The geographical distribution of meteorological parameters associated with high and low summer ozone levels in the lower troposphere and the boundary layer over the eastern Mediterranean (Cairo case)

Abstract

In continuation of previous research for evaluation of the high ozone levels observed during summer time over the eastern Mediterranean, MOZAIC profiles collected at the airport of Cairo from 1994 to 2008 are analysed. Average profiles corresponding, respectively, to the highest and the lowest ozone mixing ratios for the 0–1.5 km layer over Cairo in summer (JJA) (94 profiles) are examined along with their corresponding composite maps of geopotential height (and anomalies), vertical velocity (and anomalies), specific humidity anomalies, precipitable water anomalies, air temperature anomalies and wind speed at 850 hPa. In addition, backward trajectories arriving in the boundary layer over Cairo during the days with highest or lowest ozone mixing ratios are examined. During the 7% highest ozone days at the 0–1500 m layer over Cairo, very high ozone concentrations of about 80 ppb on average are observed from the surface up to 4–5 km altitude. The difference in ozone concentrations between the 7% highest and the 7% lowest ozone days reaches maximum values around 60 ppb close to the ground. During the highest ozone days for both 1.5–5 and 0–1.5 km layer, there are extended regions of strong subsidence in the eastern Mediterranean but also in eastern and northern Europe and over these regions the atmosphere is dryer than average. In addition, characteristic profiles with the highest ozone concentrations in the 0–1500 m layer are examined in order to assess the influence of atmospheric transport and photochemistry on the ozone concentrations over the area.

• Ozone
• atmospheric transport
• eastern Mediterranean
• Cairo

Acknowledgments

This work was supported by the Research Committee of the Academy of Athens and the Mariolopoulos-Kanaginis Foundation for the Environmental Sciences. The composite weather maps were provided by the NOAA/ESRL Physical Sciences Division, Boulder Colorado from their Web site at www.cdc.noaa.gov/. MOZAIC was funded by the European Commission. The authors acknowledge for the strong support of the European Commission, Airbus and the Airlines (Lufthansa, Austrian, Air France) who carry the MOZAIC equipment free of charge and have performed the maintenance since 1994. MOZAIC is presently funded by INSU-CNRS (France), Meteo-France and Forschungszentrum Juelich (Germany). The MOZAIC database is supported by ETHER (CNES and INSU-CNRS). Dr. J. Hjorth, JRC-Ispra, and Dr. H. Smit, FZ-Juelich, are also gratefully acknowledged for discussion and comments. The authors also acknowledge the constructive comments of the two anonymous referees.