Inland O 3 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 (NO x = NO + NO 2 ), 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 NO x 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 NO x 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).