This study presents the analysis of a 13-year time series of continuous measurements of propane (C3H8) from the WMO-GAW station of Monte Cimone (CMN, Italy) between 2011 and 2023. Background trend and pollution events are evaluated to establish how this remote site is influenced by regional and/or global emissions. Over the study period, C3H8 background mixing ratios exhibited a significant decrease of -3.8 [-5; -2.3; 95 % confidence interval] ppt yr-1. C3H8 seasonal amplitude showed a significant decrease of -6.2 [-7.4; -5.1] ppt yr-1 in the study period, driven by a reduction in winter emissions. Based on back-trajectory sensitivity analysis, CMN and Jungfraujoch (JFJ, Switzerland) were found to be predominantly influenced by air masses originating from the central European continent and the western Mediterranean basin. Using the 2022 observations of CMN and JFJ stations, and the Flexpart-Flexinvert inverse modeling framework, we estimated the distribution of regional emissions and compared it with the EDGAR bottom-up emission inventory. In particular, for Italy and France, prior emissions of C3H8 were underestimated approximately by a factor of 2, likely due to overlooked C3H8 emissions sources and/or inaccurate activity data used to compile the bottom-up inventory.

Approximately 57% of the global population lives in urban areas, and this proportion is expected to increase in the coming decades. Consequently, cities are where a large and growing share of the population experiences the impacts of climate change. Urban environments can also intensify local warming because of their morphology and physical characteristics, including building density, anthropogenic heat emissions, impervious surfaces, and the thermal inertia of urban materials. Urban green spaces, such as parks, can partly offset these effects through shading, improving human thermal comfort. However, the thermal effect of urban parks is commonly assessed using satellite-derived surface temperature, which provides only instantaneous observations and does not capture its temporal evolution.In this study, we propose an alternative method to evaluate the thermal effect of urban parks using large-eddy simulations (LES) with the PALM model system. The analysis focuses on Villa Ada, a 160 ha urban park in Rome, during a heatwave event in October 2023. Two nested simulation domains, with isotropic grid resolutions of 20 m and 10 m, are forced by boundary conditions from the MOLOCH mesoscale model. The simulations are used to investigate the diurnal variability of surface temperature and 2 m air temperature. The park thermal effect is quantified using a buffer-based approach with concentric rings extending up to 600 m from the park boundary, enabling the analysis of horizontal temperature gradients and their temporal evolution throughout the day. The framework also enables comparison among three land-cover scenarios: the current park configuration (baseline), a fully tree-covered configuration, and a short-grass configuration.Results reveal a marked diurnal cycle in the park thermal effect, with lower magnitudes in the morning, a distinct maximum in the early afternoon, and a gradual decrease toward the evening. The dense-tree scenario shows the strongest cooling effect, with values reaching up to 8.5 K for surface temperature and 6.1 K for 2 m air temperature, whereas the baseline scenario also produces cooling, though of slightly lower intensity. By contrast, the short-grass scenario leads to higher surface temperatures across all buffers, indicating a warming effect.The spatial extent of the cooling signal remains relatively stable in the baseline and dense-tree scenarios, with values typically between 330 m and 380 m. In contrast, the short-grass scenario does not show a comparable cooling signal. The results also reveal a bimodal distribution of surface temperature in the park surroundings, reflecting the contrast between vegetated and built surfaces. These findings highlight that the park cooling effect is a dynamic process, strongly controlled by diurnal evolution and surface heterogeneity, and cannot be fully assessed by instantaneous satellite observations.

HFC-134a is the most prevalent hydrofluorocarbon used as a replacement for ozone-depleting CFCs and HCFCs. Due to its high global warming potential, it is regulated under various European and global frameworks, underscoring the importance of tracking its emissions. Emissions derived by the commonly used, bottom-up, methodology are affected by a certain degree of uncertainty. The bottom-up estimates can be aided with an independent top-down estimate based on atmospheric observations combined with an atmospheric transport model. This study presents HFC-134a emissions for Europe, with a specific focus on Italy, from 2008 to 2023. The emissions were estimated using a Bayesian inversion methodology, based on atmospheric observations collected at four European stations. Our analysis reveals a slightly increasing trend in HFC-134a emissions for Italy from 2008 to 2015 of 0.17 Gg yr^-1 , followed by a steady decrease thereafter, highlighting the effect of European regulation on fluorinated gases that came into force in 2014. We observed a reduction in HFC-134a emissions in the Po Basin inferred from the inversion method for 2020, likely due to mobility restrictions imposed during the COVID-19 pandemic. The observed mild seasonality in emissions may be partly attributed to higher air-conditioning activity during summer. Comparison with the Italian National Emission Inventory indicates an improvement in iterative bottom-up estimates, with the 2024 inventory emission trend post-2015 aligning closely with our inversion results. This study emphasises the need for collaboration between the two independent approaches to enhance the accuracy of emission estimates. Such cooperation is crucial to narrowing the gap in quantifying emissions of potent greenhouse gases and effectively assessing the progress of international policies and regulations.

Urban heat islands intensify heat stress and degrade air quality in densely built areas, yet the physical processes governing near-surface thermal variability remain poorly quantified. This study applies the coupled MOLOCH and PALM model system 6.0 (PALM-4U) over Bologna (Italy) during a summer 2023 heatwave to resolve meter-scale atmospheric dynamics within the Urban Canopy Layer and Roughness Sublayer at 2 m horizontal resolution. The coupled configuration was validated against in situ meteorological observations and Landsat-8 LST data, showing improved agreement in air temperature and wind speed compared to standalone mesoscale simulations. Results reveal pronounced diurnal and vertical variability of wind speed, turbulent kinetic energy, and friction velocity, with maxima between two/three times the median building height (hc). Distinct surface-dependent contrasts emerge: asphalt and roofs act as strong daytime heat sources (Bowen ratio beta asphalt approximate to 4.8) and nocturnal heat reservoirs at pedestrian level (z approximate to 0.07 hc), while vegetation sustains daytime latent heat fluxes (beta vegetation approximate to 0.6 divided by 0.8) and cooler surface and near-surface air (Temperature anomaly of surface Delta Ts approximate to -9 degrees C and air Delta Tair approximate to -0.3 degrees C). Thermal anomalies decay with height, vanishing above z approximate to 2.5 hc due to turbulent mixing. These findings provide insight into fine-scale energy exchanges driving intra-urban thermal heterogeneity and support climate-resilient urban design.

Hydrofluorocarbons (HFCs) are a class of greenhouse gases (GHGs) primarily used as substitutes for ozone-depleting substances like chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), phased out under the Montreal Protocol. However, HFCs significantly impact global warming due to their high global warming potential. In light of the pressing need to tackle climate change and mitigate the effects of GHG emissions, the United Nations Framework Convention on Climate Change (UNFCCC) has established rigorous commitments on emission reduction. As a commitment to the UNFCCC, Annex-I countries need to report their national emission estimates for regulated GHGs, including HFCs, based on the methodologies reported in the IPCC guidelines (Intergovernmental Panel on Climate Change). According to the guidelines, the comparison of estimates with top-down (models based on atmospheric measurements) is indicated as an effective tool for verifying the accuracy of inventories and there is a growing need for independent verification of these estimates. This study reports the most recent update on emissions of 1,1,1,2-Tetrafluoroethane (CH2FCF3) from 2008 to 2023, employing inverse modelling within the European domain, with a specific focus on Italy. CH2FCF3, commercially known as HFC-134a, stands as the most prevalent HFC on a global scale. Its thermodynamic properties, akin to those of dichlorodifluoromethane (CFC-12), render it an effective refrigerant for the RAC (refrigeration and air conditioning) sector. This study reveals a notable decline in HFC-134a emissions over the past decade, followed by a recent resurgence. Specifically, Italian emissions in 2020 show a 48% reduction compared to the levels of 2011 and a subsequent increase, with emissions rebounding by 25% in 2022. The availability of near real-time validated observations combined with the most recent inversion frameworks -such as Flexpart/flexinvert+ used here, could be a valuable tool to support the Inventories used to track progress and the effectiveness of the mitigation policies adopted by each country for this class of compounds (that could be extended to others major GHGs) to maximise the effectiveness of their investments.

To address and mitigate the environmental impacts of synthetic greenhouse gases it’s crucial to quantify their emissions to the atmosphere on different spatial scales. Atmospheric Inverse modelling is becoming a widely used method to provide observation-based estimates of greenhouse gas emissions with the potential to provide an independent verification tool for national emission inventories. A sensitivity study of the FLEXINVERT+ model for the optimisation of the spatial and temporal emissions of long-lived greenhouse gases at the regional-to-country scale is presented. A test compound HFC-134a, the most widely used refrigerant in mobile air conditioning systems, has been used to evaluate its European emissions in 2011 to be compared with a previous study. Sensitivity tests on driving factors like—observation selection criteria, prior data, background mixing ratios, and station selection—assessed the model’s performance in replicating measurements, reducing uncertainties, and estimating country-specific emissions. Across all experiments, good prior (0.5–0.8) and improved posterior (0.6–0.9) correlations were achieved, emphasizing the reduced sensitivity of the inversion setup to different a priori information and the determining role of observations in constraining the emissions.The posterior results were found to be very sensitive to background mixing ratios, with even slight increases in the baseline leading to significant decrease of emissions.

<p class="p3">Air pollution from traffic is one of the leading causes of disease and premature death, potentially affecting all human body organs, depending on exposure to polluting sources. Among the main harmful agents to human health are fine particulate materials (PMs), such as PM 10 μm,<strong> </strong>PM 2.5<span class="Apple-converted-space"> μ</span>m<strong>, </strong>and PM 1<span class="Apple-converted-space"> μ</span>m. The finest particulates, like PM 2.5<span class="Apple-converted-space"> μ</span>m and PM 1<span class="Apple-converted-space"> μ</span>m, are easily inhaled, causing respiratory problems such as irritation in the airways, coughing or difficulty breathing, worsening asthma, developing chronic bronchitis, irregular heartbeat, non-fatal heart attacks, premature death in people with heart disease, decreased lung function, contributing to the developing lung cancer.<span class="Apple-converted-space"> </span></p> <p class="p3">In addition, transported by the wind and then deposited in soil or water, the fine particulate contributes to the alteration of their acidity and nutrients, causing damage to forests and agricultural plantations. </p> <p class="p3">The present study investigates the ability of non-porous (concrete, glass) and porous (vegetation) barriers to attenuate the dispersion of fine particulate from roadway traffic. Large Eddy Simulations combined with observational data are used to evaluate the effectiveness of the different barriers in reducing the particulate concentration downwind from the roadway. Different types of barriers, different distances between the road and the barrier, and different barrier heights are simulated with PALM - 4U. The simulated concentration fields are compared to the Marche Region (Italy) measurements.</p>

<p>Long term measurement activities carried out at the WMO GAW global station of Monte Cimone (CMN) provide a useful insight into the characterization of the composition of the Southern European atmosphere. Since 2003, ozone depleting substances (ODSs) and halogenated Greenhouse Gases (GHGs) have been measured at CMN in the frame of the AGAGE (Advanced Global Atmospheric Gases Experiment) programme, with the aim of tracking progress towards the implementation of the international treaties on stratospheric ozone depletion and climate, and getting a better understanding of emissions both in terms of magnitude and localisation at the regional (EU) scale. CMN is often influenced by the advection of polluted air masses from the Po basin, one of the most polluted areas in Europe, as well as by the transport from other highly anthropised regions in Central EU. However, during the cold months and at night-time in the warm season, the site is representative of the free troposphere.</p><p>By providing high quality, high frequency, continuous -almost uninterrupted- observations of ODSs (chlorofluorocarbons and hydrochlorofluorocarbons) and their radiatively active substitutes (hydrofluorocarbons) to modellers, the monitoring activities at CMN  are crucial for improving the overall sensitivity of the inverse modelling techniques used to derive emissions through the so called “top-down” approach. Such approach represents an important quasi-independent cross-check of national GHG emission inventories submitted annually by the parties to the United Nations Framework Convention on Climate Change (UNFCCC). Here we will present results of the Bayesian inverse modelling technique used to derive emissions at the EU national scale based on the observations described above.</p>

The influence of coherent vortices on the turbulence structure above and below a dense plant canopy is investigated using turbulence measurements collected at five levels on top and inside a coniferous forest on an Alpine Plateau. Five different stability regimes, from free convection to very stable stratification, were identified and considered in the analysis. Coherent structures are detected by fitting the vertical velocity auto-correlation functions with a theoretical oscillating function. This allowed to evaluate the coherent vortices characteristic timescales and to discriminate between turbulent data subsets characterized by fine-scale turbulence and subsets in which turbulence is dominated by coherent structures generated at the canopy top. An original methodology to fit cross-correlation function and to single out the most energetic frequency in presence of periodic behaviour is presented and applied to the turbulent momentum flux. The analysis shows how not far from neutral conditions the dominant time scale of the momentum flux is mainly determined by the longitudinal wind velocity component, rather than vertical one, while in free convection and very stable conditions coherent vortices do not seem to influence the momentum transport, dominated by large-scale structures. This is confirmed by the fine-scale turbulence and coherent structures efficiency in turbulence transport throughout the stability regimes.

<p>The spatial representativeness of anemometric tower measurements and the underlying hypothesis of horizontal homogeneity of the atmospheric flows have long being questioned in the literature. Further, forest are rarely situated on uniform and flat terrain in which the horizontally homogeneity of turbulence holds. The orography around the Amazon Tall Tower Observatory (ATTO) site makes no exception. The measurement site is located on a narrow plateau SW-NE oriented, surrounded by lower hills. It is then natural to investigate the spatial variability of the turbulent field around the ATTO and the INSTANT towers to understand the role played by gentle topography. The Parallelized Large-Eddy Simulation Model (PALM) is used to simulate the atmospheric flow over the Amazon Forest and to investigate the effect of topography on the Atmospheric flow within and above the roughness sublayer. The real topography of the ATTO site is considered, while a horizontally homogeneous leaf area density (LAD) profile is assumed for the canopy over the whole area. Hence, the flow variability can be totally ascribed to spatial orography gradients. The influence of orography is assessed comparing the profiles of the turbulent kinetic energy components and fluxes evaluate over flat terrain and over the real topography at different position on the horizontal plane. The dependence of the orography influence on the wind direction is investigated considering two different wind directions.</p> <p> </p>

Observations of the vertical structure of the turbulent flow in different stability regimes above and within the Amazon Forest at the Amazon Tall Tower Observatory (ATTO) site are presented. The shear length scale at the canopy top together with the coherent turbulent structures time and separation length scale were evaluated to determine influence of stability on the inception and development of the roughness sublayer. Five stability regimes were identified. The definition of an intense table regime allowed the identification of a peculiar condition characterized by low-wind and weak coherent structures confined close to the canopy top and producing negligible transport. Submeso motions dominate the flow dynamics in this regime both above and inside the roughness sublayer. The shear length scale increases with decreasing stability, presenting two asymptotes for large unstable and stable stratification and a linear behaviour close to neutral stratification. The coherent structure time and length scales are detected using an original method based on the autocorrelation functions of 5-min subsets of turbulent quantities. The vertical time scale is larger in neutral conditions and decreases for both increasing and decreasing stability, while the separation length scale at the canopy top presents a linear dependence on the shear length scale, whose slope is maximum in neutral conditions and decreases departing from neutrality. A new parameterization describing the dependence of the coherent eddies’ separation length scale on the h/L stability parameter is presented.

COVID-19 (Coronavirus disease 2019) hit Europe in January 2020. By March, Europe was the active centre of the pandemic. As a result, widespread "lockdown" measures were enforced across the various European countries, even if to a different extent. Such actions caused a dramatic reduction, especially in road traffic. This event can be considered the most significant experiment ever conducted in Europe to assess the impact of a massive switch-off of atmospheric pollutant sources. In this study, we focus on in situ concentration data of the main atmospheric pollutants measured in twelve European cities, characterized by different climatology, emission sources, and strengths. We propose a methodology for the fair comparison of the impact of lockdown measures considering the non-stationarity of meteorological conditions and emissions, which are progressively declining due to the adoption of stricter air quality measures. The analysis of these unmatched circumstances allowed us to estimate the impact of a nearly zero-emission urban transport scenario on air quality in 12 European cities. The clearest result, common to all the cities, is that a dramatic traffic reduction effectively reduces NO2 concentrations. In contrast, each city's PM and ozone concentrations can respond differently to the same type of emission reduction measure. From the policy point of view, these findings suggest that measures targeting urban traffic alone may not be the only effective option for improving air quality in cities.

This study provides a detailed analysis of the influence of atmospheric stratification on the flow dynamics above and within a dense forest for a 19-days campaign at the Amazon Tall Tower Observatory (ATTO) site. Observations taken at seven levels within and above the forest along an 81-meter and a 325-meter towers allow a unique investigation of the vertical evolution of the turbulent field in the roughness sublayer and in the surface layer above it. Five different stability classes were defined on the basis of the behavior of turbulent heat, momentum and CO2 fluxes and variance ratio as a function of h/L stability parameter (where h is the canopy height and L is the Obukhov length). The novelty is the identification of a ‘super-stable’ (SS) regime (h/L>3) characterized by extremely low wind speeds, the almost completely suppression of turbulence and a clear dominance of submeso motions both above and within the forest. The obtained data classification was used to study the influence of atmospheric stratification on the vertical profiles of turbulent statistics. The spectral characteristics of coherent structures and of submeso motions (that may influence the energy and mass exchange above the Amazon forest) have been analyzed by wavelet analyses. The role of the main structures in momentum, heat and CO2 transport at the different levels inside and above the forest and in different diabatic conditions was thoroughly investigated through multiresolution and quadrant analyses. In unstable and neutral stability, the flow above the canopy appears modulated by ejections, whereas downward and intermittent sweeps dominate the transport inside the canopy. In the roughness sublayer (z £ 2h) the coherent structures dominating the transport within and above the canopy have a characteristic temporal scale of about 100 sec, whereas above this layer the transport is mainly driven by larger scale convection (temporal scale of about 15 min). In stable conditions the height of roughness sublayer progressively decreases with increasing stability reaching the minimum value (z<1.35h) in the SS regime. Above the canopy the flow is clearly dominated by ejections but characterized by a higher intermittency mainly in SS conditions. On the other hand, the rapid shear stress absorption in the highest part of the vegetation produces a less clear dominance of sweeps and a less defined role of odd and even quadrants inside the canopy in the transport of momentum, heat and CO2. In the weakly stable regime (0.152 transport.

Methyl Chloride (CH3Cl) is a chlorine-containing trace gas in the atmosphere contributing significantly to stratospheric ozone depletion. While the atmospheric CH3Cl emissions are predominantly caused by natural sources on the global budget, significant uncertainties still remain for the anthropogenic CH3Cl emission strengths. In summer 2007 an intensive field campaign within the ACTRIS-2 Project was hosted at the Mt. Cimone World Meteorological Organization/Global Atmosphere Watch global station (CMN, 44,17° N, 10,68° E, 2165 m a.s.l.). High-frequency and high precision in situ measurements of atmospheric CH3Cl revealed significant high-frequency variability superimposed on the seasonally varying regional background levels. The high-frequency CH3Cl variability was characterized by an evident cycle over 24 h with maxima during the afternoon which points towards a systematic role of thermal vertical transport of air-masses from the regional boundary layer. The temporal correlation analysis with specific tracers of anthropogenic activity (traffic, industry, petrochemical industry) together with bivariate analysis as a function of local wind regime suggested that, even if the role of natural marine emissions appears as predominant, the northern Italy boundary layer could potentially represent a non-negligible source of CH3Cl during summer. Since industrial production and use of CH3Cl have not been regulated under the Montreal Protocol (MP) or its successor amendments, continuous monitoring of CH3Cl outflow from the Po Basin is important to properly assess its anthropogenic emissions.

The presence of wave-like structures in the planetary boundary layer and their influence on the scalar fluxes and on the surface energy balance were investigated analyzing one year of continuous measurements collected in southern Brazil. Submeso oscillating patterns in the wind velocity components, temperature and scalar (CO2, H2O) concentrations were isolated using their auto-correlation functions. The analysis showed that low wind speeds are necessary to trigger wavy motions. During night-time, in the presence of large vertical temperature gradients, horizontal meandering and internal gravity waves are dominant features of the stable boundary layer. Furthermore, a significant number of meandering cases were identified also during daytime in neutral conditions associated with low values of net radiation. One case-study showed how, during daytime, the wave-like patterns may be triggered by variations in the net radiation. Spectral analysis on the whole dataset showed that oscillations in the wind velocity and temperature field are frequently associated with CO2 and H2O wavy patterns with similar time-scales. These non-turbulent oscillations produce unpredictable large-scale contributions to vertical fluxes of temperature and scalar concentrations. The energy budget analysis showed how the choice of a proper averaging time filters out these contributions and improves the energy budget closure, as well as the estimation of the net ecosystem exchange. The results confirm the influence of submeso motions in scalar dispersion, flux patterns and surface energy balance during low wind speed conditions and stable stratification.

One of the hallmarks of the stable boundary layer is the switching between turbulent (active) and non-turbulent (passive) states. In very stable conditions, the boundary layer becomes layered with fully-developed turbulence confined to a shallow region near the surface. In the quiescent region above this near-surface layer, the turbulence is weak, intermittent and detached from the ground. These conditions promote the development of a low-level jet that re-energizes the turbulence through an elevated shear layer. The Monin–Obukhov similarity theory fails in the layered stable boundary layer thereby making the quantification of mixing and transport properties challenging for numerical models. In the present study, multi-level time series from a tall (140 m) meteorological tower are analyzed using the telegraphic approximation to investigate analogies with a general class of intermittency models that include self-organized criticality. The analogy between turbulence and self-organized criticality is restricted to clustering properties of sign changes of flow variables for describing switching between turbulent and non-turbulent states. The telegraphic approximation provides a new perspective on clustering and on external and internal intermittency for periods dominated by turbulent motions, a low-level jet and submeso motions. Some of these periods are characterized by the absence of turbulence but occasionally punctuated by bursts of intermittent turbulent events. The switching probability of active–inactive states and the lifetimes of inactive states (related to intermittent turbulent bursts) show evidence of self-organized-criticality like behaviour in terms of scaling laws. The coexistence of self-organized criticality and intermittent turbulence may offer new perspectives on the genesis of scaling laws and similarity arguments, thereby improving the performance of numerical models in the stable boundary layer.

Submeso motions add complexities to the structure of the stable boundary layer. Such motions include horizontal meandering and gravity waves, in particular when the large-scale flow is weak. The coexistence and interaction of such submeso motions is investigated through the analysis of data collected in Antarctica, in persistent conditions of strong atmospheric stratification. Detected horizontal meandering is frequently associated with temperature oscillations characterized by similar time scales (30 min) at all levels (2, 4.5 and 10 m). In contrast, dirty gravity waves superimposed on horizontal meandering are detected only at the highest level, characterized by time scales of a few minutes. The meandering produces an energy peak in the low-frequency spectral range, well fitted by a spectral model previously proposed for low wind speeds. The coexistence of horizontal and vertical oscillations is observed in the presence of large wind-direction shifts superimposed on the gradual flow meandering. Such shifts are often related to the variation of the mean flow dynamics, but also to intermittent events, localized in time, which do not produce a variation in the mean wind direction and that are associated with sharp decreases in wind speed and temperature. The noisy gravity waves coexisting with horizontal meandering persist only for a few cycles and produce bursts of turbulent mixing close to the ground, affecting the exchange processes between the surface and the stable boundary layer. The results confirm the importance of sharp wind-direction changes at low wind speed in the stable atmosphere and suggest a possible correlation between observed gravity waves and dynamical instabilities modulated by horizontal meandering.