Summertime free-tropospheric ozone pool over the eastern Mediterranean/Middle East

Abstract

Abstract.Observations show that the Mediterranean troposphere is characterized by a marked enhancement in summertime ozone, with a maximum over the eastern Mediterranean. This has been linked to enhanced photochemical ozone production and subsidence under cloud-free anticyclonic conditions. The eastern Mediterranean is among the regions with the highest levels of background tropospheric ozone worldwide. A 12 yr climatological analysis (1998-2009) of free-tropospheric ozone was carried out over the region based on the ECMWF (European Centre for Medium-Range Weather Forecasts) ERA-Interim reanalysis data and simulations with the EMAC (ECHAM5-MESSy) atmospheric chemistry-climate model. EMAC is nudged towards the ECMWF analysis data and includes a stratospheric ozone tracer. A characteristic summertime pool with high ozone concentrations is found in the middle troposphere over the eastern Mediterranean-Middle East (EMME) in the ERAInterim ozone data, Tropospheric Emission Spectrometer (TES) satellite ozone data and simulations with EMAC. The enhanced ozone over the EMME during summer is a robust feature, extending down to lower free-tropospheric levels. The investigation of ozone in relation to potential vorticity and water vapour and the stratospheric ozone tracer indicates that the dominant mechanism causing the free-tropospheric ozone pool is the downward transport from the upper troposphere and lower stratosphere, in association with the enhanced subsidence and the limited horizontal divergence observed over the region. The implications of these high freetropospheric ozone levels on the seasonal cycle of nearsurface ozone over the Mediterranean are discussed.

Reanalysis of and attribution to near-surface ozone concentrations in Sweden during 1990–2013

“…Variability in climate, such as the North Atlantic Oscillation (NAO), contributes to the variation in O 3 concentrations in the upper troposphere through variations both in the stratospheric contribution and in the transport patterns (Gaudel et al, 2015). Although the stratospheric contribution to the O 3 concentrations at the surface is generally small (3-5 ppb(v)) in Europe (Lelieveld and Dentener, 2000), it can be a relevant contribution to near-surface O 3 in certain areas and time periods (Zanis et al, 2014) and could affect the observed trend in near-surface O 3 (e.g., Fusco and Logan, 2003). Despite the large number of studies of tropospheric O 3 , a number of challenges still remain, such as explaining the near-surface concentration trends (Monks et al, 2015).…”

Tropospheric ozone and its precursors from the urban to the global scale from air quality to short-lived climate forcer

“…In highly dynamic regions such as the Mediterranean Basin (Lelieveld et al, 2002(Lelieveld et al, , 2009, the strength of the meteorological systems (Azores anticyclone and Middle Eastern depression) are key factors in explaining both the variability and the anomalies of ozone in the lower troposphere in this region . Recent observations have suggested there is a summertime free-tropospheric ozone pool over the Mediterranean (Zanis et al, 2014;Kalabokas et al, 2013). The data in Fig.…”

Tropospheric ozone maxima observed over the Arabian Sea during the pre-monsoon

“…1). The enhancement of TOC is similar in magnitude as TOC enhancements observed during the follow events: (1) the wellknown biomass burning plume in the Southern Hemisphere that was transported over the South Atlantic, the coast of South Africa, along the Indian Ocean and towards Australia (e.g., Fishman et al, 1986Fishman et al, , 1991; (2) TOC attributed to anthropogenic sources in the Northern Hemisphere, for instance northern India; and (3) the Mediterranean summer ozone pool attributed to the stratospheric-tropospheric exchange (STE) (Zanis et al, 2014). A spring (or so-called pre-monsoon; see Sect.…”