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Abstract
This work sets out the test of the GRAL model (Graz Lagrangian Model, vs.18.1) in the urban area of Modena (Po valley, Northern Italy). The simulation domain sizes 2 000 x 3 000 m2 and it features ‘microscale’ cells of 4 x 4 m2. The simulation focuses on an intersection featured by large traffic flows next to a school and a regulatory air quality monitoring station classified as an urban traffic site. The model is a lagrangian particle dispersion model and it takes into account the presence of buildings as obstacles and generating microscale wind fields accordingly, making this class of model suitable for investigating spatial pattern of atmospheric pollution in urban areas where local accumulation might occur. The simulation investigates traffic emissions of nitrogen oxides (NOx) over the period October 29 to November 10, 2016, when direct measurements of traffic flow were collected by four one-channel doppler radar traffic counters. These counters provided continuous estimate of vehicle length, speed and number. These latter data were combined with available traffic flows at rush hour by PTV VISUM mobility software and the fleet composition of the municipality to estimate the total NOx emissions by vehicular traffic over the roads included in the simulation domain. NOx simulated concentrations showed a moderate correlation with the NOx observations at the nearby monitoring site. To have a better insight on the potential and the limitations of the GRAL model, its results will be compared with the output of the lagrangian particle dispersion model PMSS over the same area.
Highlights
The Po valley is a European hotspot area for air quality, due to its recurrent wind calm episodes and high pressure conditions that lead to persistence of high concentrations of atmospheric pollutants, even at remote rural sites
These counters provided continuous estimate of vehicle length, speed and number. These latter data were combined with available traffic flows at rush hour by PTV VISUM mobility software and the fleet composition of the municipality to estimate the total nitrogen oxides (NOx) emissions by vehicular traffic over the roads included in the simulation domain
Atmospheric pollution by NOx is of main concern in the Po valley because of its rapid conversion to harmful atmospheric particles and of its critical level according to European and WHO air quality guidelines
Summary
The Po valley is a European hotspot area for air quality, due to its recurrent wind calm episodes and high pressure conditions that lead to persistence of high concentrations of atmospheric pollutants, even at remote rural sites. Despite the decrease in PM10 and PM2.5 concentration over the long term throughout the valley [1][2], the strong anthropic pressure in this area, together with its characteristic climatic conditions, increase the persistence and the homogenization of the regional air masses. This latter results in a significant impact by emission sources in the valley, affecting rural areas distant from the metropolitan areas and strong emissions [3][4][5].
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