Ozone cycles in the western Mediterranean basin: Interpretation of monitoring data in complex coastal terrain

In summer, the complex layout of the coasts and mountains surrounding the w estern Mediterranean basin favors the development of mesoscale atmospheric recirculations and the formation of ozone reservoir layers above the coasta l areas and the sea. Tropospheric ozone cycles vary here according to locat ion and exposure of the monitoring station in relation to the flows and res ervoir layers, and large differences can be encountered within tens of kilo meters. The basic premise for this work is that the representativeness of a ny station is determined by the (fore) knowledge of the processes affecting the site, at the proper timescales and space scales within its region. Thu s, available data have been combined with mesoscale analysis and modeling t o interpret the observed summer ozone cycles for the monitoring network at Castellon, on the Spanish east coast. The area is approximately 120 km by 1 20 km, is backed by coastal mountains, and includes the following: a conurb ation, industries, and a densely traveled road network parallel to the coas t. To summarize the results, a typology has been developed that relates the variability in the observed ozone cycles to the site locations, the docume nted mesoscale circulations, and the chemical reactions along the atmospher ic paths. Five types have been found to represent the cycles observed in th is region, and information available to the authors indicates that this typ ology covers most nonurban monitoring stations around the western Mediterra nean basin.