Acarbose PRA Background Suburban br Equation ILCRi is
Equation (4) ILCRi is the part of the ILCR associated with synoptic 3. Results and discussion
n Ni n Ni
ECi × BR × PF n 3.1. Benzene levels and synoptic regimes
i Increased benzene concentrations were observed primarily at the
(4) traﬃcked sites ATH and PAN, where the annual EU limit for benzene
risk and a ILCR > 10−4 as a high potential health risk (Cuadras et al., ment of benzene related air quality at the area of ATH station within the
Guidelines for Europe, ILCR values > 10−5 and < 10−4 were regarded during the same period showed a rising tendency. At all the other se-
as not recommendable (WHO, 2000; Cuadras et al., 2016; Dimitriou lected stations benzene levels were clearly within the limits posed by
Fig. 2 includes the mean synoptic charts which correspond to the 9
atmospheric circulation regimes defined by the applied cluster analysis.
Fig. 1. Map presenting the location of the 11 cities where the selected sampling sites are situated.
Annual concentrations of benzene (μg/m3) measured at the 11 sites for the years 2008–2012. Benzene concentrations exceeding the EU annual limit (5 μg/m3) are highlighted with red color.
with elevated benzene concentrations in specific regions of the Eur-opean continent. More specifically in cluster 1 the Azores anticyclone was elongated to the NE and was associated with slightly increased benzene concentrations primarily at the two French stations: CLF and STR, possibly due to atmospheric stagnation (Table 3). In cluster 2, the strong zonal flow aﬀecting Northern Europe was related to low benzene concentrations in PRA and HAM, however Southern Europe and the Mediterranean were under an extended high pressure field strongly related with an increment of benzene levels in MAD, ATH, ROM and PAN due to low air exchange conditions. The main characteristic of cluster 4 is a Acarbose high pressure system (pressure center at 1036 hPa) centered over North West Russia (NWR), causing the accu-mulation of benzene emissions at PRA, HAM, CLF, STR, WAR and GOT
sampling sites. A similar synoptic pattern with cluster 4 was also re-vealed for cluster 5 however the anticyclone over NWR was weaker (pressure center at 1026 hPa) and less extended than in cluster 5 and thus the stagnation eﬀect was only evident at PRA, HAM, CLF and STR. In cluster 7, a well-organized deep Icelandic low (pressure center at 978 hPa) is combined with the prevalence of a weak pressure gradient field above Southern and Eastern Europe. Thus, atmospheric im-mobility and light winds triggered the recirculation of polluted air principally at the areas of ATH, ROM, WAR and PAN, while PRA and STR which are located in central Europe were also aﬀected.
Minimum mean benzene concentrations at PRA, MAD, CLF, STR, ROM, WAR and PAN were indicated in cluster 6, while decreased average concentrations were also calculated in cluster 6 at HAM and
Fig. 2. Mean synoptic charts corresponding to atmospheric circulation clusters.
Average benzene concentrations and standard deviations corresponding to synoptic clusters. The percentage (%) in parentheses is the proportion of days classified in each atmospheric circulation regime. Increased average benzene concentrations at each city are highlighted with red color.
Allocation of each synoptic cluster's days within cold and warm periods.
COLD WARM SUM COLD (%) WARM (%)
ATH. This finding was not related with the synoptic pattern corre-sponding to cluster 6 and was associated with the distribution of the studied days within the years 2008–2012. From the total selected days, 61.7% of them belonged to the cold periods (16 October – 15 April) and
38.3% to the warm (16 April – 15 October) periods of the studied years, thus in most clusters the great majority of days were comprised in the cold periods (Table 4). However, 90.4% of the days gathered in cluster 6 belonged in the warm periods of the years 2008–2012 and thus lower benzene levels were attributed to reduced emissions from vehicular combustion and domestic heating systems (Masiol et al., 2014; Waked et al., 2016; Marc et al., 2016). Besides the enhanced use of private cars and heating systems during cold periods due to lower ambient tem-peratures, higher vehicle emissions in cold conditions are also expected due to the prolongation of the necessary time for the achievement of the optimal liquid fuel combustion temperature, which may result to in-complete fuel combustion and amplify benzene emissions (Marc et al., 2016). Nevertheless, no decreasing trends were detected at benzene levels primarily at GOT and secondarily at LON during the prevalence of cluster 6 (Table 3). GOT is situated at a busy traﬃc route (E6/E20) surrounded by low residential buildings (Grundstrom et al., 2015) while LON is located in a street canyon approximately 1 m away from the 6 lane A501 road which is frequently congested. Thus dinoflagellates two sampling sites did not report a drop of benzene concentrations in cluster