The development of a building-resolved air quality forecast system by a multi-scale model approach and its application to Modena Urban area, Italy

One of the main critical air pollutants in terms of health effects is nitrogen dioxide (NO2), whose levels in the last years exceeded national and WHO (World Health Organization) standards in many urban areas across the Po Valley (Northern Italy), exposing urban population to the risk of pollution-related diseases and health conditions. The main goal of this study was to develop a multi-scale modelling system able to forecast hourly NO2 and NOx concentration fields at a building-resolving scale in the urban area of Modena, a city in the middle of the Po Valley, in order to support environmental policies and to take timely protective actions given a forecast of impeding poor air quality. The modelling system relied on two different tools: the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), which is able to compute concentration fields over regional domain by considering specific emission scenarios and the Parallel Micro SWIFT and SPRAY (PMSS) modelling suite accounting for dispersion phenomena within the urban area. PMSS was used to simulate at building-scale resolution the dispersion of NO and primary NO2 produced by urban sources. Conversely, the WRF-Chem model was selected to reproduce the meteorological input for PMSS and to estimate the formation of secondary NO2. Modelled NO2 and NOx concentrations were compared with measurements at two urban stations, one at traffic site and at background location. Notwithstanding a slight underestimation, mainly evident at urban traffic stations for NOx, simulated concentrations present a large agreement with related observations. The NO2 Model Quality Objective, as defined by Fairmode guidelines, was met for both the urban stations and the other statistical indexes considered in the evaluation fulfilled the acceptance criteria for dispersion modelling in urban environment, for both NO2 and NOx concentrations. In the second section of the study, the population exposure to forecasted NO2 concentrations has been evaluated adopting a generic model of dynamic population activity. Indoor house micro-environments contributed up to 67 % of the total exposure, whilts other outdoor spaces contributed with 24%, divided between traffic environments (8 %) and other outdoor spaces (16 %). Work related buildings contributed for the ramaining share (9 %).