Examination of the atmospheric conditions associated with high and low summer ozone levels in the lower troposphere over the eastern Mediterranean

P D Kalabokas,D Boulanger,J.-P Cammas,V Thouret,A Volz-Thomas,C C Repapis

doi:10.5194/acp-13-10339-2013

Abstract

Abstract. In order to evaluate the observed high rural ozone levels in the eastern Mediterranean area during summertime, vertical profiles of ozone measured in the period 1994–2008 in the framework of the MOZAIC project (Measurement of Ozone and Water Vapor by Airbus in Service Aircraft) over the eastern Mediterranean basin (Cairo, Tel Aviv, Heraklion, Rhodes, Antalya) were analyzed, focusing in the lower troposphere (1.5–5 km). At first, vertical profiles collected during extreme days with very high or very low tropospheric ozone mixing ratios have been examined together with the corresponding back-trajectories. Also, the average profiles of ozone, relative humidity, carbon monoxide, temperature gradient and wind speed corresponding to the 7% highest and the 7% lowest ozone mixing ratios for the 1500–5000 m height layer for Cairo and Tel Aviv have been examined and the corresponding composite maps of geopotential heights at 850 hPa have been plotted. Based on the above analysis, it turns out that the lower-tropospheric ozone variability over the eastern Mediterranean area is controlled mainly by the synoptic meteorological conditions, combined with local topographical and meteorological features. In particular, the highest ozone concentrations in the lower troposphere and subsequently in the boundary layer are associated with large-scale subsidence of ozone-rich air masses from the upper troposphere under anticyclonic conditions while the lowest ozone concentrations are associated with low pressure conditions inducing uplifting of boundary-layer air, poor in ozone and rich in relative humidity, to the lower troposphere.

Highlights

Tropospheric ozone plays an important role in atmospheric climate, being an important greenhouse gas, and in the physico-chemical processes of the troposphere, as it is a major source of tropospheric free radicals responsible for the oxidation of many atmospheric substances (Finlayson-Pitts and Pitts, 1997)
Relative humidity (RH) levels (Fig. 1b) inside the boundary layer are higher than the corresponding lower troposphere levels over all airports
From the analysis of the summer vertical profiles of ozone measured in the period 1994–2008 in the framework of the MOZAIC project over five eastern Mediterranean airports, the following concluding remarks could be made: a

Summary

Introduction

Tropospheric ozone plays an important role in atmospheric climate, being an important greenhouse gas, and in the physico-chemical processes of the troposphere, as it is a major source of tropospheric free radicals responsible for the oxidation of many atmospheric substances (Finlayson-Pitts and Pitts, 1997). Varotsos et al, 1993; Kalabokas et al, 2000; Kourtidis et al, 2002; Kouvarakis et al, 2002; Zerefos et al, 2002; Lelieveld et al, 2002; Roelofs et al, 2003; Kalabokas and Repapis, 2004). Such high summer levels are a general characteristic of the ozone vertical profiles in the region. Among all the recorded profiles in mid-latitudes, the MOZAIC (Marenco et al, 1998) database has revealed that this region is noteworthy by presenting such differences (i.e. up to 20 ppb) between spring and summer seasonal profiles throughout the free troposphere (Zbinden et al, 2013).

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Conclusion