Air pollution and emission reductions over the Po-valley: Air quality modelling and integrated assessment

The Po-valley located in northern Italy at the footstep of the Alps is characterized by a high density of anthropogenic emissions and by the frequent occurrence of stagnant meteorological conditions. The area has been identified as one hot spot place where pollution levels will remain problematic in spite of the application of the current European legislation devoted to air pollution control. By 2020, health impact on population and effects on ecosystems by ozone and eutrophication are indeed calculated to be amongst the highest in Europe and anthropogenic fine particulate matter levels are expected to be responsible for a loss of ten months of life expectancy. In general, long-range transported air pollution in the Po-Valley represents only a fraction of 30-40%, stressing the importance of local control measures in the area to efficiently reduce the impact of air pollution. This paper presents an overview of two connected projects focusing on air-quality modeling and integrated assessment. The POMI (PO-valley Model Inter-comparison) exercise aims at exploring the changes in urban air-quality predicted by different Air Quality Models (AQM) in response to changes in emissions. The first phase of the project has concentrated on the elaboration of the required input data for the AQM, i.e. meteorology, monitoring, and emissions. The latter have been elaborated based on the combination of various types of data originating from different Authorities and characterized by different spatial scales and levels of detail. During this process, priority has been given to the bottom-up approach believed to be more suitable to capture local information than a pure top-down disaggregation from the national emission inventory. The available POMI results at this stage indicate model performances in line with those obtained in the frame of previous model evaluation exercise but with a marked underestimation of the fine particulate matter (in particular of its organic fraction) and a significant model variability in the modeling of ozone concentrations. Work to investigate the sensitivity of the AQM to various parameters (e.g. meteorology and emission) is on-going with the aim to better understand the air quality processes in the Po-Valley region and better represent them in the AQM In parallel to POMI, an integrated assessment tool is being developed to design and assess the effectiveness of regional abatement policies. This tool is planned to make use of information available at the local/regional scale (technological changes, emission factors…) to allow investigating the efficiency of both technical and nontechnical abatement measures and to find the optimal cost allocation. POMI provides useful information for the development of sectoral local/regional source-receptor relationships and for better accounting for the different sources of model-related uncertainties (emissions, meteorology…) in the efficacy assessment of abatement strategies. It is believed that such an approach which combines (1) collecting high quality emission inventories, (2) running extensive AQM exercises and (3) optimizing the choice of emission abatement strategies via a specific integrated assessment tool will support the local/regional Authorities in designing effective AQP in the frame of the current European air quality directive.