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Towards the coupling of a chemical transport model with a micro-scale Lagrangian modelling system for evaluation of urban NOx levels in a European hotspot.

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Title:	Towards the coupling of a chemical transport model with a micro-scale Lagrangian modelling system for evaluation of urban NOx levels in a European hotspot.
Authors:	Veratti, Giorgio¹ (AUTHOR) giorgio.veratti@unimore.it, Fabbi, Sara¹ (AUTHOR), Bigi, Alessandro¹ (AUTHOR), Lupascu, Aurelia² (AUTHOR), Tinarelli, Gianni³ (AUTHOR), Teggi, Sergio¹ (AUTHOR), Brusasca, Giuseppe³ (AUTHOR), Butler, Tim M.² (AUTHOR), Ghermandi, Grazia¹ (AUTHOR)
Source:	Atmospheric Environment. Feb2020, Vol. 223, pN.PAG-N.PAG. 1p.
Subject Terms:	Cities & towns, Urban planning, *Automobile emission control devices, City traffic, Traffic flow measurement, Chemical models, Urban transportation, Hybrid systems
Geographic Terms:	Modena (Italy)
Abstract:	A multi-scale modelling system was developed to provide hourly NO x concentration fields at a building-resolving scale in the urban area of Modena, a city in the middle of the Po Valley (Italy), one of the most polluted areas in Europe. The WRF-Chem model was applied over three nested domains and employed with the aim of reproducing local background concentrations, taking into account meteorological and chemical transformation at the regional scale with nested resolutions of 15 km, 3 km and 1 km. Conversely, the PMSS modelling system was applied to simulate 3D air pollutant dispersion, due to traffic emissions, with a very high-resolution (4 m) on a 6 km × 6 km domain covering the city of Modena. The methodology employed to account for anthropogenic emissions relies on two different strategies. Traffic emissions were based on a bottom-up approach using emission factors suggested by the European Environmental Agency with traffic fluxes estimated by the PTV VISUM model in the urban area of Modena, combined with direct traffic flow measurements performed between October 28 and November 8, 2016 which was used for the hourly vehicle modulation. Other anthropogenic emissions were taken from the TNO-MACC III inventory at the scales resolved by the WRF-Chem model. Simulations were performed for the same period whereby the traffic measurement campaign was carried out. 2 m temperature and 10 m wind speed were captured quite well by the WRF-Chem model with statistical metrics in line with similar case studies related to the Northern Italy. The NO x concentrations reproduced in the Po Valley area by WRF-Chem were on average simulated reasonably well with a general negative bias in almost all the examined rural background monitoring stations. Additionally, the deployment of an emission inventory at the original resolution (7 km) highlighted that increasing resolution from 3 km to 1 km does not generally improve the model performance. Nevertheless, simulated and observed NO x hourly concentrations in the urban area of Modena exhibit a large agreement in particular for urban traffic site where detailed traffic emission estimations proved to be very successful in reproducing the observed NO x trend. At urban background stations, despite a general underestimation of the observed concentrations, the combination of WRF-Chem with PMSS provided daily pattern in line with observations. The analysis of the modelled NO x daily cycle pointed out also that at both traffic and background urban stations the morning NO x peak concentration was on average underestimated. This could be explained with an overestimation of mixing phenomena between 07:30 a.m. and 10:00 a.m. by WRF-Chem which leads to a greater dispersion of NO x along the vertical and thus a morning underestimation. The statistical analysis showed finally that PMSS combined with WRF-Chem at both the resolutions (3 km and 1 km) and at both traffic and background sites fulfilled standard acceptance criteria for urban dispersion model evaluation, confirming that the proposed multi-modelling system can be employed as a tool to support environmental policies, epidemiological studies and urban mobility planning. A hybrid modeling system composed by the WRF-Chem model and the Parallel Micro SWIFT and SPRAY modelling suite was employed to estimate urban NO x concentrations at very high resolution (4m) in a real case study. Results show that the modeling system provides good accuracy in reproducing observations, particularly at the traffic reference site. Model performances are also compliant with validation criteria at both the urban traffic and the urban background reference stations. Image 1 • Application of a multi-scale approach to estimate urban NO x level. • Tailored traffic emissions by the combination of direct measurements and simulation. • Model performances for NO x fulfill the acceptance criteria for urban environments. • Better description of NO x in urban traffic than in urban background conditions. [ABSTRACT FROM AUTHOR]
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Database:	GreenFILE

Description
Abstract:	A multi-scale modelling system was developed to provide hourly NO x concentration fields at a building-resolving scale in the urban area of Modena, a city in the middle of the Po Valley (Italy), one of the most polluted areas in Europe. The WRF-Chem model was applied over three nested domains and employed with the aim of reproducing local background concentrations, taking into account meteorological and chemical transformation at the regional scale with nested resolutions of 15 km, 3 km and 1 km. Conversely, the PMSS modelling system was applied to simulate 3D air pollutant dispersion, due to traffic emissions, with a very high-resolution (4 m) on a 6 km × 6 km domain covering the city of Modena. The methodology employed to account for anthropogenic emissions relies on two different strategies. Traffic emissions were based on a bottom-up approach using emission factors suggested by the European Environmental Agency with traffic fluxes estimated by the PTV VISUM model in the urban area of Modena, combined with direct traffic flow measurements performed between October 28 and November 8, 2016 which was used for the hourly vehicle modulation. Other anthropogenic emissions were taken from the TNO-MACC III inventory at the scales resolved by the WRF-Chem model. Simulations were performed for the same period whereby the traffic measurement campaign was carried out. 2 m temperature and 10 m wind speed were captured quite well by the WRF-Chem model with statistical metrics in line with similar case studies related to the Northern Italy. The NO x concentrations reproduced in the Po Valley area by WRF-Chem were on average simulated reasonably well with a general negative bias in almost all the examined rural background monitoring stations. Additionally, the deployment of an emission inventory at the original resolution (7 km) highlighted that increasing resolution from 3 km to 1 km does not generally improve the model performance. Nevertheless, simulated and observed NO x hourly concentrations in the urban area of Modena exhibit a large agreement in particular for urban traffic site where detailed traffic emission estimations proved to be very successful in reproducing the observed NO x trend. At urban background stations, despite a general underestimation of the observed concentrations, the combination of WRF-Chem with PMSS provided daily pattern in line with observations. The analysis of the modelled NO x daily cycle pointed out also that at both traffic and background urban stations the morning NO x peak concentration was on average underestimated. This could be explained with an overestimation of mixing phenomena between 07:30 a.m. and 10:00 a.m. by WRF-Chem which leads to a greater dispersion of NO x along the vertical and thus a morning underestimation. The statistical analysis showed finally that PMSS combined with WRF-Chem at both the resolutions (3 km and 1 km) and at both traffic and background sites fulfilled standard acceptance criteria for urban dispersion model evaluation, confirming that the proposed multi-modelling system can be employed as a tool to support environmental policies, epidemiological studies and urban mobility planning. A hybrid modeling system composed by the WRF-Chem model and the Parallel Micro SWIFT and SPRAY modelling suite was employed to estimate urban NO x concentrations at very high resolution (4m) in a real case study. Results show that the modeling system provides good accuracy in reproducing observations, particularly at the traffic reference site. Model performances are also compliant with validation criteria at both the urban traffic and the urban background reference stations. Image 1 • Application of a multi-scale approach to estimate urban NO x level. • Tailored traffic emissions by the combination of direct measurements and simulation. • Model performances for NO x fulfill the acceptance criteria for urban environments. • Better description of NO x in urban traffic than in urban background conditions. [ABSTRACT FROM AUTHOR]
ISSN:	13522310
DOI:	10.1016/j.atmosenv.2020.117285