The Po Valley (Northern Italy) represents an important exceedance zone of the air-quality limit values for PM (particulate matter), NO₂ (nitrogen dioxide) and O₃ (ozone). This area covers the territory of most Italian northern regions and includes several urban agglomerates, such as Milan, Turin, Venice and Bologna. The area is densely populated and heavily industrialized. The paper summarizes the assessment of the impact of the current (2013) and future (2025) emissions and of the meteorological conditions on the air quality of the Po Valley. This study is one of the first outcomes of the EU LIFE-IP Clean Air Program Po Regions Engaged to Policies of Air (PREPAIR) project. The project, involving administrations and environmental agencies of eight regions and three municipalities in Northern Italy and Slovenia, started in 2017 and will end in 2024. Future emission scenarios consider the emissions reduction due to the air-quality action plans of the regions involved, of the agreements between the national authorities and regional administrations and of the PREPAIR project itself, in the overall context of the application of the current legislation of the European Union. The combination of these measures will lead to the reduction of direct emissions of PM₁₀ in the Po Valley and of the main precursors emitted in the area (NOx, nitrogen oxides and NH₃, and ammonia) by 38% for PM₁₀, 39% for NOx and 22% for NH₃, respectively. This lowering corresponds to a reduction of about 30.000 tons of primary PM₁₀, 150.000 tons of NOx, 54.000 tons of NH₃ and 1700 tons of SO₂. The results show that these expected reductions should allow us to achieve the EU PM₁₀ limit value in the Po Valley by the year 2025.

Air quality in Europe continues to remain poor in many areas, with regulation limits often exceeded by many countries. The EU Life-IP PREPAIR Project, involving administrations and environmental protection agencies of eight regions and three municipalities in Northern Italy and Slovenia, was designed to support the implementation of the regional air quality plans in the Po Valley, one of the most critical areas in Europe in terms of pollution levels. In this study, four air quality modelling systems, based on three chemical transport models (CHIMERE, FARM and CAMx) were applied over the Po Valley to assess the sensitivity of PM_2.5 concentrations to NO_x and NH₃ emission reductions. These two precursors were reduced (individually and simultaneously) from 25% up to 75% for a total of 10 scenarios, aimed at identifying the most efficient emission reduction strategies and to assess the non-linear response of PM_2.5 concentrations to precursor changes. The multi-model analysis shows that reductions across multiple emission sectors are necessary to achieve optimal results. In addition, the analysis of non-linearities revealed that during the cold season, the efficiency of PM_2.5 abatement tends to increase by increasing the emission reductions, while during summertime, the same efficiency remains almost constant, or slightly decreases towards higher reduction strengths. Since the concentrations of PM_2.5 are greater in winter than in summer, it is reasonable to infer that significant emission reductions should be planned to maximise reduction effectiveness.

A standardized methodology for the validation of short-term air quality forecast applications was developed in the framework of the Forum for Air quality Modeling (FAIRMODE) activities. The proposed approach, focusing on specific features to be checked when evaluating a forecasting application, investigates the model's capability to detect sudden changes in pollutant concentration levels, predict threshold exceedances and reproduce air quality indices. The proposed formulation relies on the definition of specific forecast modelling quality objectives and performance criteria, defining the minimum level of quality to be achieved by a forecasting application when it is used for policy purposes. The persistence model, which uses the most recent observed value as the predicted value, is used as a benchmark for the forecast evaluation. The validation protocol has been applied to several forecasting applications across Europe, using different modelling paradigms and covering a range of geographical contexts and spatial scales. The method is successful, with room for improvement, in highlighting shortcomings and strengths of forecasting applications. This provides a useful basis for using short-term air quality forecasts as a supporting tool for providing correct information to citizens and regulators.

A standardized methodology for the validation of short-term air quality forecast applications was developed in the framework of FAIRMODE activities. The proposed approach, focusing on specific features to be checked when evaluating a forecasting application, investigates the model capability to detect sudden changes of pollutants concentrations levels, to predict threshold exceedances and to reproduce air quality indices. The proposed formulation relies on the definition of specific forecast Modelling Quality Objective and Performance Criteria, defining the minimum level of quality to be achieved by a forecasting application when it is used for policy purposes. The persistence model, which uses the most recent observed value as predicted value, is used as benchmark for the forecast evaluation. The validation protocol has been applied to several forecasting applications across Europe, using different modelling paradigms and covering a range of geographical contexts and spatial scales. The method is successful, with room for improvement, in highlighting shortcomings and strengths of forecasting applications. This provides a useful basis for using short-term air quality forecast as a supporting tool for correct information to citizens and regulators.