Bird-Borne Samplers for Monitoring CO2 and Atmospheric Physical Parameters

Air quality monitoring in cities is significant for both human health and environment. Here, an innovative miniaturized active air sampler wearable by free-flying birds is presented. The device integrates a GPS logger and atmospheric calibrated sensors allowing for high spatiotemporal resolution measurements of carbon dioxide (CO2) concentration, barometric pressure, air temperature, and relative humidity. A field campaign, carried out from January to June 2021, involved the repeated release of homing pigeons (Columba livia) from downtown Rome (Italy), to sample the air on their way back to the loft, located in a rural area out of the city. The measurements suggest the importance of green urban areas in decreasing CO2 levels. Moreover, a positive relation between CO2 levels, relative humidity, and air temperature was revealed. In contrast, a negative relation with distance from the point of release, month, and time of day was found. Flight speed and the altitude of flight were related to rising CO2 levels. The easy use of such devices paves the way for the application of miniaturized air samplers to other synanthropic species (i.e., gulls), making birds convenient biomonitors for the urban environment. © 2022 by the authors

Water-channel study of flow and turbulence past a two-dimensional array of obstacles

A neutral boundary layer was generated in the laboratory to analyze the mean velocity field and the turbulence field within and above an array of two-dimensional obstacles simulating an urban canopy. Different geometrical configurations were considered in order to investigate the main characteristics of the flow as a function of the aspect ratio (AR) of the canopy. To this end, a summary of the two-dimensional fields of the fundamental turbulence parameters is given for AR ranging from 1 to 2. The results show that the flow field depends strongly on AR only within the canyon, while the outer flow seems to be less sensitive to this parameter. This is not true for the vertical momentum flux, which is one of the parameters most affected by AR, both within and outside the canyon. The experiments also indicate that, when (i.e. the skimming flow regime), the roughness sub-layer extends up to a height equal to 1.25 times the height of the obstacles (H), surmounted by an inertial sub-layer that extends up to 2.7 H. In contrast, for (i.e. the wake-interference regime) the inertial sub-layer is not present. This has significant implications when using similarity laws for deriving wind and turbulence profiles in canopy flows. Furthermore, two estimations of the viscous dissipation rate of turbulent kinetic energy of the flow are given. The first one is based on the fluctuating strain rate tensor, while the second is related to the mean strain rate tensor. It is shown that the two expressions give similar results, but the former is more complicated, suggesting that the latter might be used in numerical models with a certain degree of reliability. Finally, the data presented can also be used as a dataset for the validation of numerical models

A street graph-based morphometric characterization of two large urban areas

Urban microclimate modelling, both numerical and in the laboratory, has strong implications in many relevant health and life-style management issues e.g., in studies for assessment and forecast of air quality (for both outdoor and, as boundary conditions, indoor investigations), for thermometric trend analysis in urban zones, in cultural heritage preservation, etc. Moreover, the study of urban microclimate modelling is largely promoted and encouraged by international institutions for its implication in human health protection. In the present work, we propose and discuss an adaptive street graph-based method aimed at automatically computing the geometrical parameters adopted in atmospheric turbulent flow modelling. This method has been applied to two real cases, the Italian cities of Rome and Cagliari, and its results has been compared with the ones from traditional methods based on regular grids. Results show that the proposed method leads to a more accurate determination of the urban canyon parameters (Canyon Aspect Ratio and Building Aspect Ratio) and morphometric parameters (Planar Area Index and Frontal Area Index) compared to traditional regular grid-based methods, at least for the tested cases. Further investigations on a larger number of different urban contexts are planned to thoroughly test and validate the proposed algorithm

CFD Analysis of Urban Canopy Flows Employing the V2F Model: Impact of Different Aspect Ratios and Relative Heights

Computational fluid dynamics (CFD) is currently used in the environmental field to simulate flow and dispersion of pollutants around buildings. However, the closure assumptions of the turbulence usually employed in CFD codes are not always physically based and adequate for all the flow regimes relating to practical applications. The starting point of this work is the performance assessment of the V2F (i.e., v2¯ − f) model implemented in Ansys Fluent for simulating the flow field in an idealized array of two-dimensional canyons. The V2F model has been used in the past to predict low-speed and wall-bounded flows, but it has never been used to simulate airflows in urban street canyons. The numerical results are validated against experimental data collected in the water channel and compared with other turbulence models incorporated in Ansys Fluent (i.e., variations of both k-ε and k-ω models and the Reynolds stress model). The results show that the V2F model provides the best prediction of the flow field for two flow regimes commonly found in urban canopies. The V2F model is also employed to quantify the air-exchange rate (ACH) for a series of two-dimensional building arrangements, such as step-up and step-down configurations, having different aspect ratios and relative heights of the buildings. The results show a clear dependence of the ACH on the latter two parameters and highlight the role played by the turbulence in the exchange of air mass, particularly important for the step-down configurations, when the ventilation associated with the mean flow is generally poor

Effect of heatwaves on urban sea breeze, heat island intensity, and outdoor thermo-hygrometric comfort in Rome (Italy)

The purpose of this study is to investigate the impact of heatwaves on sea breeze, urban heat island intensity, and outdoor thermo-hygrometric comfort analysing ground-based remote sensing and in-situ meteorological measurements collected in a Mediterranean coastal metropolitan area (Rome, Italy) during the summer of 2022. The dataset (01 May - 31 August 2022) has been divided into heatwaves and not-heatwaves days to highlight the distinctive features of extreme heat episodes. Furthermore, the year 2022 was compared to 2020, the latter having been characterised by temperatures in line with the last two-decades.The heatwaves do not significantly affect the onset time and the duration of sea breeze, while its cooling effect intensifies during the heatwaves. The urban heat island intensity (UHII) is evaluated by computing the hourly-averaged air temperature difference between two stations, one in the urban centre and the other in rural surroundings. Although the daily-averaged UHII does not show significant differences among the years under investigation and the subsets, marked differences can be identified in the urban heat island daily cycle. In fact, during daytime the highest temperatures are detected in rural inland areas while, at night, the city experiences higher temperatures, especially during the heatwaves. Finally, the Mediterranean outdoor comfort index suggests that a heatwave seems to be a not sufficient condition for human thermohygrometric stress, even if stronger discomfort is experienced during heatwaves

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

On the Radiative Impact of Biomass-Burning Aerosols in the Arctic: The August 2017 Case Study

Boreal fires have increased during the last years and are projected to become more intense and frequent as a consequence of climate change. Wildfires produce a wide range of effects on the Arctic climate and ecosystem, and understanding these effects is crucial for predicting the future evolution of the Arctic region. This study focuses on the impact of the long-range transport of biomass-burning aerosol into the atmosphere and the corresponding radiative perturbation in the shortwave frequency range. As a case study, we investigate an intense biomass-burning (BB) event which took place in summer 2017 in Canada and subsequent northeastward transport of gases and particles in the plume leading to exceptionally high values (0.86) of Aerosol Optical Depth (AOD) at 500 nm measured in northwestern Greenland on 21 August 2017. This work characterizes the BB plume measured at the Thule High Arctic Atmospheric Observatory (THAAO; 76.53° N, °68.74° W) in August 2017 by assessing the associated shortwave aerosol direct radiative impact over the THAAO and extending this evaluation over the broader region (60° N-80° N, 110° W-0° E). The radiative transfer simulations with MODTRAN6.0 estimated an aerosol heating rate of up to 0.5 K/day in the upper aerosol layer (8-12 km). The direct aerosol radiative effect (ARE) vertical profile shows a maximum negative value of -45.4 Wm-2 for a 78° solar zenith angle above THAAO at 3 km altitude. A cumulative surface ARE of -127.5 TW is estimated to have occurred on 21 August 2017 over a portion (3.1 10^6 km2) of the considered domain (60° N-80° N, 110° W-0° E). ARE regional mean daily values over the same portion of the domain vary between -65 and -25 Wm-2. Although this is a limited temporal event, this effect can have significant influence on the Arctic radiative budget, especially in the anticipated scenario of increasing wildfires

Evaluation of on-site calibration procedures for SKYNET Prede POM sun–sky photometers

To retrieve columnar intensive aerosol properties from sun–sky photometers, both irradiance and radiance calibration factors are needed. For the irradiance the solar calibration constant, V0, which denotes the instrument counts for a direct normal solar flux extrapolated to the top of the atmosphere, must be determined. The solid view angle, SVA, is a measure of the field of view of the instrument, and it is important for obtaining the radiance from sky diffuse irradiance measurements. Each of the three sun-photometer networks considered in the present study (SKYNET, AERONET, WMO GAW) adopts different protocols of calibration, and we evaluate the performance of the on-site calibration procedures, applicable to every kind of sun–sky photometer but tested in this analysis only on SKYNET Prede POM01 instruments, during intercomparison campaigns and laboratory calibrations held in the framework of the Metrology for Aerosol Optical Properties (MAPP) European Metrology Programme for Innovation and Research (EMPIR) project

Bird-Borne Samplers for Monitoring CO₂ and Atmospheric Physical Parameters

Air quality monitoring in cities is significant for both human health and environment. Here, an innovative miniaturized active air sampler wearable by free-flying birds is presented. The device integrates a GPS logger and atmospheric calibrated sensors allowing for high spatiotemporal resolution measurements of carbon dioxide (CO2) concentration, barometric pressure, air temperature, and relative humidity. A field campaign, carried out from January to June 2021, involved the repeated release of homing pigeons (Columba livia) from downtown Rome (Italy), to sample the air on their way back to the loft, located in a rural area out of the city. The measurements suggest the importance of green urban areas in decreasing CO2 levels. Moreover, a positive relation between CO2 levels, relative humidity, and air temperature was revealed. In contrast, a negative relation with distance from the point of release, month, and time of day was found. Flight speed and the altitude of flight were related to rising CO2 levels. The easy use of such devices paves the way for the application of miniaturized air samplers to other synanthropic species (i.e., gulls), making birds convenient biomonitors for the urban environment

Bird-Borne Samplers for Monitoring CO2 and Atmospheric Physical Parameters

Air quality monitoring in cities is significant for both human health and environment. Here, an innovative miniaturized active air sampler wearable by free-flying birds is presented. The device integrates a GPS logger and atmospheric calibrated sensors allowing for high spatiotemporal resolution measurements of carbon dioxide (CO2) concentration, barometric pressure, air temperature, and relative humidity. A field campaign, carried out from January to June 2021, involved the repeated release of homing pigeons (Columba livia) from downtown Rome (Italy), to sample the air on their way back to the loft, located in a rural area out of the city. The measurements suggest the importance of green urban areas in decreasing CO2 levels. Moreover, a positive relation between CO2 levels, relative humidity, and air temperature was revealed. In contrast, a negative relation with distance from the point of release, month, and time of day was found. Flight speed and the altitude of flight were related to rising CO2 levels. The easy use of such devices paves the way for the application of miniaturized air samplers to other synanthropic species (i.e., gulls), making birds convenient biomonitors for the urban environment