On the seasonal variation of the surface ozone in Athens,Greece

An attempt has been made to examine the seasonal variation of the surface ozone mixing ratio in Athens, Greece during the periods 1901–1940 and 1987–1998. The first finding is that in July and August while the daytime surface ozone mixing ratio from the beginning until the end of the 20th century has increased by approximately 1.8 times, the nighttime surface ozone mixing ratio remained approximately at the same level. The second finding is that the increase in the mean daytime mixing ratio during the transition period from winter to summer is equal to the increase in the maximum daytime mixing ratios, whilst the enhancement of the nighttime surface ozone maxima is stronger than that of the nighttime mean surface ozone mixing ratio. Plausible explanation for this finding is given through mechanisms like long-range transport and photochemical processes occurring in the boundary layer, free troposphere and lower stratosphere.     

Long-term variation in surface ozone and its precursors in Athens,Greece

INTENTION, GOAL, SCOPE, BACKGROUND: Photochemical pollution is a very complex process involving meteorological, topographic, emission and chemical parameters. The most important chemical mechanisms involved in the atmospheric process have already been identified and studied. However, many unknown parameters still exist because of the large number of participating chemical reactions. OBJECTIVE: The present study investigates the processes involved in the photochemical pollution effect of an urban station located in the greater area of the Athens basin and gives a plausible explanation for the different seasonal ozone development between that station and another rural one. Furthermore, the distribution of the mean monthly surface ozone observed at the urban station during 1987-2001 is examined in order to create a relevant forecasting tool. METHODS: Averaged hourly data of O3 and NOx observations monitored at the above mentioned stations, during 1987-2001, have been used in order to derive the daytime (7:00-15:00) values. Trajectories calculated by using a 2D-trajectory code and meteorological data, during the period 1988-1996, have also been used. RESULTS AND DISCUSSION: At the urban station, the percentage negative trend of NO and NOx data in winter and summer is higher than that in spring and autumn, while the percentage ozone trend is maximum in the summer. On the contrary, the negative surface ozone trend at the rural station exhibits a minimum in summer and a maximum in autumn and winter. The mean seasonal wind-rose for the selected months shows that the northward wind flow dominates during June, the month of the lowest negative ozone trend in the rural station. Finally, the development of the forecasting tool shows that the mean monthly surface ozone data during the period (1987-2001) demonstrates a semi-log distribution. CONCLUSIONS: Air transport effect on the air pollution of the rural station (not blocked by mountains) is deduced as a possible reason for the different seasonal ozone development observed between the rural and the urban station. Finally, the discrepancies between the theoretical probabilities deduced by the model and the empirical ones appear to be very small, and the corresponding correlation coefficient is 0.99. RECOMMENDATION AND OUTLOOK: However, to interpret the aforementioned statistical results about the negative trends in ozone and its precursors, additional parameters can be taken into account. Changes in NOx concentrations, for instance, can result not only from changes in emissions or meteorological conditions. There might also be a contribution through changes in the atmospheric composition. A study of the contribution of changes in atmospheric composition to trends of observed NOx concentrations requires that a series of steps be taken (removal of meteorological influence in the time series, calculation of trends in OH concentrations, etc.).     

Photochemical formation and transport of ozone in Athens,Greece

An evaluation of the diurnal variation of the hourly ozone concentrations measured at five sites in Greater Athens from June until early September 1984 indicates that photosmog episodes in Greater Athens are associated with the sea breeze circulation. Due to local air circulation in the Athens basin, precursors of O₃ are transported to and accumulated in the Saronikos Bay during the morning hours while the land breeze is blowing. At noon, when the sea breeze sets in, the O₃ formed over the sea is brought back to the coast and to central Athens where it increases the local O₃ concentration by a factor of 3–5 within a few hours. The O₃ levels often remain high throughout the night. During the photochemical smog episodes, all of them accompanied by well-developed sea breezes, the U.S. Air Quality Standard of 120 ppb O₃ was exceeded for 4–7 h day⁻¹. Peak O₃ concentrations up to nearly 200 ppb were recorded in the smog episodes.Relatively high O₃ concentrations were measured on the island of Aegina. They tend to remain high during the night and can be attributed only to primary pollutant transport from Greater Athens advected by the land breeze. The O₃ values obtained at Mount Immitos (1000 m above MSL) suggest that, first, the sea breeze inhibits the influence of vertical thermal convection up to heights above 600 m, and second, no O₃ is noticeable from above the tropopause to ground level or from long-range transport.     

Sea-breeze circulation and photochemical pollution in Athens,Greece

The purpose of this paper is to analyse the effect of the sea-breeze on photochemical pollution in Athens, Greece. To this end, the SO₂, NO, NO₂, O₃ and CO concentrations, the vertical structure of the atmospheric boundary layer, the pollution emission rates and wind data are examined simultaneously for two typical days in August 1981 with well-defined sea-breeze circulation. The tendency of the complicated seabreeze flow field to stratify the atmosphere and thus generate layers with different constituents affects the concentrations measured near the ground and causes relatively high oxidant levels at night. As inversion layers descend or disappear, abrupt changes and short-period oscillations in concentrations are found, and can be explained by a simple multilayer box model. The diurnal variation and considerations based on simple ground-level wind trajectories indicate that recirculation of pollutants by the sea-breeze cell takes place, possibly aided by the small size of the basin and the closed topography. The passage of the sea-breeze front seems to have no direct effect. No day-to-day pollution accumulation is noticed. Thus, it becomes clear that if modeling of photochemical pollution in such coastal regions with pronounced relief is to be successful, it needs to pay close attention to both the flow field details and the vertical structure of the atmosphere, especially the ground-based inversion break-up and boundary layer collapse.     

Meteorological factors of ozone predictability at Houston, Texas

Several ozone modeling approaches were investigated to determine if uncertainties in the meteorological data would be sufficiently large to limit the application of physically realistic ozone (O3) forecast models. Three diagnostic schemes were evaluated for the period of May through September 1997 for Houston, TX. Correlations between measured daily maximum and model calculated O3 air concentrations were found to be 0.70 using a linear regression model, 0.65 using a non-advective box model, and 0.49 using a three-dimensional (3-D) transport and dispersion model. Although the regression model had the highest correlation, it showed substantial underestimates of the highest concentrations. The box model results were the most similar to the regression model and did not show as much underestimation. The more complex 3-D modeling approach yielded the worst results, likely resulting from O3 maxima that were driven by local factors rather than by the transport of pollutants from outside of the Houston domain. The highest O3 concentrations at Houston were associated with light winds and meandering trajectories. A comparison of the gridded meteorological data used by the 3-D model to the observations showed that the wind direction and speed values at Houston differed most on those days on which the O3 underestimations were the greatest. These periods also tended to correspond with poor precipitation and temperature estimates. It is concluded that better results are not just obtained through additional modeling complexity, but there needs to be a comparable increase in the accuracy of the meteorological data.     

Policies to cope with air pollution in Europe: the Auto-oil Programme in the case of Athens

Air pollution is one of the most crucial current environmental problems, especially in urban areas. To confront air pollution, the European Union has implemented several policies and programmes. Among these, the Auto-oil Programme is a cost-effective framework which involves all relevant actors (car-makers, oil industries, governments, local authorities, etc.) in concerted action. Athens faces a severe air pollution problem. In this respect, Auto-oil seems to offer a promising chance for Athens to improve its atmosphere. The present paper examines the effectiveness of the Auto-oil Programme to relieve air pollution in Athens. Several additional measures are proposed whenever it seems to be necessary.     

On the relation between seasonal synoptic circulation types and spatial air quality characteristics in Athens,Greece

The impact of weather on air pollution was examined and evaluated for the city of Athens, Greece. We used an objectively defined synoptic classification scheme consisting of six summer and eight winter circulation types. This scheme was established using a combination of both factor and cluster analysis during 1954-1999. Surface and isobaric levels of 850 hPa data were used. Factor analysis combined with cluster analysis was used to derive circulation types based on surface meteorological data for the period 1954-1999 in Athens and on surface pressure grid data. The city was divided into three sectors according to the financial and social activities of the residents. To examine the spatial characteristics of pollutant concentrations over Athens for each synoptic type, the synoptic circulation types were then correlated with both gaseous and particulate pollutant concentrations measured in each sector between 1983 and 1999. Finally, extreme and severe episodic events were studied in terms of their meteorological and synoptic characteristics.     

Investigating weekend air quality observations with the aid of Fourier analysis in Athens, Greece

Weekend air quality is analysed with the aid of Fourier analysis, in order to reveal time-series structures for Athens, Greece. For this reason, an appropriate analysis of a 10 year record from 1990–1999 of air quality data from the monitoring network in Athens is carried out for two specific monitoring sites. The aim of the paper is to investigate the temporal pattern of observations in order to reveal relations and trends. Thus, it is expected that the estimation of environmental consequences related to various incentives aimed at the reduction of air emissions will be enriched. The aim of the current work is also to demonstrate that the analysis of weekend air quality monitoring data records is an appropriate method for estimating the temporal variation of air pollution in urban agglomerations, based on appropriate approximations.     

Volatile hydrocarbons in the atmosphere of Athens,Greece

This work presents the results of one-year monitoring study of Volatile Hydrocarbons, VHCs, in the atmosphere of Athens. It is the first systematic attempt to determine the VHC levels in the Athens' atmosphere with the very well known photochemical pollution problems. The purpose of this work was to create a database concerning VHCs in order to evaluate the photochemical pollution in this area (ozone creation, case studies and meteorology). Totally, 308 samples were collected at three different sites used in the state-monitoring programme involving the criteria pollutants. Air samples were collected on Tenax TA tubes and analysed by thermal desorption and dual column GC dual FID. Fifteen selected compounds were studied; 6 alkanes and 9 benzenoid compounds. The measured values of individual alkanes ranged from 0.39 pg m(-3) to 33 pg m(-3), and those of aromatics from 0.20 pg m(-3) to 616 pg m(-3). The sum of all 15 VHC concentrations ranged between 16 and 1697 pg m(-3). The time and spatial variations in the concentration of these compounds were assessed. Volatile hydrocarbons exhibited a clear seasonal and time cycle, showing higher concentrations during winter and early morning hours. Study of the spatial variations of VHC levels showed higher concentrations at the center of the city. The variation of toluene/benzene ratio and the correlation between VHCs, criteria pollutants (CO, NOx and O3) and meteorological parameters were also assessed. It was demonstrated that a trip-line of the VHCs concentration at the city center doubles the ozone concentration at peripheral areas under favourable meteorological conditions.     

Carbonyl compounds in the urban environment of Athens,Greece

The concentration levels of 15 selected carbonyl compounds in 62 samples were determined at two sites in Athens basin from June to December 2000. Formaldehyde was the most abundant species (0.05-39 microg m(-3)), which comprised from 22% to 37% of the total measured compounds, followed by acetaldehyde (4.32-49 microg m(-3)), acetone/acrolein (0.64-198 microg m(-3)) and butanal (0.79-140 microg m(-3)). The mean formaldehyde/acetaldehyde and acetaldehyde/propanal molar ratios were calculated. No significant seasonal differences were observed for all the carbonyls. Photochemical production was found to weigh upon atmospheric levels for 83-93% in summer days, dropping below 33% in the winter. The importance of formaldehyde and acetaldehyde as a source of hydroxyl radicals in Athens was also assessed.     

Photochemical air pollutant levels and ozone phytotoxicity in the region of Mesogia–Attica, Greece

The levels of photochemical air pollutants: O₃, NO and NO₂, were monitored in Athens and in the neighbouring region of the Mesogia plain (Spata, Artemis and Markopoulo) from 1 May–31 August 2000. Phytodetection of ozone was also conducted using bioindicator plants of Bel-W3 and Zichnomirodata (KK6/5) tobacco varieties. The average maximum daily O3 concentration was 60–75 ppb, while the 24 hour average ranged from 40–65 ppb. The AOT40 (ppb hours) index was very high in Athens (16 679 over 121 days), Spata (16 325 over 110 days), Artemis (8093 over 22 days) and Markopoulo (18 646 over 113 days), suggesting potentially phytotoxic ozone levels. The ozone bioindicator plants of Bel-W3 and KK6/5 tobacco varieties were highly injured in all regions confirming the phytotoxicity of those ozone levels. The levels of NO and NO₂ recorded at the three stations, in the Mesogia plain, were considerably lower than those occurring in Athens. The data presented here provide important background information concerning pollution levels in the Mesogia plain shortly before the operation of the new international airport 'Eleftherios Venizelos' in this region (March 2001).     

An analysis of the SO2 concentration levels in Athens,Greece

In this paper, an analysis of the meteorological parameters that affect SO₂ pollution in Athens, a problem of both local and international concern, is presented. The influence of these meteorological parameters on the SO₂ concentrations has been investigated by a statistical analysis of the daily average SO₂ values measured at six locations in the Athens basin for the six years from 1974 to 1979. Wind speed, minimum temperature and amount of rain has been found to control SO₂ concentrations during the cold season while wind speed, wind direction and relative humidity are central in the warm season. Based on this, multiple regression models, both linear and non-linear, for the prediction of the next day's SO₂ concentration have been derived that explain more than 50% of the data variance. Further improvements on the modelling are contingent on the availability of boundary layer structure data and on details of the local wind field. The meteorology of high concentration episodes has also been examined and the synoptic characteristics for the onset and end of such episodes have been identified. Finally, discriminant analysis classification functions, utilizing forecast meteorological variables have been obtained which are capable of predicting accurately the occurrence of high pollution concentrations.     

Secondary effects of air pollution: ozone decreases brown rust disease potential in wheat

Young wheat plants were fumigated with 170 microg m(-3) ozone for 3 days, or with 210 microg m(-3) ozone for 7 days, for 7 hours a day. At the end of the fumigation period the plants were inoculated with brown rust (Puccinia recondita f. sp. tritici) uredospores. The development of new uredospore pustules on fumigated and control plants was evaluated as a measure of rust disease potential. The number of pustules on the ozone fumigated plants was greatly reduced in comparison with the number of plants treated with charcoal-filtered air.     

Surface ozone and NOx concentrations at a high altitude Mediterranean site,Greece

Ozone was measured in six- and NO_x in five sampling periods in 1996–97, mostly during summer, at a 1070 m altitude site in northern Peloponnese. Mean values in each sampling period ranged from 43–48 ppb exceeding the European Union 24 h plant protection standard. The background ozone concentration of 43 ppb derived from the correlation of ozone with NO^′_x also exceeded the EU plant protection standard. Ozone exhibited maxima in the afternoon and minima during the night; in certain 24–48 h periods, however, the ozone concentrations remained practically constant; in these short periods air mass back trajectories indicated air masses which originated in north Africa. NO^′_x concentrations had maximum of 24 h around noon. Their mean concentrations ranged from 0.5–0.7 ppb, smaller than respective concentrations in north-central Europe.     

Economic damages of ozone air pollution to crops using combined air quality and GIS modelling

This study aims at presenting a combined air quality and GIS modelling methodological approach in order to estimate crop damages from photochemical air pollution, depict their spatial resolution and assess the order of magnitude regarding the corresponding economic damages. The analysis is conducted within the Greater Thessaloniki Area, Greece, a Mediterranean territory which is characterised by high levels of photochemical air pollution and considerable agricultural activity. Ozone concentration fields for 2002 and for specific emission reduction scenarios for the year 2010 were estimated with the Ozone Fine Structure model in the area under consideration. Total economic damage to crops turns out to be significant and estimated to be approximately 43 M€ for the reference year. Production of cotton presents the highest economic loss, which is over 16 M€, followed by table tomato (9 M€), rice (4.2 M€), wheat (4 M€) and oilseed rape (2.8 M€) cultivations. Losses are not spread uniformly among farmers and the major losses occur in areas with valuable ozone-sensitive crops. The results are very useful for highlighting the magnitude of the total economic impacts of photochemical air pollution to the area’s agricultural sector and can potentially be used for comparison with studies worldwide. Furthermore, spatial analysis of the economic damage could be of importance for governmental authorities and decision makers since it provides an indicative insight, especially if the economic instruments such as financial incentives or state subsidies to farmers are considered.     

The occurrence of disinfection by-products in the drinking water of Athens,Greece

Application of chlorination for the disinfection of drinking water results in the formation of a wide range of organic compounds, called disinfection by-products (DBPs), which occur due to the reaction of chlorine with natural organic materials. The occurrence of DBPs was studied in samples from four drinking-water treatment plants (WTPs) and from the distribution network of Athens, Greece. Twenty-four compounds, which belong to different categories of DBPs, were monitored, including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), haloketones (HAKs), chloral hydrate (CH) and chloropicrin (CP). Sampling was performed monthly for a period of two years, from three different points at each WTP and from eight points atthe distribution network. Samples were analyzed by GC-ECD methods, which included pretreatment with liquid-liquid extraction for volatile DBPs and acidic methanol esterification for HAAs. The results of the analyses have shown the presence of disinfection by-products belonging to all categories studied in all water samples collected after prechlorination. The major categories of DBPs detected were THMs and HAAs, while the other volatile DBPs occurred at lower concentrations. The concentrations of DBPs did not in any case exceed the maximum contaminant levels (MCL) set by USEPA and WHO. However, monitoring these compounds needs to be continued, because their levels could increase due to changes in the quality of water entering the water treatment plants. Reduction of the concentrations of DBPs could be achieved by optimization of the chlorination conditions, taking into account the effect of time. Moreover, research on alternative disinfection methods (e.g. ozone, chlorine dioxide, chloramines) and their by-products should be conducted to evaluate their applicability in the case of the drinking water of Greece.     

Effect of air pollution on peri-urban agriculture: a case study

Peri-urban agriculture is vital for the urban populations of many developing countries. Increases in both industrialization and urbanization, and associated air pollution threaten urban food production and its quality. Six hour mean concentrations were monitored for SO(2), NO(2) and O(3) and plant responses were measured in terms of physiological characteristics, pigment, biomass and yield. Parameter reductions in mung bean (Vigna radiata), palak (Beta vulgaris), wheat (Triticum aestivum) and mustard (Brassica compestris) grown within the urban fringes of Varanasi, India correlated directly with the gaseous pollutants levels. The magnitude of response involved all three gaseous pollutants at peri-urban sites; O(3) had more influence at a rural site. The study concluded that air pollution in Varanasi could negatively influence crop yield.     

Characterization of atmospheric particulates, particle-bound transition metals and polycyclic aromatic hydrocarbons of urban air in the centre of Athens (Greece)

The concentrations of trace metals and polycyclic aromatic hydrocarbons (PAHs) adsorbed to total suspended particulate (TSP) and finer fractions of airborne particulate matter (PM) were determined from a site in the centre of Athens (Greece), which is characterized by heavy local traffic and is densely populated, during the winter and summer periods in 2003-2004. Also, we collected and analyzed samples of diesel and gasoline exhaust particles from local vehicles (buses, taxis and private cars) and from chimney exhaust of residential central heating appliances. A seasonal effect was observed for the size distribution of aerosol mass, with a shift to larger fine fractions in winter. The most commonly detected trace metals in the TSP and PM fractions were Fe, Pb, Zn, Cu, Cr, V, Ni and Cd and their concentrations were similar to levels observed in heavily polluted urban areas from local traffic and other anthropogenic emissions. Analysis of 16 PAHs bound to PM showed that they are mostly traffic related. In general, the fine particulate PAHs concentrations were higher than coarse particles. The most common PAHs in PM(10.2) and PM(2.1) were pyrene, phenanthrene, acenapthylene and fluoranthene, which are associated with diesel and gasoline exhaust particles. The results of this study underlined the importance of local emission sources, especially vehicular traffic, central heating and other local anthropogenic emissions. Compared with other big cities, Athens has much higher levels of airborne particles, especially of the finer fractions PM(10) and PM(2.5), correlated with traffic-related air pollution.