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[1] To study the spatial and temporal variability of tropospheric ozone in the marine boundary layer over the Aegean Sea (eastern Mediterranean), an O 3 analyzer has been installed onboard of a passenger vessel traveling on a regular basis in the Aegean Sea (from Heraklion/Crete 35°30 0 N, 25°13 0 E to Thessaloniki 40°64 0 N, 22°97 0 E) during a period of 14 months (August 1999 to November 2000. In addition, O 3 data have been obtained on a daily basis at the regional background station of Finokalia (Crete; 35°30 0 N, 25°70 0 E) since September 1997, short-term measurements of O 3 were performed over Crete during the PAUR II campaign (May 1999), and the first O 3 data from a rural area (40°32 0 N, 23°50 0 E) close to Thessaloniki at the north of Greece have been collected from March 2000 to January 2001. This survey extensive points out the existence of a welldefined seasonal cycle in boundary layer O 3 with maximum in summer both above the Aegean Sea and at Finokalia. However, the seasonal signal (defined as the summer/winter ratio) is not constant and varies as a function of air mass origin from 1.33 to 1.15 for the N-NE and SW-S sectors, respectively, in line with the geographical location of the O 3 precursor sources. Our data show the absence of any significant longitudinal gradient over Crete at least during spring and autumn and the absence of significant latitudinal gradient between the north and south Aegean Sea during all seasons for air masses having similar origin. The above results indicate that long-range transport is the main factor accounting for the elevated O 3 levels above the eastern Mediterranean Sea. Thus (1) O 3 data from Finokalia, where the longest time series are available for the area, have regional significance and (2) over the entire Aegean basin, ozone values are above the 32 ppbv European Union (EU) phytotoxicity limit throughout the year and above the 53 ppbv EU health protection limit most of the time during the dry season of the year. The very significant correlation between black carbon (BC) and O 3 observed during an intensive campaign in May 2000 provides an indication that the high O 3 concentrations at Finokalia resulted from ageing of air masses strongly affected by combustion processes.

Abstract.A detailed study of the levels, the temporal and diurnal variability of the main compounds involved in the biogenic sulfur cycle was carried out in Crete (Eastern Mediterranean) Dimethylsulfide (DMS) levels ranged from 2.9 to 136 pmol·mol −1 (mean value of 21.7 pmol·mol −1 ) and showed a clear diurnal variation with daytime maximum. During nighttime DMS levels fall close or below the detection limit of 2 pmol·mol −1 . Concurrent measurements of OH and NO 3 radicals during the campaign indicate that NO 3 levels can explain most of the observed diurnal variation of DMS. Dimethylsulfoxide (DMSO) ranged between 0.02 and 10.1 pmol·mol −1 (mean value of 1.7 pmol·mol −1 ) and presents a diurnal variation similar to that of DMS. SO 2 levels ranged from 220 to 2970 pmol·mol −1 (mean value of 1030 pmol·mol −1 ), while nss-SO 2− 4 and MS − ranged from 330 to 7100 pmol·mol −1 , (mean value of 1440 pmol·mol −1 ) and 1.1 to 37.5 pmol·mol −1 (mean value of 11.5 pmol·mol −1 ) respectively.Of particular interest are the measurements of gaseous MSA and H 2 SO 4 . MSA ranged from below the detection limit (3×10 4 ) to 3.7×10 7 molecules cm −3 , whereas H 2 SO 4 ranged between 1×10 5 and 9.0×10 7 molecules cm −3 . TheCorrespondence to: N. Mihalopoulos (Mihalo@chemistry.uoc.gr) measured H 2 SO 4 maxima are among the highest reported in literature and can be attributed to high insolation, absence of precipitation and increased SO 2 levels in the area. From the concurrent SO 2 , OH, and H 2 SO 4 measurements a sticking coefficient of 0.52±0.28 was calculated for H 2 SO 4 . From the concurrent MSA, OH, and DMS measurements the yield of gaseous MSA from the OH-initiated oxidation of DMS was calculated to range between 0.1-0.4%. This low MSA yield implies that gaseous MSA levels can not account for the observed MS − levels. Heterogeneous reactions of DMSO on aerosols should be considered to explain the observed levels of MS − .

Abstract. Over the last two decades, new particle formation (NPF), i.e., the formation of new particle clusters from gas-phase compounds followed by their growth to the 10-50 nm size range, has been extensively observed in the atmosphere at a given location, but their spatial extent has rarely been assessed. In this work, we use aerosol size distribution measurements performed simultaneously at Ersa (Corsica) and Finokalia (Crete) over a 1-year period to analyze the occurrence of NPF events in the Mediterranean area. The geographical location of these two sites, as well as the extended sampling period, allows us to assess the spatial and temporal variability in atmospheric nucleation at a regional scale. Finokalia and Ersa show similar seasonalities in the monthly average nucleation frequencies, growth rates, and nucleation rates, although the two stations are located more than 1000 km away from each other. Within this extended period, aerosol size distribution measurements were performed during an intensive campaign (3 July to 12 August 2013) from a ground-based station on the island of Mallorca, as well as onboard the ATR-42 research aircraft. This unique combination of stationary and mobile measurements provides us with detailed insights into the horizontal and vertical development of the NPF process on a daily scale. During the intensive campaign, nucleation events occurred simultaneously both at Ersa and Mallorca over delimited time slots of several days, but different features were observed at Finokalia. The results show that the spatial extent of the NPF events over the Mediterranean Sea might be as large as several hundreds of kilometers, mainly determined by synoptic conditions. Airborne measurements gave additional information regarding the origin of the clusters detected above the sea. The selected cases depicted contrasting situations, with clusters formed in the marine boundary layer or initially nucleated above the continent or in the free troposphere (FT) and further transported above the sea.

Measurements of atmospheric ions in the size range 0.8–42 nm were conducted at the environmental research station of the University of Crete at Finokalia from April 2008 to April 2009 in the frame of the EUCAARI project. Both positive and negative atmospheric ions were found to have a clear annual cycle, with minimum concentrations in summer. Their concentrations were found to strongly vary on the prevailing meteorology and the presence of pollutants in the atmosphere. There were 53 new particle formation events recorded. It was found that under certain meteorological conditions and atmospheric composition, enhanced ion concentrations can be observed during the night. Overall, 39 night-time events were observed, all of them observed for the negatively charged particles while only 21 were observed for the positively charged particles. Night-time enhanced ion concentrations were more frequent during spring and autumn and no such events were recorded from July to September. It was found that the presence of pollutants in the atmosphere leads to a decrease of atmospheric ions, especially at cluster sizes (1.25–1.66 nm). Additionally, the meteorological conditions affect the abundance of atmospheric ions greatly, a strong anti-correlation was found between air ions concentrations on the one hand and temperature and wind velocity on the other. Enhanced ion concentrations at night were found to be more frequent when air masses had traveled over the island of Crete