The turbulent exchange of momentum within and above tall forested canopies plays a central role in regulating surface–atmosphere interactions, particularly in complex ecosystems such as the Amazon rainforest. The dense and heterogeneous canopy structure interacts strongly with the flow, challenging the applicability of classical boundary-layer concepts that assume the presence of a well-defined inertial sublayer. Under non-neutral stratification, these assumptions are further weakened as large coherent structures and submeso motions introduce additional variability and intermittency. Observations from the Amazon Tall Tower Observatory (ATTO) indicate that convective structures from the outer layer in unstable stratification and low-frequency submeso motions in stable conditions disrupt the conventional boundary-layer and mixing-layer frameworks.

To address these challenges, a scale-wise co-spectral budget model is developed to analyze the vertical velocity spectrum E_ww(k_x) and its relationship to vertical momentum transport. The model explicitly balances mechanical production, pressure decorrelation, and longitudinal buoyancy production or destruction in the momentum co-spectral budget. Results reveal that the momentum flux co-spectrum F_wu(k_x) depends not only on E_ww(k_x) but also on the longitudinal heat-flux co-spectrum F_uθ(k_x).

Across both stable and unstable regimes, the scaling of F_wu(k_x)​ is primarily governed by F_uθ(k_x), while E_ww(k_x) exhibits more variable behavior. The analysis identifies a robust k_x^−7/3​ scaling in F_uθ(k_x) across the inertial subrange, whereas the classical Kolmogorov k_x^−5/3​ scaling in E_ww(k_x) is not universally observed. Moreover, the de-correlation time between longitudinal and vertical velocity fluctuations follows ε^−1/3k_x^−2/3​ within the inertial subrange but remains nearly constant for larger scales, independent of stability. These findings highlight the critical role of stratification and canopy structure in shaping multi-scale momentum exchange in the roughness sublayer.

Dry deposition of ozone (O₃) can occur through different pathways, primarily stomatal and non-stomatal. While stomatal uptake is well studied, non-stomatal processes, such as chemical reactions with nitric oxide (NO) and volatile organic compounds, are often overlooked. In particular, the reaction with NO can represent a highly efficient sink, potentially accounting for up to ~20% of total O₃ deposition (Finco et al., 2018).

NO is mainly emitted from soils microbial processes, with forest soils constituting an important global source. Numerous studies have shown that following rainfall events, NO emissions may exhibit strong peaks lasting several days.

The work presented here aimed to investigate O₃ and NO dynamics within a forest ecosystem by comparing summer periods characterized by low and high NO emissions. Measurements were conducted at Bosco Fontana Nature Reserve, a mixed oak–hornbeam forest in the Po Valley. The analysis is based on data collected through eddy covariance flux measurements of O₃ and NO at two heights (above and below canopy), measurements of vertical concentration of gasses, and measurements of soil NO fluxes obtained by means of dynamic soil chambers.

Results provide new evidence of the role of soil-derived NO in forest–atmosphere O₃ exchanges. Periods of elevated soil NO emissions corresponded to increased NO concentrations near the surface (2 and 8 m), indicating a direct influence of soils on the lower atmosphere. At the same time, higher O₃ deposition velocities were observed at 8 and 40 m, consistent with the strengthening of the chemical sink.

Overall, findings emphasize the importance of soil-emitted NO in enhancing non-stomatal O₃ removal in forests, highlighting the need to integrate this process into dry deposition parameterizations.

DECIPHER (Disentangling mechanisms controlling atmospheric transport and mixing over mountains across space–time scales) investigates multi-scale exchanges of energy, momentum, and tracers between the surface and atmosphere, with a focus on thermally driven flows in the Italian Alps. We report the project’s initial observational phase, comprising two coordinated field campaigns along with an overview of topography, instrumentation, and weather during the field campaigns, and present selected case studies.

The first campaign (23 July-29 October 2024) took place at Col Margherita (2543 m ASL) in the Eastern Italian Alps. Here, optical particle counter (OPC) measurements were taken to characterize the fine (diameter < 1 µm) and coarse (diameter ≥ 1 µm) fractions of aerosols over the site. Two episodes of enhanced coarse-mode aerosol at Col Margherita were identified and further investigated using Doppler and Raman lidars and standard meteorological data from Passo Valles (2032 m a.s.l.), 3 km downslope.

The second field campaign (2 October-10 November 2024) was carried out in the Monte Baldo mountain range on a steep east-facing slope. A two-level eddy covariance tower, complemented by a four-way net radiometer, soil sensors, and thermohygrometers distributed along the slope, was deployed to investigate surface-layer processes and turbulent fluxes associated with slope-wind systems. A typical day with fully developed thermally-driven slope winds was highlighted using eddy covariance tower measurements.

Together, the two campaigns represent preparatory efforts aimed at informing and supporting a larger observational initiative scheduled for summer 2025 at the Monte Baldo site under the international cooperation initiative TEAMx (Multi-scale transport and exchange processes in the atmosphere over mountains - programme and experiment).

La chioma forestale rappresenta un’interfaccia cruciale per i processi di scambio tra atmosfera e biosfera, in cui la chimica atmosferica gioca un ruolo determinante nella regolazione della qualità dell’aria, del bilancio energetico e del ciclo del carbonio. In questo contesto, l’ozono troposferico emerge come un attore chiave: da un lato costituisce un ossidante reattivo in grado di degradare composti organici volatili biogenici (BVOC) emessi dalla vegetazione, modulando la formazione di aerosol secondari e radicali ossidrilici; dall’altro, rappresenta un fattore di stress per le piante, influenzando la fisiologia fogliare e gli scambi gassosi. Nonostante i progressi sperimentali e modellistici, la chimica intra-canopy rimane tuttora non completamente compresa, a causa della complessità delle interazioni tra microclima, emissioni biogeniche e processi di deposizione (Monson & Holland, 2001; Goldstein et al., 2004). La comprensione delle dinamiche dell’ozono all’interno della chioma, incluse le sue interazioni con superfici fogliari, emissioni biogeniche e processi microclimatici, è quindi essenziale per valutare l’impatto delle foreste sulla composizione atmosferica e, reciprocamente, gli effetti della qualità dell’aria sulla funzionalità ecosistemica.
La velocità di deposizione rappresenta infatti uno dei due principali driver della deposizione. In questo lavoro verranno analizzati i dati di velocità deposizione per l’ozono, ottenute tramite la tecnica dell’eddy covariance da misure effettuate al di sopra (40 m) e all’interno (8 m) della canopy forestale di Bosco Fontana (Marmirolo, MN). Verrà mostrata l’influenza dei principali driver ambientali (temperatura, umidità relativa, radiazione, friction velocity, accoppiamento/disaccoppiamento tra chioma e atmosfera), vegetativi (presenza o meno di foglie) ed emissivi (emissione di NO dal suolo) in due annate contrastanti dal punto di vista meteorologico.

Urban areas, responsible of over 70% of CO₂ emissions, are one of the most important sources of GHG gases. Accurate quantification of city emissions through direct observations is crucial for assessing the effectiveness the adopted mitigation strategies.

As part of the ICOS Cities project (https://www.icos-cp.eu/projects/icos-cities), four eddy covariance towers were installed in the Paris area to capture the variability of CO₂, heat and radiation fluxes across an urban-to-rural gradient. The selected sites were chosen to be representative of a highly urbanised and densely built-up area (Jussieu), an urban forest (Vincennes), a semi-urban area (Saclay) and a heterogeneous area combining highly urbanised zones with vegetated patches (Romainville). Additionally, the observations from the urban sites were integrated with the EC flux measurements from the ecosystem sites of Fontainebleau (FR-FON, forest) and Grignon (FR-GRI, crop).

CO₂ and heat flux measurements showed seasonal dynamics that reflected the respective degrees of urbanisation of the sites and the presence of biogenic sinks. At the urban sites of Jussieu and Romainville, the sensible heat flux, H, was generally higher than the latent heat flux, LE. At Jussieu in particular, H remained positive throughout the day and night, indicating the presence of a local heat source. In contrast, the forested site of Vincennes exhibited higher latent heat fluxes than in Jussieu and Romainville, often with similar intensity to sensible heat fluxes. Our analysis identified both Jussieu and Romainville as net sources of CO₂, with the highest daily emissions during the winter months, and slight daytime CO₂ uptake during summer. However, the two sites displayed distinct diurnal CO₂ flux patterns due to the different temporal variability of dominant emission sources (stationary combustion and traffic) or to people commuting from the city center (Jussieu) during the day to residential areas (Romainville) at night. The mixed urban forest of Vincennes showed instead strong biogenic signature, with CO₂ fluxes characterized by daytime uptake (down to -10 µmol m⁻²s⁻¹) during the growing season. A comparison between EC flux measurements and emission inventories estimates for the city of Paris will be presented.

Ozone dry deposition to vegetated surfaces is caused by stomatal uptake made by plant leaves and by ozone disruption on external vegetal surfaces, like leaf cuticles, and soil.

Although the stomatal deposition pathway has been widely studied because of its implications for the negative effect of ozone on plant growth and productivity, the non-stomatal deposition pathways have been scarcely addressed for long time, and they are not completely understood yet.

In 2020, Clifton et al. proposed for the first time a mechanistic model to predict non-stomatal deposition of ozone on dry and wet leaf cuticles as well as on soils. However, the model was purely theoretical, and no attempts were made to validate it using real measurements on the field.

This work presents the first attempt to calibrate and validate Clifton’s model of non-stomatal resistances for a broadleaf forest. For this purpose, the total ozone deposition resistance obtained by implementing the Clifton’s model was compared with that derived from the eddy covariance flux measurements made in 2021 and 2022 at Bosco Fontana (Italy). Moreover, the resistance partitioning allowed a closer comparison with the cuticular resistances predicted by the model.

The soil deposition resistance of ozone was then compared with that measured by means of automatic soil chambers at the same site in 2024 and 2025.

The results showed good agreement with the Clifton’s prediction for the cuticular resistance, and less satisfactory agreement with soil resistance to O3 deposition. This seems to be due to the litter that covers the soil beneath the forest canopy, which alters the expected responses of Clifton’s model for (bare) soils.

Clifton’s model has the potential to describe non-stomatal deposition in forests. However, it requires modification to account for real field conditions in which litter covers forest soils, and to account for chemical sinks in the trunk space, which are completely neglected by the model.