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The Iberian Peninsula (IP) and the Western Mediterranean Basin (WMB) are characterized by its complex topography and a particular location between two continents and a major ocean and a smallwarm sea. The combination of mesoscale wind flows, emissions and complex local orography is crucial in the production and transport of photochemical pollutants within the domain. These particularities and the global circulation at middle latitudes induce several different meteorological situations affecting the IP, and a particular behavior of the dynamics of air pollutants related to this atmospheric evolution. To quantify the variability of the synoptic meteorology of the region, a cluster analysis of the different synoptic situations of 4 years of meteorological data was applied. In order to assure a full coverage of the different air quality scenarios, seven meteorological situations were selected to simulate and discuss the dynamics of air pollutants over the IP. Simulation covers a domain of 1392 × 1104 km2 centered in the IP, that uses EMEP-based emissions corresponding to year 2000. Model resolution is 24-km horizontally, and 16 layers of variable thickness in altitude. Dynamical meteorological fields were derived from MM5 model. Photochemistry is represented by Models-3/CMAQ model with CBM-IV chemical mechanism including heterogeneous chemistry. Model simulations were evaluated by comparing data from meteorological and air quality stations with simulation outputs. The results revealed that summer situations are characterized by high daily-average levels of photochemical pollutants over the whole IP and the WMB. Furthermore, high ozone levels during the central part of the day exceed the regulatory thresholds established in European Directive 2002/3/EC. The combination of sea breezes, upslope winds and important valley canalizations transports pollutants from coastal areas inland, causing high levels of photochemical pollution. In addition, the anticyclonic situation modelled also shows high ozone levels at noon due to the important subsidence and poor wind development across the region within the whole troposphere. The advective situations present low ozone levels related to the intense flows that do not contribute to the conditions for the photochemical production of ozone. The particular behavior of the dynamics of the region connected to the emission location contributes to the development of episodes of air pollution in several regions of the IP. Also, the maritime traffic around the IP plays an important role on the ozone levels over the Alboran sea (southwestern Mediterranean coast). These results help understanding the contribution of the different processes to the atmospheric pollution episodes in a complex region as the IP. [ABSTRACT FROM AUTHOR]

The Western Mediterranean Basin (WMB) is surrounded by high coastal mountains and is influenced by the Mediterranean sea. In summer it becomes isolated from the traveling lows and their frontal systems. The meteorology and the origin of the air masses arriving at the Iberian Peninsula are highly influenced by the Azores high pressure system which is located over the Atlantic Ocean and that intensifies during the warm season inducing very weak pressure gradient conditions all over the region. A number of studies have shown that during this period, layering and accumulation of pollutants such as ozone and aerosols were taking place along the northeastern Iberian Peninsula (NEIP) (Millán et al., 1992, 1997). Baldasano et al. (1994) and Soriano et al. (2001) combined a numerical approach with an elastic-lidar sounding campaign to study the circulatory patterns of air pollutants over Barcelona (NEIP) in a typical summertime situation, where pollutant layers were, formed by the return flow of the breeze and forcings caused by the complex orography combined with the compensatory subsidence. This was confirmed and detailed in a regular basis by Pérez et al. (2004). The complex topography of the NEIP induces a extremely complicated structure of the flow because of the development of α and β-mesoscale phenomena that interact with synoptic flows. The characteristics of the breezes have important effects in the dispersion of pollutants emitted. In addition, the flow can be even more complex because of the non-homogeneity of the terrain, the land-use and the types of vegetation. [ABSTRACT FROM AUTHOR]