Abstract
Abstract. Over the Mediterranean region, elevated tropospheric ozone (O3) values are recorded, especially in summer. We use the thermal Infrared Atmospheric Sounding Interferometer (IASI) and the Weather Research and Forecasting Model with Chemistry (WRF-Chem) to understand and interpret the factors and emission sources responsible for the high O3 concentrations observed in the Mediterranean troposphere. Six years (2008–2013) of IASI data have been analyzed and results show consistent maxima during summer, with an increase of up to 22% in the [0–8] km O3 column in the eastern part of the basin compared to the middle of the basin. We focus on summer 2010 to investigate the processes that contribute to these summer maxima. Using two modeled O3 tracers (inflow to the model domain and local anthropogenic emissions), we show that, between the surface and 2 km, O3 is mostly formed from anthropogenic emissions, while above 4 km it is mostly transported from outside the domain or from stratospheric origins. Evidence of stratosphere-to-troposphere exchange (STE) events in the eastern part of the basin is shown, and corresponds to a low water vapor mixing ratio and high potential vorticity.
Highlights
Tropospheric ozone (O3) is a greenhouse gas, air pollutant, and a primary source of the hydroxyl radical (OH), the most important oxidant in the atmosphere (Chameides and Walker, 1973; Crutzen, 1973)
We focus our analysis on summer 2010, which corresponds to the year of the anthropogenic emission inventory used in the model
Six years of tropospheric O3 observations provided by the Infrared Atmospheric Sounding Interferometer (IASI) mission above the Mediterranean are shown
Summary
Tropospheric ozone (O3) is a greenhouse gas, air pollutant, and a primary source of the hydroxyl radical (OH), the most important oxidant in the atmosphere (Chameides and Walker, 1973; Crutzen, 1973). Previous observations and studies have shown that tropospheric O3 over the Mediterranean exhibits a significant increase during summertime, especially in the east of the basin (Kouvarakis et al, 2000; Im et al, 2011; Gerasopoulos et al, 2005, 2006a; Richards et al, 2013; Zanis et al, 2014) Meteorological conditions such as frequent clear-sky conditions (Fig. 1a) and high exposure to solar radiation (Fig. 1b) in summer enhance the formation of photochemical O3 due to the availability of its precursors. Zbinden et al (2013), using aircraft data from the MOZAIC (Measurements of OZone and water vapour by in-service AIrbus airCraft) program over 15 years (1994–2009), showed that the tropospheric O3 columns in the east of the Mediterranean reached a maximum of 43.2 DU (Dobson units) during June–July This recorded maximum exceeds the maximum recorded for Beijing for the same period, for example.
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