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Simple Summary: We studied the nesting population trends of the colonially nesting heron species in Greece from 1988 to 2018, aiming to identify drivers of these trends and thus inform colony/wetland conservation measures. Two species (Cattle Egret and Squacco Heron) had a positive trend, while three species (Black-crowned Night Heron, Little Egret and Grey Heron) had a negative trend. The Purple Heron presented a stable trend. Our results suggest that: (a) The Natura 2000 network and the operation of the protected areas Management Authorities have positively affected heron species nesting population trend or range expansion, (b) national wetland restoration efforts have facilitated the expansion of most heron species' breeding range via the establishment of new colonies, and (c) colonies located outside protected areas were—especially in the case of the Grey Heron—most likely to have a declining nesting population trend. The drivers behind the observed population trends differed among species, even among those sharing the same breeding sites. This suggests that the nesting population trends could be due to ecological changes at both the breeding and at the wintering sites. Our results emphasize the importance of continuing wetland restoration efforts, developing heron-friendly farming practices, and adopting a systematic nationwide survey of colonies. Heron colonies are dynamic components of wetlands. Therefore, their systematic monitoring is important for the management of both birds and wetlands. During the period 1988–2018, we counted breeding pairs of seven colonial breeding heron species at 65 colonies across 37 wetlands in Greece. We considered as annual variables of a population: (a) years since 1988, (b) Natura 2000 network inclusion, (c) protected area management authority overseeing, (d) wetland type (new or restored), and (e) new colonies (established after 2003). The Cattle Egret Bubulcus ibis and the Squacco Heron Ardeola ralloides had a positive breeding population trend. The Black-crowned Night Heron Nycticorax nycticorax, Little Egret Egretta garzetta, and Grey Heron Ardea cinerea had a negative trend, while the Purple Heron Ardea purpurea population was stable. The Great White Egret Ardea alba bred sporadically at only a few sites which precluded the evaluation of its population trend. The informative population variables differed among species, even of those at the same colony, which suggests trends are also affected by conditions at wintering grounds. The study highlights the need for the systematic monitoring of heron colonies and the protection of foraging/breeding areas in order to reverse the observed negative population trends. [ABSTRACT FROM AUTHOR]

Low-cost sensors (LCSs) for particulate matter (PM) concentrations have attracted the interest of researchers, supplementing their efforts to quantify PM in higher spatiotemporal resolution. The precision of PM mass concentration measurements from PMS 5003 sensors has been widely documented, though limited information is available regarding their size selectivity and number concentration measurement accuracy. In this work, PMS 5003 sensors, along with a Federal Referral Methods (FRM) sampler (Grimm spectrometer), were deployed across three sites with different atmospheric profiles, an urban (Germanou) and a background (UPat) site in Patras (Greece), and a semi-arid site in Almería (Spain, PSA). The LCSs particle number concentration measurements were investigated for different size bins. Findings for particles with diameter between 0.3 and 10 μm suggest that particle size significantly affected the LCSs' response. The LCSs could accurately detect number concentrations for particles smaller than 1 μm in the urban (R2 = 0.9) and background sites (R2 = 0.92), while a modest correlation was found with the reference instrument in the semi-arid area (R2 = 0.69). However, their performance was rather poor (R2 < 0.31) for coarser aerosol fractions at all sites. Moreover, during periods when coarse particles were dominant, i.e., dust events, PMS 5003 sensors were unable to report accurate number distributions (R2 values < 0.47) and systematically underestimated particle number concentrations. The results indicate that several questions arise concerning the sensors' capabilities to estimate PM2.5 and PM10 concentrations, since their size distribution did not agree with the reference instruments. [ABSTRACT FROM AUTHOR]

Simple Summary: The European turtle dove (Streptopelia turtur) is a migratory species that overwinters in sub-Saharan Africa, migrating to Europe each spring to breed. Over the past four decades, turtle dove populations have declined by as much as 79%, making the species vulnerable to extinction. A major threat to the species is illegal killing (poaching) during its spring migration through the Mediterranean coasts of Europe. According to the international action plan for the conservation of the species, eradicating this threat is key for reversing the European turtle dove population declines by 2028. In this study, we used a network of acoustic sensors to record the gun hunting pressure at known hunting sites in the Ionian Islands, Greece—a known poaching hot-spot—over four spring migrations (2019–2022). Based on the number of gunshots recorded, we estimate that up to 57,095 turtle doves were killed or injured across the region in 2021. We anticipate that these findings will generate the resolve needed among responsible authorities to eradicate the spring migration in the Ionian Islands, and propose the roll out acoustic monitoring grids in additional poaching hot-spots along the migration routes of the turtle dove. The European turtle dove (Streptopelia turtur) is an Afro-Palearctic migrant whose populations have declined by 79% from 1980 to 2014. In 2018, the International Single Species Action Plan for the Turtle Dove (ISSAP) was developed with the goal of enabling, by 2028, an increase in turtle dove numbers along each of the three migration flyways (western, central, eastern). To achieve this, the illegal killing of turtle doves, a critical threat to the species, has to be eradicated. The Ionian Islands off the west coast of Greece lie on the eastern flyway and are considered a major turtle dove poaching hot-spot during spring migration. Quantifying wildlife crime, however, is challenging. In the absence of a reliable protocol for monitoring spring poaching levels, the agencies tasked with tackling the problem have no means of assessing the effectiveness of the anti-poaching measures and adapting them if required. Using passive acoustic monitoring (PAM) methods, we recorded gun hunting intensity at known turtle dove poaching sites during the 2019–2022 spring migrations (2–10 sites/season) with unprecedented spatial and temporal resolution. Based on published gunshot to killed/injured bird ratio for similar species (corroborated with discussions with local hunters) and an estimate of the proportion of hunting sites monitored by our PAM grid (using gunshot detection range estimates from control gunshots), we estimated that in 2021, up to 57,095 turtle doves were killed or injured across five Ionian Islands (Zakynthos, Paxi, Antipaxi, Othoni, and Mathraki). The 2022 estimate was almost half, but it is unclear as to whether the change is due to a decline in poachers or turtle doves. We propose ways of improving confidence in future estimates, and call for a temporary moratorium of autumn turtle dove hunting in Greece—as per ISSAP recommendation—until spring poaching is eradicated and the eastern flyway population shows signs of a full recovery. Finally, we hope our findings will pave the way for the development of PAM grids at turtle dove poaching hot-spots across all migration flyways, contributing to the global conservation of the species. [ABSTRACT FROM AUTHOR]

In August 2021, a historic heatwave was recorded in Greece which resulted in extreme wildfire events that strongly affected the air quality over the city of Athens. Saharan dust was also transferred over Greece in the same period due to the prevailing southern winds. The impact of these events on air quality and surface solar radiation are investigated in this study. Event characterization based on active and passive remote sensing instrumentation has been performed. The study shows that significantly increased levels of air pollution were recorded during the end of July/first week of August. The smoke led to unusually high AOD values (up to 3.6), high Ångström Exponent (AE) (up to 2.4) and a strong and negative dependence of single scattering albedo (SSA) on wavelength that was observed to decrease from 0.93 at 440 nm to 0.86 at 1020 nm signifying the presence of strong absorbing aerosols. While, the dust event led to high AOD (up to 1.4), low AE (up to 0.9) and positive dependence of SSA on wavelength that was observed to increase from 0.89 at 440 nm to 0.95 at 1020 nm indicating large forward scattering due to coarse particles. Furthermore, the analysis of the smoke aerosol optical properties during the transfer from the source to a distance of about 240 km revealed that the SSA and AE changed significantly during the transfer, which lasted approximately 9 h. The transport of the plume led to an impressive change in the spectral shape of SSA whose value significantly increased pointing to the aging of smoke and the dilution of plumes while the transport. The impact of dust and smoke on spectral solar irradiance reveals significant differences in the spectral shape of attenuation caused by the two different aerosol species. The attenuation of solar irradiance in UV-B irradiance was found to be least in case of dust and highest due to smoke (up to 60 % or more) and intermediate in the case of a mixture of smoke and dust. The attenuation was comparatively less in NIR region (mostly within 20 % but it even reached up to 40 % in the presence of smoke) and VIS region (but greater than NIR region). Also, the AOD variations from climatology led to decrease in UV Index up to 53 %, in vitamin-D up to 50 %, in photosynthetically active radiation up to 21 % and in GHI up to 17 %, with implications on health, agriculture and energy. This study highlights the wider impacts of wildfires that are part of the wider problem of the Mediterranean countries, whose frequency is predicted to increase in view of the projected increasing occurrence of summer heatwaves. [ABSTRACT FROM AUTHOR]

The Evros delta is one of the most important wetlands for wintering waterfowl in Greece and the most popular among waterfowl hunters. This study addresses hunting activity and harvest while also investigating the relationship between weather conditions and hunting activity to suggest ways of improving waterfowl management. We counted wintering waterfowl and hunter numbers, and conducted hunter bag surveys during December-February over four hunting seasons. We calculated a 10-day goose and duck Preferential Shooting Index (PSI), which is the ratio of observed number of shot birds to the number of birds expected to have been shot if the birds were shot in proportion to their availability. Common Teal, Mallard and Greater White-fronted Goose were the most abundant species both in the field and in hunter bags. The mean number of hunters/day was 99.9, with each one shooting on average 2.5 birds/day. The overall waterfowl harvested accounted for 1.3% of the total waterfowl population. For geese this proportion was six times higher (8.7%), while for ducks alone and protected species was 1.2% and 1.4% respectively. Geese were shot more often than expected (PSI 6.55), while ducks and protected species were shot according to their availability (PSI 0.86 and 1.02, respectively). Wind speed, precipitation and geese number in the field were the best predictors of overall harvest and number of hunters. To reduce goose overshooting and the probability of protected species being accidentally shot, we suggest habitat management actions for the geese feeding areas and hunters' awareness raising. [ABSTRACT FROM AUTHOR]

A novel method for the short-term (15–240 min) forecasting of cloudiness in Greece is presented by taking into account that this is the main atmospheric factor responsible for the spatial and temporal distribution of surface solar irradiance. Images from the Spinning Enhanced Visible and Infrared Imager onboard the Meteosat Second Generation satellite, for a 3-year time period and with high spatial and temporal resolution (0.05°, 15 min), were processed to retrieve the cloud clearness index (CCI) and used for the training and testing of an artificial neural network (ANN). The estimated and the measured values of CCI are in good agreement and emphasis is given to the spatial distribution of the seasonal errors. The ANN was trained according to pre-classified areas that present similar cloud characteristics and could provide estimations of surface solar irradiance in synergy with models that calculate surface irradiance under clear skies. [ABSTRACT FROM AUTHOR]

Cloud properties derived from the SEVIRI (Spinning Enhanced Visible and Infrared Imager) instrument, on board the MSG (Meteosat Second Generation) satellite, have been used to retrieve the surface global solar irradiance incident on a horizontal surface GHI (global horizontal irradiance) and the DNI (direct normal irradiance) with a temporal resolution of 15 min. The daily amount of solar energy as well as monthly and annual sums, are estimated. Based on a 6-year study period (2008–2013), a monthly climatology is derived. Results are compared with ground-based measurements in Greece. Comparison shows a general good agreement between satellite and ground data, with the highest differences occurring in cases of broken or very thick cloudiness. The highest collected monthly solar energy values are found during summer months, in Southern Peloponnese, Crete and Cyclades islands, and exceed 250 kWh m −2 . The annual average energy for GHI is 1400–1500 kWh m −2 in Northern Greece and up to 1900 kWh m −2 in Southern Peloponnese, Crete and the islands. For DNI, values increase to about 9% in Northern Greece and around 15% in Southern Greece. [ABSTRACT FROM AUTHOR]

Fecal lead (Pb) levels were investigated in the threatened European population of the Lesser White-fronted Goose (LWfG, Anser erythropus ) and of the non-threatened Greater White-fronted Goose (GWfG, Anser albifrons ) wintering in two wetland areas in northern Greece in order to assess the potential risk from Pb exposure. Fecal, soil and food plant samples were analyzed. Levels of Pb were normalized using Al concentrations in order to separate the effect of possible ingestion of Pb shot from that of soil or sediment accidentally ingested with food. All concentrations are expressed on a dry weight basis. Geometric means of Pb content in the feces of LWfG were 6.24 mg/kg at Evros Delta and 7.34 mg/kg at Lake Kerkini (maximum values of 28.61 mg/kg and 36.68 mg/kg, respectively); for fecal samples of GWfG geometric means were 2.39 mg/kg at Evros Delta and 6.90 mg/kg at Kerkini (corresponding maximum values of 25.09 mg/kg and 42.26 mg/kg). Soil Pb was in the range of 5.2–60.2 mg/kg (geometric mean = 22.6 mg/kg) for the Evros Delta and between 13.4 and 64.9 mg/kg (geometric mean = 28.1 mg/kg) for Kerkini. A general linear model fitted to the data showed that Pb levels were very closely dependent on Al levels in the feces from both species and at both sites indicating soil or sediment were the only significant source of Pb; species and site, as well as their interaction, were not statistically significant factors. For both species and at both sites exposure to Pb was evidently very mild and the observed levels of Pb were well below the proposed thresholds for lethal or sublethal effects of Pb poisoning. Soil ingestion appeared to gradually increase from October to December for LWfG at Kerkini, corresponding to a gradual depletion of their food source. [ABSTRACT FROM AUTHOR]

Measurements of total ozone over Greece have been performed with NILU-UV multi-channel radiometers since 2005. In this study, the measurements at two stations, Thessaloniki and Athens, of the ultraviolet (UV) monitoring network are compared with ozone values derived from Brewer spectroradiometers at the same sites. The overall percentage difference on daily averages (including measurements for solar zenith angle below 70˚) is below (1 ± 3.5)% at both sites. The cloud modification factor (CMF), specified as the ratio of measured irradiance with a model-derived cloud-free value, is being used to examine the effect of cloudiness on the retrieved ozone abundances. During days with average CMF values above 0.7, the difference in total ozone measurements is within ± 5%. The use of momentary ozone values from the radiometers with this limitation in CMF reduces the difference of the average values to (0.0 ± 2.2)% for Athens and (0.21 ± 2.8)% for Thessaloniki. [ABSTRACT FROM AUTHOR]

The variability of ultraviolet and photosynthetically active radiation (PAR) during the total solar eclipse of 29 March 2006 was examined in this study. The measurements from NILU-UV multichannel radiometers at 7 stations of the Greek UV Network were used, where the maximum eclipse percentage ranged from 73.1% to 94.8%. In addition, an extra instrument was established at a remote Greek island, Kastelorizo, which was within the Moon's umbral shadow. The reduction of irradiance at 305 and 312 nm relative to non-eclipse conditions at all sites was almost 1.5 times more than the corresponding decrease in the UVA and visible part of the spectrum and reached 98% for eclipse percentage equal to 94%. The availability of several instruments in close proximity to the path of the umbral shadow provided a challenging test for the models. The measured changes in UV and visible irradiance were compared with 1-D model calculations accounting for the limb darkening effect. The agreement between measurements and modeled values at all sites is within 3% for eclipse percentages of less than 30% and becomes worse as the eclipse progresses. The 1-D model reproduced the spectral effect of the eclipse in UVA and PAR wavelength regions within 3% for eclipse percentages up to 50%, but only the half of the observed change was captured as the eclipse progressed. At three sites, where the eclipse maximum was more than 94%, the measured irradiance at 305 nm for eclipse percentages of more than 85% decreased with slower rates than for longer wavelengths. As a result, the total ozone values, derived from the 305/320 nm ratios, apparently decreased significantly for high eclipse percentages. The effect is similar at all three sites, but the interpretation of this observation remains a challenge. Comparison results with 3-D model calculations shortly before, during and shortly after totality were performed for the first time and revealed an agreement with measurements within 20% in the UV-A region. However, the modeled estimates of irradiance at 312 nm are three times lower than measured values. [ABSTRACT FROM AUTHOR]

Abstract: Measured ozone and temperature vertical profiles from Thessaloniki, Greece, were used together with the mid-latitude standard profiles as input data in a radiative transfer model. Calculations of direct and global solar irradiance, actinic flux, UV-B and CIE weighted integrals for solar zenith angles of 30°, 70° and 85° were performed and analyzed. Variable temperature values and ozone redistribution may change UV radiation reaching the surface significantly more than the proposed measurement uncertainties for high solar zenith angles. A specific measured profile corresponding to air masses of polar origin probed over Thessaloniki was selected and the differences in vertical distribution of UV-B radiation were discussed. Obtained results revealed that the use of an inappropriate temperature and ozone profile may lead to significant changes at small UV-B wavelengths and high solar zenith angles. In this case, the use of seasonal average vertical profiles of ozone and temperature for a given area may be carefully utilized when accurate model spectral calculations are needed and comparison with measurements in the troposphere performed. [Copyright &y& Elsevier]

Results are presented from the Actinic Flux Determination from Measurements of Irradiance (ADMIRA) campaign to measure spectral global UV irradiance and actinic flux at the ground, beneath an atmosphere well defined by supporting measurements. Actinic flux is required to calculate photolysis rates for atmospheric chemistry, yet most spectral UV measurements are of irradiance. This work represents the first part of a project to provide algorithms for converting irradiances to actinic fluxes with specified uncertainties. The campaign took place in northern Greece in August 2000 and provided an intercomparison of UV spectroradiometers measuring different radiation parameters, as well as a comprehensive radiation and atmospheric dataset. The independently calibrated spectroradiometers measuring irradiance and actinic flux agreed to within 5%, while measurements of spectral direct irradiance differed by 9%. Relative agreement for all parameters proved to be very stable during the campaign. A polarization problem in the Brewer spectrophotometer was identified as a problem in making radiance distribution measurements with this instrument. At UV wavelengths actinic fluxes F were always greater than the corresponding irradiance E by a factor between 1.4 and 2.6. The value of the ratio F : E depended on wavelength, solar zenith angle, and the optical properties of the atmosphere. Both the wavelength and solar zenith angle dependency of the ratio decreased when the scattering in the atmosphere increased and the direct beam proportion of global irradiance decreased, as expected. Two contrasting days, one clear and one with higher aerosol and some cloud, are compared to illustrate behavior of the F : E ratio. [ABSTRACT FROM AUTHOR]

Cloudiness is the dominant factor that affects the transfer of solar irradiance through the atmosphere. Especially the type of clouds, their high spatial and temporal variability, velocity and position relatively to the Sun, could cause events ranging from total reduction to substantial enhancements of surface solar irradiance. In study, the enhancements of Global Horizontal Irradiance (GHI) at South Greece for 2 years are examined. We use 1–min averages of GHI, sunshine duration and synchronized estimations of cloud coverage and type from a digital imaging system. A radiative transfer model is used to estimate GHI under clear skies. For solar zenith angles lower than 80°, 4% of total GHI measurements are considered as enhancements. It is shown that the effect of thick clouds on the GHI enhancements is significantly higher when compared to the thin ones. We also examine cases that correspond to instantaneous clearness index values higher than 1 (K t > 1): 228 extreme enhancement events are found including 5 cases with GHI values higher than 1367 W/m2 and a maximum value of 1420 W/m2. These results suggest that such events are common and should be included in the design and simulation of the performance of solar energy systems. • GHI measurements for 2 years at a typical South-East site were examined. • 4% of GHI measurements were considered as enhancement cases. • 228 extreme events were found (clearness index values higher than 1). • The majority of enhancements were identified in springtime with extreme GHI values close to 1420 W/m2. [ABSTRACT FROM AUTHOR]

Measurements of PM 2.5 concentrations in five major Greek cities over a two-year period using calibrated low-cost sensor-based particulate matter (PM) monitors (Purple Air PA-II) were combined with local meteorological parameters, synoptic patterns and air mass residence time models to investigate the factors controlling PM 2.5 spatiotemporal variability over continental Greece. Fourteen sensors nodes in Athens, Patras, Ioannina, Xanthi, and Thermi (in the Metropolitan Area of Thessaloniki) were selected out of more than 100 of a countrywide network for detailed analysis. The cities have populations ranging from 65k to 3M inhabitants and cover different latitudes along the South-North axis. High correlations between the daily average PM 2.5 levels were observed among all sites, indicating strong intra- and inter-city covariance of concentrations, both in cold and warm periods. Higher PM 2.5 concentrations in all cities during the cold period were primarily associated with low temperatures and stagnant anticyclonic conditions, favoring the entrapment of residential heating emissions from biomass burning. Anticyclonic conditions were also connected to an increased frequency of PM 2.5 episodes, exceeding the updated daily guideline value (15 μg m−3) of the World Health Organization (WHO). During the warm period, nearly uniform PM 2.5 levels were encountered across continental Greece, independently of their population size. This uniformity strongly suggests the importance of long-range transport and regional secondary aerosol formation for PM 2.5 during this period. Peak concentrations were associated mainly with regional northern air flows over Greece and the Balkan Peninsula. The use of the measurements from dense air quality sensor networks, provided that a robust calibration protocol and continuous data quality assurance practices are followed, appears to be an efficient tool to gain insights on the levels and variability of PM 2.5 concentrations, underpinning the characterization of spatial and seasonal particularities and supporting real-time public information and warning. [Display omitted] • A network of low cost PM 2.5 sensors in five Greek continental cities was used. • An intra- and inter-city positive covariance of PM 2.5 concentrations was detected. • Anticyclonic conditions caused daily PM 2.5 episodes across Greece in cold seasons. • Uniform PM 2.5 levels (8.0–10.8 μg m−3) were measured by all sensors in warm seasons. • CWT and PSCF models indicated regional PM 2.5 contributions in warm seasons. [ABSTRACT FROM AUTHOR]

The health benefits of solar UVB and vitamin D in reducing the risk of cancer and several other diseases have been well documented in recent years. In this study, quality-checked spectral UV irradiance measurements from three European stations (Jokioinen, Finland; Bilthoven, The Netherlands; and Thessaloniki, Greece) are used and the vitamin D effective dose (VDED) is calculated. The maximum average daily VDED is measured during the second half of June and it is up to 250 times higher than the corresponding winter minimum value. At each site, a polynomial fit between the VDED and the erythemal dose rates is proposed. The average VDED rates at local noon exceed a detection threshold value for the cutaneous production of vitamin D at Thessaloniki and Bilthoven throughout the year. The proposed standard vitamin dose cannot be attained, even for skin types I-III and exposure time of 60 minutes around local noon, under physiological atmospheric conditions at Bilthoven and Jokioinen during 3 and 4 months respectively. The daily VDED values, using the CIE action spectrum, are higher from 2% and 8% during summer and winter respectively at all sites, compared with those derived by the action spectrum proposed by MacLaughlin et al. (Science, 1982, 216, 1001-1003). These differences are comparable with the uncertainty of spectral measurements.