On the complexity of the boundary layer structure and aerosol vertical distribution in the coastal Mediterranean regions: A case study

The planetary boundary layer structure in the coastal areas, and particularly in complex orography regions such as the Mediterranean, is extremely intricate. In this study, we show the evolution of the planetary boundary layer based on in situ airborne measurements and ground-based remote sensing observations carried out during the MORE (Marine Ozone and Radiation Experiment) campaign in June 2010. The campaign was held in a rural coastal Mediterranean region in Southern Italy. The study focuses on the observations made on 17 June. Vertical profiles of meteorological parameters and aerosol size distribution were measured during two flights: in the morning and in the afternoon. Airborne observations were combined with ground-based LIDAR, SODAR, microwave and visible radiometer measurements, allowing a detailed description of the atmospheric vertical structure. The analysis was complemented with data from a regional atmospheric model run with horizontal resolutions of 12, 4 and 1 km, respectively; back-trajectories were calculated at these spatial resolutions. The observations show the simultaneous occurrence of dust transport, descent of mid-tropospheric air and sea breeze circulation on 17 June. Local pollution effects on the aerosol distribution, and a possible event of new particles formation were also observed. A large variability in the thermodynamical structure and aerosol distribution in the flight region, extending by approximately 30km along the coast, was found. Within this complex, environment-relevant differences in the back-trajectories calculated at different spatial resolutions are found, suggesting that the description of several dynamical processes, and in particular the sea breeze circulation, requires high-resolution meteorological analyses. The study also shows that the integration of different observational techniques is needed to describe these complex conditions; in particular, the availability of flights and their timing with respect to the occurring phenomena are crucial

Characterization of nitrogen dioxide variability using ground-based and satellite remote sensing and in situ measurements in the Tiber valley (Lazio, Italy)

The spatial-temporal distributions of nitrogen dioxide (NO2) in a rural area of Tiber valley were evaluated over one year (March 2022-February 2023) using remote sensing and in situ measurements. Surface concentration monitoring was conducted using a Pandora-2s spectrometer and a chemiluminescence analyzer operated at the Liberti Observatory (CNR-IIA). In spring, when the growing season and the agricultural activities increase, NO2 peaks were detectable by the Pandora but not by the in situ analyzer. The tropospheric Pandora and TROPOMI VCD products showed similar temporal patterns as those of the analyzer at the Observatory. High TROPOMI VCD levels in spring were detected at the Observatory and at six sites selected as representative of rural, residential, and industrial environments. WRF simulations found that high pollution events, observed by the Pandora and analyzer, occurred in calm wind conditions, favouring the accumulation of NO2 locally emitted. The complementary dataset provided by remote sensing and in situ techniques efficiently captured the spatial-temporal NO2 variability in a rural site exposed to low emission sources, thus supporting future decisional policies and actions

Spatial-temporal assessment of air quality in Rome (Italy) based on anemological clustering

The relationship between atmospheric circulation and air pollution is investigated by analysing in-situ measurements collected at four monitoring stations located in the coastal area of central Italy over the period 2014–2020. The study is based on the prior identification of three typical circulation patterns, obtained via the k-mean clustering of surface anemological data. The present analysis explores the relation between atmospheric dynamics and concentrations of nitrogen oxides (NO and NO2), NO2/NOx (NOx = NO + NO2), ozone (O3), and particulate matters (PM2.5 and PM10). When local circulation systems prevail, the best air quality conditions are observed, as the onset of the sea breeze permits clean, marine air masses to be advected to the urban area of Rome. On the other hand, when synoptic winds persistently blow from the northeast, the highest concentrations of atmospheric pollutants are recorded. Finally, when both synoptic and local winds blow from the southeast, the complex anemological regime results in low ventilation and quite poor air quality conditions. The largest differences among clusters are observed during winter, when the north-easterly winds can persist for more than ten consecutive days, with the enhanced atmospheric stability limiting the development of the mixed layer, causing the increase of ground-level pollutants concentration

An application of Wright functions to the photon propagation

In a previous note a generalized Beer's law was discussed in relation to the space-fractional Poisson process to explain possible deviations from the exponential extinction law in spatially correlated media. Here a different point of view will be developed, applying a Wright type function to describe the probability of photon transmission in random media. We find the analytic form of the photon mean-free-path (MFP) related to such Wright law of extinction. We also give an estimate of the deviation from an exponential law, showing the utility of our approach and discussing a comparison with the predictions given by the classical Beer's law in uniform media. (c) 2013 Elsevier Ltd. All rights reserved

Classification of synoptic and local-scale wind patterns using k-means clustering in a Tyrrhenian coastal area (Italy)

In coastal regions, the complex interaction of synoptic-scale dynamics and breeze regimes influence the local atmospheric circulation, permitting to distinguish typical yet alternative patterns. In this paper, the k-means clustering algorithm is applied to the hourly time series of wind intensity and direction collected by in-situ weather stations at seven locations within 30 km from the western coastline of central Italy, in the proximity of Rome, over the period 2014-2020. The selection of both wind-integral quantities and ad hoc objective parameters allows for the identification of three characteristic clusters, two of which are closely related to the synoptic circulation and governed by persistent winds, blowing from either the northeast or the southeast direction throughout the day. In the latter case, synoptic and mesoscale contributions add up, giving rise to a complex circulation at the ground level. On the contrary, the third cluster is closely related to the sea breeze regime. The results allow the identification of some general information about the low-level circulation, showing that the synoptic circulation dominates in winter and, partly, in spring and autumn, when high ventilation and low recirculation conditions occur. Conversely, during summer the sea breeze regime is more frequent and stronger, generating intense air recirculation. Our analysis permits to discern rigorously and objectively the typical coastal meteorological patterns, only requiring anemological in-situ data

Safety In Research Institutions: How to Better Communicate the Risks using Numerical Simulations

What are the risks for the personnel following a gas leak in a laboratory? How effective are the safety measures (gas detection) put in place? Are users aware of how fast they can be exposed? These questions have been approached with the intent to better communicate to the users the risks involved in their daily activities by showing how a gas is dispersed in their laboratory. In order to do so, a software tool performing Computation Fluid Dynamics (CFD) simulations of a pollutant gas dispersion in a room has been developed by the Chemical and Physical Safety Group (GSCP) at EPFL in collaboration with Optimad Engineering srl. The software and its physical model have been based on experimental data obtained by the GSCP used as a benchmark for the numerical simulation results. As side deliverables, these results are been used to place gas leak detectors in the most efficient location, thus optimizing the cost of safety measures. Furthermore, the simulation results have then been used to create videos showing the pollutant gas dispersion in the laboratory. A real case is presented in order to reveal the power of the used dual methodology: modelling as a mean of communication for an effective training/teaching of the personnel. The visual representation of the risks has a greater impact than any other means of communication availabl

Aerosol optical characteristics in the urban area of Rome, Italy, and their impact on the UV index

The aerosol optical characteristics in the urban area of Rome were retrieved over a period of 7 years from March to September 2010–2016. The impact of aerosol single scattering albedo (SSA), optical depth (AOD), estimated at 400 nm, and Ångström exponent on the ultraviolet (UV) index has been analyzed. Aerosol optical properties are provided by a PREDE-POM sun-sky radiometer of the ESR/SKYNET network and the UV index values were retrieved by a Brewer spectrophotometer both located in Rome. Chemical characterization of urban PM10 (particulate matter 10 micrometers or less in diameter) samples, collected during the URBan Sustainability Related to Observed and Monitored Aerosol (URBS ROMA) intensive filed campaign held in summer 2011 in the same site, was performed. PM macro-components were grouped in order to evaluate the contribution of the main macro-sources (SOIL, SEA, SECONDARY INORGANIC, ORGANICS and TRAFFIC) and the analysis of the modulation of their concentration was found to strongly affects the absorption capability of the atmosphere over Rome. The surface forcing efficiency, provided by the decreasing trend of UV index with AOD, which is the primary parameter affecting the surface irradiance, was found very significant, probably masking the dependence of UV index on SSA and Ångström exponents. Moreover it was found greater for larger particles and with a more pronounced slope at the smaller solar zenith angle. In Rome large particles are generally less absorbing since related to the presence of SOIL and SEA components in the atmosphere. The former contribution was found much higher in summer months because of the numerous episodes of Saharan dust transport

Impact of synoptic meteorological conditions on air quality in three different case studies in Rome, Italy

This study analyses the influence of synoptic weather conditions on atmospheric particulate matter concentration and composition during an intensive measurement campaign, performed in the urban area of Rome (Italy) in winter 2017. To evaluate the effect of local particulate sources, data from several urban and rural ground-based air quality stations were considered. The analysis involved the following atmospheric parameters: wind speed and direction near the ground, air temperature, specific humidity, height and evolution of the mixing layer. Furthermore, the daily variability of aerosol optical depth, tropospheric and near-surface nitrogen dioxide amounts were investigated. Results show that the natural removal of particulate matter is favoured by intense, continental winds. Contrariwise, when persistent thermal inversion occurs, pollutant dispersion is very limited and high concentrations are recorded by urban stations. Finally, in the case of Saharan dust outbreaks, an increase in the particulate content in both urban and rural stations is notable. Consequently, specific measurements aimed at improving air quality in urban environments should be planned according to synoptic weather and aerosol forecasts. This keeps valid in specific conditions of long-range transport of desert dust particles when the natural contribution could exceed that of pollutants from anthropogenic emissions

The Boundary Layer Air Quality-Analysis Using Network of Instruments (BAQUNIN) Supersite for Atmospheric Research and Satellite Validation over Rome Area

The Boundary-layer Air Quality-analysis Using Network of Instruments (BAQUNIN) supersite is presented. The site has been collecting pollutant concentrations and meteorological parameters since 2017. Currently, BAQUNIN consists of three observation sites located in the city center of Rome (Italy), and in the neighboring semi-rural and rural areas. To the best of our knowledge, BAQUNIN is one of the first observatories in the world to involve several passive and active ground-based instruments installed in multiple locations, managed by different research institutions, in a highly polluted megacity affected by coastal weather regimes. BAQUNIN has been promoted by the European Space Agency to establish an experimental research infrastructure for the validation of present and future satellite atmospheric products and the in-depth investigation of the planetary and urban boundary layers. Here, the main characteristics of the three sites are described, providing information about the complex instrumental suite and the produced data. The supersite adopts a policy of free sharing of its validated dataset with the community. Finally, the BAQUNIN potential is demonstrated with a case study involving a major fire that occurred in a waste treatment plant near the urban center of Rome, and the consequent investigation of the plume properties revealed by different instruments