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Number size distributions of atmospheric aerosol particles were simultaneously measured at a kerbside and an urban background site in the city of Thessaloniki, Greece, from June to October 2009. New particle formation events were observed ca. 27% of the days at the urban kerbside site and 29% of the days at the urban background site. In almost all the cases the events started between 10:00 and 12:00, and continued for several hours. The total number concentration (TNC) of the particles having diameters from 10 to ca. 500 nm during the events increased from 1.4 × 10 4 to 6.5 × 10 4 #/cm 3 at the urban kerbside site, and from 0.2 × 10 4 to 2.4 × 10 4 #/cm 3 at the urban background site. At the urban kerbside site, 9% of the days exhibited class I events (i.e., events followed by a clear growth of the newly formed particles), 10% class II (i.e., events during which the concentration of nucleation mode particles were high but their growth was not continuous), 67% were characterised as non-event days, and 14% of the days exhibited no clear particle formation pattern (undefined). At the urban background site, 15% of the days were classified as class I, 5% as class II, 75% of the days showed no nucleation, whereas only 5% of the days were undefined. While the fraction of event days (both class I and class II) at both sites was similar (ca. 20%), the higher fraction of class I events observed at Eptapyrgio can be attributed to the cleaner environment of the urban background site that allows better identification of the particle concentration increase. The nucleation bursts show a similar pattern at both sites, with the newly formed particles reaching a final size of ca. 80–100 nm. A distinct difference between the two stations was that the smallest particles observed during the new-particle formation events had a diameter of ca. 10 nm (i.e., the smallest particles we could observe) at the kerbside site and ca. 20 nm at the urban background site. This is an indication that the new particles observed at the urban background station are formed elsewhere and are transported to the site. Estimated concentrations of H 2 SO 4 using a proxy model, suggest that these are high enough to explain the nucleation events despite that the available aerosol surface was high, especially at the urban kerbside site.

Organic carbon (OC) and elemental carbon (EC) concentrations, associated to PM10 and PM2.5 particle fractions, were concurrently determined during the warm and the cold months of the year (July-September 2011 and February-April 2012, respectively) at two urban sites in the city of Thessaloniki, northern Greece, an urban-traffic site (UT) and an urban-background site (UB). Concentrations at the UT site (11.3 ± 5.0 and 8.44 ± 4.08 14 μg m(-3) for OC10 and OC2.5 vs. 6.56 ± 2.14 and 5.29 ± 1.54 μg m(-3) for EC10 and EC2.5) were among the highest values reported for urban sites in European cities. Significantly lower concentrations were found at the UB site for both carbonaceous species, particularly for EC (6.62 ± 4.59 and 5.72 ± 4.36 μg m(-3) for OC10 and OC2.5 vs. 0.93 ± 0.61 and 0.69 ± 0.39 μg m(-3) for EC10 and EC2.5). Despite that, a negative UT-UB increment was frequently evidenced for OC2.5 and PM2.5 in the cold months possibly indicative of emissions from residential wood burning at the urban-background site. At both sites, cconcentrations of OC fractions were significantly higher in the cold months; on the contrary, EC fractions at the UT site were prominent in the warm season suggesting some influence from maritime emissions in the nearby harbor area. Secondary organic carbon, being estimated using the EC tracer method and seasonally minimum OC/EC ratios, was found to be an appreciable component of particle mass particularly in the cold season. The calculated secondary contributions to OC ranged between 35 and 59 % in the PM10 fraction, with relatively higher values in the PM2.5 fraction (39-61 %). The source origin of carbonaceous species was investigated by means of air parcel back trajectories, satellite fire maps, and concentration roses. A local origin was mainly concluded for OC and EC with limited possibility for long range transport of biomass (agricultural waste) burning aerosol.

Health can be impacted in many ways by exposure to chemical stressors in urban areas. Epidemiological research community has established consistent associations between traffic related air pollution and various health outcomes. Nevertheless, many urban environments, due to practical reasons (bulk of equipment) and mainly due to economical constraints, are characterised by the absence of the necessary monitoring infrastructure, for pollutants such as toluene. This chemical stressor is associated with numerous risks to human health, mainly with acute and chronic effects on the central nervous system. Due to the lack of monitoring data, it may be convenient to identify and establish a set of possible empirical relationships between health stressors in order to assess air quality trends of traffic related pollution in an urban area and support decision making. The use of environmental statistics can be meaningful towards this direction. This paper aims at developing and presenting a tractable approach, in order to reliably forecast toluene levels in EU urban environments. Multiple stepwise regression analysis is used for this purpose and a strong statistical relationship is detected mainly between toluene, benzene and CO. The adopted regression models are validated in order to depict their applicability and representativeness. In addition the models are applied to Thessaloniki, Greece, which is considered one of the most polluted cities within Europe. A comparison between available measurements, predictions based on the developed statistical models and air quality modelling output, provides discussion for transferability issues of such statistical relations between cities, but also interesting insights for the specific city. In general the presented results demonstrate that the adopted approach is capable of capturing toluene concentration trends and should be considered as complementary to air quality monitoring.

During the last years several attempts were made to introduce various air quality indices, defined for a specific air pollutant or a mixture of pollutants, based on standards and guidelines proposed by international organizations. In this work, air quality data (CO, SO 2 , O 3 , PM 10 and NO 2 ) corresponding to the six-year period between 2004 and 2009 and collected at three monitoring stations in Thessaloniki, the second largest Greek city, were used in order to compute three different air quality indices. The first index was based on individual pollutants and was employed to characterise the air quality status for each one of the air pollutants separately, whereas the second index was based on a combination of pollutants in both the short and the long terms. The results showed that when individual pollutants were used, the air quality in the city-centre could be characterised as “bad” for 47% of the days for PM 10 , “bad” for 89% of the days for NO 2 and “bad to severe” for 13% of the days for O 3 . Similarly, the indices based on a mixture of pollutants showed that in the city centre 43% of the days are “problematic to very poor” in terms of the air quality, whereas in the suburbs 54% of the days are found in the range of “good to very good”. Furthermore, the use of biometeorological air quality indices that take into account the adverse health effects of air pollution on public health showed that the overall air quality is poor in the city centre for 58% of the days studied, while at the peripheral sites and during Sundays the air quality seems to be improved significantly, with relevant percentages equal to 18% and 13% respectively. Moreover, weekly and neighbourhood patterns were detected by all groups of indices. On the whole, all of the methodologies used revealed that the air quality in Thessaloniki is poor and that PM 10 is the main contributor to this.

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

Air pollution episodes in urban coastal areas follow certain pre-determined patterns, being associated with certain local meteorological conditions and emission of primary pollutants. In this study, the synoptic and local scale atmospheric circulation that prevails during air pollution episodes in a coastal major city in Greece, Thessaloniki, is examined for a period of 15 years (1989–2004). The study signifies the importance of studying air pollution meteorological patterns between coastal areas with different terrain characteristics. For Thessaloniki, it was found that the episodes occur mainly during the cold period of the year, while four types of synoptic scale circulation were recognized (I, II, III, IV) and five patterns of the local scale circulation (A1, A2, B1, B2 and B3). The highest percentage of episodes is associated with the presence of an anticyclone over the northern Greece (types I and IV), being characterized by weak or very weak surface pressure gradient intensity, according to the position and extension of the anticyclone. Moreover, a temperature increase of at least 1°C during the previous 3 days is required in the lower troposphere. Consistent with the synoptic conditions, the development of the sea breeze plays a crucial role in the occurrence of the episodes, even in the cold period of the year, when the sea breeze can still develop with smaller frequency and intensity. Finally, it was found that a small number of episodes is related with the advection of polluted air masses from the industrial area in the northwest of the city and from the Eordaia area in the west, which is the largest lignite producing area of Balkans.

The identification of local and remote particulate pollution sources, as well as the understanding of the factors determining the spatial and temporal variability of the particulate matter in urban areas is an issue of increasing public concern, since the above actions are absolutely essential for the design of effective particulate pollution control strategies. In the present study, the sources and the factors affecting the particulate pollution were studied in Thessaloniki, the second largest Greek city, in order to develop the necessary scientific framework for the subsequent development of integrated mitigation and control strategies and the design and implementation of effective environmental policies. Hourly PM(2.5) and PM(c) concentrations from two monitoring sites (the Egnatia-Dimarchio and the Eptapyrgio stations) were therefore correlated to gaseous pollutant concentrations (CO, NO, NO(2), NO(x), SO(2) and O(3)) and meteorological parameters (temperature, wind speed and relative humidity) during the 2-year period between June 2006 and May 2008. The analysis revealed that both sites experienced poor air quality, while a large number of exceedances of the daily and annual EC objectives were observed, especially during the cold season. Positive correlation between particles and NO(x) in OHM, provided evidence about higher combustion-related emissions during the cold season, whereas increased contribution of secondary particles was suggested during the warm season. In addition, Principal Component Analysis was used to identify the main particulate pollution sources, while the quantification of the combustion and the non-combustion-related fraction of particles was performed through Regression Analysis. Specifically, the non-combustion-related fraction ranged between 25.1 and 72.7%, depending on the site and the season. Finally, concentration roses were constructed in order to gain insight into the distribution of local emission sources around the monitoring sites. (C) 2011 Elsevier Ltd. All rights reserved. Atmospheric Environment

The measurement of expired carbon monoxide (CO) is a direct and non-invasive method for the detection of exposure to CO.Our aim was to investigate the impact ofatmospheric pollution and smoking on expired CO in kiosk workers in Thessaloniki, Greece.Twenty kiosks were selected in the commercial centre of city. The workers were all men aged 30.5 +/- 5.5 years. Measurements of expired CO and environmental CO were carried out twice per day, during two different seasons of the year, summer and winter. Expired CO was measured via a MicroCOMeter equipped with a fuel cell type electrochemical sensor. The CO levels in ambient air were determined using the method of Non-Dispersive Infra-Red analysis.Ambient CO levels were 2.11 +/- 0.64 ppm at h. 17:00 and 3.64 +/- 1.45 at h. 21:00 in winter and 1.26 +/- 0.17 ppm at h. 17:00 and 1.73 +/- 0.22 at h. 21:00 in summer. Expired CO in non-smokers was 3.2 +/- 2.7 ppm at h. 17:00 and 4.2 +/- 3.2 at h. 21:00 in winter and 1.3 +/- 1 ppm at h. 17:00 and 2.2 +/- 1.4 at h. 21:00 in summer. In smokers it was +/- 5.2 ppm at h. 17:00 and 13.9 +/- 7.5 at h. 21:00 in winter and 10 +/- 4.8 ppm at h. 17:00 and 18 +/- 7 at h. 21:00 in summer. All these differences were statistically significant. The concentrations of expired CO were significantly correlated with the number of the cigarettes smoked.The levels of expired CO in kiosk workers increase mainly due to smoking and to a lesser degree due to environmental pollution.

Spectral measurements of the aerosol optical depth (AOD) and the Ångström coefficient were conducted at Thessaloniki, Greece (40.5° N, 22.9° E) between January 1997 and December 2005 with a Brewer MKIII double-monochromator spectroradiometer. The dataset was compared with collocated measurements of a second spectroradiometer (Brewer MKII) and a CIMEL sun-photometer, showing correlations of 0.93 and 0.98, respectively. A seasonal variation of the AOD was observed at Thessaloniki, with AOD values at 340 nm of 0.52 and 0.28 for August and December respectively. Back trajectories of air masses for up to 4 days were used to assess the influence of long-range transport from various regions to the aerosol load over Thessaloniki. It is shown that part of the observed seasonality can be attributed to air masses with high AOD originating from North-Eastern and Eastern directions during summertime. The analysis of the long-term record (9 years) of AOD showed a downward tendency. A similar decreasing tendency was found in the record of the PM$_{10}$ aerosol measurements, which are conducted near the surface at 4 air-quality monitoring stations in the area of the city of Thessaloniki.

[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.