The global annual mean atmospheric CO₂ growth rate in 2023 was one of the highest since records began in 1958, comparable to values recorded during previous major El Niño events. We do not fully understand this anomalous growth rate, although a recent study highlighted the role of boreal North American forest fires. We use a Bayesian inverse method to interpret global-scale atmospheric CO₂ data from NASA's Orbiting Carbon Observatory (OCO-2). The resulting a posteriori CO₂ flux estimates reveal that from 2022 to 2023, the biggest changes in CO₂ fluxes of net biosphere exchange (NBE) – for which positive values denote a flux to the atmosphere – were over the land tropics. We find that the largest NBE increase is over eastern Brazil, with small increases over southern Africa and Southeast Asia. We also find significant increases over southeastern Australia, Alaska, and western Russia. A large NBE increase over boreal North America, due to fires, is driven by our a priori inventory, informed by independent data. The largest NBE reductions are over western Europe, the USA, and central Canada. Our NBE estimates are consistent with gross primary production estimates inferred from satellite observations of solar-induced fluorescence and from satellite observations of vegetation greenness. We find that warmer temperatures in 2023 explain most of the NBE change over eastern Brazil, with hydrological changes more important elsewhere across the tropics. Our results suggest that the ongoing environmental degradation of the Amazon is now playing a substantial role in increasing the global atmospheric CO₂ growth rate.

Northern Italy is one of the most polluted and densely populated areas in Europe. The diversity of land use in the Po basin makes this region an important contributor to greenhouse gas emissions from different sources. Medium and large cities, as well as industrialised areas, contribute significantly to emissions from industrial processes, combustion, waste management and natural gas distribution.As part of the H2020 RI-URBANS project (https://riurbans.eu/) and in synergy with PNRR “ITINERIS” Project, a pilot study has been carried out in the Milan urban area with the aim of supporting the local authorities to evaluate the effectiveness of air quality policies and the effects of pollutants on human health. A one-year long measurement campaign was carried out using a mobile platform in the premises of the CNR facility (AdRMi1, 45°28’47"N 9°13’54"E; 120 m a.s.l.), located in in the urban area of Milan, in the University district. The mobile platform has been equipped with a suite of instruments (ACSM, Vocus Chemical Ionization TOF-MS, Aethalometer, NOx CLD) to provide near real time (NRT) information on aerosol source partitioning and to characterise nanoparticle contributions from urban hot spots. From July 2023 to March 2024, the mobile platform has been equipped with a Cavity Ring Down Analyser for continuous observations of carbon dioxide (CO2) and methane (CH4).In this work we will provide a first characterization of the diel cycles and seasonal variations (from late summer to early spring) of atmospheric CO2 and CH4 in the urban area of Milan. Thanks to the combined analysis of other atmospheric tracers, first insights about the influence by atmospheric processes (i.e. PBL dynamics) and emission sources (fossil fuel and biomass burning combustion, biogenic, waste management) will be discussed. Finally, we provided a preliminary “top-down” estimate of CH4 emission for the Milan urban area by using the interspecies correlation approach: the obtained values were higher (but still within the range of uncertainties) than emissions provided by statistical “bottom-up” inventories (e.g. INEMAR).Acknowledgments: RI-URBANS t has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101036245. This reserach was partially supported by the European Unione- Next Generation EU, Missione 4 Componente 2 - CUP B53C22002150006 - IR0000032 – ITINERIS, Italian Integrated Environmental Research Infrastructures System

Accurately separating the contributions of different sources to recent atmospheric methane (CH ₄ ) growth is crucial for better quantifying the present and future responses of CH ₄ emissions to changing climate and anthropogenic activity. Here, we run atmospheric inversions to assess global and regional CH ₄ emissions from microbial, fossil, and pyrogenic sources from 2000 to 2022, using measurements of atmospheric CH ₄ and its stable carbon isotope ratio ( ¹³ C: ¹² C, expressed relative to a standard as δ ¹³ C-CH ₄ ). We confirm that global total CH ₄ emissions has increased by 15% from 2000 to 2022, with dominated contribution from microbial emissions. Both microbial and fossil emissions increased during 2007–2013 relative to 2000–2006, with the largest contributions from temperate Asia. From 2014–2017, microbial emissions from tropical regions, particularly South America and Africa, were the dominant driver of the overall increase, while fossil emissions remained stable in Europe and North America. Between 2020 and 2022, microbial emissions surged in the African and Asian tropics, whereas fossil emissions declined across most industrial regions. Notably, inversions constrained only by CH ₄ observations did not capture the decline in fossil emissions during 2020–2022, a decline potentially related to the COVID-19 pandemic, policy-driven changes, and decreases in CH ₄ emissions intensity, highlighting the critical role of isotopic measurements in independently verifying changes in fossil emissions. Further, our inversion with isotopic constraints estimates a more prominent increase in wetland emissions that is 20–30% more strongly correlated with variations in terrestrial water storage during 2003–2022, demonstrating the importance of climate-driven natural sources in explaining long-term CH ₄ growth.

In this article, we present the results of the chemical and microbiological characterization of clouds water collected at Monte Cimone (CMN) in Italy at 2165 m a.s.l. during the MC3 (Molecular Composition of Clouds at mt. Cimone) campaign, which took place in October 2024. Twenty-six cloud samples are analyzed. Chemical analyses, including ions, oxidants, trace metals, and microbiological analyses with cell counting, are performed. The chemical characterization and back-trajectories analysis reveal that Mt. Cimone is a site under the influence of marine air masses, coming mainly from southern Europe and from the Mediterranean region. During the measurement campaign, 3 sampling periods are identified: period (1) 7–10 October, with air masses mainly originating from Spain and Atlantic Ocean with a majority of Cl− and Na+ that are characteristics of marine origin; period (2) 16–18 October with air masses originating from North of Africa, impacted by a Saharan dust event with a high concentration in Ca2+; period (3) 22–23 October marked by air masses originated from southern Italy under polluted influence with a high concentration in NO3-. Across the campaign, DOC ranged from 1.6 to 4.3 mgC L−1, while H2O2 reached its maximum during period 3 (71.8±35.4 µmol L−1), highlighting enhanced oxidant levels under polluted conditions. This study paves the way to further scientific campaigns intended to better comprehend cloud water composition at Mt. Cimone.

Methane (CH4) is a potent greenhouse gas with a global warming potential of about 84 over a 20-year timescale, and an atmospheric lifetime of about 9 years. The increase in CH4 emissions has contributed about 0.6°C to the observed global warming since pre-industrial times. The ongoing increase in atmospheric CH4 undermines efforts to mitigate climate change. To effectively mitigate CH4, it is essential to understand the location, strength and temporal variability of its most important sources, which vary in different regions. A widely used method to distinguish emissions from different source categories is the measurement of CH4 isotopic composition. Such measurements provide additional insight because different CH4 production processes emit CH4 with different isotopic composition.Traditionally, CH4 isotope measurements have been carried out on atmospheric air samples under controlled laboratory conditions, but since a few years, instruments measuring isotopic composition continuously at monitoring stations have become available. An important application of continuous isotopic CH4 measurements is the evaluation of regional scale emissions with respect to the existing emission inventories. In model simulations using emissions from these inventories, the relative contributions of different source categories to observed enhancements can be calculated. This information can be used to simulate time series of the isotopic composition. By comparing these simulations with observed isotopic data, we can not only assess whether total emissions in a model are over- or underestimated, but also identify which source categories are responsible for any discrepancies.The mobile isotope ratio mass spectrometry system developed at Utrecht University has been deployed at more than 10 different locations in Europe over the past decade, in most cases for approximately 7 months. The recorded 20-min resolution and high precision isotope data of both d13C and d2H provide empirical constraints to the CH4 source mix at the different locations. The combination with high resolution model simulations has provided many new insights into regional scale emissions. We present an overview of key findings and discuss the value of high resolution isotope measurements for improving our understanding of the regional budgets of this important greenhouse gas.

We report the installation and first two years of operation of an EM27/SUN Fourier transform spectrometer at the CNR-ISAC facility in Bologna, Italy, the first instrument of its kind operating in the Po Valley, one of the European region mostly affected by anthropogenic pollution. The instrument is integrated into the COCCON network and it retrieves total columns and column-averaged dry air mole fractions of CO₂, CH₄, CO, and H₂O using the PROFFAST processing chain as per standardized COCCON protocols. The data is filtered with the fitted solar gas shift in the O₂ absorption band for quality controls, and here we study the seasonality of the retrieved products. To assess the relationship between column-integrated and near-surface measurements, we present a case-study comparison against a co-located Cavity Ring-Down Spectroscopy analyzer for CO₂ and CH₄ over a single day, using ceilometer-derived Mixed Aerosol Layer height to interpret the differing diurnal variability between the two techniques, with CRDS showing substantially larger amplitude swings driven by boundary-layer dynamics and surface emission/sink processes. We further validate the EM27/SUN against TROPOMI satellite retrievals of XCH₄ and total-column CO over the full observing period, finding low systematic biases (-0.13% and 0.60% respectively) consistent with satellite mission requirements and comparable to TCCON stations at similar latitudes. As a case-study, we show that both instruments jointly detected an anomalous CO enhancement in July-August 2024 attributable to long-range transport of Canadian wildfires smoke, illustrating the capability of ground-based FTIR observations to identify high-altitude pollution intrusions undetectable by in-situ instrumentation alone. These results establish the EM27/SUN in Bologna as a robust reference for satellite validation and a valuable tool for characterizing atmospheric transport events in the Po Valley.