Fire-conditioned degradation now rivals deforestation as an independent source of carbon loss across Amazonia. We argue that fire and degradation are first-order risks to Nature-based solutions and must be embedded explicitly in monitoring, reporting and verification (MRV), as well as crediting and jurisdictional finance. Fire-conditioned degradation now rivals deforestation as an independent source of carbon loss across Amazonia. This Comment argues that fire and degradation are first-order risks to Nature-based solutions and must be embedded explicitly in monitoring, reporting and verification (MRV), as well as crediting and jurisdictional finance.

Fog formation over tropical forests remains poorly characterized, despite its potential role in bioaerosol dispersion and ecosystem processes. Here, we analyzed fog samples collected at the Amazon Tall Tower Observatory using flow cytometry and culture-based techniques to characterize viable microbial communities. Microbial cell concentrations varied over an order of magnitude across 13 fog events, reaching up to 8 & times; 104 cells per ml of fog water. Flow cytometry consistently detected metabolically active cells, while culturing and mass spectrometry-based identification yielded eight viable bacterial species and seven fungal taxa. The bacteria Serratia marcescens, Ralstonia pickettii and Sphingomonas paucimobilis exhibited seasonal variations in prevalence. The fungal species identified were primarily mesophilic saprophytes and endophytes, commonly associated with soil and plant surfaces. Our findings indicate that fog harbors viable microbes, including Serratia marcescens and Ralstonia pickettii, which may imply a relevance of fog for microbial dispersal, colonization and nutrient cycling in the Amazon rainforest.

Biological particles are a substantial component of Amazonian aerosols, yet their community composition, spatiotemporal variability, and atmospheric impacts remain poorly understood. Here, we present a comprehensive study of archaeal, bacterial, and fungal bioaerosol communities in the Amazon rainforest, collected at 42 m and 323 m height above ground at the Amazon Tall Tower Observatory (ATTO). Archaea exhibited overall low prevalence, dominated by potential marine clades. Under rainforest background conditions, the bacterial community varied strongly with time and height, indicating an inhomogeneous source distribution and strong long-range influence. In contrast, the fungal bioaerosol community exhibited low variability over time and height, suggesting persistent, widespread, and uniform regional sources. During an African dust intrusion, the bacterial community composition changed drastically. A strong increase in relative sequence abundance of bacteria belonging to the phylum Bacillota, known to be abundant in Saharan dust, suggests a substantial influx of bacterial bioparticles and genetic material from Africa. In contrast, the fungal community remained unaffected, likely due to a masking effect of local emissions. During the dust event, the total mass concentrations of coarse mode aerosol particles (>1 µm) and of atmospheric endotoxins, that can trigger respiratory diseases, increased by factors up to 4. This study serves as a key foundation to unravel the mechanisms of bioparticle and dust cycling and their effects on biodiversity, climate, and public health during Earth history up to current and future environmental conditions in the Anthropocene.

Indigenous Lands are critical for protecting Indigenous Peoples and the Amazon. Yet, they are increasingly exposed to socio-environmental frontiers, bringing violence, illegal resource extraction and deforestation. Urgent action is required to prevent irreversible harm to both people and forests, particularly in Brazil’s Vale do Javari Indigenous Land.

Atmospheric deposition of micro-nutrients like Fe has been shown to be important for ocean biogeochemistry. The largest source of atmospheric Fe and other elements (e.g., Ca, Al, Si, and Ti) is desert dust, although there are significant non-dust sources in some regions (e.g., combustion, sea salts, volcanoes). However, past estimates of these elements have been substantially uncertain due to limited information about the composition of the desert source regions. Here we use elemental distributions estimated from new Earth Surface Mineral Dust Source Investigation (EMIT) observations, which provide mineralogical composition at the surface of the Earth based on imaging spectroscopy measurements from the International Space Station. We focus on total elemental amounts, not on the soluble fraction. We add in other sources of these elements (anthropogenic and natural) and compare to a compilation of available surface concentration data from stations over land and from shipborne observations. The combined observational and model synthesis provides new information about the distribution and deposition of these elements. Our results suggest that the modeled distribution is similar to available observations, but discrepancies still exist in both natural desert dust regions as well as regions dominated by anthropogenic sources. Comparisons between the model estimated Ca/Al ratios and observations in some dust dominated regions suggest an underestimate of Ca/Al ratios. Global budgets for Ca, Al, Fe, Si, and Ti suggest that desert dust remains the dominant source, although volcanic and anthropogenic contributions are important in some regions. Changes in elemental distributions since preindustrial times were also estimated.

The large extension and diversity of the Brazilian Amazon biome hampers the assessment of the regional-scale carbon budget based solely on local observations. Considering the shortage of observations, this study aims to examine the carbon fluxes throughout the Brazilian Amazon biome using a process-based model (JULES, Joint UK land environment simulator). A sensitivity analysis detected five critical model parameters for the Amazon tropical broadleaf evergreen forest, optimized using carbon flux and meteorological data from four forest sites. The simulations with the new parametrization were compared with JULES default parameter values and with simulations of the Vegetation Photosynthesis and Respiration Model (VPRM). Net ecosystem exchange (NEE) and gross primary production (GPP) estimates were improved at all sites, reaching a Root Mean Squared Error (RMSE) about 30 % lower in comparison to the default version. The optimized parameter values varied among the four sites, indicating that a single parameterization for the whole Amazonia may not be adequate. JULES model parameters were spatialized for the Brazilian Amazonia, based on canopy height and leaf area index gridded data. Applying JULES with spatially dependent parameterization for the year 2021 resulted in a carbon sink of -1.34 Pg C yr-1. Regional differences were observed in the carbon fluxes, with a carbon source of 0.75 kg C m-2 yr-1 in the southwest and north, likely explained by increased ecosystem respiration in older and taller forests.

Atmospheric aerosols play a crucial role in modulating the energy available to the Earth's surface, influencing the hydrological cycle, ecosystems, and climate. In the Amazon, previous studies have mainly examined how aerosols scatter and absorb radiation. However, little is known about their interactions with energy partitioning (i.e., sensible and latent heat fluxes). Here, we investigate how regimes of high (AOD >0.40) and low (AOD <0.13) aerosol optical depth (AOD) affect surface energy and carbon dioxide (CO2) fluxes in an undisturbed Amazon rainforest. For this, we used long-term meteorological measurements from the Amazon Tall Tower Observatory (ATTO) collected between 2016 and 2022. We find that enhanced aerosol presence reduces both sensible heat flux and energy available for evapotranspiration by approximately 13.5 % and 2.1 % respectively, while increasing CO2 uptake (i.e., CO2 flux becoming more negative) by about 39.5 %. The impact of aerosols on turbulent surface fluxes is reflected in a cooling of approximately 0.9 degrees C at the canopy top, caused by a 2.8% reduction in incoming shortwave radiation. These results demonstrate that aerosols modify turbulent energy exchange, with consequences for the forest microclimate and the coupled carbon and water cycles.

Primary biological aerosols such as pollen, fungal spores, bacteria and plants debris have traditionally been associated with the coarse particle mode. In contrast, small organic particles in the submicron range have largely been attributed to secondary formation processes, as few primary biogenic sources were known [1-3]. Due to their hygroscopic properties, bioaerosols may act as cloud condensation nuclei (CCN) and ice nuclei (IN), potentially influencing cloud formation and precipitation [4]. In the Amazon rainforest, coarse particles are typically present at lower number concentrations, whereas fine organic particles are more abundant and thus are known to contribute significantly to cloud microphysics under certain conditions [1,5].In this study, we investigate a previously overlooked primary biogenic source of organic aerosol droplets linked to spore release by many fungi and lichens, with measurements conducted at the Amazon Tall Tower Observatory (ATTO) site in Brazil [6]. Many lichenized and non-lichenized Ascomycota release spores actively, building pressure in their reproductive cells through osmolyte-driven water influx until the spores are suddenly expelled.We combined controlled laboratory experiments with ambient field measurements to characterize particles emitted during this process. Particle size distributions were measured in isolated chamber experiments using two complementary particle sizers covering a broad size range, providing information on both particle size and emission strength. Field experiments gave insights into emission patterns and triggers under natural tropical forest conditions. Droplets were additionally collected by impaction for further microscopic and chemical analyses. The chemical composition was determined using scanning transmission X-ray microscopy with near-edge X-ray absorption and fine structure (STXM-NEXAFS) spectroscopy, as well as high performance liquid chromatography (HPLC) with electrospray ionisation ultra-high resolution orbitrap mass spectrometry (ESI-UHR-Orbitrap-MS).This integrated approach allows us to assess the size, chemical composition, and emission strength of fungal aerosol emissions. The findings provide new insights into the contribution of sub- and supermicron fungal emissions to organic aerosol populations and their potential implications for atmospheric processes.[1] Pöschl, U., et al. (2010). Rainforest aerosols as biogenic nuclei of clouds and precipitation in the Amazon. Science, 329, 1513–1516. https://doi.org/10.1126/science.1191056[2] Barbosa, C. G. G., et al. (2022). Amazon rainforest aerosols: Characterization and implications for climate. npj Climate and Atmospheric Science, 5, 73. https://doi.org/10.1038/s41612-022-00294-y[3] Graham, B., et al. (2003). Source attribution and seasonality of Amazon aerosol: Implications for cloud formation. Journal of Geophysical Research: Atmospheres, 108. https://doi.org/10.1029/2003JD004049[4] Pöhlker, M. L., et al. (2023). Global organic and inorganic aerosol hygroscopicity and its effect on radiative forcing. Nature Communications, 14(1), 6139. https://doi.org/10.1038/s41467-023-41695-8[5] Moran-Zuloaga, D., et al. (2018). Long-term study on coarse mode aerosols in the Amazon rainforest with frequent intrusion of Saharan dust plumes. Atmospheric Chemistry and Physics, 18(13), 10055–10088. https://doi.org/10.5194/acp-18-10055-2018[6] Andreae, M. O., et al. (2015). The Amazon Tall Tower Observatory (ATTO): Overview of pilot measurements on ecosystem ecology, meteorology, trace gases, and aerosols. Atmospheric Chemistry and Physics, 15(18), 10723–10776. https://doi.org/10.5194/acp-15-10723-2015

Aerosol particles formed by new particle formation (NPF) are essential for cloud condensation nuclei and can strongly influence cloud properties and climate. However, the mechanisms behind NPF in the Amazon boundary layer have remained elusive. Classical "banana" NPF events, common in other continental regions, are rarely observed in the Amazon, while most detected sub-50 nm particles have been linked to precipitation- and downdraft-related episodes, often called Amazonian banana events. Here, we analyse a decade of particle number size distributions (10-420 nm) from the Amazon Tall Tower Observatory (ATTO) during the wet season and demonstrate the presence of a distinct phenomenon called Quiet NPF. This process represents a subtle but persistent background particle formation, occurring on days without clear banana-type growth signatures. Using a statistical approach, we show that Quiet NPF links freshly formed 10 nm particles to their subsequent growth into the Aitken mode. This mechanism is characterized by a growth rate of 2.4 +/- 0.1 nm h-1, about half that of Amazonian banana events, but occurs much more frequently. Quiet NPF accounts for similar to 45 % of 10-25 nm particle production during the wet season, revealing an overlooked but important source of nanoparticles that contributes to sustaining Amazonian aerosol populations.

The Amazon rain forest plays an important role in the biogeochemistry, water cycle, and climate of the South American continent and the Earth system. The Amazon Tall Tower Observatory (ATTO) has been established to study and quantify forest-atmosphere interactions under natural conditions, as well as the transformation of the Amazon ecosystem as a result of increasing perturbations related to deforestation and climate change. Here, we present the design and first results of a custom-made Robotic Lift system, RoLi, installed to automatically measure high-resolution vertical profiles along the 325 m tall ATTO tower at high spatial and temporal resolution at vertical profiling speeds up to 0.5ms-1. The RoLi payload of up to 80kg can be flexibly adjusted and comprises meteorological, trace gas, and aerosol instruments with short inlet lines, minimizing potential wall losses and related artifacts that may occur in longer sampling tubes of tall towers. First measurement results show spatiotemporal patterns in the altitude profiles of temperature, humidity, fog, and aerosol particle concentration and size. This proves RoLi's technical capability to resolve the diel interplay of convectively mixed daytime and stable stratified nighttime conditions. The RoLi data will help to better constrain the gradients and exchange of air masses, gases, and particles across the forest-atmosphere interface and related mixing processes in the lowermost planetary boundary layer.

Biomass burning plays a fundamental role in shaping landscapes and global ecosystem dynamics, with far-reaching impacts on the carbon balance, biodiversity, atmospheric composition, climate, air quality, and human health. In South America, which accounts for approximately 15% of global biomass burning emissions, accurate and accessible emission estimates are essential for long-term monitoring and for delineating policies to support neutral carbon development. We introduce the South American Biomass Burning Inventory (SAMBBI), the first open-access, continuous biomass burning emission inventory for South America, based on the regional model Brazilian Biomass Burning Emissions Model with Fire Radiative Power (BEM_FRP). SAMBBI represents a major advancement in understanding biomass burning emission dynamics and patterns by providing continuous, regularly updated emission estimates from 2003 onwards. This inventory will include emission estimates for the following species released during biomass burning: carbon monoxide (CO), carbon dioxide (CO₂), methane (CH₄), and fine and coarse particulate matter (PM₂.₅ and PM₁₀). SAMBBI aims to achieve five key goals: (1) automating routines and processes to ensure continuous and standardised emission estimates; (2) ensuring the continuity and consistency of emission estimates in the post-MODIS era; (3) facilitating access to emission estimates for researchers, policymakers, and society; (4) predicting biomass burning emissions using artificial intelligence; and (5) quantifying the extent to which fire suppression in the Amazon improves air quality in the largest cities of Brazil, including the São Paulo Metropolitan Area with a population of over 20 million inhabitants. To achieve these goals, SAMBBI will (1) develop a pioneering approach to integrate data from multiple sensors, ensuring continuity in emission time series; (2) create a web platform for dashboard visualisation and seamless access to emission estimates across multiple spatial and temporal resolutions by scientists and stakeholders; (3) develop and train artificial intelligence models using environmental, climatic, and land-use predictors to forecast biomass burning emissions; and (4) conduct air quality simulations with and without Amazonian fire emissions using SAMBBI-driven inputs to quantify the urban pollution burden attributable to Amazonian fires and the potential gains from fire suppression. With these advancements, SAMBBI will constitute an innovative and accessible inventory for enhanced regional and global air pollution assessments, serving as a reference for environmental research and evidence-based policymaking.

Abstract. The Amazon Basin plays an important role in the global climate and carbon budget, with natural emissions and removals of CO2 and CH4 prevailing in the wet season. Accurate modeling of the transport of greenhouse gases (GHG) is essential for understanding the contributions of sources, sinks, and atmospheric processes. High-resolution atmospheric models offer a compromise between computational cost and physical realism, capturing mesoscale processes that influence GHG transport in the Amazon. We evaluate the WRF-GHG model (Weather Research and Forecasting Model with GHG module) using CO2 and CH4 measurements from the Amazon Tall Tower Observatory (ATTO) and aircraft observations during the CAFE-Brazil campaign in January 2023. Simulations employed two domains centered at ATTO, with MapBiomas land cover data, region-specific parameters for CO2 biogenic emissions and removals, and multiple wetland CH4 emission configurations. Comparisons with ATTO indicate that the regionally adapted biogenic flux parameterizations improved the representation of CO2 and net ecosystem exchange (NEE). For CH4, CAMS Inversion-optimized flux product best reproduces observed concentrations, while the Kaplan diagnostic model and WetCHARTs inventories overestimate near-surface mole fractions. The model predicts diurnal CH4 fluctuations, controlled by boundary-layer dynamics and atmospheric transport, that were not observed at ATTO. Comparisons with CAFE-Brazil aircraft data indicated regional wetland sources and wind-driven transport driving the observed CH4 enhancements. These findings underscore the importance of improving the parameterization of biogenic fluxes to enhance the capability of models in complex tropical environments like the Amazon Basin and to accurately describe the complex circulation between rivers, upland areas, and floodplains.

Atmospheric aerosols in the Amazon forest exhibit strong temporal variability driven by seasonally changing sources and boundary-layer processes [1]. In central Amazonia, wet-season conditions are typically dominated by biogenic emissions and secondary organic aerosol (SOA) formation, whereas dry-season conditions are strongly influenced by biomass-burning emissions and long-range transport events [2]. This variability makes the region a natural laboratory for investigating aerosol–boundary layer interactions and vertical exchange processes.The occurrence of convection, turbulence, and boundary-layer dynamics promotes the vertical motion of particles and trace gases [3]. These processes govern the exchange of particles between atmospheric layers, allowing surface-emitted aerosols to reach the free troposphere through deep convection, while SOA formed at higher levels may be reintroduced into the boundary layer through subsidence and downdrafts. Convective downdrafts associated with precipitation have also been shown to increase ground-level ozone concentration, contributing to new particle formation and growth [4].In this context, this study aims to evaluate particle and ozone fluxes over the central Amazon, quantifying the importance of vertical transport mechanisms for the atmospheric composition within the lower troposphere. A diverse range of ground-based measurements performed at the 325-m Amazon Tall Tower Observatory (ATTO) was employed, combining long-term aerosol observations, sonic anemometer measurements, and a novel robotic lift system [5] that enables continuous vertical profiling of aerosol properties.Both eddy covariance and flux-gradient techniques were employed to derive vertical fluxes of particles and ozone during clean wet season conditions. The gradient-based analysis reveals coherent vertical flux patterns associated with rainfall intensity, boundary-layer stratification, and diurnal evolution. Deposition aerosol fluxes dominated, with a mean value of −0.28(12) × 10⁶ m⁻² s⁻¹, in agreement with other flux studies conducted in the Amazon region [6]. Furthermore, negative ozone fluxes were also consistently observed during strong precipitation, indicating the downward transport of ozone-rich air from upper levels in these events.This study sheds light on the magnitude and importance of multiple vertical transport mechanisms, including emission, dry and wet deposition, downdrafts, and the diurnal evolution of the boundary layer, for the variability of aerosol concentrations in the Amazon. Our results provide quantitative constraints on sources, sinks, and transformation pathways of aerosol particles, contributing to an improved understanding of aerosol–turbulence interactions in tropical forest environments and their implications for the local climate. [1] P. Artaxo, et al. Tellus Series B 24.1 (2022): 24–163.[2] R. Valiati, et al. Atmos. Chem. Phys. 25.21 (2025): 14923–14944.[3] L. A. T. Machado, et al. Atmos. Chem. Phys. 21.23 (2021): 18065–18086.[4] L. A. T. Machado, et al. Nat. Geosci. 17 (2024): 1225–1232.[5] S. Brill, et al. Atmos. Meas. Tech. 19.1 (2026): 101–118.[6] L. Ahlm, et al. Atmos. Chem. Phys. 9.24 (2009): 9381–9400.

Tire wear particles (TWPs), an emerging anthropogenic micro- and nanoplastic aerosol, are carbon-containing and light-absorbing. Yet the radiative forcing of TWPs has been difficult to assess due to the lack of optical property data. Here, our calculations based on valence electron energy loss spectroscopy (VEELS) and Mie theory reveal that airborne TWPs exhibit pronounced spectral dependence, with enhanced absorption in the visible and predominantly scattering behavior in the infrared band. At the wavelength of 550 nm, their complex refractive index N of ~ 1.35 − 0.28 i indicates substantial light absorption (absorption coefficient k ≈ 0.28), lying between the k of strongly (e.g., black carbon BC, soot) and weakly (e.g., brown carbon BrC) absorbing aerosols. Global simulations further show collocated but opposite-signed radiative forcing at the surface and the top of the atmosphere (surface cooling and TOA heating). The strongest forcing arises from the Northern Hemisphere mid-latitudes, particularly east-central North America, west-central Europe, and East Asia. Clouds further amplify the TOA response, yielding a global annual mean direct radiative forcing (DRF) of 0.0847 W m − 2 , broadly comparable to that of BrC and ~ 1/4 of that of BC. Together, these results identify TWPs as a previously underappreciated absorbing aerosol class. They have non-negligible impacts on global warming, especially given their substantial radiative efficiency and increasing atmospheric abundance.

The years 2023 and 2024 were characterized by unprecedented warming across the globe, underscoring the urgency of climate action. Robust science advice for decision makers on subjects as complex as climate change requires deep cross- and interdisciplinary understanding. However, navigating the ever-expanding and diverse peer-reviewed literature on climate change is enormously challenging for individual researchers. We elicited expert input through an online questionnaire (188 respondents from 45 countries) and prioritized 10 key advances in climate-change research with high policy relevance. The insights span a wide range of areas, from changes in methane and aerosol emissions to the factors shaping citizens' acceptance of climate policies. This synthesis and communications effort forms the basis for a science-policy report distributed to party delegations ahead of the 29th session of the Conference of the Parties (COP29) to inform their positions and arguments on critical issues, including heat-adaptation planning, comprehensive mitigation strategies, and strengthened governance in energy-transition minerals value chains.

The Amazon rainforest plays an important role in global climate systems, particularly in regional precipitation patterns, atmospheric circulation, and Earth's energy balance. Convective systems in this region are intricately linked to these broader climatic processes. Through a combination of ground-based, satellite, and aircraft observations, we find that Amazonian convective clouds are particularly sensitive to aerosol concentrations, being highly aerosol-limited. This study explores the relationship between cloud droplet concentrations and ambient aerosol particles, both within the Amazon and in broader regions, evaluating various parameterizations commonly used in global climate models. Machine learning methods were used to capture the relationships between various aerosol, cloud, and meteorological parameters in the Amazon rainforest. To gain deeper insight into the microphysical processes within individual clouds, we examine the evolution of the cloud droplet effective radius (rₑ) as a function of cloud temperature (T), looking into the vertical structure of deep convective cumulus clouds.

The Amazon, the world’s largest tropical forest, plays a critical role in the global carbon cycle. It has a large carbon pool and acts as a major carbon sink. However, in 2023–2024, a compound heatwave-drought (CHWD) event (HD2023) hit the Amazon region, resulting in extreme temperatures and soil moisture deficits, threatening the region’s carbon sink capacity. Using advanced multisource satellite data and meteorological reanalysis, we quantified the impact of various climatic factors on vegetation productivity during HD2023 and analyzed its progression. Our findings showed that HD2023 led to a 530 Tg C decline in gross primary productivity (GPP) and 0.003 reduction in near-infrared reflectance of vegetation. The strongest phase of the event spanned 5 months, causing persistently high temperatures and reduced precipitation, leading to a continuous decline in soil moisture and marked reduction in GPP. The most severe decrease in GPP occurred in January 2024. The event originated in the northwest and gradually spread to the southeast. Soil moisture was the dominant factor in the decline of photosynthesis across vegetation types, whereas high solar radiation mitigated the impact of drought in evergreen broad forests and savannas. Moreover, the sensitivity of GPP to CHWD varied across vegetation types, ranking as grassland > savanna > evergreen broad forest. This study assessed the impact of HD2023 on regional carbon flux in the Amazon. As climate projections indicate future increases in climate extremes over the Amazon, it is important to identify the drivers of this impact on the carbon cycle of the Amazon.

The Metropolitan Area of São Paulo (MASP) in Brazil has reduced its vehicular emissions in the last decades. However, it is still affected by air pollution events, mainly in the winter, characterized as a dry season. The chemical composition of fine particulate matter (PM2.5) was studied in the MASP during a 100 d dry period in 2019. PM2.5 samples underwent an extensive chemical characterization (including inorganic and organic species), ecotoxicity was assessed using a bioluminescence-based assay, and submicrometer particle number size distributions were simultaneously monitored. PM2.5 concentrations exceeded the new World Health Organization's daily guidelines on 75 %​​​​​​​ of sampling days, emphasizing the need for strengthening local regulations. Source apportionment (positive matrix factorization, PMF5.0) was performed, and the sources related to vehicular emissions remain relevant (over 40 % of PM2.5). A high contribution of biomass burning was observed, reaching 25 % of PM2.5 mass and correlated with sample ecotoxicity. This input was associated with north and northwest winds, suggesting other emerging sources besides sugarcane burning (forest fires and sugarcane bagasse power plants). A mixed factor of vehicular emissions and road dust resuspension increased throughout the campaign was related to stronger winds, suggesting a significant resuspension. The sulfate secondary formation was related to humid conditions. Additionally, monitoring size particle distribution allowed the observation of particle growth on days impacted by secondary formation. The results pointed out that control measures of high-PM2.5 events should include the control of emerging biomass-burning sources in addition to stricter rules concerning vehicular emissions.