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Variability of ozone in the Eastern Mediterranean during a 7-year study

Kopanakis Ilias, Glytsos Theodoros, Kouvarakis Georgios N., Gerasopoulos Evangelos, Mihalopoulos, Nikolaos, Lazaridis Michail

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Summary

Ozone measurements have been performed in the period 2003–2009 at Akrotiri (suburban) and Finokalia (coastal) monitoring stations on the island of Crete, Greece. The main objectives were to investigate the concentration levels of ozone in the region of Crete, its spatial and temporal variability, the effect of air mass origin and local sources on ozone levels, and the frequency of exceedances of the EU limits for ozone concentrations in the area. The observed mean values for Akrotiri and Finokalia stations were 44.5 ± 8.5 and 49.1 ± 10.6 ppbv, respectively. Ozone concentrations were higher during the 8-month period between March and October (52.3 ± 6.8 and 53.0 ± 7.4 ppbv for Akrotiri and Finokalia station, respectively) whereas, in the period November–February, the concentrations were lower (37.7 ± 4.7 and 39.1 ± 6.9 ppbv, respectively). The above values indicate that there is not a west-east gradient of ozone concentration in the studied area. At both stations, AOT40 limit values were higher than the limit set by the European Union (Directive 2008/50/EC). Exceedances of the EU target value were encountered during 88 and 67 % of the time in Akrotiri and Finokalia stations, respectively. Differences on the diurnal patterns and daily ozone maxima between the two stations were attributed to the different characteristics of the two stations and to the effect of local pollution sources to Akrotiri station. The average value of the amplitude of the daily cycle (calculated as the difference between maximum and minimum values) in the case of Akrotiri was 8.3 ppbv, and it was about two times the corresponding value in Finokalia (4.7 ppbv), which is an indication of the effect of the anthropogenic emission produced in the city of Chania to the Aktotiri station environment. At Finokalia, the maximum values were observed 2–4 h later than those at Akrotiri. During springtime, the difference in the maximum values appearance was close to 4 h, with the maximum at Akrotiri at 16:00 (LT) and at Finokalia at about 20:00 (LT). This time difference supports the transfer of gaseous precursors and already formed ozone molecules toward Finokalia.

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