical products in near real time. The objective of this study is to verify for the case of Thessaloniki, the long-term consistency of the aerosol load estimates between the operational and the SCC derived data, in order to adopt the SCC for operational processing. The observed differences would introduce inhomogeneities in the time series when switching to SCC, so a full reprocessing is required. An investigation of the parameters affecting the comparisons is presented, considering the differences in the algorithms.

Vertical Separation of Desert Dust and Biomass Burning Aerosol Layers Over Thessaloniki Using the Synergy of Sunphotometer and Lidar Data

In this study we separate the layers of the dust aerosol component, arriving from the Saharan desert region, from the smoke layers, originating from fires in Ukraine during selected multi-layered measurement cases over the Balkans. We apply the Lidar-Radiometer Inversion Code (LIRIC) which is capable to derive the mass concentration profiles for the fine and coarse mode particles, using combined sunphotometer and lidar data. Lidar and CIMEL measurements, performed at the Laboratory of Atmospheric Physics of the Aristotle University of Thessaloniki, Greece (40.5N, 22.9E), were used for this purpose. The vertical separation of the layers is further examined against model simulation. Back trajectories from the Lagrangian model HYSPLIT are used in combination with MODIS satellite data for fires spots, in order to examine the origin of the aerosol layers. The daily evolution of the event is also analyzed using lidar and CIMEL measurements.

Validation of ASH Optical Depth and Layer Height from IASI using Earlinet Lidar Data

The 2010 eruptions of the Icelandic volcano Eyjafjallajokull attracted the attention of the public and the scientific community to the vulnerability of the European airspace to volcanic eruptions. The European Space Agency project “Satellite Monitoring of Ash and Sulphur Dioxide for the mitigation of Aviation Hazards”, called for the creation of an optimal End-to-End System for Volcanic Ash Plume Monitoring and Prediction. This system is based on improved and dedicated satellite-derived ash plume and sulphur dioxide level assessments, as well as an extensive validation, using among others ground-based measurements (Koukouli et al., 2014). The validation of volcanic ash levels and height extracted from IASI/MetopA is presented in this work with emphasis on the ash plume height and ash optical depth levels. European Aerosol Research Lidar Network [EARLINET] lidar measurements are compared to different satellite estimates for two eruptive episodes. The validation results are extremely promising within the estimated uncertainties of each of the comparative datasets.