Short- and long-term variability of spectral solar UV irradiance at Thessaloniki, Greece: effects of changes in aerosols, total ozone and clouds

Fountoulakis, Ilias; Bais, A. F.; Fragkos, Konstantinos; Meleti, C.; Tourpali, Kleareti; Zempila, Μ. Μ.

doi:10.5194/acp-16-2493-2016

Cited by 61 publications

(61 citation statements)

References 83 publications

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“…Matthias and Bösenberg (2002 alyzed the boundary layer height in Hamburg using three years of lidar data while Behnert et al (2007) In all those cases, the timeseries mentioned above did not cover enough years for the production of long-term trends. On the other hand, Kazadzis et al (2007) and Fountoulakis et al (2016) analyzed longer datasets for Thessaloniki that allowed them to investigate the long-term variability and the annual cycles of the aerosol optical depth in the UV for Thessaloniki 25 using retrieved AOD from two different Brewer spectrophotometers in the periods 1997-2005 and 1994-2006 respectively. In their case, however, it was not possible to provide information on the aerosol vertical distribution due to the nature of their instrumentation.…”

Section: Introductionmentioning

confidence: 99%

Are EARLINET and AERONET climatologies consistent? The case of Thessaloniki, Greece

Σιώμος¹,

Balis²,

Voudouri³

et al. 2018

Preprint

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Abstract. In this study we investigate the climatological behavior of the aerosol optical properties over Thessaloniki during the years [2003][2004][2005][2006][2007][2008][2009][2010][2011][2012][2013][2014][2015][2016][2017]. For this purpose, measurements of two independent instruments, a lidar and a sunphotomer, were deployed.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 in order to obtain the annual cycles and trends of multiple optical and geometrical aerosol 5 properties in the boundary layer, in the free troposphere and for the whole atmospheric column. The analysis resulted in consistent statistically significant and decreasing AOD 355nm trends of -21.0% and -16.6% per decade in the study period over Thessaloniki for the EARLINET and the AERONET datasets respectively. Therefore, the analysis implies that the EARLINET sampling schedule can be quite effective in producing data that can be applied to climatological studies. It has also been confirmed that the observed decreasing trend is mainly attributed to changes in the aerosol properties inside the boundary 10 layer. Seasonal profiles of the most dominant aerosol mixture types have been generated from the lidar data. The higher values of the extinction at 355nm appear in summer, while the lower ones appear in winter. The dust component is much more dominant in the free troposphere than in the boundary layer during summer, while the opposite is observed in winter. The strongest biomass burning episodes tend to occur during summer in the free troposphere and are probably attributed to wildfires rather than agricultural fires that are predominant during spring and autumn. This kind of information can be quite useful for 15 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.1 Atmos. Chem. Phys. Discuss., https://doi

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Section: Introductionmentioning

confidence: 99%

Are EARLINET and AERONET climatologies consistent? The case of Thessaloniki, Greece

Σιώμος¹,

Balis²,

Voudouri³

et al. 2018

Preprint

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“…This could be attributed to a reduction of the aerosol load coming from local sources. A change in the aerosol type, such as a shift to less absorptive particles in the PBL, could also be responsible for this behavior (Fountoulakis et al, 2016). Further research on the aerosol microphysical properties could contribute to gaining insight into this matter.…”

Section: Long-term Changesmentioning

confidence: 99%

“…They used retrievals of AOD from two different Brewer spectrophotometers in the periods 1997-2005 and 1994-2006. For instance, Kazadzis et al (2007) detected a seasonal variation in the monthly means of AOD at 340 nm with maximum optical depth values in the summer months and minimum in wintertime, while Fountoulakis et al (2016) detected a trend of AOD at 320 nm of −0.09 ± 0.01 per decade. In their case, however, it was not possible to provide information on the aerosol vertical distribution due to the nature of their instrumentation.…”

Section: Introductionmentioning

confidence: 99%

“…However, the limited number of years did not permit the calculation of long-term trends. On the other hand, Kazadzis et al (2007) and Fountoulakis et al (2016) analyzed longer datasets, based on spectral irradiance measurements for Thessaloniki, that allowed them to investigate the long-term variability and the annual cycles of the aerosol optical depth in the UV for Thessaloniki. They used retrievals of AOD from two different Brewer spectrophotometers in the periods 1997-2005 and 1994-2006.…”

Section: Introductionmentioning

confidence: 99%

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Are EARLINET and AERONET climatologies consistent? The case of Thessaloniki, Greece

et al. 2018

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Abstract. In this study we investigate the climatological behavior of the aerosol optical properties over Thessaloniki during the years [2003][2004][2005][2006][2007][2008][2009][2010][2011][2012][2013][2014][2015][2016][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 (EAR-LINET) 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 EAR-LINET 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.

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“…Furthermore, other aerosol properties, like the single-scattering albedo, may vary significantly over urban sites such as Thessaloniki (Bais et al, 2005), which can introduce extra uncertainties in the effect of aerosols on the estimated UV irradiances which are of the same order of magnitude as the uncertainty due to the variability in the AOD (e.g., Kazadzis et al, 2009;Fountoulakis et al, 2016a).…”

Section: Evaluation Of Temis Satellite-based Uv Products With Nilu-uvmentioning

confidence: 99%

TEMIS UV product validation using NILU-UV ground-based measurements in Thessaloniki, Greece

et al. 2017

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Abstract. This study aims to cross-validate ground-based and satellite-based models of three photobiological UV effective dose products: the Commission Internationale de l'Éclairage (CIE) erythemal UV, the production of vitamin D in the skin, and DNA damage, using high-temporalresolution surface-based measurements of solar UV spectral irradiances from a synergy of instruments and models. The satellite-based Tropospheric Emission Monitoring Internet Service (TEMIS; version 1.4) UV daily dose data products were evaluated over the period 2009 to 2014 with groundbased data from a Norsk Institutt for Luftforskning (NILU)-UV multifilter radiometer located at the northern midlatitude super-site of the Laboratory of Atmospheric Physics, Aristotle University of Thessaloniki (LAP/AUTh), in Greece. For the NILU-UV effective dose rates retrieval algorithm, a neural network (NN) was trained to learn the nonlinear functional relation between NILU-UV irradiances and collocated Brewer-based photobiological effective dose products. Then the algorithm was subjected to sensitivity analysis and validation. The correlation of the NN estimates with target outputs was high (r = 0.988 to 0.990) and with a very low bias (0.000 to 0.011 in absolute units) proving the robustness of the NN algorithm. For further evaluation of the NILU NN-derived products, retrievals of the vitamin D and DNA-damage effective doses from a collocated Yankee Environmental Systems (YES) UVB-1 pyranometer were used. For cloud-free days, differences in the derived UV doses are better than 2 % for all UV dose products, revealing the reference quality of the ground-based UV doses at Thessaloniki from the NILU-UV NN retrievals. The TEMIS UV doses used in this study are derived from ozone measurements by the SCIAMACHY/Envisat and GOME2/MetOp-A satellite instruments, over the European domain in combination with SEVIRI/Meteosat-based diurnal cycle of the cloud cover fraction per 0.5• (lat × long) grid cells. TEMIS UV doses were found to be ∼ 12.5 % higher than the NILU NN estimates but, despite the presence of a visually apparent seasonal pattern, the R 2 values were found to be robustly high and equal to 0.92-0.93 for 1588 all-sky coincidences. These results significantly improve when limiting the dataset to cloud-free days with differences of 0.57 % for the erythemal doses, 1.22 % for the vitamin D doses, and 1.18 % for the DNA-damage doses, with standard deviations of the order of 11-13 %. The improvement of the comparative statistics under cloud-free cases further testifies to the importance of the appropriate consideration of the contribution of clouds in the UV radiation reaching the Earth's surface. For the urban area of Thessaloniki, with highly variable aerosol, the weakness of the implicit aerosol information introduced to the TEMIS UV dose algorithm was revealed by comparison of the datasets to aerosol optical depths at 340 nm as reported by a collocated CIMEL sun photometer, operating in Thessaloniki at LAP/AUTh as part of the NASA Aerosol Robotic Network.

show abstract

Short- and long-term variability of spectral solar UV irradiance at Thessaloniki, Greece: effects of changes in aerosols, total ozone and clouds

Cited by 61 publications

References 83 publications

Are EARLINET and AERONET climatologies consistent? The case of Thessaloniki, Greece

Are EARLINET and AERONET climatologies consistent? The case of Thessaloniki, Greece

Are EARLINET and AERONET climatologies consistent? The case of Thessaloniki, Greece

TEMIS UV product validation using NILU-UV ground-based measurements in Thessaloniki, Greece

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