Atmospheric dynamics and ozone cycle during sea breeze in a Mediterranean urbanized complex coastal site

Persistent high pressure conditions affect the Mediterranean basin during summertime, favoring the occurrence of sea breeze circulation that influences ozone production and transport, giving rise to complex recirculation patterns in coastal areas. Those features were investigated during a summer ozone episode in Naples (Southern Italy), one of the largest and densest conurbations around the Mediterranean. Aircraft measurements were performed at heights from 150 to 1500 m a.g.l., compared and integrated with high resolution meteorological and air quality model simulations, to investigate local circulation and pollutants dynamics. The integration of airborne measurements, surface observations and modelling allowed to establish an interpretational framework of the photochemical phenomena in the area. Sea breeze and local emissions give rise to production of ozone inland of Naples, causing high concentrations over the region located between the coast and the Apennine chain. Ozone is then injected in the upper boundary layer and transported towards the sea by the wind rotation occurring above 500 m a.s.l., causing a complex vertical layering of concentration, with maxima between 500 and 800 m. The vertical growth of ozone concentration profile is also contributed by the decrease of the boundary layer depth occurring when the breeze front reaches the inland area carrying NOx from the densely-populated coast, favoring titration process near the surface. Although the whole airshed results as a net producer of ozone, local surface concentrations are determined by a complex interaction of atmospheric flow and chemistry at different scales, furtherly supporting the need of coordinated efforts to control smog precursors over wider areas.