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The term neurodegenerative diseases include a long list of diseases affecting the nervous system that are characterized by the degeneration of different neurological structures. Among them, Alzheimer disease (AD), Parkinson disease (PD), and amyotrophic lateral sclerosis (ALS) are the most representative ones. The vast majority of cases are sporadic and results from the interaction of genes and environmental factors in genetically predisposed individuals. Among environmental conditions, electromagnetic field exposure has begun to be assessed as a potential risk factor for neurodegeneration. In this review, we discuss the existing literature regarding electromagnetic fields and neurodegenerative diseases. Epidemiological studies in AD, PD, and ALS have shown discordant results; thus, a clear correlation between electromagnetic exposure and neurodegeneration has not been demonstrated. In addition, we discuss the role of electromagnetic radiation as a potential non-invasive therapeutic strategy for some neurodegenerative diseases, particularly for PD and AD.

International audience; Atmospheric electric fields (AEFs) are produced by both natural processes and electrical infrastructure and are increasingly recognized to influence and interfere with various organisms and biological processes, including human well-being. Atmospheric electric fields, in particular electromagnetic fields (EMFs), currently attract a lot of scientific attention due to emerging technologies such as 5G and satellite internet. However, a broader retrospective analysis of available data for both natural and artificial AEFs and EMFs is hampered due to a lack of a semantic approach, preventing data sharing and advancing our understanding of its intrinsic links. Therefore, here we create an ontology (ENET_Ont) for existing (big) data on AEFs within the context of biological systems that is derived from different disciplines that are distributed over many databases. Establishing an environment for data sharing provided by the proposed ontology approach will increase the value of existing data and facilitate reusability for other communities, especially those focusing on public health, ecology, environmental health, biology, climatology as well as bioinformatics.

In this work, the spatiotemporal variability of surface solar radiation (SSR) is examined over the Eastern Mediterranean region for a 31-year period (1983–2013). The CM SAF SARAH (Satellite Application Facility on Climate Monitoring Solar surfAce RAdiation Heliosat) satellite-based product was found to be homogeneous (based on relative Standard Normal Homogeneity Tests — SNHTs, 95% confidence level) as compared to ground-based observations, and hence appropriate for climatological studies. Specifically, the dataset shows good agreement with monthly observations from five quality assured stations in the region with a mean bias of 7.1 W/m 2 or 3.8% and a strong correlation. This high resolution (0.05° × 0.05°) product is capable of revealing various local features. Over land, the SSR levels are highly dependent on the topography, while over the sea, they exhibit a smooth latitudinal variability. SSR varies significantly over the region on a seasonal basis being three times higher in summer (309.6 ± 26.5 W/m 2 ) than in winter (100.2 ± 31.4 W/m 2 ). The CM SAF SARAH product was compared against three satellite-based and one reanalysis products. The satellite-based data from CERES (Cloud and the Earth's Radiant Energy System), GEWEX (Global Energy and Water Cycle Experiment) and ISCCP (International Satellite Cloud Climatology Project) underestimate SSR while the reanalysis data from the ERA-Interim overestimate SSR compared to CM SAF SARAH. Using a radiative transfer model and a set of ancillary data, these biases are attributed to the atmospheric parameters that drive the transmission of solar radiation in the atmosphere, namely, clouds, aerosols and water vapor. It is shown that the bias between CERES and CM SAF SARAH SSR can be explained through the cloud fractional cover and aerosol optical depth biases between these datasets. The CM SAF SARAH SSR trend was found to be positive (brightening) and statistically significant at the 95% confidence level (0.2 ± 0.05 W/m 2 /year or 0.1 ± 0.02%/year) being almost the same over land and sea. The CM SAF SARAH SSR trends are closer to the ground-based ones than the CERES, GEWEX, ISCCP and ERA-Interim trends. The use of an aerosol climatology for the production of CM SAF SARAH, that neglects the trends of aerosol loads, leads to an underestimation of the SSR trends. It is suggested here, that the inclusion of changes of the aerosol load and composition within CM SAF SARAH would allow for a more accurate reproduction of the SSR trends.

We present an analysis of the impact of circulation weather types (CT) on a factor that might influence biological systems and the human condition, the electric state of the atmosphere. We present results on the influence of CT to the magnitude, the direction (positive or negative), the fluctuation magnitude, and the short-term peaks of the atmospheric electric field (potential gradient, PG), using data from a station in Greece. CTs with high vorticity centers over Greece are associated with high positive and negative excursions of the PG, higher PG variability, and rain events. CTs with thinner 850–500 hPa layer are associated with higher daily mean values of fair-weather PG. We also examine the influence of CT on the frequency and amplitude of the naturally occurring extremely low-frequency electric field fluctuations known as Schumann resonances (SR) using data from a station in Hungary. The first and second mode SR frequencies are increased during CTs associated with higher 500 hPa geopotential heights and higher 850–500 hPa layer thickness. This hints to a lower-upper atmosphere coupling. So, CTs not only influence the general temperature and humidity conditions to which the biosphere is exposed, but they also affect its exposure to atmospheric electric fields.

Here, we examine the aerosol - cloud relations over three major urban clusters of China, representative of three different climatic regimes, under different water vapor conditions and cloud heights, using Aerosol Optical Depth at 550 nm (AOD), Cloud Fraction (CC), Cloud Optical Depth (COD), Water Vapor (WV) and Cloud Top Pressure (CTP) data from the MODIS instrument. Over all regions and for all seasons, CC is found to increase with increasing AOD, WV and cloud height. Aerosols, at low WV environments and under constant CTP, have less impact on CC than at high WV environments. Furthermore, AOD has a varying influence on COD depending on CTP. Finally, COD is found to increase with height for low and middle height clouds, and with increasing AOD, especially at low AOD. Our results demonstrate that the role of WV in the observed satellite-based aerosol - cloud relations is significant for all cloud heights.

The most recent release of MODIS atmospheric product (Collection 6) is already used in studies concerning the greater Mediterranean region. However, an assessment of the differences and similarities of the last two MODIS collections (6 and 5.1) is missing. In this paper, a first comparison of the MODIS/Terra and Aqua Collection 6 and Collection 5.1 AOD at a wavelength of 550 nm (AOD550) data is presented with a focus on the Mediterranean region. It is shown that Collection 6 AODs are either higher or lower than Collection 5.1 AODs over different continental areas while, over ocean, Collection 6 AODs are higher almost everywhere (11% for MODIS/Terra and 8% for MODIS/Aqua). Generally, Collection 6 retrieves higher AODs than Collection 5.1, especially for MODIS/Terra. The evaluation of Collection 6 and 5.1 AOD550 data against sunphotometric observations from 23 AERONET stations in the area reveals that Collection 6 exhibits a better agreement with the ground-based data. The Collection 6 AOD550 data exhibit a statistically significant negative trend of the order of about −0.001/year (∼−0.5%/year) for MODIS/Terra and −0.002/year (∼−1.0%/year) for MODIS/Aqua. For the region studied, Collection 6 trends are largely reduced compared to Collection 5.1 trends by ∼0.003/year for MODIS/Terra data while for MODIS/Aqua data the trends have not changed significantly (only by ∼0.0003/year).

This work focuses on the evaluation of the MACC (Monitoring atmospheric composition and climate) reanalysis dust product over Europe. Europe receives significant amounts of dust on an annual basis primarily from the large neighboring area sources (Sahara Desert, Arabian Peninsula) and from smaller local sources. Dust affects a number of processes in the atmosphere modulating weather and climate and exerts an impact on human health and the economy. Hence, the ability of simulating adequately the amount of dust and its optical properties is essential. For the evaluation of the MACC reanalysis, pure dust satellite-based retrievals from CALIOP/CALIPSO are utilized for the period 2007–2012. Specifically, the CALIOP/CALIPSO data used here come from an optimized retrieval scheme that was originally developed within the framework of the LIVAS (Lidar Climatology of Vertical Aerosol Structure for Space-Based LIDAR Simulation Studies) project. The natural aerosol extinction coefficients from MACC and the dust optical depth patterns at 550 nm are validated against dust extinction coefficients and dust optical depth patterns at 532 nm from CALIOP/CALIPSO. Our results highlight the important role that space-based lidars may play in the improvement of the MACC aerosol product.

Here we examine the annual and seasonal aerosol–cloud relations over three major urban clusters of China, at different cloud heights, using a decade of Aerosol Optical Depth at 550 nm (AOD), Cloud Cover (CC), Cloud Optical Depth (COD), Water Vapor (WV) and Cloud Top Pressure (CTP) data from the MODIS instrument. Over all regions and for all seasons, CC is found to increase with increasing AOD, WV and cloud height. Aerosols, at low WV environments and under constant CTP, have less impact on CC than at high WV environments. In addition, AOD has a varying influence on COD depending on CTP. Finally, COD is found to increase with height for low and middle height clouds, and with increasing AOD, especially at low AOD, the latter being in line with the expected first indirect effect.

The ability of RegCM4 regional climate model to simulate surface solar radiation (SSR) patterns over Europe is assessed through an evaluation of a decadal simulation against satellite-based observations from the Satellite Application Facility on Climate Monitoring (CM SAF). The model simulates adequately the SSR patterns over the region slightly overestimating SSR (bias of ~+2.5 % for the period 2000–2009). Cloud macrophysical and microphysical properties from RegCM4 such as cloud fractional cover (CFC), cloud optical thickness (COT) and cloud effective radius (Re) are evaluated against data from CM SAF. The same is done for aerosol optical properties such as aerosol optical depth (AOD), asymmetry factor (ASY), and single scattering albedo (SSA) using data from the MACv1 aerosol climatology, and other parameters, such as surface broadband albedo (ALB) using data from the CERES satellite sensors, and water vapor amount (WV) using data from the ERA-Interim reanalysis. The good agreement between RegCM4 and satellite-based SSR observations is a result of counterbalancing effects of these parameters. The contribution of each parameter to the RegCM4-CM SAF SSR deviations is estimated with the combined use of the aforementioned data and a radiative transfer model (SBDART). CFC, COT and AOD are the major determinants of these deviations.

This paper presents the unique features and functionality of the AMFIC Web Satellite Database (AMFIC-WSDB) which was developed within the Air quality Monitoring and Forecasting In China (AMFIC) European Union (EU) project. The method used for the analysis of the SCIAMACHY ENVISAT CH"4, CO, NO"2 and SO"2 satellite data that emerged from the AMFIC work packages, in order to be hosted by the AMFIC-WSBD, is described. Today, there is an increased demand for satellite data not only from specialized users but also from researchers and public institutions for research, management, information and education purposes. The AMFIC-WSDB has been developed to address the need of those users for fast and easy access to atmospheric composition data. Together with the web interface, it constitutes an integrated system, hosting spatially and temporally homogenized satellite products. The main idea behind the AMFIC-WSDB (http://www.amfic.satellite-earth-simulator.com/) is to offer timeseries ascii files through a set of interactive maps. This makes the database ideal not only for those interested in global datasets but also for users interested in specific geographical spots. Data from other state-of-the-art environmental satellite sensors (e.g. MODIS, OMI and GOME-2) could be easily integrated in the database in the future.

In this study, the aerosol weekly cycle patterns over Central Europe are defined, using high resolution aerosol data from TERRA MODIS satellite instrument. A decadal (2/2000-2/2010) high resolution gridded dataset was compiled using MODIS TERRA level-2 data. The general aerosol optical depth (AOD 550nm ) weekly patterns were defined at a 0.1° × 0.1° resolution using the weekly cycle index (WCI). To remove episodic dust transport events, two different aerosol flags, employing fine mode ratio (FMR 550nm ) and AOD 550nm data, were applied diagnostically. The region of interest is Central Europe, which is an area with a recorded aerosol weekly cycle. The main body of the positive (midweek peak) weekly cycle plume extends over the central part of Central Europe with the WCI levels gradually lowering until the weekly cycle becomes negative (weekend peak) when moving away from the main body of the plume. There is not a clear connection between the WCI patterns and topography while there is a correlation between a positive weekly cycle in summer and population density. The use of the two aerosol flags does not change the WCI patterns giving an indication of the continental character of the plume. A clear Monday minimum appears over the regions which are characterized by a high positive WCI. Monday shifts to Tuesday when moving to the East which is indicative of an aerosol transport from the dominating westerly wind flow. The investigation of the WCI and the average percent departure (APD) for the day of weekly maximum/minimum, for 22 stations examined in previous weekly cycle studies, reveals that the weekly cycle is positive and statistically significant for only a few stations situated in France, Germany, Czech Republic and Belgium. The 1° × 1° MODIS TERRA data in most cases can give an indication of the local aerosol weekly cycle strength and phase. It is shown here that the satellite derived day of the weekly maximum and minimum is in general in line with results from ground-based studies; however, the weekly variability does not agree with the variability shown in these studies. The investigation of the seasonal WCI and maximum/minimum day patterns reveals that the signal of the positive weekly cycle plume appearing over Central Europe is very strong during summer. The day of maximum AOD 550nm ranges between Wednesday, Thursday and Friday becoming Saturday for the Eastern regions. The day of minimum is Monday for the central parts becoming Tuesday for the Eastern regions. This summer shift of the day of maximum and minimum for regions situated in the Central and Eastern Central Europe is an indication of the transport of the aerosols from the dominating westerly wind flow. Parts of the summer positive weekly cycle plume can be observed in spring and autumn.

In this work, we focus on the spatial and temporal variability of the aerosol weekly cycle over Europe as these were recorded from TERRA MODIS and AQUA MODIS satellite instruments. Aerosol optical properties retrieved from MODIS TERRA (February 2000–February 2009) and AQUA (July 2002–December 2008) were used to produce an aerosol weekly cycle index. First, the general aerosol optical depth (AOD550 nm) weekly patterns were defined at a 1° × 1° resolution using the satellite-based index and six regions of interest were selected. To remove episodic dust transport events, two different aerosol flags, employing fine mode ratio (FMR550 nm) and AOD550 nm data, were applied diagnostically, showing that the observed weekly cycles over Europe are due to continental aerosols. A second spatial averaging method was then used for the investigation of the weekly variability and the statistical significance of the weekly cycle over each of the previously selected regions. Three major weekly cycle plumes are observed over Europe. A strong positive (higher values during midweek) weekly cycle plume appears over Central Europe, while a strong negative (higher values during weekend) weekly plume appears over the Iberian Peninsula and the North-eastern Europe. The temporal examination of the weekly cycles shows that in some areas there are seasonal differences in the sign of the weekly cycle. The aerosol weekly variability over different regions in Europe was examined in conjunction with the dominating synoptic wind patterns from the NCEP/NCAR reanalysis, showing that the seasonal weekly cycle plumes over regions situated in the eastern Europe and the Mediterranean Sea could be partly attributed to the westerly transport of continental aerosols.

Many studies have focused on geological formations, such as mud volcanoes, which abound in the Greater Area of the Eastern Mediterranean (GAEM; 25° N-50° N, 5° E-55° E). This geological source is thought to provide a significant portion of the global methane (CH4) emissions. However, studies in the GAEM have focused on specific locations rather than extensive areas, which has led to a gap in our understanding of the spatial and temporal variability of CH4 atmospheric mixing ratios. Here, we present characteristics of methane loading over land in the GAEM using dry air columnar data (XCH4) retrieved from SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Cartography) satellite measurements with the Weighting Function Modified Differential Optical Absorption Spectroscopy (WFM-DOAS) version 1.0 algorithm. We defined methane annual, seasonal and monthly spatial patterns over the area using 2003 and 2004 measurements. The annual mean XCH4 levels over the study area were estimated to be 1761 ± 27 ppb for 2003 and 1758 ± 26 ppb for 2004. A seasonal variability with a summer-autumn peak was observed for both 2003 and 2004, August being the month with the highest methane concentrations. The northeastern part of the area exhibits the highest XCH4 values while the high elevation regions defined by the triangle of eastern Turkey, the Persian Gulf and the Caspian Sea and the region of the eastern coast of the Red Sea exhibit the lowest levels. A latitudinal gradient was observed for the area during 2003 and 2004. A comparison of measured XCH4 levels above two of the world's most renowned mud volcano regions situated in the GAEM with anticipated methane columnar concentrations as modelled for eruption cases shows that no mud volcano eruptions were observed from SCIAMACHY during 2003 or 2004.

Despite indications of high hydrogen sulfide levels in some urban environments, only sparse measurements have been reported in the literature. Here we present one full year of hydrogen sulfide measurements in an urban traffic site in the city of Thessaloniki, Greece. In this 1-million-population city the H2S concentrations were surprisingly high, with a mean annual concentration of 8 μg m−3 and wintertime mean monthly concentrations up to 20 μg m−3 (12.9 ppb). Daily mean concentrations in the winter were up to 30 μg m−3 (19.3 ppb), while hourly concentrations were up to 54 μg m−3 (34.8 ppb). During calm (wind velocity

In this work we present the contribution of the Laboratory of Atmospheric Pollution and Pollution Control Engineering of Democritus University of Thrace in the AMFIC-Air Monitoring and Forecasting In China European project. Within the framework of this project our laboratory in co-operation with DRAXIS company will create and manage a web satellite data base. This system will host atmospheric pollution satellite data for China and for the whole globe in general. Atmospheric pollution data with different spatial resolution such as O3 and NO2 total columns and measurements of other important trace gasses from GOME (ERS-2), SCIAMACHY (ENVISAT) and OMI (EOS- AURA) along with aerosol total load estimates from AATSR (ENVISAT) will be brought to a common spatial and temporal resolution and become available to the scientific community in simple ascii files and maps format. Available will also be the results from the validation procedure of the satellite data with the use of ground-based observations and a set of high resolution maps and forecasts emerging from atmospheric pollution models. Data will be available for two geographical clusters. The one cluster includes the greater area of China and the other the whole globe. This integrated satellite system will be fully operational within the next two years and will also include a set of innovative tools that allow easy manipulation and analysis of the data. Automatic detection of features such as plumes and monitoring of their evolution, data covariance analysis enabling the detection of emission signatures of different sources, cluster analysis etc will be possible through those tools. The AMFIC satellite system shares a set of characteristics with its predecessor, AIRSAT. Here, we present some of these characteristics in order to bring out the contribution of such a system in atmospheric sciences. Abstract In this work we present the contribution of the Laboratory of Atmospheric Pollution and Pollution Control Engineering of Democritus University of Thrace in the AMFIC-Air Monitoring and Forecasting In China European project. Within the framework of this project our laboratory in co-operation with DRAXIS company will create and manage a web satellite data base. This system will host atmospheric pollution satellite data for China and for the whole globe in general. Atmospheric pollution data with different spatial resolution such as O3 and NO2 total columns and measurements of other important trace gasses from GOME (ERS-2), SCIAMACHY (ENVISAT) and OMI (EOS- AURA) along with aerosol total load estimates from AATSR (ENVISAT) will be brought to a common spatial and temporal resolution and become available to the scientific community in simple ascii files and maps format. Available will also be the results from the validation procedure of the satellite data with the use of ground-based observations and a set of high resolution maps and forecasts emerging from atmospheric pollution models. Data will be available for two geographical clusters. The one cluster includes the greater area of China and the other the whole globe. This integrated satellite system will be fully operational within the next two years and will also include a set of innovative tools that allow easy manipulation and analysis of the data. Automatic detection of features such as plumes and monitoring of their evolution, data covariance analysis enabling the detection of emission signatures of different sources, cluster analysis etc will be possible through those tools. The AMFIC satellite system shares a set of characteristics with its predecessor, AIRSAT. Here, we present some of these characteristics in order to bring out the contribution of such a system in atmospheric sciences. Abstract In this work we present the contribution of the Laboratory of Atmospheric Pollution and Pollution Control Engineering of Democritus University of Thrace in the AMFIC-Air Monitoring and Forecasting In China European project. Within the framework of this project our laboratory in co-operation with DRAXIS company will create and manage a web satellite data base. This system will host atmospheric pollution satellite data for China and for the whole globe in general. Atmospheric pollution data with different spatial resolution such as O3 and NO2 total columns and measurements of other important trace gasses from GOME (ERS-2), SCIAMACHY (ENVISAT) and OMI (EOS- AURA) along with aerosol total load estimates from AATSR (ENVISAT) will be brought to a common spatial and temporal resolution and become available to the scientific community in simple ascii files and maps format. Available will also be the results from the validation procedure of the satellite data with the use of ground-based observations and a set of high resolution maps and forecasts emerging from atmospheric pollution models. Data will be available for two geographical clusters. The one cluster includes the greater area of China and the other the whole globe. This integrated satellite system will be fully operational within the next two years and will also include a set of innovative tools that allow easy manipulation and analysis of the data. Automatic detection of features such as plumes and monitoring of their evolution, data covariance analysis enabling the detection of emission signatures of different sources, cluster analysis etc will be possible through those tools. The AMFIC satellite system shares a set of characteristics with its predecessor, AIRSAT. Here, we present some of these characteristics in order to bring out the contribution of such a system in atmospheric sciences. Abstract In this work we present the contribution of the Laboratory of Atmospheric Pollution and Pollution Control Engineering of Democritus University of Thrace in the AMFIC-Air Monitoring and Forecasting In China European project. Within the framework of this project our laboratory in co-operation with DRAXIS company will create and manage a web satellite data base. This system will host atmospheric pollution satellite data for China and for the whole globe in general. Atmospheric pollution data with different spatial resolution such as O3 and NO2 total columns and measurements of other important trace gasses from GOME (ERS-2), SCIAMACHY (ENVISAT) and OMI (EOS- AURA) along with aerosol total load estimates from AATSR (ENVISAT) will be brought to a common spatial and temporal resolution and become available to the scientific community in simple ascii files and maps format. Available will also be the results from the validation procedure of the satellite data with the use of ground-based observations and a set of high resolution maps and forecasts emerging from atmospheric pollution models. Data will be available for two geographical clusters. The one cluster includes the greater area of China and the other the whole globe. This integrated satellite system will be fully operational within the next two years and will also include a set of innovative tools that allow easy manipulation and analysis of the data. Automatic detection of features such as plumes and monitoring of their evolution, data covariance analysis enabling the detection of emission signatures of different sources, cluster analysis etc will be possible through those tools. The AMFIC satellite system shares a set of characteristics with its predecessor, AIRSAT. Here, we present some of these characteristics in order to bring out the contribution of such a system in atmospheric sciences.

International audience; Methane in air and seawater was measured in the Eastern Black Sea during the 10?18 December 1999 BIGBLACK project cruise. The measurements allowed for the calculation of supersaturation ratios and methane fluxes across the air-sea interface. CH4 mixing ratios in air were generally in the 1.8?2.0 ppmv range, while surface (4 m depth) seawater concentrations varied from 4 to 93 ppmv. Above active seep areas, the water was supersaturated to around 500% with respect to the overlying atmosphere. Accordingly, flux densities varied greatly and were up to 3300 umol m?2 day?1. In the Sevastopol harbour, supersaturations up to around 3000%, similar to those at the Danube Delta, were observed, while in the Istanbul harbour supersaturations could not be determined because the very high values of water concentrations led to detector saturation. Simple modelling shows that the observed fluxes do not have any substantial impact on the methane content of the Black Sea atmosphere, as they would only raise its concentrations by less than 50 ppt. On the other hand, calculations performed as part of the CRIMEA project show that mud volcano eruptions could episodically raise the methane concentrations well above their regional background for several tens of kilometres downwind. These calculations, which also apply to mud volcano eruptions elsewhere on the globe, indicate that the spatial extend and the magnitude of the atmospheric perturbation is such that its observation might lie within the capabilities of existing satellite instrumentation such as SCIAMACHY on ENVISAT.

We present LIVAS, a 3-dimentional multi-wavelength global aerosol and cloud optical climatology, optimized to be used for future space-based lidar end-to-end simulations of realistic atmospheric scenarios as well as retrieval algorithm testing activities. LIVAS database provides averaged profiles of aerosol optical properties for the potential space-borne laser operating wavelengths of 355, 532, 1064, 1570 and 2050 nm and of cloud optical properties at the wavelength of 532 nm. The global climatology is based on CALIPSO observations at 532 and 1064 nm and on aerosol-type-dependent spectral conversion factors for backscatter and extinction, derived from EARLINET ground-based measurements for the UV and scattering calculations for the IR wavelengths, using a combination of input data from AERONET, suitable aerosol models and recent literature. The required spectral conversion factors are calculated for each of the CALIPSO aerosol types and are applied to CALIPSO extinction and backscatter data correspondingly to the aerosol type retrieved by the CALIPSO aerosol classification scheme. A cloud climatology based on CALIPSO measurements at 532 nm is also provided, neglecting wavelength conversion due to approximately neutral scattering behavior of clouds along the spectral range of LIVAS. Averages of particle linear depolarization ratio profiles at 532 nm are provided as well. Finally, vertical distributions for a set of selected scenes of specific atmospheric phenomena (e.g., dust outbreaks, volcanic eruptions, wild fires, polar stratospheric clouds) are analyzed and spectrally converted so as to be used as case studies for space-borne lidar performance assessments. The final global climatology includes 4-year (1 January 2008–31 December 2011) time-averaged CALIPSO data on a uniform grid of 1×1 degree with the original high vertical resolution of CALIPSO in order to ensure realistic simulations of the atmospheric variability in lidar end-to-end simulations.

Benzene, toluene, sulphur dioxide, ozone and nitrogen dioxide were measured at a mean level of 13.5 m above ground in a narrow, four-lane street canyon (height 30 m, width 20 m) in Thessaloniki, Greece during the period January–July 1997 by means of a commercial differential optical absorption spectrometer (OPSIS DOAS). Primary pollutant levels were found to be 2.5–4.4 times higher during the cold part of the year than during the warm part of the year, the winter/summer ratio increasing with the reaction rate constant with OH for each of the measured species. Ozone, on the other hand, exhibited a winter/summer ratio of 0.36. NO 2 originates from both primary and secondary sources; its winter/summer concentration ratio of 1.4 lies, therefore, between those of primary pollutants and ozone. Pollution levels were influenced considerably by wind speed, while for the street canyon under study wind direction did not influence pollutant levels considerably. While primary pollution was found to decrease with increasing wind speed, ozone increased. Benzene mean levels during the study period were around 6 ppb and hence much higher than the EU annual limit value of 5 μg m −3 (1.44 ppb at STP). Toluene mean levels were around 14 ppb and hence also several times above the WHO recommendation of 2 ppb for 24 h. The apportionment of traffic emissions in four time zones used in most inventories in urban airshed models was tested using benzene and toluene measurements at low ( −1 ) wind speeds. The agreement between model emissions and calculated emissions apportionment into the four time zones was good, except for Zone D (23:00–1:59), where model inventory emissions were somewhat too low.

Intensive measurements of UV solar irradiance, total ozone and surface ozone were carried out during the solar eclipse of 11 August 1999 at Thessaloniki, Greece and Stara Zagora, Bulgaria, located very close to the footprint of the moon's shadow during the solar eclipse with the maximum coverage of the solar disk reaching about 90% and 96% respectively. It is shown that during the eclipse the diffuse component is reduced less compared to the decline of the direct solar irradiance at the shorter wavelengths. A 20-minute oscillation of erythemal UV-B solar irradiance was observed before and after the time of the eclipse maximum under clear skies, indicating a possible 20-minute fluctuation in total ozone presumably caused by the eclipse induced gravity waves. The surface ozone measurements at Thessaloniki display a decrease of around 10–15 ppbv during the solar eclipse. Similarly, ozone profile measurements with a lidar system indicate a decrease of ozone up to 2 km during the solar eclipse. The eclipse offered the opportunity to test our understanding of tropospheric ozone chemistry. The use of a chemical box model suggested that photochemistry can account for a significant portion of the observed surface ozone decrease.

The present paper presents some of the results from the EU-funded Photochemical Activity and solar Ultraviolet Radiation (PAUR) and Photochemical Activity and solar Ultraviolet Radiation Modulation Factors (PAUR II) projects that are relevant to the photochemistry of the Eastern Mediterranean under variable conditions. Compared to S-SW flows, northern flows result in higher ozone values above the PBL. Usually during N flow the aerosol optical depth is also lower, thus resulting in higher NO 2 photodissociation rates. In one case of northern flow, the Etesian synoptic regime, N-NE flows are associated with high wind speeds and result to even lower aerosol optical depth. S-SW flow during springtime in some cases brings air loaded with Saharan dust particles over the region that is poor in tropospheric ozone and precursors. Often, these cases are associated with southern stratospheric circulation, resulting in reduced total ozone amounts and hence increased ozone photolysis rates, whereas the dust load reduces nitrogen dioxide photolysis rates. Results are presented from a spectral radiation model, which simulates the spectral UV radiation during some of the above cases. Measurement results from the Athens basin and rural Aegean sites are presented, that compare the ozone levels between normal N flow conditions and Etesian flow.

A regional-scale photochemistry model with 50 km horizontal resolution and 20 layers in the vertical is described. The model's domain includes Europe and most of the North Atlantic and the Arctic region. Model results for the summer months April–September 1996 are presented and compared to measurements. Emphasis is on the Aegean Sea where extensive measurements were made as part of the European Union project Photochemical Activity and Solar Ultraviolet Radiation (PAUR). The model sensitivity with respect to changes in UV radiation, caused by moderate variations in the total ozone column (25 Dobson units), are explored and shown to be small. Aerosol optical depth was calculated from Mie scattering theory using the modeled total sulphate column and used to calculate perturbations of the photolysis rates due to sulphate aerosols. Only small effects on monthly averaged ozone are found with the inclusion of aerosols. For individual days, occasional large variations in calculated ozone levels are seen when the aerosol optical depth is fixed at a high value. The inclusion of aerosols result in a slight reduction of high ozone events over central parts of Europe.

This paper describes the sources contributing to two seasonal peaks in columnar SO2 amounts measured with a Brewer spectrophotometer at Thessaloniki, Northern Greece since 1982. The SO2 Brewer measurements combined with those at ground level, meteorological analysis and numerical simulations provide estimates on the contribution of local and remote sources to the SO2 column. It is shown that more than 50% of the observed SO2 column can be attributed to lignite-burning sources in Bulgaria, Romania and former Yugoslavia, this percentage rising to 70% at periods with NE flow at 850 hPa. Winds from the NW-N-NE contribute around 60% to the observed mean SO2 column during winter and 75% during the summer. When including all wind directions at 850 hPa, the Greek sources, including the lignite-burning power plant complexes to the WSW of the city, contribute around 40% to the SO2 column. These results are in qualitative agreement with independent observations from inversion of GOME measurements.

Benzene, toluene and p -xylene were measured above the buildings level in Thessaloniki, Greece for around eight months during the period December 1993–August 1994 by means of a commercial differential optical absorption spectrometer (OPSIS DOAS). Daily mean mixing ratios for benzene and toluene varied between 1–6 and 1–32 ppb, respectively. The data indicate that the annual mean benzene concentrations most probably lie in the range 2–3 ppb, which is below the guide values but above the target values of European countries that have set limits for benzene. Mean diurnal variations of benzene and toluene during summer and winter months reflect the effects of emission, photochemical degradation and mixing. Benzene and toluene hourly values correlated well with each other and with NO 2 . Toluene and benzene hourly values were negatively correlated with ozone during summertime. During wintertime, considerable enhancements of benzene and toluene mixing ratios might be associated with the passage of synoptic weather systems of fair weather. Although the measurement of p -xylene is, in principle, efficiently performed with the DOAS technique, the OPSIS instrument p -xylene measurements contradict current understanding of its sources and sinks and are thus attributed to errors of the instrument in the evaluation of this substance.

Quasi-continuous measurements of NOx, CO and C5–C12 hydrocarbons made during the MEDCAPHOT-TRACE experiment in a street canyon with heavy traffic load were used to estimate the CO/NOx and 36 individual NMHC/NOx traffic emission ratios in the Athens basin. A traffic emission inventory has been compiled for Athens and aspects of this inventory were tested against measurements. The results indicate that although the main features of the 9:00 to 15:00 variations of the NMHC/NOx and CO/NOx inventory emission ratios are in agreement with observations, during the rest of the day the fine structure of the variations of these ratios cannot be accurately predicted by the inventory. Comparison of pollutant emission ratios derived from ambient measurements with emission ratios predicted by existing inventories for Athens reveals serious discrepancies. Further, the experimental results and theoretical considerations indicate that the speciation of evaporative emissions changes with increasing ambient temperature in favour of the most volatile HC species, thus changing the speciation of traffic emissions during the course of the day. This is an aspect that is not taken into account in present urban photochemical modelling inventories.

During 30.05. - 16.06. 1996 on-line GC/FID measurements of NMHC in the range of C 4 C 12 were carried out at a suburban site within the Greater Athens Area (GAA). Due to persisting strong Etesian winds that primarily transport rural air masses to the GAA back-ground conditions within the GAA could be observed. This allowed discrimination between anthropogenic and biogenic species since significantly different diurnal variations of these compounds were found.

Seven vertical profiles of methyl bromide measured between 1987 and 1995 in the tropical, mid-latitude and Arctic stratosphere are reported. Three of these profiles are previously unpublished, and four are previously published and are here reevaluated and brought on to the same calibration scale as the other ones. The profiles were derived by the analysis of air samples collected by the MPAE balloon-borne cryogenic sampler at various latitudes and at heights from around 6 km to around 30 km. Methyl bromide was not detected above the first 7 km of the tropical stratosphere, while at higher latitudes it sometimes persisted to altitudes greater than 13 km above the tropopause. Concurrent measurements of the man-made Halons 1211 (CBrClF 2 ) and 1301 (CBrF 3 ) and the natural compound CH 2 Br 2 indicate that methyl bromide accounts for 55-70% of the bromine transported into the stratosphere from these four species.

Global cement production has increased twofold during the last decade. This increase has been accompanied by the installation of many new plants, especially in Southeast Asia. Although various aspects of pollution related to cement production have been reported, the impact of primary material deposition practices on ambient air quality has not yet been studied. In this study, we show that deposition practices can have a very serious impact on levels of ambient aerosols, far larger than other cement production-related impacts. Analyses of ambient particulates sampled near a cement plant show 1.3-30.4 mg/m(3) total suspended particulates in the air and concentrations of particles with a diameter of 10 μm or less at 0.04-3 mg/m(3). These concentrations are very high and seriously exceed air quality standards. We unequivocally attribute these levels to outdoor deposition of cement primary materials, especially clinker, using scanning electron microscopy/energy-dispersive X-ray spectroscopy. We also used satellite-derived aerosol optical depth maps over the area of study to estimate the extent of the spatial impact. The satellite data indicate a 33% decrease in aerosol optical depth during a 10-year period, possibly due to changing primary material deposition practices. Although the in situ sampling was performed in one location, primary materials used in cement production are common in all parts of the world and have not changed significantly over the last decades. Hence, the results reported here demonstrate the dominant impact of deposition practices on aerosol levels near cement plants.

Heat waves are projected to become more frequent, longer-lasting, and intense. At the same time, urban areas are confronted with the urban heat island (UHI) phenomenon, which adds to the thermal stress experienced during hot spells. Focusing on the Paris area during the hot summer of 2003, we investigated the influence of heat waves on UHI intensity, i.e., the urban-rural temperature contrast. In a first step, this was done based on observed temperatures from an urban and a rural site, showing that per C increase in the daytime temperature, the nighttime UHI intensity increased by 0.086 C. Recognizing the limited spatial representativeness of the urban experimental site, located in a park, we then performed simulations with an urban climate model, covering the wider Paris area for the summer of 2003. First, a validation was done using the aforementioned temperature measurements to do so. Subsequently, we estimated the sensitivity of the nighttime UHI intensity with respect to the daytime temperature, this time using simulated temperatures of the densely built-up areas in the center of Paris, yielding an increase of UHI intensity of 0.19 C per C increase in the daytime temperature. While these results only apply to the domain and period studied, they do confirm recent reports that the UHI intensity increases during heat waves. The results also show that for the cooler parts of the urban fabric (e.g., parks), the UHI intensification during heat waves is around half of that of the dense urban fabric, thus providing some insights into possible mitigation strategies for the future.

One stratospheric carbonyl sulfide (COS) vertical profile in the Arctic polar vortex has been retrieved from air samples collected by the MPAE balloon-borne cryogenic sampler on January 18, 1992, at Kiruna, Sweden. The measurements were made in the altitude range 7.5–28.5 km. The upper tropospheric volume mixing ratios of COS were 355±60 pptv. The stratospheric profile shows that COS is subject to considerable subsidence this time of the year. The lowest VMRs were encountered at around 20 km altitude, while above that height a COS increase was observed. A possible explanation could be reversible uptake of COS by frozen sulfuric acid aerosols.

The Day of Week (DoW) variability of total cloud cover (TCC) and aerosol optical depth (AOD550) and its statistical significance over six European regions is investigated using 10 years of summertime satellite observations from TERRA and AQUA MODIS. In general, positive (higher values during midweek) weekly cycles in both AOD550 and TCC appear over Central Europe (CE), while a strong negative weekly cycle appears over the Iberian Peninsula and NE Europe (NEE). A very similar TCC and AOD550 weekly variability appears over CE, SW Europe (SWE) and NEE and a rather similar one over Central Mediterranean (CM). Possible scenarios that could explain the common weekly variability of aerosols and cloud cover through the aerosol indirect effects are discussed. An effort is made to verify our results and the proposed aerosol-cloud interaction scenarios with the use of independent satellite TCC data from the ISCCP and ground-based precipitation data from the ECA&D project.

Vertical profiles of CBrClF2 (Halon-1211), CBrF3 (Halon-1301) and methyl bromide (CH3Br) were measured during EASOE by means of cryogenic sampling and subsequent GC-analyses. Three flights of the MPAE balloon-borne sampler were carried out on January 18, February 6 and March 20, 1992, from Kiruna/Sweden. Stratospheric falloff rates of these substances, which constitute the dominant source of organically bound bromine in the atmosphere, were found, like those of other source gases measured during EASOE, to be considerably larger than those observed at midlatitudes. Total BrOx released from the three source gases was found to increase from about zero at 8 km to 11.4 pptV at 19 km altitude.

Simultaneous measurements of ozone and —for the first time in Munich—of PAN were carried out at two sites in the urban area of Munich during two periods (16 June–15 September 1989 and 1 January–30 April 1990). Maximum mixing ratios reached 75 ppbv for ozone (10-min-average) and 5.6 ppbv for PAN (20-min-value), respectively. Ozone showed more pronounced diurnal variations than PAN. In both cases they were related to diurnal variations of the global radiation and the mixing ratios of NOx. Regarding ozone linear correlation analysis with meteorological parameters revealed distinct dependencies, especially on UV radiation, whereas the results for PAN reflected its more complicated formation. As far as dependencies on wind velocity are concerned, both ozone and PAN exhibited maximum mixing ratios in cases where the wind velocity was below 5 ms−1. With increasing wind velocity both mixing ratios tended towards their natural background concentrations. Investigations concerning the influence of the wind direction did not disclose any particular local effects, but rather a relationship to the general weather situations. On the whole, PAN could be considered as a more characteristics indicator of smog conditions than ozone due to its low background concentrations and its thermal instability.

For the determination of regionally averaged fluxes and budgets of atmospheric trace constituents, the ultimate goal of the European Environment Research EUROTRAC, several ecosystems must be investigated, each representative of larger areas. One of the most wide-spread vegetation type is the coniferous forest, in which several compartments exist such as soil, trunk space, canopy and ‘free’ atmosphere above, which differ considerably in biology, chemistry and meteorology, but increase strongly by feedback processes caused by turbulent mixing and chemical reactions. To understand forest/atmosphere relations in detail, measurements are needed which provide concentrations, emission and deposition data of various chemical compounds as well as micrometeorological quantities. These measurements have to be carried out simultaneously in all storeys of a forest over extended periods and must be highly resolved with respect to time and space. In a first step detailed small-scale studies must be performed. This paper describes the scientific approach for integrated multi-disciplinary studies at Schachtenau, a research site in Central Europe's largest continuous forest, and presents first results from joint experiments.

Following the Cretaceous/Tertiary (K/T) mete- oritic impact some 65 Myr ago, large portions of above- ground terrestrial biomass were burned. As a result, large amounts of various trace gases were injected to the atmo- sphere, inducing a wide range of effects on climate and ecosystems. Here, it is commented on the previously un- accounted for emission to the atmosphere of methyl bro- mide (CH3Br) and methyl chloride (CH3Cl) from extensive biomass burning that followed the impact. Based on reported biomass burning emission rates of the above organohalo- gens relative to CO2, it is estimated that their emissions from global fires resulted in tropospheric mixing ratios of around 20-65.8 ppbv organic Cl and 110-390 pptv organic Br. The above calculated mixing ratios of organic chlorine and bromine are more than an order of magnitude greater than their present, anthropogenically perturbed level and, although the ocean ultimately might absorb them, we ar- gue here that they could still remain in the atmosphere for many years, and a substantial fraction could be transported to the stratosphere, thus substantially affecting the ozone layer. This would have led to very serious increases in short wave- length UV radiation reaching the lowermost atmosphere. sequences of bolides >10 7 Mt result from injections of dust, NO, and water vapour in the stratosphere. Ozone loss is then a consequence of enhanced NO levels and accelerated heterogeneous chemistry. After the removal of radiation- blocking dust, smoke, and NO2 from the atmosphere, sig- nificantly increased doses of UV-B radiation could reach the ground for periods up to several years as a result of ozone depletion. However, if a shielding layer of stratospheric sul- phate particles forms, much of the UV-B may be blocked from reaching the surface during the first few years after the impact.

[1] Model studies show that changes in photodissociation rates resulting from changes in ozone column densities induce changes in lower tropospheric ozone, which vary significantly with location and time of the year. The validity of the model results is tested against daily total ozone and ground level ozone at three selected stations (Samoa, Mauna Loa, and Hohenpeissenberg). Observational data for a period of more than 1 decade have been analyzed. Comparisons are made of model-simulated distribution of ozone and its precursors (NOx and CO) at the three stations. Further comparisons are made of observed and model-calculated sensitivity in surface ozone to reduction in ozone column densities. Calculations performed with a global-scale chemical transport model (CTM) with extensive ozone chemistry reproduce well the observed levels and seasonal distribution of NOx, CO, and ozone at remote background stations (Samoa and Mauna Loa) and at stations in more polluted regions (Hohenpeissenberg). A chemical box model is used to demonstrate the chemical link between surface ozone changes and changes in total ozone for different NOx levels. Model studies and analysis of the observational data show that ground level ozone at the remote, low-NOx stations of Mauna Loa and Samoa is correlated positively with total ozone, with an exception at Mauna Loa during winter months. A reduction in ozone column densities, which leads to enhanced photochemical activity, reduces ozone levels at ground level. The sensitivity of surface ozone to changes in total ozone is particularly large in the low-NOx regime at Samoa. An anticorrelation between ground level ozone and total ozone is found at the Hohenpeissenberg station both in the observational data and in the model results during wintertime with high NOx levels. Enhanced photochemical activity leads to enhanced ozone production. There is, however, a disagreement between the observed and CTM-modeled sensitivity in surface ozone to ozone column density during the summer months at Hohenpeissenberg. The strong anticorrelation found in the observations, giving increases in surface ozone at low ozone column densities, is not present in the CTM model studies. It is suggested that a correlation between low ozone column densities and stagnant high-pressure systems is an important cause for the observed anticorrelation.

Stable brominated hydrocarbons, beside their role in the geochemical cycling of bromine, may enter the stratosphere, where they can efficiently catalyze ozone destruction through the release of inorganic bromine (Br y ). Three vertical profiles of dibromomethane (CH 2 Br 2 ) are reported here, derived from the analyses of air samples collected by the MPAE balloon-borne cryogenic sampler at 17°N in 1990 and at 68°N in 1992 and 1995. Upper tropospheric volume fractions of this compound from below detection limit to 1.7 pptv were measured. Although CH 2 Br 2 as already below the detection limit at the tropopause during one of those flights, it was present in the first 2-4 km of the stratosphere in measurable quantities during the other two flights. Concurrent Ch 3 Br and Halons 1211 (CBrClF 2 ) and 1301 (CRrF 3 ) measurements suggest that CH 2 Br 2 could contribute up to 20% of Br y released in this altitude region while it could deliver around 10% of the total bromine entering the stratosphere.

[1] One year of hydrogen sulfide measurements in an urban traffic site were used to assess the importance of traffic in the overall high ambient air burden of H2S (mean annual concentration of 8 μg/m3). During calm nighttime hours, hourly values of H2S were correlated positively with those of CO (R2 = 0.75) and SO2 (R2 = 0.70), suggesting a common source from traffic. For the driving conditions of the measurement site, H2S automotive emissions are around 24% w/w those of SO2, while European inventories calculate these at only 2.5%. H2S annual traffic emissions, based on the existing emission inventories for CO and SO2 are calculated at 0.199–0.311 × 10−3 Tg a−1 for Thessaloniki and are extrapolated to 0.030–0.0485 Tg a−1 for the EU15 countries and 2.6 Tg a−1 for Europe and Eurasia. It appears that traffic emissions make up a significant contribution to the global H2S budget.

There are not many published results from regional modeling for the Eastern Mediterranean. These limited publications are examined with regard to the agreement of the modeled ozone distributions with recent datasets that become available from rural sites in the area. Possible reasons for the large discrepancies between modeled and measured summertime ozone levels are discussed, and it is concluded that a targeted modeling effort is needed to explain the differences satisfactorily and achieve an improvement of the used models. Such an effort should require comparison of the modeled distributions of ozone, its precursors and meteorological parameters both at the surface and in the vertical within the area of interest.

[1] In this paper we compare radiative transfer model calculations of the actinic flux in the UV spectral region with airborne measurements of the actinic flux, obtained during the Photochemical Activity and Ultraviolet Radiation (PAUR) campaign, which took place in the Aegean Sea, Greece, in June 1996, in order to assess the accuracy of the model in calculating photolysis rates, when the model input parameters are well defined from measurements. The model can simulate the total actinic flux (4 pi sr) in the UV-A region with an accuracy of 5% for all altitudes (0.1-12 km) in the cloud free troposphere, while in the UV-B the impact of the vertical distribution of ozone and aerosol can lead to differences, of about 5-10% at low altitudes up to 20% at higher altitudes. Next, the photolysis rates of J((OD)-D-1) and J(NO2) measured during the PAUR 2, in Crete, Greece (35.5degreesN, 23.8degreesE), in May 1999, at two altitudes (Gerani 30 m and Prases 1000 m), are compared with the respective model calculations in order to examine the effect of the alternating Sahara dust/maritime aerosol environments imposed to these photolysis rates, as well as to examine their differences due to the altitude difference. It is shown that high levels of tropospheric ozone and absorbing aerosols can cause a decrease in the photolysis rates of ozone near the surface, even under conditions of reduced total ozone content. This fact indicates that tropospheric ozone can be disproportionately important as a filter against UV-B radiation when most scattering of the radiation by air molecules and dust occurs in the troposphere. This behavior is not simulated accurately using a radiative transfer model constrained by observations of ozone and aerosol optical depths. The differences of the of the photolysis rates between the two altitudes as determined by the model and by the measurements, differ significantly for the Sahara dust event, indicating that during this event in the boundary layer, there is a mixture of desert and nonabsorbing aerosols.

[1] A variety of surface chemical measurements, including surface ozone, NO, NO2, NOx, peroxyacetyl nitrate, and nonmethane hydrocarbon, were carried out at a rural coastal site, Nopigia, Crete, and at a rural elevated site, Prases, Crete, within the framework of the Photochemical Activity and Ultraviolet Radiation (PAUR) II experiment, which took place in Greece and Italy in early summer (1–31 May 1999). The total ozone exhibited very large fluctuations (larger than 90 Dobson units, 1 DU = 2.69 × 1016 molecules cm−2) during the campaign with maximum values of around 400 DU during 10 May and minimum values of

[1] The Photochemical Activity and Ultraviolet Radiation (PAUR) II project (a continuation of an earlier PAUR I project) had the purpose of studying the interrelationships between changes in total ozone, tropospheric aerosols, UV radiation and photochemical activity. As part of PAUR II project, a campaign took place in Greece and Italy during May–June 1999, with the participation of 15 European and 3 American research institutions. A variety of radiation and gaseous and aerosol atmospheric composition and optical characteristics measurements were made during the campaign. Radiative transfer models and three-dimensional (3-D) regional chemistry transport models (CTM) were applied and compared to the available data set of PAUR II. The present overview paper gives an introduction to the project and to the meteorological and environmental conditions that prevailed and outlines some results that are extensively described in the subsequent papers which form this special section. The modulation of the UVB field in the presence of different types of aerosols, its transmittance and role in the photochemistry of the particular eastern Mediterranean environment is overviewed. Using a 3-D CTM, it is shown that even a 50% reduction in Greek anthropogenic emissions has only a small effect in reducing the ozone levels over the eastern Mediterranean in summer. The environmental conditions, which prevailed during the PAUR I and PAUR II campaigns, offered cases of background conditions over the Aegean Sea as well as conditions with Saharan dust episodes and extremes in total ozone.

[1] To study the spatial and temporal variability of tropospheric ozone in the marine boundary layer over the Aegean Sea (eastern Mediterranean), an O3 analyzer has been installed onboard of a passenger vessel traveling on a regular basis in the Aegean Sea (from Heraklion/Crete 35°30′N, 25°13′E to Thessaloniki 40°64′N, 22°97′E) during a period of 14 months (August 1999 to November 2000). In addition, O3 data have been obtained on a daily basis at the regional background station of Finokalia (Crete; 35°30′N, 25°70′E) since September 1997, short-term measurements of O3 were performed over Crete during the PAUR II campaign (May 1999), and the first O3 data from a rural area (40°32′N, 23°50′E) close to Thessaloniki at the north of Greece have been collected from March 2000 to January 2001. This survey extensive points out the existence of a well-defined seasonal cycle in boundary layer O3 with maximum in summer both above the Aegean Sea and at Finokalia. However, the seasonal signal (defined as the summer/winter ratio) is not constant and varies as a function of air mass origin from 1.33 to 1.15 for the N-NE and SW-S sectors, respectively, in line with the geographical location of the O3 precursor sources. Our data show the absence of any significant longitudinal gradient over Crete at least during spring and autumn and the absence of significant latitudinal gradient between the north and south Aegean Sea during all seasons for air masses having similar origin. The above results indicate that long-range transport is the main factor accounting for the elevated O3 levels above the eastern Mediterranean Sea. Thus (1) O3 data from Finokalia, where the longest time series are available for the area, have regional significance and (2) over the entire Aegean basin, ozone values are above the 32 ppbv European Union (EU) phytotoxicity limit throughout the year and above the 53 ppbv EU health protection limit most of the time during the dry season of the year. The very significant correlation between black carbon (BC) and O3 observed during an intensive campaign in May 2000 provides an indication that the high O3 concentrations at Finokalia resulted from ageing of air masses strongly affected by combustion processes.

The Photochemical Activity and solar Ultraviolet Radiation (PAUR I) and Photochemical Activity and solar Ultraviolet Radiation Modulation Factors (PAUR II) projects had the aim of studying various aspects of ultraviolet radiation and photochemistry interrelationships. PAUR I aimed at studying the interrelationships between total ozone, UV-B radiation, aerosol load, air pollutants, photodissociation rates of NO2 and O3 and tropospheric ozone. PAUR II has the aim of studying the interactions between UV-B, total ozone, tropospheric ozone and photochemical activity in the presence of alternating maritime and Saharan aerosols. The present paper presents the main concepts underlying the two projects, the approach followed and a brief overview of some of the results obtained so far. Further, the main results of PAUR I that are relevant to tropospheric ozone chemistry over the Eastern Mediterranean are presented.

The purpose of this study is to clarify the origin of columnar SO2 episodes seen at Thessaloniki (40,5°N, 22.9°E) during the period 1994, to compare the columnar SO2 values with surface measurements of SO2 and explain the second maximum peak which appears in August in the columnar SO2 time-series, recorded by a Brewer spectrophotometer since 1982. This continuous record provides an average columnar SO2 of 2 m-atm-cm during the 15 years of operation. Although the maximum concentrations of columnar SO2 originate form local sources in the winter, significant columnar SO2 amounts are also seen in the summer. On a few occasions however, as high as 5–7 m-atm-cm of columnar SO2 have been measured both in winter and summer period. Although the former originate from local sources in the city of Thessaloniki, it appears that the sources were not local during the summer. This study aims at identifying the origin of these high total columnar SO2 sources which are formed in regions located at distances from 50 to 200 km, or more, to the north-northeast of Thessaloniki.

State space models for tropospheric urban ozone prediction are introduced and compared with linear regression models. The linear and non-linear state space models make accurate short-term predictions of the ozone dynamics. The average prediction error one hour in advance is 7 microg/m(3) and increases logarithmically with time until it reaches 26 microg/m(3) after 30 days. For a given sequence of solar radiation inputs, predictions converge exponentially with a time scale of 8 hours, so that the model is insensitive to perturbations of more than 150 microg/m(3) O(3). The slow increase of the prediction error in addition to the uniqueness of the prediction are encouraging for applications of state space models in forecasting ozone levels when coupled with a model that predicts total radiation. Since a radiation prediction model will be more accurate during cloud-free conditions, in addition to the fact that the state space models perform better during the summer months, state space models are suitable for applications in sunny environments.

Carbonyl sulfide is found as a major sulfur compound in anodic gases of commercial aluminium electrolysis. Recent spectroscopic measurements on industrial aluminium smelters found typical CO/COS ratios between 80 and 200. This results in specific COS emissions of between 1 and 7 kg/t(Al) if all COS is released into the atmosphere. In 1993 aluminium production would have been responsible for between 0.02 and 0.14 Tg of COS emissions. Currently, aluminium production does not seem to influence the total atmospheric COS budget to an extent beyond its natural variability. If recent growth rates of global aluminium production are sustained, however, COS emissions would quadruple until 2030. Together with increasing aircraft emissions into the stratosphere, an increase of the sulfate background aerosol is to be expected that could significantly enhance ozone depletion. The use of inert anodes is recommended to reduce aluminium production emissions of COS and CF4, C2F6, CO2, and CO at the same time.

During the solar eclipse of August 11, 1999, intensive measurements of UV solar irradiance and total ozone were performed at a number of observatories located near the path of the Moon's shadow. At the Laboratory of Atmospheric Physics (LAP) of the Aristotle University of Thessaloniki, Greece, global and direct spectra of UV solar irradiances (285–365 nm) were recorded with a double monochromator, and erythemal irradiances were measured with broadband pyranometers. In addition, higher-frequency measurements of global and direct irradiances at six UV wavelengths were performed with a single Brewer spectrophotometer. Total ozone measurements were also performed with Dobson and Brewer spectrophotometers at Hradec Kralove (Czech Republic), Ispra (Italy), Sestola (Italy), Hohenpeissenberg (Germany), Bucharest (Romania), Arosa (Switzerland), and Thessaloniki (Greece). From the spectral UV measurements the limb darkening effect of the solar disk was tentatively quantified from differences of measured solar spectral irradiances at the peak of the eclipse (near to limb conditions) and before the eclipse. Two blackbody curves were fit to the preeclipse and peak eclipse spectra, which have shown a difference in effective temperatures of about 165°K between the limb and the whole of the solar disk. The limb darkening effect is larger at the shorter UV wavelengths. The ratio of the diffuse to direct solar irradiances during the eclipse shows that the diffuse component is reduced much less compared to the decline of the direct solar irradiance at the shorter wavelengths. Moreover, a 20-min oscillation of erythemal UV-B solar irradiance was observed before and after the time of the eclipse maximum under clear skies, indicating a possible 20-min fluctuation in total ozone, presumably caused by the eclipse-induced gravity waves. This work also shows that routine total ozone measurements with a Brewer or a Dobson spectrophotometer should be used with caution during a solar eclipse. This is because the diffuse light increases by more than 30% with respect to the direct solar radiation, increasing more at the shorter wavelength side of the UV spectrum. This plausible mechanism introduces an artificial decrease in total ozone during solar eclipse of more than 30 Dobson units (DU), which is confirmed by all Brewer and Dobson measurements. Changes in total ozone cited earlier in the refereed literature have not been confirmed in the present study.

[1] During the last 5 years, information on the regional tropospheric ozone levels over the eastern Mediterranean has become available but was confined to measurements at ground level. Here available information is expanded with measurements at two more rural ground level sites spanning 8 latitude, ozonesonde ascents, lidar observations, ship cruises, and aircraft flights. During wintertime the ozone monthly values are 1020 ppbv higher than values at other European sites, while during summertime the values are comparable. This results in regional ozone background levels in the area that are above the European Union (EU) 32 ppb/ 24 hours phytotoxicity limit during the entire year. Late spring lidar observations show that south and southwestern synoptic flows which are associated with Saharan dust events result in lower ozone above the planetary boundary layer (PBL) by 20-35 ppbv as compared to these during northerly flows, which transport air from continental Europe. These lidar observations along with ship measurements during July show that ozone is enhanced 1.5-2.2 times in the continental outflow, when compared to aged maritime air or air from the African continent. These results along with ozonesonde observations suggest that ozone abatement in the area is largely beyond the control of regional emissions and can be controlled only with emission reductions on a European scale. During September, measured background NO and NO2 levels between 3 and 4.5 km above sea level ranged from 1 to 221 pptv and from 102 to 580 pptv, respectively. The troposphere contains around 40-70 Dobson units of ozone during summer and around 20-30 Dobson units during winter.