Study of the ADMS–URBAN model for assessing air pollution due to the vehicular traffic in Ravenna

Vehicles traffic can be considered as the main atmospheric pollution source in Italian urban areas. It is estimated to be responsible for 41% of PM10, 42% of NMVOC, 46% of NOx and 90% of CO emissions in Emilia – Romagna Region. The European legislation (Directive 96/62/CE) sets the possibility to complete information derived from the urban air quality monitoring network with other tools as mobile monitoring stations, biomonitoring or modelling systems in order to assess quality air. The Environmental Regional Agency (Arpa) of the Emilia – Romagna Region has chosen ADMS – Urban model as means to support Air Quality Assessment and Management. ADMS – Urban 1.6, developed at the CERC 1,6, is an advanced Gaussian dispersion model 1 which can simulate the dispersion in atmosphere of pollutants released from industrial, domestic and road traffic sources , expecially suitable for urban areas. In the model, the boundary layer is characterised by the Monin – Obukhov length and the boundary layer height. It’s possible to take account of hourly variations in emissions throughout the day and on different days of the week entering specific coefficients (called “time varying emission factors”), representing the ratio between real emissions and emissions from standard operating conditions (that entered into the model as input). The Danish model OSPM, developed at the NERI, is incorporated into the model to consider the street canyon effect and i.e. to calculate the concentrations at points which lie in roads lined with buildings higher than 0.5 m. Moreover the ADMS – Urban model can take into account chemical reactions between NO, NOx and Ozone, of wet and dry deposition processes and of pollutant background concentrations. The model performance depends on the input data accuracy and undergoes changes according as the input datasets entered and the working conditions. We utilised thus different input datasets in order to determine the model’s best operational conditions. The ADMS – Urban model has previously been validated in a large number of studies. Clearly, the dispersion models need to be validated in various environments and for the whole range of meteorological conditions occurring in the real atmosphere. The main objective of this work was thus to validate the model in the Ravenna urban area, in order to evaluate if it’s suitable to support the Air Quality Assessment and Management. To obtain this, we entered road sources and set the model to predict Short – Term CO and PM10 concentrations at specified points situated on the air quality monitoring network stations. Carbon monoxide is interesting for the model validation because it almost completely derives from vehicular emissions in urban areas and so it can be considered as the best traffic tracing. PM10 instead has been predicted because its high levels represent a critical winter problem in metropolitan areas. The present paper also evaluates the model performance diagnostically. In fact, we have analysed the performance in terms of relevant meteorological parameters as wind speed and direction and atmospheric stability.