Simulation of the effects of critical factors on ozone formation and accumulation in the greater Athens area

In the present study, the temporal and spatial dynamics of the ozone production in the greater Athens area (GAA) is examined by using the photochemical UAM-V model coupled with the meteorological MM5 model. Several numerical experiments were performed in order to investigate and to quantify the effect of critical factors that conduce to the ozone formation and accumulation during ozone episodes. The initial scenario is able to reproduce the observed ozone patterns, but it underestimates the observed peaks in most of the downwind suburban stations. Using process analysis, we demonstrate the contribution of chemical and physical processes to ozone formation and destruction. The inclusion of biogenic emissions and their distribution based on a satellite vegetation index, as well as the adjustment of the speciation of the anthropogenic NMVOC emissions according to specific characteristics measured in street and aged city plumes, lead to a more realistic description of the urban mixture and thus of the ozone production. The effect of the urban sector introduced via a simplified urbanized meteorological data set, provoke a differentiation of the spatial pattern attributed to the accumulation of the primary NOX pollutants inside the city center and to the consequent limited horizontal advection toward the peripheral zone. Finally, the ozone background turned out to be a key factor for the model performance. The statistical evaluation of the results reveals the importance and the necessity of implementing all the above modifications; the persistence of some discrepancies is associated with meteorological or modeling coupling limitations.