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Your search keyword '"Bais, Alkiviadis F."' showing total 5 results
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5 results on '"Bais, Alkiviadis F."'

2. An Assessment of the Relative Importance of Factors Impacting Surface UV Radiation Based on Simulations of the 6th Phase of the Coupled Intercomparison Project.

Author

Chatzopoulou, Anthi, Tourpali, Kleareti, Bais, Alkiviadis F., Braesicke, Peter, and Ruhnke, Roland

Subjects
ATMOSPHERIC aerosols, ULTRAVIOLET radiation, ATMOSPHERIC models, SOCIOECONOMICS, OZONE
Abstract

Aerosols, ozone, surface reflectivity, and clouds are, among other factors, important for the modulation of UV radiation levels at the Earth's surface. In this study, these variables were extracted from climate model integrations that contributed to CMIP6 and from MACC global reanalysis provided by the CAMS. From the 1950s until the end of the 21st century and for various shared socioeconomic pathways considered by CMIP6, we conclude that total ozone will increase globally in 2100 by up to 11% under SSP5-8.5 relative to the 1950s, while under SSP1-2.6, ozone is not projected to recover to pre-ozone depletion levels. AOD at 550 nm shows reductions in 2090-2100 over the Northern Hemisphere of up to -0.38. Compared to CAMS, CMIP6 models show a general overestimation for total ozone of up to 2.5% in extra-polar regions for models with interactive chemistry. This implies systematically lower UV radiation from models based on these projections. [ABSTRACT FROM AUTHOR]

Published
2023
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3. Retrieval of Total NO2 Columns Using Direct-Sun Differential Optical Absorption Spectroscopy Measurements in Thessaloniki.

Author

Nikolis, Dimitrios, Karagkiozidis, Dimitris, and Bais, Alkiviadis F.

Subjects
NITROGEN dioxide, LIGHT absorption, TRACE gases, CALIBRATION
Abstract

The monitoring of trace gases in the troposphere has been routinely performed at the Laboratory of Atmospheric Physics, Thessaloniki, Greece, for a decade now, by multiple Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) instruments. Even though measurements of trace gas concentrations in the troposphere are of great interest in terms of air quality, the MAX-DOAS technique is only sensitive to absorbers in the lowest few kilometers of the atmosphere. In this work, we present a methodology for the retrieval of total NO2 columns in the atmosphere by applying the DOAS technique on direct sun spectra (DS-DOAS) measured with a new research-grade system. The advantages and limitations of the total NO2 retrieval methodology, based on DS-DOAS, are discussed. The accuracy and the quality of the retrieved columns were assessed by comparison with a collocated Pandora system that also measures total NO2 column amounts using a similar technique with independent calibration. [ABSTRACT FROM AUTHOR]

Published
2023
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4. Possible Effects of Greenhouse Gases to Ozone Profiles and DNA Active UV-B Irradiance at Ground Level.

Author

Eleftheratos, Kostas, Kapsomenakis, John, Zerefos, Christos S., Bais, Alkiviadis F., Fountoulakis, Ilias, Dameris, Martin, Jöckel, Patrick, Haslerud, Amund S., Godin-Beekmann, Sophie, Steinbrecht, Wolfgang, Petropavlovskikh, Irina, Brogniez, Colette, Leblanc, Thierry, Liley, J. Ben, Querel, Richard, and Swart, Daan P. J.

Subjects
GREENHOUSE gases, GREENHOUSE effect, OZONE, DNA fingerprinting, CHEMICAL processes
Abstract

In this paper, we compare model calculations of ozone profiles and their variability for the period 1998 to 2016 with satellite and lidar profiles at five ground-based stations. Under the investigation is the temporal impact of the stratospheric halogen reduction (chemical processes) and increase in greenhouse gases (i.e., global warming) on stratospheric ozone changes. Attention is given to the effect of greenhouse gases on ultraviolet-B radiation at ground level. Our chemistry transport and chemistry climate models (Oslo CTM3 and EMAC CCM) indicate that (a) the effect of halogen reduction is maximized in ozone recovery at 1–7 hPa and observed at all lidar stations; and (b) significant impact of greenhouse gases on stratospheric ozone recovery is predicted after the year 2050. Our study indicates that solar ultraviolet-B irradiance that produces DNA damage would increase after the year 2050 by +1.3% per decade. Such change in the model is driven by a significant decrease in cloud cover due to the evolution of greenhouse gases in the future and an insignificant trend in total ozone. If our estimates prove to be true, then it is likely that the process of climate change will overwhelm the effect of ozone recovery on UV-B irradiance in midlatitudes. [ABSTRACT FROM AUTHOR]

Published
2020
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5. Deriving Aerosol Absorption Properties from Solar Ultraviolet Radiation Spectral Measurements at Thessaloniki, Greece.

Author

Fountoulakis, Ilias, Natsis, Athanasios, Siomos, Nikolaos, Drosoglou, Theano, and Bais, Alkiviadis F.

Subjects
ULTRAVIOLET radiation measurement, AEROSOLS, SOLAR spectra, SOLAR ultraviolet radiation, OPTICAL depth (Astrophysics), LIGHT absorption, ABSORPTION
Abstract

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. [ABSTRACT FROM AUTHOR]

Published
2019
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