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DYNOZONE: Total column and surface ozone variability over the Iberian Peninsula: Dynamical and Chemical atmospheric factors
Coordinator - Ana Cristina Carvalho (UNL)
CESAM Responsible researcher - José M. Castanheira
Programme - PTDC/CTE-ATM/105507/2008
Execution dates - 2010-10-01 - 2013-09-30 (36 Months)
Funding Entity - FCT
Funding for CESAM - 41238.05 €
Total Funding - 133847.78 €
Proponent Institution - Universidade Nova de Lisboa
Participating Institutions
Universidade de Aveiro
Fundação Ensino e Cultura Fernando Pessoa (FECFP)
Instituto Tecnológico e Nuclear (ITN/MCTES)

Over Portugal there is a lack of systematic studies in order to understand the dynamical processes that are contributing for the surface atmospheric compositions, namely the STE contribution to elevated surface ozone concentrations, as opposed to local production or long range transport from external pollution sources. Specifically whenever it occurs during winter time, records of high ozone are not considered as a valid measurement by Portuguese authorities. It is therefore of considerable importance to identify all relevant processes properly, which might contribute to critical ozone levels. Because total column of ozone is the controlling factor of the UV radiation, it is important to understand how climate changes in atmospheric circulation may have contributed for the column decline at milatitudes, in particular over the Iberian Peninsula.

Both in the stratosphere and in the troposphere the ozone concentrations are regulated by chemical mechanisms involving the radiative activation of chemical species (among other factors). Whereas there is a consensus among scientist that the kinetic-photochemical processes are the main factors for the summer seasonal maximum value, in what concerns the spring ozone maximum scientists diverge in opinions for its explanation, in part due to the difficulty to untangle the contributions of global and local scale processes. Monks (2000) have made a revision of the mechanisms that may contribute for this spring ozone maxima, that includes several factors concurring to photochemistry such stratosphere-troposphere exchange (STE) associated to vertical tropospheric dynamic mechanisms (e.g. cut-off lows).

Stratospheric influence on surface tropospheric ozone is recognized by EPA to be more frequent in late winter early Spring (EPA, 2006). Studies of this influence rely both on chemistry transport models (CTM) as well as on measured time series of ozone and chemical species that signal stratospheric air masses, such as the 7Be, 10Be, as well as low values of moisture quantities, and others (Hov, 1998). The time series analysis of chemical species measurements at mountain sites are of preference, such as the Alpine sites (Stohl et al, 2000; Bonasoni et al, 2000) and Kislovodsk High Mountain Station (Tarasova et al., 2009). Nevertheless, the stratospheric ozone have also been detected at regular air quality networks (San José, et al, 2005).

Meteorological weather prediction systems are the numerical tools more frequently chosen to understand the dynamical processes leading to a STE. Also three dimension (3D) CTM applications may be found in literature both for global scales (Grew 2007) and synoptic/regional scales (Ebel et al, 2008). Less common, it is the use of 3D CTM for the study of STE at the synoptic/regional scale including data assimilation algorithms. The EURAD model system has data assimilation algorithms concerning surface observations and emissions (Elbern et al, 2007), but ozone vertical profiles from satellite ozone measurements are missing.

By its impact, both on human health, crops productivity and on materials, the ozone is legislated in Portugal (DL 320/2003) and in the European Community by the 2008/50/EC Directive. In the aim of this Directive, the member´s states are obligated to inform, justify and present a plan action of ozone precursors emissions control in case of ozone episodic situations. The main objectives of the present project are to identify and justify, on a scientific base, the no photochemical origin of some ozone events and the contribution of climatic atmospheric circulation change for the decline of ozone column at milatitudes.

To accomplish these major objectives the project team will analyse surface ozone concentration long records along with radionuclides time series available for Lisbon and Azores. A database of events of surface ozone concentrations with stratospheric intrusion contributions will be constructed. These events will be further investigated through thermo-hydrodynamic variables used as tracers, and also ozone concentrations, included in the reanalysis data. The chemical-dynamical processes of such events will be also studied by means of the EURAD model applications, for which a data assimilation procedure will be developed accounting for ozone satellite vertical profiles and surface ozone measurements.

The SPARC and MOZAIC projects, among other studies (Pan et al, 2007), have contribute to the comprehension of tropopause definition and STE. Since more reanalysis data are meanwhile available for longer periods, it is very important to update the climatologies of tropopauses and multiple tropopauses (as indicators of tropopause folds) such as the ones published by Elbern et al (1998). The project team will also study multiple tropopause events due to its importance on STE budgets calculations and its relation with the total ozone column values.

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