Aerosol Optical Depth of the Main Aerosol Species over Italian Cities Based on the NASA/MERRA-2 Model Reanalysis

The Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) provides data at 0.5° × 0.625° resolution covering a period from 1 January 1980 to the present. Natural and anthropogenic aerosols are simulated in MERRA-2, considering the Goddard chemistry, aerosol, radiation, and transport model. This model simulates the sources, sinks, and chemistry of mixed aerosol tracers: dust, sea salt, hydrophobic and hydrophilic black carbon and organic carbon, and sulfate. MERRA-2 aerosol reanalysis is a pioneering tool for investigating air quality issues, noteworthy for its global coverage and its distinction of aerosol speciation expressed in the form of aerosol optical depth (AOD). The aim of this work was to use the MERRA-2 reanalysis to study urban air pollution at a national scale by analyzing the AOD. AOD trends were evaluated for a 30-year period (1987–2017) over five Italian cities (Milan, Rome, Cagliari, Taranto, and Palermo) in order to investigate the impacts of urbanization, industrialization, air quality regulations, and regional transport on urban aerosol load. AOD evolution predicted by the MERRA-2 model in the period 2002–2017 showed a generalized decreasing trend over the selected cities. The anthropogenic signature on total AOD was between 50% and 80%, with the largest contribution deriving from sulfate

WRF Sensitivity Analysis in Wind and Temperature Fields Simulation for the Northern Sahara and the Mediterranean Basin

Different configurations for the Weather Research and Forecasting (WRF) model were evaluated to improve wind and temperature fields predictions in the Northern Sahara and the Mediterranean basin. Eight setups, associated with different combinations of the surface layer physical parameters, the land surface model, and the grid nudging parameters, were considered. Numerical simulations covered the entire month of November 2017. Model results were compared with surface data from meteorological stations. The introduction of the grid nudging parameters leads to a general improvement of the modeled 10 m wind speed and 2 m temperature. In particular, nudging of wind speed parameter inside the planetary boundary layer (PBL) provides the most remarkable differences. In contrast, the nudging of temperature and relative humidity parameters inside the PBL may be switched off to reduce computational time and data storage. Furthermore, it was shown that the prediction of the 10 m wind speed and 2 m temperature is quite sensitive to the choice of the surface layer scheme and the land surface model. This paper provides useful suggestions to improve the setup of the WRF model in the Northern Sahara and the Mediterranean basin. These results are also relevant for topics related with the emission of mineral dust and sea spray within the Mediterranean region

Air Pollution from Natural and Anthropogenic Sources over Mediterranean Region: Assessment of an Online Coupled Meteorological and Air Quality Model

Nel presente elaborato viene proposto uno studio per comprendere e quantificare in modo migliore ed approfondito delle fonti di inquinamento atmosferico in Italia e nella regione mediterranea circostante. Sospette fonti di inquinanti includono attività umane, idrocarburi naturali da foreste (isoprene e terpeni) ed episodi di polvere minerale trasportata dal vento prevalentemente dal deserto del Sahara. Una profonda comprensione di queste fonti è fondamentale per lo sviluppo di azioni mirate a mitigare l’inquinamento atmosferico. Lo studio considera principalmente gli idrocarburi e la polvere naturali, utilizzando un modello di trasporto chimico all'avanguardia (“Weather Research and Forecasting with Chemistry”). Il modello ambientale WRF-Chem è un sistema di previsione a scala regionale "online" (meteorologia e chimica dell’atmosfera sono computati in maniera parallela e non in serie) progettato per simulare una vasta gamma di processi chimici, meteorologici, gas e aerosol dettagliati con un completo accoppiamento tra le diverse componenti e fasi. Il presente studio documenta due diverse applicazioni realizzate attraverso il modello WRF-Chem al fine di migliorare la sua rappresentazione dei processi chimici di gas e aerosol. La prima applicazione include la descrizione, l'esame e il test di una serie di aggiornamenti apportati al modello MEGAN versione 2.04 (“Model of Emission Gas and Aerosols from Nature”), modello per le emissioni biogeniche implementato in WRF-Chem, attraverso due diversi casi studio (ovvero il primo a livello europeo e il nella zona sud-est degli Stati Uniti). La seconda applicazione prevede l’applicazione del modello (WRF-Chem) per la valutazione delle intrusioni di polvere di sahariane nell'Europa meridionale e il loro confronto con le emissioni antropogeniche nell'arco di un intero anno (2017). Lo studio di sensibilità del modello di emissioni biogeniche (MEGAN), a livello europeo, include quattro simulazioni. La prima è (1) quella di controllo: il database MEGAN è stato utilizzato senza alcuna modifica (Megan_V2.04); nella seconda (2) tutti i fattori di attività (γi) sono stati modificati seguendo gli aggiornamenti apportanti all’ultima versione del MEGAN (versione 2.10) (Megan_Gamma). La (3) terza simulazione aggiunge i PFT (Plant Functional Type – classificazione in base al tipo di vegetazione), i fattori di emissione variano al variare del tipo di pianta (Megan_GammaPFT); infine, l'ultima (4) calcola il fattore di emissione di isoprene all'interno dell'algoritmo di emissione MEGAN, invece di ricavarlo direttamente dal database di input come per tutte le altre simulazioni (Megan_GammaPFTISO). I risultati delle emissioni di isoprene e α-pinene dimostrano che l'aggiornamento del codice MEGAN aumenta notevolmente le emissioni (ad esempio, nella città di Zagabria si ha un aumento di circa 100 mol/km2hr e a Kiev di circa 50 mol/km2h). Il confronto con l’inventario AIRBASE (rete europea per la qualità dell'aria e l'ambiente) ha mostrato che la distribuzione temporale e spaziale dell'ozono (O3) è ben rappresentata; la simulazione di controllo ha dimostrato i risultati migliori, dal momento che le simulazioni, considerando gli aggiornamenti effettuati al modello MEGAN, aumentano la concentrazione di ozono di circa 20-40 ppb. Gli altri gas considerati (NO2 e CO) sono risultati molto sottostimati, rispettivamente di un fattore 2 e 10, indipendentemente dalla simulazione considerata, poiché gli aggiornamenti apportate al modello MEGAN non influenzano tali composti. D'altra parte, il caso studio statunitense include due simulazioni: quella di controllo (Megan_V2.04) e una simulazione considerando tutti gli aggiornamenti apportati al modello di emisione MEGAN (Megan_GammaPFTISO). Le simulazioni sono state effettuate in concomitanza con la campagna sperimentale NOMADSS (“Nitrogen, Oxidants, Mercury and Aerosol Distributions, Sources and Sinks”) (effettuata dal 1° giugno 00:00 UTC al 15 giugno 00:00 UTC, 2013) in modo da approvare gli aggiornamenti effettuati con tale set di dati. I valori modellati di O3 confermano il caso studio europeo, aggiornando le emissioni biogeniche, le concentrazioni di ozono aumentato del 10%; le concentrazioni di NOx sono sovrastimate, come il caso europeo, ma con migliori risultati. Infine, anche le concentrazioni di isoprene sovrastimano considerevolmente i dati sperimentali fino a un fattore 5 (la discrepanza media è di circa 7000 ppt). La seconda applicazione di WRF-Chem prevede due simulazioni con durata annuale (dal 1° gennaio 2017 00:00 UTC al 1° gennaio 2018 00:00 UTC): la prima considera solo l'emissione di polvere minerale (chem_opt = 401 - "DUSTONLY”), mentre la seconda considera tutti i tipi di emissioni (biogeniche, incendi e antropogeniche) (chem_opt = 201 - "MOZMOSAIC"); entrambe le simulazioni per le polveri desertiche utilizzano lo schema di emissione GOCART (Goddard Chemistry Aerosol Radiation and Transport). Le rianalisi NCEP/NCAR e la rete di stazioni superficiali archiviate dell'Università del Wyoming sono state utilizzate per valutare la risoluzione spaziale della temperatura, dell'umidità relativa e della velocità e direzione del vento, dimostrando una grande capacità del modello WRF-Chem di riprodurre i dati sperimentali. L'associazione tra la densità di massa della colonna di polvere modellata [kg/m2] e il campo con la relativa rianalisi MERRA-2 (“Modern-Era Retrospective Analysis for Research and Applications”) ha mostrato una evidente sovrastima del modello per il carico di polvere minerale nelle regioni maggiori del Nord Africa (sovrastima di un fattore di 10 - MERRA-2 = 2x10-4 kg/m2; WRF-Chem = 2x10-3 kg/m2). La sovrastima del modello è confermata dal confronto di entrambe le simulazioni con i prodotti di AOD (Aerosol Optical Depth - 550 nm) della rete di rilevazione AERONET (Aerosol Robotic NETwork): le stazioni di Roma e Napoli analizzate riportano pressoché lo stesso andamento di AOD durante il periodo analizzato, anche i valori massimi di AOD vengono catturati, ma la massa di polveri minerali è sovrastimata da entrambe le simulazioni (nel mese di maggio - AODDUSTONLY = 0.9; AODMOZMOSAIC = 1.2; AODAERONET = 0.3).A study to better understand and quantify the source of air pollution in Italy and the surrounding Mediterranean region is proposed. Suspected sources of pollutants include human activities, natural hydrocarbons from forests (isoprene and terpenes) and episodes of wind-blown mineral dust from the Sahara Desert. A deep understanding of these sources is fundamental to developing science-based mitigation actions. The study addresses specifically the natural hydrocarbons and dust, using a state-of-the-art chemistry transport model (Weather Research and Forecasting with Chemistry). The WRF-Chem system is an “online” regional scale prediction model designed to simulate many detailed meteorological, gas and aerosol chemical processes, with full coupling between the different components and phases. This study documents two different applications, and their evaluation, that have been made using WRF-Chem model in order to improve its representation of gas and aerosol chemical processes. The first application includes the description, examination and test of a set of updates made to the MEGAN version 2.04 (Model of Emission Gas and Aerosols from Nature) model, one of the BVOC (biogenic volatile organic compound) emission model includes in WRF-Chem, by two different test cases (i.e. the first at European level, and the second, at United States level). The main objective of the second WRF- Chem application, involves the assessment of Sharan dust outbreaks to the southern Europe and how they compare to anthropogenic emissions over a whole year (2017). The MEGAN sensitivity study, at European level, includes four simulations. The first one is (1) the control one: the MEGAN database has been used without any change (Megan_V2.04); on the (2) second one all the activity factors (γi) have been modified following the MEGAN version 2.10 (Megan_Gamma). The (3) third simulation adds the PFTs (Plant Functional Type) emission factors changes to the activity factors (Megan_GammaPFT); finally, the (4) last one calculates more the isoprene emission factor within the MEGAN emission algorithm, instead of reading it directly from the input database (Megan_GammaPFTISO). The simulations listed above, are applied to simulate an intense ozone event that took place over central Italy in August 13th, 2015. Results for isoprene and α-pinene emissions demonstrate the updating the MEGAN code the emissions increase considerably (i.e. Zagreb has an increase about 100 mol/km2hr and Kiev about 50 mol/km2 hr). The comparison with the AIRBASE (European Environment Agency air quality network) showed that only the temporal and spatial distribution of the O3 are well represented; the control simulation demonstrated the ozone better results, since the updates simulations increase the ozone concentration of nearly from 20 to 40 ppb. The other trace gases considered (NO2 and CO) model results are very underestimate, respectively by a factor of 2 and 10 regardless of simulations considered, since the MEGAN updates does not affect that compounds. On the other hands, the U.S. MEGAN sensitivity case of study, includes two simulations: the control one (Megan_V2.04) and a simulation with all code changes applied (Megan_GammaPFTISO). They are concurrently with the NOMADSS (Nitrogen, Oxidants, Mercury and Aerosol Distributions, Sources and Sinks) field campaign (from June 1th 00:00 UTC to June 15th 00:00 UTC, 2013), in order to validate the updates with that dataset. Isoprene concentrations overestimate the NOMADSS considerably up to a factor of 5 (average discrepancy is about 7000 ppt). The O3 modeled values confirm the European case of study, updating MEGAN ozone concentrations increase by 10 %; the NOx concentrations are overestimate, as European case, but with better agreement. The MEGAN updates do not take effects on the NOx concentrations. Last WRF-Chem application has one-year time duration (from January 1st 2017 00:00 UTC to January 1st 2018 00:00 UTC) where two simulations are carried out: the first considering only the dust emission (chem_opt = 401 – “DUSTONLY” simulation) and the second one considering all the type of emissions (biogenic, biomass burning and anthropogenic) (chem_opt = 201 – “MOZMOSAIC” simulation); both of simulations use the GOCART (Goddard Chemistry Aerosol Radiation and Transport) dust emission scheme. The NCEP/NCAR reanalysis and the University of Wyoming surface stations network have been used to assess the spatial resolution of simulated temperature, relative humidity and wind speed and direction, showing a great capability of WRF- Chem model to reproduce the experimental data and its spatial trend. The association between the modeled dust column mass density [kg/m2] and the field with the corresponding MERRA-2 (Modern-Era Retrospective Analysis for Research and Applications) reanalysis showed an evident dust load overestimated over the North-Africa regions (i.e. by a factor of 10 - MERRA-2 = 2x10- 4 kg/m2; WRF-Chem = 2x10-3 kg/m2). The dust modeled overestimate is confirmed by the comparison of both simulations with the AERONET AOD (550 nm) products; i.e. Rome and Naples stations have nearly the same year trend, AOD peaks are captured as well, but the dust magnitude is overestimated from both simulations (e.g. May – AODDUSTONLY = 0.9; AODMOZMOSAIC = 1.2; AODAERONET = 0.3)

Exposure Assessment of Ambient PM2.5 Levels during a Sequence of Dust Episodes: A Case Study Coupling the WRF-Chem Model with GIS-Based Postprocessing

A sequence of dust intrusions occurred from the Sahara Desert to the central Mediterranean in the second half of June 2021. This event was simulated by means of the Weather Research and Forecasting coupled with chemistry (WRF-Chem) regional chemical transport model (CTM). The population exposure to the dust surface PM2.5 was evaluated with the open-source quantum geographical information system (QGIS) by combining the output of the CTM with the resident population map of Italy. WRF-Chem analyses were compared with spaceborne aerosol observations derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) and, for the PM2.5 surface dust concentration, with the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) reanalysis. Considering the full-period (17–24 June) and area-averaged statistics, the WRF-Chem simulations showed a general underestimation for both the aerosol optical depth (AOD) and the PM2.5 surface dust concentration. The comparison of exposure classes calculated for Italy and its macro-regions showed that the dust sequence exposure varies with the location and entity of the resident population amount. The lowest exposure class (up to 5 µg m−3) had the highest percentage (38%) of the population of Italy and most of the population of north Italy, whereas more than a half of the population of central, south and insular Italy had been exposed to dust PM2.5 in the range of 15–25 µg m−3. The coupling of the WRF-Chem model with QGIS is a promising tool for the management of risks posed by extreme pollution and/or severe meteorological events. Specifically, the present methodology can also be applied for operational dust forecasting purposes, to deliver safety alarm messages to areas with the most exposed population

Analysis of the ETNA 2015 Eruption Using WRF–Chem Model and Satellite Observations

The aim of the present work is to utilize a new functionality within the Weather Research and Forecasting model coupled with Chemistry (WRF–Chem) that allows simulating emission, transport, and settling of pollutants released during the Etna 2015 volcanic activities. This study constitutes the first systematic application of the WRF–Chem online-based approach to a specific Etna volcanic eruption, with possible effects involving the whole Mediterranean area. In this context, the attention has been focused on the eruption event, recorded from 3–7 December 2015, which led to the closure of the nearby Catania International Airport. Quantitative meteorological forecasts, analyses of Etna volcanic ash transport, and estimates of the ash ground deposition have been performed. In order to test the performance of the proposed approach, the model outputs have been compared with data provided by satellite sensors and Doppler radars. As a result, it emerges that, as far as the selected eruption event is concerned, the WRF–Chem model reasonably reproduces the distribution of SO2 and of volcanic ash. In addition, this modeling system may provide valuable support both to airport management and to local stakeholders including public administrations

Effects of Variable Eruption Source Parameters on Volcanic Plume Transport: Example of the 23 November 2013 Paroxysm of Etna

International audienceThe purpose of the present paper is to investigate the effects of variable eruption source parameters on volcanic plume transport in the Mediterranean basin after the paroxysm of Mount Etna on 23 November 2013. This paroxysm was characterized by a north-east transport of ash and gas, caused by a low-pressure system in northern Italy. It is evaluated here in a joint approach considering the WRF-Chem model configured with eruption source parameters (ESPs) obtained elaborating the raw data from the VOLDORAD-2B (V2B) Doppler radar system. This allows theinclusion of the transient and fluctuating nature of the volcanic emissions to accurately model the atmospheric dispersion of ash and gas. Two model configurations were considered: the first with the climax values for the ESP and the second with the time-varying ESP according to the time profiles of the mass eruption rate recorded by the V2B radar. It is demonstrated that the second configuration produces a considerably better comparison with satellite retrievals from different sensors platforms (Ozone Mapping and Profiler Suite, Meteosat Second-Generation Spinning Enhanced Visible and Infrared Imager, and Visible Infrared Imaging Radiometer Suite). In the context of volcanic ash transport dispersion modeling, our results indicate the need for (i) the use of time-varying ESP, and (ii) a joint approach between an online coupled chemical transport model like WRF-Chem and direct near-source measurements, such as those carried out by the V2B Doppler radar system