Search

Carbon dioxide (CO2) uptake by plant photosynthesis, referred to as gross primary production (GPP) at the ecosystem level, is sensitive to environmental factors, including pollutant exposure, pollutant uptake, and changes in the scattering of solar shortwave irradiance (SWin) − the energy source for photosynthesis. The 2020 spring lockdown due to COVID-19 resulted in improved air quality and atmospheric transparency, providing a unique opportunity to assess the impact of air pollutants on terrestrial ecosystem functioning. However, detecting these effects can be challenging as GPP is influenced by other meteorological drivers and management practices. Based on data collected from 44 European ecosystem-scale CO2 flux monitoring stations, we observed significant changes in spring GPP at 34 sites during 2020 compared to 2015–2019. Among these, 14 sites showed an increase in GPP associated with higher SWin, 10 sites had lower GPP linked to atmospheric and soil dryness, and seven sites were subjected to management practices. The remaining three sites exhibited varying dynamics, with one experiencing colder and rainier weather resulting in lower GPP, and two showing higher GPP associated with earlier spring melts. Analysis using the regional atmospheric chemical transport model (LOTOS-EUROS) indicated that the ozone (O3) concentration remained relatively unchanged at the research sites, making it unlikely that O3 exposure was the dominant factor driving the primary production anomaly. In contrast, SWin increased by 9.4 % at 36 sites, suggesting enhanced GPP possibly due to reduced aerosol optical depth and cloudiness. Our findings indicate that air pollution and cloudiness may weaken the terrestrial carbon sink by up to 16 %. Accurate and continuous ground-based observations are crucial for detecting and attributing subtle changes in terrestrial ecosystem functioning in response to environmental and anthropogenic drivers.

The case study of 'Bosco Fontana', a densely-vegetated forest located in the north of Italy, is analysed both experimentally and numerically to characterise the internal ventilation of a finite forest with a vertically non-homogeneous canopy. Measurements allow for the evaluation of the turbulent exchange across the forest canopy. The case study is then reproduced numerically via a two-dimensional RANS simulation, successfully validated against experimental data. The analysis of the internal ventilation leads to the identification of seven regions of motion along the predominate-wind direction, for whose definition a new in-canopy stability parameter was introduced. In the vertical direction, the non-homogeneity of the canopy leads to the separation of the canopy layer into an upper foliage layer and a lower bush layer, characterised respectively by an increasing streamwise velocity and turbulence intensity, and a weak backflow. The conclusions report an improved description of the dynamic layer and regions of motion presented in the literature.

This paper highlights advantages and drawbacks due to the use of portable and low-cost devices for aerosol sampling, showing their performances during an aerosol monitoring campaign with the parallel use of the gravimetric sampling reference method and a cascade impactor. A specific monitoring campaign was held running all instruments in parallel in indoor, confined, and outdoor environments characterized by local emission sources or particulate matter background concentra-tions. PM2.5 concentrations were used to compare data emerging from the different instruments adopted. Significant underestimation of PM2.5 emerged when comparing data coming from optical sensors with those estimated by the cascade impactor, whose data resulted in being coherent with gravimetric determination, integrated over the same sampling time. A cause–effect relationship between PM2.5 concentrations and specific emission sources was found when observing the daily patterns of all the real-time sampling devices. It emerged that optical devices are useful for detecting concentration trends, the presence of peak values, or changes in the background value, even if with limited accuracy and precision. The comparison with particle size distributions obtained by the cascade impactor data allowed us to define which particle sizes are not detected by different optical devices, evidencing a low representativeness of optical low-cost sensors for health exposure measurements. The correlations among the specific particle size fractions detected by the cascade im-pactor and their specific emission sources were particularly high for car emissions in a semi-confined garage area.

Leaf area index (LAI) is a key ecological indicator for describing the structure of canopies and for modelling energy exchange between atmosphere and biosphere. While LAI of the forest overstory can be accurately assessed over large spatial scales via remote sensing, LAI of the forest understory (LAIu) is still largely ignored in ecological studies and ecosystem modelling due to the fact that it is often too complex to be destructively sampled or approximated by other site parameters. Additionally, so far only few attempts have been made to retrieve understory LAI via remote sensing, because dense canopies with high LAI are often hindering retrieval algorithms to produce meaningful estimates for understory LAI. Consequently, the forest understory still constitutes a poorly investigated research realm impeding ecological studies to properly account for its contribution to the energy absorption capacity of forest stands. This study aims to compare three conceptually different indirect retrieval methodologies for LAIu over a diverse panel of forest understory types distributed across Europe. For this we carried out near-to-surface measurements of understory reflectance spectra as well as digital surface photography over the extended network of Integrated Carbon Observation System (ICOS) forest ecosystem sites. LAIu was assessed by exploiting the empirical relationship between vegetation cover and light absorption (Beer-Lambert- Bouguer law) as well as by utilizing proposed relationships with two prominent vegetation indices: normalized difference vegetation index (NDVI) and simple ratio (SR). Retrievals from the three methods were significantly correlated with each other (r = 0.63–0.99, RMSE = 0.53–0.72), but exhibited also significant bias depending on the LAI scale. The NDVI based retrieval approach most likely overestimates LAI at productive sites when LAIu > 2, while the simple ratio algorithm overestimates LAIu at sites with sparse understory vegetation and pre

Information about forest background reflectance is needed for accurate biophysical parameter retrieval from forest canopies (overstory) with remote sensing. Separating under- and overstory signals would enable more accurate modeling of forest carbon and energy fluxes. We retrieved values of the normalized difference vegetation index (NDVI) of the forest understory with the multi-angular Moderate Resolution Imaging Spectroradiometer (MODIS) bidirectional reflectance distribution function (BRDF)/albedo data (gridded 500 m daily Collection 6 product), using a method originally developed for boreal forests. The forest floor background reflectance estimates from the MODIS data were compared with in situ understory reflectance measurements carried out at an extensive set of forest ecosystem experimental sites across Europe. The reflectance estimates from MODIS data were, hence, tested across diverse forest conditions and phenological phases during the growing season to examine their applicability for ecosystems other than boreal forests. Here we report that the method can deliver good retrievals, especially over different forest types with open canopies (low foliage cover). The performance of the method was found to be limited over forests with closed canopies (high foliage cover), where the signal from understory becomes too attenuated. The spatial heterogeneity of individual field sites and the limitations and documented quality of the MODIS BRDF product are shown to be important for the correct assessment and validation of the retrievals obtained with remote sensing.

Our understanding of the processes that control the burden and budget of tropospheric ozone has changed dramatically over the last 60 years. Models are the key tools used to understand these changes, and these underscore that there are many processes important in controlling the tropospheric ozone budget. In this critical review, we assess our evolving understanding of these processes, both physical and chemical. We review model simulations from the International Global Atmospheric Chemistry Atmospheric Chemistry and Climate Model Intercomparison Project and Chemistry Climate Modelling Initiative to assess the changes in the tropospheric ozone burden and its budget from 1850 to 2010. Analysis of these data indicates that there has been significant growth in the ozone burden from 1850 to 2000 (approximately 43 + 9%) but smaller growth between 1960 and 2000 (approximately 16 + 10%) and that the models simulate burdens of ozone well within recent satellite estimates. The Chemistry Climate Modelling Initiative model ozone budgets indicate that the net chemical production of ozone in the troposphere plateaued in the 1990s and has not changed since then inspite of increases in the burden. There has been a shift in net ozone production in the troposphere being greatest in the northern mid and high latitudes to the northern tropics, driven by the regional evolution of precursor emissions. An analysis of the evolution of tropospheric ozone through the 21st century, as simulated by Climate Model Intercomparison Project Phase 5 models, reveals a large source of uncertainty associated with models themselves (i.e., in the way that they simulate the chemical and physical processes that control tropospheric ozone). This structural uncertainty is greatest in the near term (two to three decades), but emissions scenarios dominate uncertainty in the longer term (2050–2100) evolution of tropospheric ozone. This intrinsic model uncertainty prevents robust predictions of near-term change

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Reducing surface ozone to meet the European Union’s target for human health has proven challenging despite stringent controls on ozone precursor emissions over recent decades. The most extreme ozone pollution episodes are linked to heatwaves and droughts, which are increasing in frequency and intensity over Europe, with severe impacts on natural and human systems. Here, we use observations and Earth system model simulations for the period 1960–2018 to show that ecosystem–atmosphere interactions, especially reduced ozone removal by water-stressed vegetation, exacerbate ozone air pollution over Europe. These vegetation feedbacks worsen peak ozone episodes during European mega-droughts, such as the 2003 event, offsetting much of the air quality improvements gained from regional emissions controls. As the frequency of hot and dry summers is expected to increase over the coming decades, this climate penalty could be severe and therefore needs to be considered when designing clean air policy in the European Union.

Soil deposition is an essential pathway for tropospheric ozone (O3) removal, but its controlling factors remain unclear. Here, we explored the variability of soil O3 resistance in response to soil texture. To this aim, data of O3 deposition over bare soil obtained from micrometeorological measurements under contrasted meteorological conditions for five sites were used. The results obtained are twofold: (i) soil resistance (Rsoil) increased with soil surface relative humidity (RHsurf), but (ii) this relationship exhibited large site-by-site variability. Further analysis showed that the minimum soil resistance (corresponding to completely dry soil surface or RHsurf = 0%) and the increase of Rsoil with RHsurf are both linked to soil clay content. These results can be explained by (i) the soil surface available for O3 deposition at a microscopic scale which is a function of the soil specific surface area, and (ii) the capacity of a soil to adsorb water according to its clay content and therefore to reduce the surface active for O3 deposition. From these results, a new parameterization has been established to estimate Rsoil as a function of RHsurf and soil clay fraction.

The Division Models and Technologies for Risks Reduction of the ENEA Sustainability Department was established in July 2015 with the specific aim of assemble all the resources, both human and instrumental, that could propose reflections, analyzes and assessments about the interactions among energy strategies, emissions of pollutants and greenhouse gases, air quality, climate change and resulting impacts on health and ecosystems. The use of numerical models, at different spatial scales, to describe the physical and chemical processes affecting the atmosphere and the ocean is at the hearth of the history and activities of the research groups involved. Nevertheless, great effort and commitment was also dedicated to the development of integrated models to explore links and feedback between the different aspects of the same system. These unique platforms called IAM (Integrated Assessment Modelling) help and support policy-makers to develop and promote sustainable policies. With this vision we have been developing the national model MINNI (Integrated National Model in support to the International Negotiation on Air Pollution) since 2003. It includes the Integrated Assessment Model GAINS-Italia, which helped our Country: to negotiate revisions of European and International Directives and Protocols with technical data and national scenario simulations; to support technically the actions needed to deal with European infringement procedures; to help the Regional Authorities to fully understand and use the measurements until they have become totally autonomous; to support the early season of the Air Quality Regional Plans together with the assessment of the measures identified in them. A parallel and equally far-sighted vision has been offered by our colleagues of the actual Division who have been dealing for years with the “pollution effects”. They hold significant roles within the International Convention on Long Range Transboundary Air Pollution (CLRTAP) of the United Natio

This study focuses on the environmental impact assessment of three different high efficiency residential pellet boilers manufactured by an Austrian company. A Life Cycle Analysis (LCA) and an Environmental Life Cycle Costing (ELCC) analysis were performed, along with air quality modelling simulations for two EU case studies to evaluate CO, PM10, SO2, NO2 concentration reductions due to the substitution of the innovative boilers in place of obsolete and non environmentally compliant biomass boilers. The SimaPro software (v. 8.05.13, Recipe Midpoint Method) was used for the LCA and ELCC analysis while CALPUFF (v. 6.42) was used for air quality simulations. Boilers emission and efficiency factors operating in real life conditions were used as input data for all environmental impact assessment analysis. Results showed an interesting reduction of both the environmental impact and pellet consumption cost (linked to the highest monetary value in the ELCC analysis) associated to the most innovative boiler model among the three envisaged. Furthermore, it emerged that air quality could be improved in the short term (2020) with the substitution of obsolete and end of life biomass boilers with high efficiency pellet boilers in EU areas where biomass is the main source of residential heating. A potential reduction of local CO, SO2 and PM10 concentrations from 9% to 23% depending on the pollutant and on the specific case study considered is found for the short term scenario (2020) with respect to the baseline scenario (2010). No significant differences in air quality were evidenced for NO2 concentrations.

Correzione alla review citata

Fluorescence transient (FT) analysis (fast kinetics) was carried out on sun and shade leaves of beech seedlings in an experimental field at Curno (North Italy), during the 2008 growing season (June–August). The aim of the research was to determine: (1) morphology in sun leaves as long term acclimation to high light; (2) short term responses to high light, i.e. during the course of the day; (3) evolution of responses during the growing season and the ageing process. Sun leaves differ from shade leaves by their lower trapping capacity (expressed by the ratio FV/FM) and higher capacity to reduce end acceptors beyond PSI (expressed by phase I–P of the FT). These features were assessed at pre-dawn, when the entire plant is fully dark-adapted. Short term responses (differences between midday and pre-dawn assessments) occur especially in sun leaves, indicating that the photosynthetic machinery reacts to the high excitation pressure by increasing photochemical and non-photochemical de-excitation processes. Other responses concern the inactivation of the oxygen evolving system and a stability loss of the tripartite system reaction centre (RC) – harvesting light complex – core antenna, expressed by the onset of K and L-bands at midday. Sun leaves are well acclimated to high light from a structural and functional point of view, however, the irradiance at midday provokes conditions of instability in the photosynthetic machinery, possibly through reactive oxygen species (ROS) production at both PSII and PSI sides. The temporal patterns across the growing season indicate the progression of senescence processes, that are more pronounced in sun leaves which present a permanent (chronic) condition of photoinhibition. Differences between sun and shade leaves decrease over time.

At alpine scale, the efficiency of fire danger forecast services, prevention activities and fire fighting actions has significantly improved in the last decades. Ongoing trends show a strong decrease both in the overall frequency of forest fires and in the mean extension of burnt area per single fire occurrence. In spite of that, forest fires still represent one of the main threats impacting alpine forests. In the next future, ongoing climate changes could play a relevant role in influencing both the frequency, the geographical patterns and the regimes of fires in the Alpine area. Moreover, they could play a relevant role in inducing the occurrence of big or extreme fires. As a consequence, great efforts should be made to monitor the evolution of fire patterns in the Alps and to identify fire danger indexes highly performing in the Alpine region. Two Alpine Space projects (MANFRED and ALP FFIRS) recently co-operated on these topics. This paper synthesizes the results of the collaboration, aiming mainly at (1) understanding if extreme fire occurrences are significantly influenced by meteo-climatic conditions and (2) identifying the Fire Danger Indices having the best performance in the prediction of extreme occurrences. In the framework of this joint action, a pan-alpine dataset of fires has been generated (more than 82.000 fires, about 26.000 occurrences in the time span 2000 - 2009). The dataset maps the points of ignition and describes each event with a standard set of attributes. Extreme fires (99th percentile of the attribute Total Burnt Area) occurred in the period 2003-2009 were identified and used to test a selection of about 19 Fire Weather Indices, with non-parametric statistics, to investigate their ability in distinguishing between fire/non fire days and between common fire conditions and extreme fire conditions.

The wild tomato species Lycopersicon pimpinellifolium (currant tomato) was exposed to different O3 concentration, both in controlled environment fumigation facilities and in open-top chambers, to assess its sensitivity and to verify its potential as a bioindicator plant. Plants appeared particularly sensitive to O3 at an early stage of growth, responding with typical chlorotic spots within 24 h after exposure to a single pulse of 50 ppb for 3 h, and differentiating peculiar symptoms, such as reddish necrotic stipples, bronzing and extensive necrosis, depending on O3 concentration. Histo-cytochemical investigations with 3,3′-diaminobenzidine, to localize H2O2, and Evans blue, to detect dead cells, suggested that currant tomato sensitivity to O3 could be due to a deficiency in the anti-oxidant pools. The combination of these stainings proved to be useful, either to predict visible symptoms, early before their appearance, and to validate leaf ozone injury. © 2005 Elsevier Ltd. All rights reserved.

A new parameterisation of ozone uptake by vegetation, based on the observational determination of functional dependence of stomala ozone conductances on environmental parameters such as temperature, wind speed, top-of-canopy ozone concentrations, water vapour pressure deficit, and soil water content, is proposed. Measurements of ozone fluxes and related parameters have been made using micrometeorological methods over wheat in the Po river plain, Northern Italy. The results show the discrepancy between the AOT40 index, based on the ozone concentration cumulated function over the season, and the cumulated stomatal ozone flux. The new parameterisation proposes a corrected AOT index, which takes environmental and plant physiological effects into account. The corrected AOT is in agreement with the cumulated stomatal ozone uptake flux.

This study examines defoliation and discoloration findings collected throughout the Italian Level I network between 1997 and 2000. Prior to this period no Quality Assurance procedures had been implemented, so that earlier findings cannot be considered reliable. The aim of the study is to compare different indices used in reporting findings, in order to determine the full potential and limitations of each. In international surveys, findings are normally expressed in terms of individual trees presenting a defoliation level greater than 25%; this criterion, however, has been challenged since it is not based on scientific evidence. By analysing the distribution of defoliation values (grouped in 5% classes) relating to the main species (Fagus sylvatica, Quercus pubescens, Quercus cerris, Picea abies), the study examines the behaviour of statistical indices such as the median, the mode and the mean. Instead of using the traditional 25% threshold to determine the part of the population with the highest defoliation values, a procedure is suggested whereby a different threshold can be determined for each species. It is established based on the 90° percentile of cumulative defoliation values recorded over the four-year period. Each index used to report findings possesses its own information potential, and the findings may at times appear contradictory. The use of a combined defoliation and discoloration index (Ilce = Lacking Crown Equivalent Index) is also proposed, but the results obtained do not differ in substance from the results relating to defoliation alone. The functional limitations of this index are due mainly to the way the data are collected: for this reason suggestions are made on how to improve the procedure in future surveys.

Ozone deposition fluxes have been measured over a wheat field in Northern Italy in May-June 2001 with the eddy-correlation method in order to evaluate the amount of ozone taken up by plants during the whole grain filling period, from anthesis to harvest. Ozone uptake by plants is due to its penetration through the stomata; for this reason stomata] ozone fluxes were determined, using the analogy with water vapour fluxes (Penman-Monteith approach), which are easily measured. The total ozone dose was obtained by integrating the stomatal ozone fluxes over time. The observational results showed that ozone fluxes decrease with time, following the maturation and the senescence of plants. On the average, the stomatal flux was found to be 50-60% of the total flux, but this fraction decreased during the senescence, emphasizing the importance of non-stomatal ozone deposition pathways. The approach consisting on evaluating the total ozone dose by integrating stomatal fluxes was then compared to the currently used procedure based on the evaluation of the exposure index AOT40, which uses ozone concentrations. Important differences between these two methods are highlighted. The integration of stomatal ozone fluxes appears more suitable for the evaluation of physiological uptake than the use of the exposure index. (C) 2002 Elsevier Science Ltd. All rights reserved.

In recent years multidisciplinary surveys examining the impact of pollutants on forest ecosystems have been carried out in the Valtellina (Northern Italy, Alpine region). A large part of the activity of these surveys has involved the study of ozone and its distribution in the area, development of the exceedances maps (AOT40) and their validation by means of field observation of visible foliar symptoms in the indigenous and sensitive forest vegetation. The present paper reports the results of a field survey carried out in 1998 on the visible symptoms expressed by several native species (trees, shrubs and herbs). A non-systematic grid of 81 plots was assessed throughout the valley. Due to the high variability of the physical (altitude, slope, exposure, etc.) and vegetational (species assemblage, tree age, forest structure) features, the comparability among the plots was found to be very weak, so only the presence or absence of leaf injuries was assessed. Results do not show any correlation between the distribution of foliar symptoms in Valtellina and ozone levels. Rather, leaf injuries follow the same distribution of environmental modifying factors (such as depth and moisture of the soil) and tree sensitivity. © 2003 Elsevier Science Ltd. All rights reserved.

The ozone exposure risk for vegetation in Lombardy (Northern Italy) has been assessed by the AOT40 exposure index, based on data taken from the existing local monitoring networks covering 5 growing seasons (1994 to 1998). One-square kilometer exposure maps were obtained by using geostatistic techniques (ordinary kriging) followed by an altitude detrendization of measurement’s temporal series to account for the domain’s large topographic heterogeneity. Risk areas (Level I maps) were identified using a GIS and overlaying the ozone-criticallevel exceedance maps on the distribution maps of forests and sensitive species. The critical ozone exposure level of 10 000 ppb h, adopted by UN/ECE protocols, is exceeded over the whole Lombardy Territory over the 6-month growing season. The highest risk areas are the northwest pre-alpine and alpine belt, directly impacted by the photo-oxidant plume generated by the Milan urban area. Difficulties met in creating a proper Level II risk assessment for forests in mountain areas have been bypassed by comparing ozone exposures with summer climate features. Soil water availability was assumed not to be a significant modifying factor in the mountains of this region because of the frequent summer rains, whereas the opposite held true for wind ventilation which is generally weak. Field surveys have reported foliar injuries attributable to ozone in different species of forest trees and shrubs, which provide further evidence of potentially phytotoxic ozone levels

During the summer of 2001, 2-year-old Fraxinus excelsior and Fagus sylvatica plants were subjected to ozone-rich environmental conditions at the Regional Forest Nursery at Curno (Northern Italy). Atmospheric ozone concentrations and stomatal conductance were measured, in order to calculate the foliar fluxes by means of a one-dimensional model. The foliar structure of both species was examined (thickness of the lamina and of the individual tissues, leaf mass per area, leaf density) and chlorophyll a fluorescence was determined as a response parameter. Stomatal conductance was always greater in Fraxinus excelsior, as was ozone uptake, although the highest absorption peaks did not match the peaks of ozone concentration in the atmosphere. The foliar structure can help explain this phenomenon: Fraxinus excelsior has a thicker mesophyll than Plagus sylvatica (indicating a greater photosynthesis potential) and a reduced foliar density. This last parameter, related to the apoplastic fraction, suggests a greater ability to disseminate the gases within the leaf as well as a greater potential detoxifying capacity. As foliar symptoms spread, the parameters relating to chlorophyll a fluorescence also change. PI (Performance Index, Strasser, A., Srivastava, A., Tsimilli-Michael, M., 2000. The fluorescence transient as a tool to characterize and screen photosynthetic samples. In: Yunus, M., Pathre, U., Mohanty, P., (Eds.) Probing Photosynthesis: Mechanisms, Regulation and Adaptation. Taylor & Francis, London, UK, pp. 445-483.) has proved to be a more suitable index than Fv/Fm (Quantum Yield Efficiency) to record the onset of stress conditions. (C) 2003 Elsevier Science Ltd. All rights reserved.

Ozone is the most harmful air pollutant for plant ecosystems in the Mediterranean and Alpine areas due to its biological and economic damage to crops and forests. In order to evaluate the relation between ozone exposure and vegetation injury under on-field conditions, suitable ozone monitoring techniques were investigated. In the framework of a 5-year research project aimed at ozone risk assessment on forests, both continuous analysers and passive samplers were employed during the summer seasons (1994-1998) in different sites of a wide mountain region (80 x 40 km2) on the southern slope of the European Alps. Continuous analysers allowed the recording of ozone hourly concentration means necessary both to calculate specific exposure indexes (such as AOT, SUM, W126) and to record daily time-courses. Passive samplers, even though supplied only weekly mean concentration values, made it possible to estimate the altitude concentration gradient useful to correct the altitude dependence of ozone concentrations to be inserted into exposure indexes. In-canopy ozone profiles were also determined by placing passive samplers at different heights inside the forest canopy. Vertical ozone soundings by means of tethered balloons (kytoons) allowed the measurement of the vertical concentration gradient above the forest canopy. They also revealed ozone reservoirs aloft and were useful to explain the ozone advection dynamic in mountain slopes where ground measurement proved to be inadequate. An intercomparison between passive (PASSAM, CH) and continuous measurements highlighted the necessity to accurately standardize all the exposure operations, particularly the pre- and postexposure conservation at cold temperature to avoid dye (DPE) activity. Advantages and disadvantages from each mentioned technique are discussed.