We investigated the short-term effects of particulate matter with aerodynamic diameter <10γg/m3 (PM10), sulfur dioxide (SO2), nitrogen dioxide (NO2) and ozone (O3) on pediatric asthma emergency admissions in Athens, Greece over the period 2001-2004. We explored effect modification patterns by season, sex, age and by the presence of desert dust transported mainly from the Sahara area.We used daily time-series data provided by the children's hospitals and the fixed monitoring stations. The associations were investigated using Poisson regression models controlling for seasonality, weather, influenza episodes, day of the week and holiday effects.A 10γg/m3 increase in PM10 was associated with a 2.54% increase (95% confidence interval (CI): 0.06%, 5.08%) in the number of pediatric asthma hospital admissions, while the same increase in SO2 was associated with a 5.98% (95% CI: 0.88%, 11.33%) increase. O3 was associated with a statistically significant increase in asthma admissions among older children in the summer. Our findings provide limited evidence of an association between NO2 exposure and asthma exacerbation. Statistically significant PM10 effects were higher during winter and during desert dust days, while SO2 effects occurred mainly during spring.Our study confirms previously reported PM10 effects on emergency hospital admissions for pediatric asthma and further provides evidence of stronger effects during desert dust days. We additionally report severe effects of SO2, even at today's low concentration levels. © 2011 Elsevier Inc.

Surface air temperature trends in the wider region of Greece during the period 1951-2007, related to atmospheric circulation, are examined in this work. A network of 31 meteorological stations in the Hellenic area and the Asia Minor coasts and National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis datasets were used for this purpose. The NCEP/NCAR reanalysis datasets were created by assimilating climate observations from different sources including ships, satellites, ground stations, radiosonde observations and radar. The general purpose of conducting the reanalyses was to produce multiyear global state-of-the-art gridded representations of atmospheric states, generated by a constant model and a constant data assimilation system. The findings of the analysis show that the mean annual surface air temperature in the wider region of Greece exhibits a pronounced cooling trend from the beginning of the 1950s up to the mid-1970s. It then remained at low levels until the beginning of the 1990s, and then increased up to 2000, when a turning-point is clear although the temperature remained at high levels. The well-known atmospheric circulation indices of the wider region of Europe, namely the North Atlantic Oscillation Index (NAOI), the Mediterranean Oscillation Index (MOI) and the North Sea Caspian Pattern Index (NCPI), were used to investigate the relationship between surface air temperature and atmospheric circulation in this region of the Eastern Mediterranean. The surface air temperature is not correlated to the NAOI, while it is statistically significantly (95% confidence level (CL)) correlated to the MOI, but only during wintertime. On the contrary, good correlations, which are statistically significant (95% CL), appear between the NCPI and the surface air temperature during all seasons, but particularly in winter. © 2011 Taylor & Francis.

In recent years, significant changes in precipitation regimes have been observed and these manifest in socio economic and ecological problems especially in regions with increased vulnerability such as the Mediterranean region. For this reason, it is necessary to estimate the future projected precipitation on short and long-term basis by analyzing long time series of observed station data. In this study, an effort was made in order to forecast the monthly maximum, minimum, mean and cumulative precipitation totals within a period of the next four consecutive months, using Artificial Neural Networks (ANNs). The precipitation datasets concern monthly totals recorded at four meteorological stations (Alexandroupolis, Thessaloniki, Athens, and Patras), in Greece. For the evaluation of the results and the ability of the developed prognostic models, appropriate statistical indexes such as the coefficient of determination (R2), the index of agreement (IA) and the root mean square error (RMSE) were used. The findings from this analysis showed that the ANN's methodology provides satisfactory precipitation totals in four consecutive months and these results are better results, than those obtained using classical statistical methods. A fairly good consistency between the observed and the predicted precipitation totals at a statistical significance level of p < 0.01 for the most of the examined cases has been revealed. More specifically, the Index of Agreement (IA) ranges between 0.523 and 0.867 and the coefficient of determination (R2) ranges between 0.141 and 0.603. The most accurate forecasts concern the mean monthly and the cumulative precipitation for the next four consecutive months. © 2011 Springer Science+Business Media B.V.

To describe the tourism potential of an area, not only single meteorological parameters have to be taken into account, but also thermal sensation and people's thermal comfort. The latter can be estimated by the use of human energy balance models and the derived thermal indices, which comprise all relevant meteorological parameters like air temperature, air humidity, wind speed, and short and long wave radiation fluxes. This paper makes an attempt to assess and analyze climatological parameters and the thermal comfort of Crete, its variations and trends for the period of time 1955-2001. In addition, a definition and quantification of the island's tourism potential is carried out. Long term data from several stations are used from the existing climatic and synoptic network of Crete, including daily mean, maximum and minimum temperature, relative humidity, wind speed, and cloud cover over the whole island, in order to derive the daily Physiologically Equivalent Temperature (PET) and precipitation. In addition, possible trends of thermal comfort and precipitation on an annual and seasonal basis are analyzed. Additionally, data of the 10-minutes climatology of the Climate Research Unit of the University of Norwich have been processed in order to create high resolution (1 km) mean monthly maps for climatological parameters such as air temperature, precipitation and Physiologically Equivalent Temperature. © 2011 Global NEST Printed in Greece. All rights reserved.

Urban particulate matter (PM 10-PM 2.5 and PM 2.5) from Athens (Greece) atmosphere, primarily investigated by SEM-EDS, was further studied in the FLUO and SUL-X beamlines of ANKA Synchrotron facility (KIT, Germany). The SR μ-XRF study showed both geological (e.g. CaTi, CaK and CaSrKRb) and anthropogenic particles exhibiting heavy metal combinations such as FeCo, FeCoCuV and ZnV. It was also revealed that very hazardous metalloids and heavy metals, namely As and Pb, are concentrated in isolated respirable (PM 2.5) microparticles. It was attempted to investigate the oxidation state of As by means of μ-XANES. The As K-edge XANES spectrum of the sample shows a main peak at about 11.874 keV which matches adequately with the As(V) reference spectrum but part of the As seems to have a lower oxidation state (most probably As(III)). This is the first non-bulk study with regard to the partitioning and solid-state speciation of hazardous chemical elements in urban atmospheric microparticles from greater Athens area, rated as an alpha-world city with a population of ca. 4 million people. © 2011 Elsevier B.V. All rights reserved.

The main objective of the present study is to perform a trend analysis and investigate the possible changes in the frequency and wind intensity of the Etesians during June to September of the years 1979 to 2009. The analysis is based mainly on the use of Reanalysis-1 data from the National Centers for Environmental Prediction/National Center for Atmospheric Research. The results are indicative of negative trends in the frequency and wind speed (WS) of the Etesians. During the 31-year period studied, the total number of Etesian days from June to September decreased by about 4.6 days, while the monthly maximum intensity of the daily WS was reduced by almost 1 m s-1. The above indications are strengthened by similar results derived from the trend analysis of observational wind data in the central Aegean for the years 1955 to 2002. The negative trend in the frequency of the Etesian days could be explained by a decreasing trend in the pressure gradient between the central and southern Europe high-pressure center and the Middle East low-pressure center, which cause the Etesians system. In the study, a possible association between the Southern Oscillation and the Etesian winds is also revealed. The negative trend in the frequency and WS of the Etesian winds could imply a reduced cooling mechanism in the eastern Mediterranean in the summer period due to climate change. © 2011 Springer-Verlag.

In this study, the trends and variability of annual precipitation totals and annual rain days over land within the Mediterranean region are analyzed. Long term ground-based observations concerning, on one hand, monthly precipitation totals (1900-2010) and rain days (1965-2010) from 40 meteorological stations within the Mediterranean region were obtained from the Hellenic National Meteorological Service and the World Climate Data and Monitoring Programme (WCDMP) of the World Meteorological Organization. On the other hand, high spatial resolution (0.5 × 0.5 ) gridded monthly data CRU TS 3.1 were acquired from the Climatic Research Unit, University of East Anglia, for the period 1901-2009. The two datasets were compared by means of trends and variability, while the influence of the North Atlantic Oscillation (NAO) in the Mediterranean precipitation was examined. In the process, the climatic changes in the precipitation regime between the period 1961-1990 (reference period) and the period 2071-2100 (future climate) were presented using climate model simulations (RACMO2.1/KNMI). The future climate projections were based on SRES A1B. The findings of the analysis showed that statistically significant (95% confidence level) negative trends of the annual precipitation totals exist in the majority of Mediterranean regions during the period 1901-2009, with an exception of northern Africa, southern Italy and western Iberian peninsula, where slight positive trends (not statistically significant at 95% CL) appear. Concerning the annual number of rain days, a pronounced decrease of 20 %, statistically significant (95% confidence level), appears in representative meteorological stations of east Mediterranean, while the trends are insignificant for west and central Mediterranean. Additionally, NAO index was found to be anticorrelated with the precipitation totals and the number of rain days mainly in Spain, southern France, Italy and Greece. These correlations are higher within the rain season (October-March) than the entire year. Based on the results of regional climate model RACMO2.1/KNMI, precipitation is very likely to decrease almost 20% in the period 2071-2100 compared to 1961-1990, under SRES A1B. © Author(s) 2011.

The paper studies the climatology of the Discomfort Index (DI) and the Common Air Quality Index (CAQI) in a large Mediterranean urban center (Greater Thessaloniki Area), examines the relations between the indices and the climatic conditions in the study area and investigates the linkage between the Urban Heat Island (UHI) effect and the enhanced discomfort and poor air quality in the city center. Discomfort conditions are more enhanced during July and August. Atmospheric conditions when the population suffers discomfort and feels severe stress are found mainly in the summer season hours with total frequency that can be up to about 4% in a month. Throughout the year, air quality conditions are unhealthier in the stations of urban characterization. Very high daily CAQI values are more frequent during the cold period (about 14%) than during the warm period (1-2%) of the year in the urban stations. Daily DI∈≥24°C could be more associated to increased temperature than relative humidity and is strongly related to high and very high CAQI values. During summer, when daily CAQI is ≥76, the feeling of discomfort is the most probable. Consequently, a strong synergy between discomfort and bad air quality exists in summertime. High and very high CAQI values and the discomfort feeling by the majority of the population are related to stagnant atmospheric conditions. During summer season, the poor air quality and the unfavorable comfort conditions for the majority of the population in the city center are associated with the greater frequency of a more intense UHI effect. The above phenomenon is more pronounced during nighttime than daytime. © 2011 Springer Science+Business Media B.V.

In this study, the variability and trends of the mean annual and seasonal maximum and minimum surface air temperature in Greece are examined, using monthly data sets of 26 meteorological stations from the Hellenic National Meteorological Service (HNMS) and gridded data from the National Center for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) Reanalysis project for the period 1955-2001. NCEP-NCAR reanalysis data sets are created by assimilating climate observations from different sources, including ships, satellites, ground stations, radiosonde observations and radar. The general purpose of conducting reanalyses is to produce multi-year global state-of-the-art gridded representations of atmospheric states, generated by a constant model and a constant data-assimilation system. The trends of the mean extreme air temperatures were evaluated, using the Mann-Kendall criterion, and, in the process, factor analysis was applied to both the stations' and the NCEP-NCAR grid points time series. Regarding the mean maximum air temperature, the first main factor, which explains a high percentage of the total variance, presents a statistically significant (CL = 95%) negative trend only during the winter. The first main factor of the mean minimum air temperature manifests a statistically significant (CL = 95%) positive trend during the summer and the year, and a statistically significant (CL = 95%) negative trend in autumn and winter. These findings were compared to the respective ones of the NCEP-NCAR reanalysis data and significant differences in the spatial distribution and temporal variability of the extracted new factors were found. These differences between the two examined data sets could be attributed to topographical factors such orography and land-sea distribution, which could not be represented properly by the reanalysis model. © 2011 Taylor & Francis.

The objective of this study is to examine the synergistic environmental impacts (thermal bioclimatic conditions and air quality due to particulate pollution) with cardiovascular and respiratory syndromes, in Heraklion in the northern part of Crete Island, during a Saharan dust episode on March 22-23, 2008. Daily counts of admissions for cardiovascular and respiratory syndromes were obtained from the two main hospitals in Heraklion. The corresponding daily meteorological parameters, such as maximum and minimum air temperature, relative humidity, wind speed and cloud cover, from the meteorological station of Heraklion (Hellenic National Meteorological Service), were processed in order to estimate and analyze the bioclimatic conditions expressed by the Physiologically Equivalent Temperature (PET), which is based on the energy balance models of the human body. Dust concentrations were derived from the SKIRON forecast model of the University of Athens, while Moderate Resolution Imaging Spectroradiometer (MODIS) products such as aerosol optical depth at 550 nm (AOD550), aerosol small mode fraction (SM), Ångström exponent in the 550-865 nm band and mass concentration, were used for the episode. Besides, daily composite anomalies (reference period: 1968-1996) of the air temperature and vector wind from the middle to the lower atmospheric levels (500 hPa - mean sea level) on March 23, 2008, were calculated from the reanalysis datasets of the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR). The analysis of MODIS and SKIRON products showed that high AOD 550 values (>0.9) and high dust concentration (>250 μg/m 3), respectively, appear on March 23, 2008, while the respiratory admissions were five-fold than the mean daily admissions on the same day of the emergence of the Saharan dust episode (key day). According to the analysis, this is due to the existence of coarse-mode particles along the dust pathway, which trigger respiratory syndromes more than cardiovascular, which are associated more with ultra-fine particles. The admissions concerning the cardiovascular syndromes did not appear any significant change. The analysis of the bioclimatic conditions on the key day revealed that moderate thermal stress existed and this may be attributed mainly to the geomorphology of the island, which is responsible for special weather conditions such as Fohn winds. The drier atmospheric conditions, as a result of strong, desiccating winds on the leeward side of the mountains, contribute more to the already high hospital admissions for respiratory symptoms. © Gebrüder Borntraeger, Stuttgart 2011.

The goal of this study is the analysis of heat waves and their impact on humans, using human biometeorological indices, which are based on the energy balance of the human body. The implications for humans are not only described through the intensity of the heat waves, but also through their duration over consecutive days. Both intensity and duration were analyzed for the Greater Athens Area during the period 1955 to 2001. The analysis was carried out using the daily physiologically equivalent temperature and the daily minimum air temperature. Based on these two parameters, the results showed an increase in the average duration of heat waves. Furthermore, the use of the Gaussian filter revealed the intra-annual variation of heat stress conditions and their relevance to humans. The results could be used for the management of the negative consequences of heat waves in cities suffering from environmental pollution and also for climate impact studies. © 2010 Springer-Verlag.

Biomass burning and associated emissions of aerosols into the atmosphere play a vital role in atmospheric composition and climate change. During summer of 2007, Greece faced the worst natural disaster recorded in recent decades in terms of human losses, number of fire outbreaks and extent of the estimated burned area (more than 12% of the total forested areas in Greece). The present study aims at analyzing the impact of these fire events in western Peloponnese on atmospheric aerosol concentrations using satellite data. MODIS-derived Aerosol Optical Depth (AOD), effective radius, Ångström exponent, mass concentration, cloud-condensation nuclei (CCN) and OMI Aerosol Index (AI), single scattering albedo, absorption and extinction optical depths were analyzed. MODIS data showed smoke plumes traversing thousands of kilometers southwards influencing the central Mediterranean as well as the north African coastal regions. These thick smoke plumes dramatically affected AOD and aerosol-mass concentrations over the region and altered the microphysical aerosol properties, such as the effective radius and absorption coefficient. Model calculations suggested that the shortwave radiation at the ground was reduced by ∼50 Wm2, while that at the top of the atmosphere was reduced by ∼20 Wm2 resulting in atmospheric heating of ∼30 Wm2 over the areas affected by the smoke plumes. © 2010 Elsevier Ltd.