The Impact of Meteorology on Air Quality Simulations over the Po Valley in Northern Italy

Abstract

The Po valley in Northern Italy has been identified as a hot spot area in Europe where pollutant levels are expected to remain problematic in the years to come despite the application of the legislation devoted to air pollution control. High anthropogenic emissions in combination with frequently occurring stagnant atmospheric conditions cause very high PM (particulate matter) concentrations in winter. The POMI project (PO valley Model Inter-comparison exercise) has been set-up to evaluate the capabilities of current air quality models to reproduce the concentration levels reached in this area. One of the outcomes of the project has been the confirmation that air quality models do under-estimate quite significantly the observed PM concentrations in this region. A series of sensitivity test have been run in order to understand the reasons for this underestimation and in particular to highlight the impact of meteorology on modeled concentrations. Different nudging techniques of observations from regulatory networks into MM5 (meteorlogical model) are explored in an attempt to improve the simulation of frequent low wind regimes in the Po valley. The sensitivity of CHIMERE (chemical transport model) is evaluated for January 2005, a period with high PM concentrations. Strengths and weaknesses of the approaches on simulating PM in one of the most polluted and complex areas in Europe are discussed.