In Europe, emissions of many air pollutants have decreased substantially over the past decades, resulting in improved air quality across the region. However, air pollutant concentrations are still too high, and air quality problems persist. The Po Valley, located in the northern part of Italy, is one of the most critical area of the country in terms of pollution level. The reason to this problem is not only related to the high population density with its related activities, but it is also due to the orographic conformation of the territory which appears surrounded by mountains on three sides: the Alps to the west and to the north and the Apennines to the south. These geographical characteristics lead to meteorological conditions unfavorable to the atmospheric dispersion: average annual wind speed less than 2 m s-1, recurrent thermal inversions at low altitude, low mixing layer heights and persistent foggy and hazy events during winter time. One of the main critical air pollutants in terms of health effects is nitrogen dioxide (NO2), whose levels in the last years exceeded national and WHO (World Health Organization) standards in many urban areas across the Po Valley, exposing urban population to the risk of pollution-related diseases and health conditions. The main goal of this study was to develop a multi-scale modelling system able to provide hourly NOx (NO + NO2) concentration fields at a building-resolving scale in the urban area of Modena, a city in the middle of the Po Valley, in order to support environmental policies, epidemiological studies and urban mobility planning. The modelling system relied on two different models: the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), which is able to compute concentration fields over regional domain by considering specific emission scenarios, and the Parallel Micro SWIFT and SPRAY (PMSS) modelling suite accounting for dispersion phenomena within the urban area. The PMSS modelling suite was used to simulate at building-scale resolution the NOx dispersion produced by urban traffic flows in the city of Modena. Conversely, the WRF-Chem model was selected to estimate the NOx background concentrations on multiple domains with a nesting technique, in order to take into account emissions both at regional and local scale by excluding traffic emissions sources over the city of Modena. In the first part of the work the modelling system was performed for the period between 28 October and 8 November 2016, the same period whereby a direct vehicle flow measurement campaign was carried out continuously with 4 Doppler radar counters in a four-lane road in Modena, in order to reproduce emission hourly modulation rates. In second section of the study the modelling system was set-up with the aim of produce hourly forecast of NO2 and NO concentrations, up to one day ahead, for the city of Modena for the entire month of February 2019. Simulated and observed hourly concentrations exhibited a large agreement in particular for urban traffic site where detailed traffic emission estimations proved to be very successful in reproducing the observed 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. Finally, the statistical analysis showed that PMSS combined with WRF-Chem 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 human exposures and health impact assessments as well as the effects of local traffic policies on urban air quality.

La Pianura Padana, situata nella parte settentrionale dell'Italia, è una delle aree più critiche del paese per livelli d’inquinamento. La ragione di questo problema non è solo legata all'elevata densità di popolazione con relative attività antropiche, ma è anche dovuta alla conformazione orografica del territorio, delimitato dalla catena alpina ad ovest e a nord e dagli Appennini a sud. Queste caratteristiche geografiche determinano condizioni meteorologiche sfavorevoli alla dispersione atmosferica, quali: velocità medie annue del vento inferiori a 2 m s-1, inversioni termiche ricorrenti nei primi strati di atmosfera a contatto con il suolo, ridotte altezze dello strato rimescolato e persistenti nebbie durante il periodo invernale. Uno degli inquinanti atmosferici più rilevanti per effetti critici sulla salute umana è il biossido di azoto (NO2), i cui livelli negli ultimi anni hanno superato i limiti nazionali e dell’OMS in molte aree urbane della Pianura Padana, esponendo la popolazione al rischio di patologie legate all’inquinamento. L’obiettivo principale di questo studio è stato lo sviluppo di un sistema di modellazione multi-scala in grado di fornire campi di concentrazione oraria di NOx (NO + NO2) sulla città di Modena ad una scala spaziale in grado di risolvere gli effetti dovuti alla presenza degli edifici, al fine di supportare politiche ambientali, studi epidemiologici e di aiutare la pianificazione della mobilità urbana. Il sistema di modellazione si basa su due diversi tool: il modello euleriano di chimica e di trasporto WRF-Chem, in grado di calcolare campi di concentrazione su un dominio regionale considerando specifici scenari di emissione, e Parallel Micro SWIFT e SPRAY (PMSS) suite modellistica sviluppata per risolvere i fenomeni di dispersione all'interno di ambienti urbani. PMSS è stato utilizzato per simulare la dispersione di NOx prodotta dai flussi di traffico urbano nella città di Modena, mentre il modello WRF-Chem è stato applicato per stimare le concentrazioni di NOx di fondo su più domini innestati fra loro, utilizzando emissioni a scala regionale ed escludendo allo stesso tempo le fonti di emissioni da traffico entro la città di Modena. Nella prima parte del lavoro il sistema di modellazione è stato impiegato per riprodurre le concentrazioni comprese nell’arco temporale tra il 28 ottobre e l'8 novembre 2016, corrispondente al periodo in cui è stata condotta una campagna di rilevazione dei flussi di traffico, attraverso radar Doppler su una strada di Modena a quattro corsie, al fine di riprodurre una modulazione temporale delle emissioni il più possibile realistica. Nella seconda parte dello studio lo stesso sistema di modellazione è stato utilizzato per produrre previsioni orarie delle concentrazioni di NO2 e NO, fino ad un giorno in avanti, per tutto il mese di febbraio 2019 sulla città di Modena. Le concentrazioni orarie simulate e osservate mostrano un andamento molto concorde fra loro, specialmente per il sito di traffico urbano, dove le stime dettagliate sulle emissioni del traffico si sono dimostrate molto efficaci nel riprodurre la tendenza osservata. Nella stazione urbana di fondo, nonostante una generale sottostima delle concentrazioni osservate, la combinazione di WRF-Chem con PMSS ha fornito comunque un andamento medio giornaliero in linea con le osservazioni. Infine, l'analisi statistica ha mostrato che il sistema di modellazione, in entrambi i siti urbani (di traffico e di fondo), soddisfa i criteri di accettazione standard per la valutazione dei modelli di dispersione urbana, confermando che tale sistema può essere impiegato come strumento per verificare gli effetti delle politiche locali riguardanti il traffico e a supporto di valutazioni di impatto sulla salute umana.

Sviluppo di un sistema ad alta risoluzione spaziale per la previsione della qualità dell'aria urbana tramite approccio modellistico multi-scala e sua applicazione alla città di Modena / Giorgio Veratti , 2020 Mar 10. 32. ciclo, Anno Accademico 2018/2019.

Sviluppo di un sistema ad alta risoluzione spaziale per la previsione della qualità dell'aria urbana tramite approccio modellistico multi-scala e sua applicazione alla città di Modena

VERATTI, GIORGIO
2020

Abstract

In Europe, emissions of many air pollutants have decreased substantially over the past decades, resulting in improved air quality across the region. However, air pollutant concentrations are still too high, and air quality problems persist. The Po Valley, located in the northern part of Italy, is one of the most critical area of the country in terms of pollution level. The reason to this problem is not only related to the high population density with its related activities, but it is also due to the orographic conformation of the territory which appears surrounded by mountains on three sides: the Alps to the west and to the north and the Apennines to the south. These geographical characteristics lead to meteorological conditions unfavorable to the atmospheric dispersion: average annual wind speed less than 2 m s-1, recurrent thermal inversions at low altitude, low mixing layer heights and persistent foggy and hazy events during winter time. One of the main critical air pollutants in terms of health effects is nitrogen dioxide (NO2), whose levels in the last years exceeded national and WHO (World Health Organization) standards in many urban areas across the Po Valley, exposing urban population to the risk of pollution-related diseases and health conditions. The main goal of this study was to develop a multi-scale modelling system able to provide hourly NOx (NO + NO2) concentration fields at a building-resolving scale in the urban area of Modena, a city in the middle of the Po Valley, in order to support environmental policies, epidemiological studies and urban mobility planning. The modelling system relied on two different models: the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), which is able to compute concentration fields over regional domain by considering specific emission scenarios, and the Parallel Micro SWIFT and SPRAY (PMSS) modelling suite accounting for dispersion phenomena within the urban area. The PMSS modelling suite was used to simulate at building-scale resolution the NOx dispersion produced by urban traffic flows in the city of Modena. Conversely, the WRF-Chem model was selected to estimate the NOx background concentrations on multiple domains with a nesting technique, in order to take into account emissions both at regional and local scale by excluding traffic emissions sources over the city of Modena. In the first part of the work the modelling system was performed for the period between 28 October and 8 November 2016, the same period whereby a direct vehicle flow measurement campaign was carried out continuously with 4 Doppler radar counters in a four-lane road in Modena, in order to reproduce emission hourly modulation rates. In second section of the study the modelling system was set-up with the aim of produce hourly forecast of NO2 and NO concentrations, up to one day ahead, for the city of Modena for the entire month of February 2019. Simulated and observed hourly concentrations exhibited a large agreement in particular for urban traffic site where detailed traffic emission estimations proved to be very successful in reproducing the observed 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. Finally, the statistical analysis showed that PMSS combined with WRF-Chem 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 human exposures and health impact assessments as well as the effects of local traffic policies on urban air quality.
The development of a building-resolved air quality forecast system by a multi-scale model approach and its application to Modena urban area
10-mar-2020
GHERMANDI, Grazia
BIGI, Alessandro
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11380/1200723
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