Inland O3 Production Due to Nitrogen Dioxide Transport Downwind a Coastal Urban Area: A Neural Network Assessment

The tropospheric production of O-3 is complex, depending on nitrogen oxides (NOx = NO + NO2), volatile organic compounds (VOCs), and solar radiation. We present a case study showing that the O-3 concentration is higher in a rural area, 14 km downwind from a coastal town in Central Italy, compared with the urban environment. The hypothesis is that the O-3 measured inland results from the photochemical processes occuring in air masses originating at the urban site, which is richer in NOx emissions, during their transport inland.To demonstrate this hypothesis, a feed forward neural network (FFNN) is used to model the O-3 measured at the rural site, comparing the modeled O-3 and the measured O-3 in different scenarios, which include both input parameters related to local O-3 production by photochemistry and input parameters associated with regional transport of O-3 precursors. The simulation results show that the local NOx concentration is not a good input to model the observed O-3 (R = 0.17); on the contrary including the wind speed and direction as input of the FFNN model, the modelled O-3 is well correlated with that measured O-3 (R = 0.82).