Abstract. Carbon monoxide (CO) is a crucial atmospheric trace gas, significantly influencing the atmosphere's oxidative capacity and indirectly affecting climate. However, the net land-atmosphere exchange of CO remains highly uncertain due to the scarcity of long-term monitoring. This study presents and analyses a 10-year-long CO flux data series from a tall-tower eddy covariance (EC) system operated in a rural Central European region. The measured fluxes were evaluated separately for cases when the flux footprint of the measurement covered almost exclusively quasi-natural areas (arable land, forests), and for cases when the footprint of the measurement covered populated areas (villages, roads). The vegetation-dominated sector (agricultural fields and forests) acted as a weak net CO source from April to September with an average emission of 0.58 nmol m‑2 s‑1 (monthly range 0.31–0.91 nmol m‑2 s‑1), with the highest value occurring in July. The diurnal peaks of the median hourly emissions can be observed around noon, and they range from 1.59 to 2.66 nmol m‑2 s‑1. The nighttime (20–04 h LST) hourly median values range from ‑1.01 to +1.17 nmol m‑2 s‑1. Their deviations from zero are not statistically significant at a p<0.05 probability level. Solar radiation was identified as the primary driver of CO exchange. The measured emissions from the populated areas significantly exceed the activity-based estimations, presumably due to the underestimation of the emissions from residential heating. This study also presents the advantages and challenges of tall-tower EC flux measurements.

A szénvegyületek, döntő részben a szén-dioxid, meghatározó szerepet tölt be a Föld éghajlatának alakításában. A tanulmány áttekinti a szén természetes biogeokémiai körforgalmát és azt, hogy ebben milyen változásokat okozott az emberi tevékenység. Bemutatja a légköri szén-dioxid legfontosabb forrásait és nyelőit, valamint az ezekkel kapcsolatos folyamatokat. Tisztázza, hogy bár a lég-kör és az egyéb szférák közötti bruttó anyagforgalomhoz képest az emberi kibocsátás viszonylag csekély, a légkör szén-dioxid tartalmát alakító nettó anyagforgalomban meghatározó jelentőségű.

Hydrofluorocarbons (HFCs) are potent greenhouse gases widely used in refrigeration, air-conditioning, and heat pump systems. Accurate monitoring of HFC emissions is essential to evaluate compliance with climate regulations and inform mitigation strategies. This study presents trends of HFC emissions across north-western Europe between 2013 and 2024, derived from atmospheric inverse modelling combining atmospheric measurements at eleven monitoring stations with two transport models (NAME and FLEXPART) and three Bayesian inversion systems (InTEM, ELRIS, RHIME). Although global emissions continue to rise for most HFCs, in north-western Europe our results show an overall steady decline in total HFC emissions from 40 +/- 3 Tg CO2-eq yr-1 in 2016 (prior to enhanced regulation) to 29 +/- 2 Tg CO2-eq yr-1 in 2023, following EU F-gas Regulations. This reduction is driven primarily by decreasing emissions of HFC-134a, HFC-143a and HFC-125 despite increasing HFC-32 emissions due to its adoption as a lower-global-warming-potential alternative refrigerant. Comparisons with national inventories reported to the United Nations Framework Convention on Climate Change (UNFCCC) show generally good agreement over north-western Europe but reveal discrepancies for specific compounds and countries, particularly for HFC-134a and HFC-125 in France and Germany during the earlier years of the study period. The recent expansion of the European measurement network demonstrates potential to improve spatial coverage and resolution of inverse emission estimates, especially in southern and central Europe. This study highlights the value of multi-model inversions to provide robust emission estimates with realistic, hence actionable, uncertainty characterisation.

Urban areas are global hotspots of anthropogenic greenhouse gas emissions; however, distinguishing between fossil fuel combustion and biogenic fluxes remains challenging due to the complexity of the urban environment. High-precision atmospheric observations are essential for validating "bottom-up" emission inventories and guiding local green strategies. This study presents a comprehensive comparative analysis examining atmospheric CO2 and CH4 mole fractions, as well as atmospheric radiocarbon (14C) signals, from May 2025 in Debrecen (an urban environment) and two elevations at the regional background station in Hegyhátsál (ICOS HUN).During the research campaign, Picarro Cavity Ring-Down Spectroscopy (CRDS) analyzers were employed at both sites for continuous, high-resolution measurement of CO2 and CH4 concentrations. These measurements were complemented by a two-week integrated 14CO2 sampling, followed by Accelerator Mass Spectrometry (LEA-AMS) analysis. This dual-tracer approach enables the separation of the Debrecen CO2excess into fossil and biogenic components.Our results highlight that the urban-derived excess varies dynamically relative to the regional background. The continuous mole fraction data reveal characteristic diurnal and seasonal patterns, with wintertime enrichment of CO2 and CH4, driven by reduced boundary layer mixing and increased heating demand. Analysis of CH4:CO2 correlations provides further insight into sector-specific emissions, distinguishing between traffic-dominated and heating-dominated periods. By combining high-frequency concentration measurements with isotopic constraints, our study provides a more precise understanding of the urban carbon cycle in a mid-sized city in Hungary, highlighting the importance of parallel urban-rural monitoring networks in verifying climate protection measures.

The study analyses in situ CO2 mole fraction, (CO2)-C-14, and fossil based excess CO2 mole fraction (C-foss) data at Hegyh & aacute;ts & aacute;l (HUN) rural monitoring station (Central Europe) supplemented by passive monitoring of C-14 content of tree-rings. Through the observed period (2014-2020) we focused on revealing trends in atmospheric CO2 and C-14 levels, particularly during the year of the first COVID lockdown, in comparison to the preceding five years. In addition, monthly integrated samples of atmospheric CO2 and tree-rings from the six years were subjected to C-14 analysis. The passive tree-ring measurements focuses on two major urban areas (Budapest and Debrecen) in Hungary, along with the rural monitoring site. Results show a steady increase in CO2 levels at HUN between 2014 and 2020. The calculated fossil based excess CO2 concentrations for the initial year of COVID are in good agreement with the previous five-year averages both at 115 m and 10 m elevations. These results also show seasonal variations of CO2 mole fractions, peaking in winter and decreasing in summer. Tree-ring results from Debrecen show a good alignment with the results of the atmospheric monitoring station, and it does not show a significant fossil contribution in the urban background area during the vegetation periods. Tree-ring results from Budapest show a stronger fossil contribution compared to the Debrecen ones. Our atmospheric CO2 results do not show a large decrease in fossil CO2 atmospheric contribution during the first lockdown. We found that the use of this passive CO2 monitoring technique can provide a valuable tool for investigating such differences.

The global impact of COVID-19 on communities and economies has led to questions about decreasing environmental risks and pollution due to the decreased industrial and transport activity. One of the key concerns revolves about the atmospheric rise in CO2 levels and the associated arising fossil carbon load, constituting the global climate change. The quantification of fossil-origin atmospheric carbon load is addressed through the use of natural radiocarbon (14C), a unique scientific tool. Fossil sources lack 14C activity, while recent biogenic carbon contains radiocarbon. This study centers on revealing long-term trends in atmospheric 14C levels, particularly during the year of the pandemic, in comparison to the preceding five years in Hungary. Atmospheric CO2 and tree rings from the studied six years were subjected to 14C analysis from three distinct locations. One of the examined cities, Budapest - Hungary's capital - is a highly urbanized land with a reported 1.7 million population. Despite the city's extensive vehicular and human activity, a "state of danger" was in effect in Hungary from March to June 2020 due to the first wave of COVID-19. The sampling sites had been characterized by a busy urban environment, with a mix of vehicular activities contributing to the local atmosphere. The second urban sampling site is Debrecen, a smaller but evolving city that can be found in the eastern part of Hungary. It’s the second largest Hungarian city - around 200 thousand citizens – and it is currently experiencing an industrial revolution by the construction of major factories. Significant contribution to pollution in this area come from urban vehicular traffic and the surrounding agricultural regions. The background 14C signal used in the study is from the easternmost Integrated Carbon Observation System(ICOS) atmospheric regional background station (HUN) and NOAA background site, at Hegyhátsál. Mole fraction has been continuously monitored at four elevations at HUN station since September 1994. For this research integrated atmospheric 14CO2 samples, supplemented with CO2 mole fraction measurements, were used from October 2014 to December 2020. The data was studied from the aspect of temporal variation and altitudinal differences. CO2 mole fraction data of the free tropospheric background ICOS station at Jungfraujoch (Switzerland) were used. The outcomes of the trend analysis reveal the fluctuations in atmospheric fossil carbon load throughout the pandemic, which offers valuable insights into the environmental effects of reduced human activities in Hungary. Prepared with the professional support of the Doctoral Student Scholarship Program of the Co-operative Doctoral Program of the Ministry of Innovation and Technology financed from the National Research, Development and Innovation Fund and supported by the PARIS project (Grant Agreement No. 820846), which is funded by the European Commission through the Horizon 2020 research programme.

The main goal of ICOS Hungary was to expand the geographical coverage of the ICOS network towards Eastern Europe. As Hungary is located in the zone of westerlies winds in Europe, adding measurement stations East of the existing ICOS network may significantly reduce the uncertainty of the continental atmospheric CO2 and CH4 budget models. Since the joining of HUN it is (almost) the easternmost ICOS atmospheric background station. ICOS has high expectations for all the stations seeking to join the observation system. These expectations include ensuring the highest quality and employing state-of-the-art equipment available in the stations. Atmospheric stations wishing to connect to the network has to develop their gas handling systems themselves. This requirement places additional responsibility on the operators of stations to create their own systems, allowing them to tailor gas handling processes to their unique needs and in accordance with ICOS network specifications. The gas handling system for the HUN station, was built in the collaboration between ATOMKI and Isotoptech Zrt., that has been developed for the possibility of commercial use also. This developed system has been operational in Hegyhatsal since the spring of 2022. The core of the system's is a Picarro analyzer (CO2, CH4 and H2O), that requires properly filtered and semidried air for operation. According to the expectations, the developed system meets all the ICOS requirements, including minimized response time, addressing memory effects, and ensuring appropriate flushing capacity. It operates in five independent sampling height (at HUN connected to elevations at 115m, 82m, 50m, 10m and a spare one) with a sampling rate of 10 l/min. Each line uses 2-micron filters before the Picarro, and one multiport VALCO rotary valve runs for efficient and precise environmental GHG gas analysis. For the purpose of ensuring analytical security, high-performance KNF inert pumps are employed for sample transfer/flushing in order to maintain the integrity and reliability of the analytical process. From 2022 the monitoring station continuously measures atmospheric concentrations of CO2, CH4, and other trace gases at the four sampling levels. The entire novel, compact gas handling equipment (made by Isotoptech) has stand-alone design, with a footprint of less than 1 m2, 2 m height, integrates all the components, and is designed for easy mobility. The gas handling system has undergone one year of routine operation with minimal maintenance requirements, proving to be reliable and consistently operational even while it is managed remotely from a distance of 500 km, without significant disruptions. Prepared with the professional support of the Doctoral Student Scholarship Program of the Cooperative Doctoral Program of the Ministry of Innovation and Technology financed from the National Research, Development and Innovation Fund and supported by the PARIS project (Grant Agreement No. 820846), which is funded by the European Commission through the Horizon 2020 research programme.

A metán a légkörben legnagyobb mennyiségben előforduló szerves vegyület. Kémiai reakciói révén meghatározó szerepet tölt be a troposzferikus ózonképződésben, üvegházhatású gázként pedig nem elhanyagolható mértékben befolyásolja a Föld éghajlatát. A tanulmány áttekinti a légköri metán forrásait és nyelőit, a metán által vezérelt légköri kémiai folyamatokat, továbbá a metánkoncentráció időbeli alakulását.

The paper reviews and evaluates a 30-year-long atmospheric CO2 data series measured at the Hegyhátsál tall-tower greenhouse gas monitoring site, a member of the World Meteorological Organization (WMO) Global Atmosphere Watch (GAW), US National Oceanic and Atmospheric Administration (NOAA), and pan-European Integrated Carbon Observation System (ICOS) networks. The paper also gives the technical description of the monitoring system and its changes over time and introduces the environment of the station. This low-elevation (248 m above mean sea level – m a.m.s.l.), mid-continental central European site shows a 3.90 ± 0.83 µmol mol−1 offset relative to the latitudinally representative marine boundary layer reference concentration, presumably due to European net anthropogenic emissions. The long-term trend (2.20 µmolmol-1yr-1) closely follows the global tendencies. In the concentration growth rate, the ENSO effect is clearly detectable with a 6–7-month lag time. The summer diurnal concentration amplitude is slightly decreasing due to the faster-than-average increase in the nighttime concentrations, which is related to the warming climate. The warming climate also caused a 0.96 ± 0.41 d yr−1 advance at the beginning of the summer CO2-deficit season in the first half of the measurement period, which did not continue later. The summer CO2-deficit season was extended by 9.0 ± 6.1 d during the measurement period.

Hatékony üvegházgázkibocsátás-csökkentési stratégiák kidolgozása, a vállalások betartásának ellenőrzése megvalósíthatatlan megfelelő mérőhálózat nélkül. Az európai Integrált Szén-dioxid-megfifigyelési Rendszert (Integrated Carbon Observation System – ICOS) 2015-ben hozták létre. Magyarország 2022-ben csatlakozott, és az első magyarországi mérőállomás 2024 májusában kapta meg a hivatalos ICOS minősítést. A tanulmány az ICOS létrejöttét, felépítését, működését, valamint a magyar részvételt tekinti át.

A számos kutatás és módszertani fejlesztés ellenére az evapotranspiráció az egyik legnehezebben becsülhető komponense a vízmérlegnek. Az egyik közvetlen módszer, amivel az evapotranspirációt becsülni tudjuk, az ún. eddy-kovariancia mérés, amelyet a sok befolyásoló tényező és alapfelvetés miatt számottevő bizonytalanság terhel. Kutatásunk célja az evapotranspiráció mértékének és korlátainak meghatározása és becslése gyepes és szántóföldi területek felett a Magyarországon rendelkezésre álló hosszú idejű eddy-kovariancia mérések alapján.

Although small rural settlements are only minor individual sources of greenhouse gases and air pollution, their high overall quantity can significantly contribute to the total emissions of a region or country. The emissions of the rural lifestyle may be remarkably different from that of the urban and industrialized regions, but nevertheless they have been hardly studied so far. In this study, flux measurements at a tall-tower eddy covariance monitoring site and the footprint model FFP are used to determine the real-world wintertime CO, N2O, and CO2 emissions of a small village in western Hungary. The recorded emission densities, dominantly derived from residential heating, are 3.5 μg m-2 s-1, 0.043 μg m-2 s-1, and 72 μg m-2 s-1 for CO, N2O, and CO2, respectively. While the measured CO and CO2 emissions are comparable with those calculated using the assumed energy consumption and applying the according emission factors, the nitrous oxide emission exceeds the expected value by a magnitude. This may indicate that the nitrous oxide emissions are significantly underestimated in the emission inventories, and modifications in the methodology of emission calculations are necessary. Using a 3-dimensional forward transport model, we further show that, in contrast to the flux measurements, the concentration measurements at the regional background monitoring site are only insignificantly influenced by the emissions of the nearby village.

Although small rural settlements are only minor individual sources of greenhouse gases and air pollution, their high overall occurrence can significantly contribute to the total emissions of a region or country. Emissions from a rural lifestyle may be remarkably different than those of urban and industrialized regions, but nevertheless they have hardly been studied so far. Here, flux measurements at a tall-tower eddy covariance monitoring site and the footprint model FFP are used to determine the real-world wintertime CO, N2O, and CO2 emissions of a small village in western Hungary. The recorded emission densities, dominantly resulting from residential heating, are 3.5, 0.043, and 72 µg m−2 s−1 for CO, N2O, and CO2, respectively. While the measured CO and CO2 emissions are comparable to those calculated using the assumed energy consumption and applying the according emission factors, the nitrous oxide emissions exceed the expected value by a magnitude. This may indicate that the nitrous oxide emissions are significantly underestimated in the emission inventories, and modifications in the methodology of emission calculations are necessary. Using a three-dimensional forward transport model, we further show that, in contrast to the flux measurements, the concentration measurements at the regional background monitoring site are only insignificantly influenced by the emissions of the nearby village.

In the first half of the 19th century, it became clear that the atmosphere plays a crucial role in governing the Earth’s climate. By the middle and second half of the century, it was clear that the atmosphere’s ability to retain heat was mainly due to water vapor and carbon dioxide, and that changes in their quantity would lead to changes in the Earth’s climate. Even then, industrial activity was already known to emit significant amounts of carbon dioxide, and at the turn of the 19th century to the 20th, it was suggested that coal combustion could change the planet’s climate over time. The first attempts to demonstrate the climate-changing effects of human activity were made in the 1930s, but it was not until the mid-20th century that there was clear evidence for carbon dioxide accumulating in the atmosphere, largely as a result of human activity. This paper highlights some of the perhaps less widely known episodes in atmospheric greenhouse research. This historical review of science also makes the reader aware that today’s climate research is no longer primarily concerned with the causes of current climate change, but with the rate and extent to which the highly complex climate system is responding to the atmospheric energy forcing.

Continental greenhouse gas monitoring networks extensively use tall towers for higher spatial representativeness. In most cases, several intakes are built along the tower to give information also on the vertical concentration profile of the components considered. Typically, a single gas analyzer is used, and the intake points are sequentially connected to the instrument. It involves that the continuous concentration signal is only sampled for discrete short periods at each intake point, which does not allow for a perfect reconstruction of the original concentration variation. It increases the uncertainty of the calculated hourly averages usually used by the atmospheric transport and budget models. The purpose of the study is to give the data users an impression of the potential magnitude of this kind of uncertainty, as well as how it depends on the number of intakes sampled, on the length of the sampling period at each intake, on the season, and on the time of the day. It presents how much improvement can be achieved using linear or spline interpolation between the measurement periods instead of the simple arithmetic averaging of the available measurements. Although the results presented here may be site-specific, the study calls attention to the potentially rather heterogeneous spatial and temporal distribution of the uncertainty of the hourly-average concentration values derived from tall-tower measurements applying sequential sampling.

Precipitation was collected on daily basis at K-puszta regional background monitoring station located near Kecskemét, in the western part of the Great Hungarian Plain, between 1 April 2013 and 31 December 2017 for stable hydrogen and oxygen analyses. The sample collection period covered 24 hours, from 07:00 to 07:00 h LT (Local Time) the next day. Stable hydrogen and oxygen isotope composition of the daily precipitation samples were measured using a Liquid Water Isotope Analyser (LWIA-24d) manufactured by Los Gatos Research Ltd. The dataset includes 472 stable isotopic data representing the continuation of the beforehand monitoring started in 2012 [1]. The dataset provides a unique opportunity to combine daily meteorological data and stable isotope composition of daily precipitation which can help to improve our understanding of the processes and factors at relatively high resolution that govern δD and δ18O values of the precipitation. In addition, the dataset can be used as an isotope hydrological benchmark in comparison with stable isotope dataset obtained from surface- and groundwater or other sources (e.g. climate proxies, agricultural products). Thus, research related to isotope hydrology, agriculture, paleoclimate can benefit from this dataset. Interpretation of this dataset focusing on the relationship between meteorological factors and stable isotope composition of precipitation is in progress.

The methane emissions from the Hungarian Pannonian Basin are not well qualified, due to a lack of measurements of CH4 mole fraction and delta C-13(CH4) in the air. This study reports methane measurements in air samples from Hungary, placing them in the context of regional and global background data, to investigate the inputs to the methane burden in Central Europe. CH4 mole fraction and delta C-13(CH4) from the Hungarian tall tower station, Hegyhatsal, and additional data from Mace Head (Ireland) and Zeppelin (Svalbard) are used with back trajectory modeling to identify central European source areas and their seasonal variation between the summer vegetation and winter heating periods. Methane measurements in air masses sampled in the European interior, have significantly higher maxima and seasonal amplitudes than at the Mace Head and Zeppelin European background sites. The mean CH4 mole fraction value is about 80 ppb higher than the comparable marine background, and values above 2,000 ppb were frequently observed between February 2013 and December 2015. The mean delta C-13(CH4) value -47.5 +/- 0.3 parts per thousand (2 sigma) was comparable to values at all three monitoring sites, but specific pollution events were detected at Hegyhatsal. Concentration weighted trajectory modeling, meteorological parameters, stable carbon isotopic composition (delta C-13(CH4)), and Miller-Tans analysis show that the main factors influencing CH4 at the Hegyhatsal, apart from diurnal and seasonal changes in the planetary boundary layer, are emissions from residential heating and industrial CH4 emissions during the winter.

We developed a high-resolution surface flux inversion system based on the global Eulerian–Lagrangian coupled tracer transport model composed of the National Institute for Environmental Studies (NIES) transport model (TM; collectively NIES-TM) and the FLEXible PARTicle dispersion model (FLEXPART). The inversion system is named NTFVAR (NIES-TM–FLEXPART-variational) as it applies a variational optimization to estimate surface fluxes. We tested the system by estimating optimized corrections to natural surface CO2 fluxes to achieve the best fit to atmospheric CO2 data collected by the global in situ network as a necessary step towards the capability of estimating anthropogenic CO2 emissions. We employed the Lagrangian particle dispersion model (LPDM) FLEXPART to calculate surface flux footprints of CO2 observations at a spatial resolution of 0.1∘×0.1∘. The LPDM is coupled with a global atmospheric tracer transport model (NIES-TM). Our inversion technique uses an adjoint of the coupled transport model in an iterative optimization procedure. The flux error covariance operator was implemented via implicit diffusion. Biweekly flux corrections to prior flux fields were estimated for the years 2010–2012 from in situ CO2 data included in the Observation Package (ObsPack) data set. High-resolution prior flux fields were prepared using the Open-Data Inventory for Anthropogenic Carbon dioxide (ODIAC) for fossil fuel combustion, the Global Fire Assimilation System (GFAS) for biomass burning, the Vegetation Integrative SImulator for Trace gases (VISIT) model for terrestrial biosphere exchange, and the Ocean Tracer Transport Model (OTTM) for oceanic exchange. The terrestrial biospheric flux field was constructed using a vegetation mosaic map and a separate simulation of CO2 fluxes at a daily time step by the VISIT model for each vegetation type. The prior flux uncertainty for the terrestrial biosphere was scaled proportionally to the monthly mean gross primary production (GPP) by the Moderate Resolution Imaging Spectroradiometer (MODIS) MOD17 product. The inverse system calculates flux corrections to the prior fluxes in the form of a relatively smooth field multiplied by high-resolution patterns of the prior flux uncertainties for land and ocean, following the coastlines and fine-scale vegetation productivity gradients. The resulting flux estimates improved the fit to the observations taken at continuous observation sites, reproducing both the seasonal and short-term concentration variabilities including high CO2 concentration events associated with anthropogenic emissions. The use of a high-resolution atmospheric transport in global CO2 flux inversions has the advantage of better resolving the transported mixed signals from the anthropogenic and biospheric sources in densely populated continental regions. Thus, it has the potential to achieve better separation between fluxes from terrestrial ecosystems and strong localized sources, such as anthropogenic emissions and forest fires. Further improvements in the modelling system are needed as our posterior fit was better than that of the National Oceanic and Atmospheric Administration (NOAA)'s CarbonTracker for only a fraction of the monitoring sites, i.e. mostly at coastal and island locations where background and local flux signals are mixed.

This study presents a detailed statistical analysis on the relationship of precipitation water origin and its stable hydrogen and oxygen isotope compositions for six sites in Hungary. We carried out a moisture source diagnostic by analyzing backward trajectories as it has become a common method for identifying moisture uptake locations. For providing 96 hours long precipitation-event based backward trajectories, we used the NOAA HYSPLIT model on daily basis for six sites of three elevation, 500 m, 1500 m and 3000 m. The moisture uptake regions were determined by calculating specific humidity along the trajectories. Five possible moisture source regions for precipitation were defined: Atlantic Ocean, North European Seas, Mediterranean Sea, Black Sea, Carpathian Basin and European continental areas excluding the Carpathian Basin. The main water vapor source areas are in order the continental regions following by the Mediterranean Sea and the Atlantic Ocean. However, there are spatial differences among the sampling sites reflecting the importance of the geographical locations. Principal component analysis based on the d-excess value of precipitation events showed that source regions such as the Carpathian Basin, the Atlantic Ocean and Mediterranean Sea are separated on the plain determined by the first two principal components. In order to evaluate the impact of the moisture source region on the d-excess value of precipitation events, we carried out ANOVA on the precipitation-event based macrosynoptic classification (Hess-Brezowsky and Péczely). Our results suggest that there are significant differences between amount-weighted d-excess values belonging to different macrosynoptic patterns and these types are related to precipitation events from different moisture source regions. Cluster analysis confirmed the differences in precipitation stable isotope values according to the moisture sources. The observations (precipitation events) were projected on the plain outspreaded by the first two principal components. The coordinates of the observations in this coordinate-system are separated according to the three main moisture source regions. Cluster analysis was also carried out based on d-excess values. The investigation showed that lower d-excess values are related to the Atlantic Ocean, while higher values to the Mediterranean Sea. Thus, we can conclude that the moisture source has strong impact on the stable isotope composition of precipitation water even relative far from the marine regions. The research was supported by the ÚNKP-19-3 New National Excellence Program of the Ministry for Innovation and Technology, the National Research, Development and Innovation Office (project No. OTKA NK 101664, PD 121387) and the AgroMo project (GINOP-2.3.2-15-2016-00028).