Abstract
Atmospheric dispersion models are a useful tools to assess air quality and emission source contributions in urban areas. Eulerian chemical and transport models (CTMs) can assess the regional background, that is the baseline level in the region of the city, and the urban background, that is the increment of concentration due to the emissions of the city, but they are not able to properly assess the very local contribution of emission sources at pollution hotspots within the city, because of their relatively large grid step. For the assessment of local sources’ contribution, Lagrangian dispersion models can be profitably used, especially when high spatial resolution modelling is required. Actually, Lagrangian models rely on a more realistic spatialization of urban emissions, unevenly distributed because of the road network layout (for traffic emissions) and of the built environment structure (for space heating emissions); additionally, Lagrangian models also account for wind field modifications induced by buildings. In this work, air quality modelling results for fine particles (PM2.5) in the city centre of Milan obtained by means of the AUSTAL2000 Lagrangian model are compared with those of CAMx Eulerian model. Model simulations where performed for a 1.7x1.7 km2 area in Milan and focused on three receptor points selected in order to represent sites with both different features in terms of the surrounding built environment and different exposure to the local emission sources. Namely, the receptors correspond to a green area, to a residential and shopping area near Milan main square, and to a congested crossroad on the inner ring road of the city centre. Comparison results show that the outcome of the Eulerian model at the local scale is only representative of a background level, similar to Lagrangian model’s outcome for the green area receptor, but fails to reproduce concentration gradients and hot-spots, driven by local sources’ emissions.
Highlights
Ambient air quality in urban areas represents a significant public health problem because of the negative impacts on respiratory and cardiovascular health and because of premature deaths as a result of population exposure to atmospheric pollutants [1] [2] [3]
Thanks to the PSAT Source Apportionment Tool [12] embedded in CAMx, it was possible to assess the impact of the emission sources located in the study area on the air quality in the area itself, so that the contributions to the ambient concentration levels estimated by CAMx and by AUSTAL2000 could be properly compared
AUSTAL2000 results highlight the difference between the receptor strongly affected by local sources (TRAFFIC) and the receptors less exposed to traffic emissions (DUOMO) and located in an urban background site (PARK)
Summary
Ambient air quality in urban areas represents a significant public health problem because of the negative impacts on respiratory and cardiovascular health and because of premature deaths as a result of population exposure to atmospheric pollutants [1] [2] [3]. Atmospheric dispersion models are useful tools to assess air quality and emission sources’ contributions to the pollutant concentration levels in urban areas [5] [6] [7].
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