The roles of regional accumulation and advection of ozone during high ozone episodes in Slovenia: A WRF/Chem modelling study

The main objective of this study was to investigate the causes as well as the temporal and spatial dynamics of ozone pollution during three high ozone episodes in the northeastern Mediterranean Basin using surface measurements and WRF/Chem model simulations. The simulation results revealed that the analyzed episodes were mainly caused by the impact of accumulation of pollution rich in ozone over the northern Adriatic. Two mechanisms were simulated: (1) the accumulated pollutants occasionally encroaching and retreating, impacting the coastal areas; and (2) broad advection impacting areas further inland in the northeastern Mediterranean Basin including Slovenia. The simulations also show that in some specific conditions the elevated ozone levels over continental Slovenia can be separated from the direct Mediterranean influences by the Alpine-Dinaric mountain ridge. The simulations show a trend of underestimating maximum and overestimating minimum ozone concentrations, but the overall statistics agree fairly well with the statistics of the measured ozone concentrations.

Research highlights
► The study focuses on origin of ozone pollution during three high concentration episodes.
► Characteristics of the accumulation and advection phases of ozone are identified.
► Ozone-rich layers accumulated over the Adriatic Sea and coastal regions during the episodes.
► The accumulated pollution was advected inland by the southwesterly flows.