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

Abstract

The tropospheric production of O3 is complex, depending on nitrogen oxides (NOx = NO + NO2), volatile organic compounds (VOCs), and solar radiation. We present a case study showing that the O3 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 O3 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 O3 measured at the rural site, comparing the modeled O3 and the measured O3 in different scenarios, which include both input parameters related to local O3 production by photochemistry and input parameters associated with regional transport of O3 precursors. The simulation results show that the local NOx concentration is not a good input to model the observed O3 (R = 0.17); on the contrary including the wind speed and direction as input of the FFNN model, the modelled O3 is well correlated with that measured O3 (R = 0.82).