Abstract Paleoclimate reconstructions of wildfire using ice cores often rely on high‐resolution aerosol records of refractory black carbon (rBC) or ammonium (NH 4 + ). The interpretation of such records, however, can be hindered by uncertainties related to long‐range atmospheric transport, spatial distribution and strength of emissions, as well as glaciochemical noise introduced to the record during and after deposition. Here, we use arrays of parallel ice cores collected from two sites in Greenland, each with differing characteristics including accumulation rate, elevation, and meteorology, to assess the spatial variability and site representativeness of their rBC and NH 4 + records. The higher accumulation site, Summit, was found to preserve a more coherent signal of both aerosols across multiple ice core records and was more representative of the total site signal than the lower accumulation site, Tunu. Representativeness analyses indicate that a single core at Summit is as representative of the theoretical total site signal as a combined three core composite record from Tunu for rBC and NH 4 + at annual resolution. This work suggests that high temporal resolution records of these aerosols using a single core from either site have considerable uncertainties, highlighting the need for careful consideration of the effects of site conditions on aerosol representativeness for wildfire reconstruction.

Abstract. We determine European emissions of sulfur hexafluoride (SF6) from 2005 to 2021 using a large ensemble of atmospheric inversions. To assess uncertainty, we systematically vary key inversion parameters across 986 sensitivity tests and apply a Monte Carlo approach to randomly combine these parameters in 1,003 additional inversions. Our analysis focuses on high-emitting countries with robust observational coverage — UK, Germany, France, and Italy — while also examining aggregated EU-27 emissions. SF6 emissions declined across all studied regions except Italy, largely attributed to EU F-gas regulations (2006, 2014), however, national reports underestimated emissions: (i) UK emissions dropped from 65 (±13) t yr−1 in 2008 to 20 (±6) t yr−1 in 2018, aligning with the reports from 2018 onward; (ii) French emissions fell from 88 (±37) t yr−1 (2005) to 51 (±28) t yr−1 (2021), exceeding reports by 73 %; (iii) Italian emissions fluctuated (31–67 t yr−1), surpassing reports by 88 %; (iv) German emissions declined from 166 (±41) t yr−1 (2005) to 95 (±11) t yr−1 (2021), aligning reasonably well with reports; (v) EU-27 emissions decreased from 484 (±213) t yr−1 (2005) to 255 (±58) t yr−1 (2021), exceeding reports by 40 %. A substantial drop from 2017 to 2018 mirrored the trend in southern Germany, suggesting regional actions were taken as the 2014 EU regulation took effect. Our sensitivity tests highlight the crucial role of dense monitoring networks in improving inversion reliability. The UK system expansions (2012, 2014) significantly enhanced result robustness, demonstrating the importance of comprehensive observational networks in refining emission estimates.

The Arctic has seen dramatic changes in recent decades. Here we use a simple metric, the Arctic residence time of air, that is, the time air spends uninterruptedly north of 70N, to evaluate how these changes have affected the high‐latitude atmospheric circulation in the last 40 years. We find that, on average, near‐surface air resides between 7 (winter) and 12 (summer) days in the Arctic. This residence time has decreased almost year‐round since the 1980s, especially pronounced in the seasonal transition periods (fall: 0.9 days; spring: 1.4 days). The more pronounced reduction in spring also affects higher atmospheric layers. Our analysis indicates that this reduction is likely linked to the observed sea ice loss, decrease in snow cover, and increase in temperature. Furthermore, it indicates a speed‐up of the circulation, effectively making the Arctic less isolated and more prone to influences from mid‐latitudes.

Atmospheric heavy metal pollution from metal smelting, mining, and fossil fuel combustion poses a major threat to human health and the environment. Anthropogenic emissions from the territory of the former Soviet Union (FSU) considerably contributed to heavy metal pollution in Europe. However, due to limited monitoring and fragmentary reporting, FSU emission levels remain poorly quantified and recent trends are controversial. This study compares post-SU anthropogenic emissions of heavy metals (Ag, Bi, Cd, Cu, Pb, Sb, Zn) to those from the SU era based on new state-of-the-art emission estimates for 1975-2015 and ice-core reconstructions spanning the period 1700-2018. Ice-core records from the Tsambagarav and Belukha glaciers in the Altai region reveal marked increases in heavy metal concentrations during 1930-2018, with peak pollution levels from the FSU territory in the 1970s and 2000s, coinciding with periods of industrial growth. According to the new emission estimates, all seven heavy metals experienced a continuous 60-90 % decline in emissions between 1975 and 2015. The ice-core data confirm such a significant reduction for Cu, Sb, and Zn. However, concentrations of Ag, Bi, Cd, and Pb remained elevated in 2010-2018, at 40-70 % of their 1970s levels. These persistently high recent levels, along with the secondary concentration peaks in the early 21st century, suggest that emissions from reemerging metal production in the FSU countries after the dissolution of the SU are underestimated.

Atmospheric ammonia (NH3) is a key transboundary air pollutant that contributes to the impacts of nitrogen and acidity on terrestrial ecosystems. Ammonia also contributes to the atmospheric aerosol that affects air quality. Emission inventories indicate that NH3 was predominantly emitted by agriculture over the 19th and 20th centuries but, up to now, these estimates have not been compared to long-term observations. To document past atmospheric NH3 pollution in south-eastern Europe, ammonium (NH4+) was analysed along an ice core extracted from Mount Elbrus in the Caucasus, Russia. The NH4+ ice-core record indicates a 3.5-fold increase in concentrations between 1750 and 1990 CE. Remaining moderate prior to 1950 CE, the increase then accelerated to reach a maximum in 1989 CE. Comparison between ice-core trends and estimated past emissions using state-of-the-art atmospheric transport modelling of submicron-scale aerosols (FLEXPART (FLEXible PARTicle dispersion) model) indicates good agreement with the course of estimated NH3 emissions from south-eastern Europe since ∼ 1750 CE, with the main contributions from south European Russia, Türkiye, Georgia, and Ukraine. Examination of ice deposited prior to 1850 CE, when agricultural activities remained limited, suggests an NH4+ ice concentration related to natural soil emissions representing ∼ 20 % of the 1980–2009 CE NH4+ level, a level mainly related to current agricultural emissions that almost completely outweigh biogenic emissions from natural soil. These findings on historical NH3 emission trends represent a significant contribution to the understanding of ammonia emissions in Europe over the last 250 years.

The atmosphere is an important transport medium for polymeric anthropogenic particles such as microplastics (MPs). The analysis of particles deposited on the snowpack enables monitoring the abundance and transport of MPs and semi-synthetic fibers. In the current study, the abundance of MPs and man-made textile fibers in deposited snow in Western Siberia, Russia, was investigated in a large area ranging from the Altai Mountains (52 degrees 01 '' N) to the Arctic Circle (66 degrees 30 '' N). Rayon fibers accounted for 44% of all detected particles, while the remaining 56% were MPs made of PET, PA, PC, PP and other plastics. The highest number of MPs and fibers per unit area was 2817 +/- 915 items m- 2 with an estimated daily deposition rate of 25.8 items m- 2 d- 1. The maximum calculated mass particle load was 4444 +/- 1530 mg m- 2 or 34.9 +/- 12 mg L- 1 of melted snow. Particle concentrations in snow were generally higher in the southern parts of Western Siberia but did not significantly correlate with population density. The Lagrangian dispersion model FLEXPART was used to estimate the geographical patterns of potential sources of the fibers detected in the snow in Western Siberia. Our analysis shows that particles can reach the sampling sites via both short-range and long-range atmospheric transport, including the possibility of crossborder transport for the smaller particle sizes.

Numerical methods and advanced simulation codes play a crucial role in helping us understand complex atmospheric processes. As technology progresses, it's important to develop sophisticated code for accurate and efficient simulations. In this update to FLEXPART, a Lagrangian model used in numerous studies for the past 30 years, we've made significant improvements. This version of FLEXPART shows improvements in accuracy and computational efficiency. By using native ECMWF coordinates, we reduced conservation errors by about 8-10% for semi-conserved quantities like potential vorticity. The shape of aerosol particles are now properly accounted for, greatly improving the accuracy of the deposition of non-spherical particles (e.g. microplastic fibers). Additionally, the incorporation of OpenMP parallelisation makes the model better suited for handling large input data and extended simulation periods. We've also introduced new methods for the input and output of particles in FLEXPART. Users can now run FLEXPART with their own particle input data, making it more adaptable for specific research scenarios.

Sulfur dioxide (SO2) is an air pollutant which can have harmful effects on both human health and the environment. Furthermore, SO2 also contributes to climate change — SO2 emissions form sulfate aerosols that act as cloud condensation nuclei, increasing cloud formation and decreasing solar radiation reaching the surface. An accurate knowledge of past SO2 emissions is therefore essential to quantify and model the associated global climate forcing. Current bottom-up SO2 emission inventories used for historical Earth System Modeling (ESM) are poorly constrained by observations prior to the late 20th century. Here we revisit and evaluate the historical SO2 emission inventories of the last 150 years used in the Coupled Model Intercomparison Project Phase 6 (CMIP6). Our emission reconstruction is based on an inversion technique employing an array of ice core records of deposited sulfur and atmospheric transport/deposition modeling. The inversion technique minimizes discrepancies between the spatial-temporal patterns of emission inventories and the observed deposition at the ice core sites. We find substantial differences between reconstructed SO2 emissions and existing bottom-up inventories which do not fully capture the spatial-temporal emission patterns. Our results imply that changes to existing historical emission inventories might be necessary in order to ensure an accurate modeling of the Earth’s climate sensitivity within future ESM simulations.

Sulfur hexafluoride (SF6) is a highly potent and long-lived greenhouse gas whose atmospheric concentrations are increasing due to human emissions. In this study, we determine European SF6 emissions from 2005 to 2021 using a large ensemble of atmospheric inversions. To assess uncertainty, we systematically vary key inversion parameters across 986 sensitivity tests and apply a Monte Carlo approach to randomly combine these parameters in 1003 additional inversions. Our analysis focuses on high-emitting countries with robust observational coverage – UK, Germany, France, and Italy – while also examining aggregated EU-27 emissions. SF6 emissions declined across all studied regions except Italy, largely attributed to EU F-gas regulations (2006, 2014), however, national reports underestimated emissions: (i) UK emissions dropped from 68 (47–77) t yr−1 in 2008 to 19 (15–26) t yr−1 in 2018, aligning with the reports from 2018 onward; (ii) French emissions fell from 78 (51–117) t yr−1 (2005) to 35 (19–54) t yr−1 (2021), exceeding reports by 88 %; (iii) Italian emissions fluctuated (25–48 t yr−1), surpassing reports by 107 %; (iv) German emissions declined from 182 (155–251) t yr−1 (2005) to 97 (88–104) t yr−1 (2021), aligning reasonably well with reports; (v) EU-27 emissions decreased from 403 (335–501) t yr−1 (2005) to 225 (191–260) t yr−1 (2021), exceeding reports by 20 %. A substantial drop from 2017 to 2018 mirrored the trend in southern Germany, suggesting regional actions were taken as the 2014 EU regulation took effect. Our sensitivity tests highlight the crucial role of dense monitoring networks in improving inversion reliability. The UK system expansions (2012, 2014) significantly enhanced result robustness, demonstrating the importance of comprehensive observational networks in refining emission estimates.

Meteorological reanalyses are crucial datasets in atmospheric research, providing the foundation for many scientific applications. However, most reanalyses follow a Eulerian framework, providing data at specific, fixed points in space and time. This fixed-location approach is suitable for many scientific analyses, but studies focused on transport in the atmosphere would benefit from a Lagrangian framework, which provides data along dynamic, continuous trajectories following the movement of air. To achieve this, the Lagrangian particle dispersion model FLEXPART was driven offline with data from ECMWF's (European Centre for Medium-Range Weather Forecasts) latest reanalysis, ERA5, to convert the Eulerian ERA5 data into a Lagrangian format. FLEXPART utilises the grid-scale winds from ERA5 and stochastic parameterisations of turbulence and convection to advect particles in a domain-filling mode, where the global atmosphere is represented by 6 million particles that move freely in the atmosphere, with their number density following closely the density of air. The resulting new Lagrangian Reanalysis (LARA: 10.5281/zenodo.14639472, ) dataset has been stored in an easily searchable database and made accessible to researchers all over the world. It will enable a wide range of studies, including global and regional analyses of extreme events, water and energy transport in the atmosphere, and atmospheric energy budgets. Here, we describe the data format and how the data can be accessed and analysed. Using four examples, we give a non-exhaustive list of possible applications for which LARA could be used for. We show methods for how the evolution of air masses and their properties can be studied and how climatologies can be established. Our examples include a study of the evolution of the Hadley cell circulation, a climatology of warm conveyor belt events, a measure of continentality based on the time it takes for air to reach land from the ocean, and an evaluation of the dynamical consistency between subsequent ERA5 meteorological fields.

Ancient texts and archaeological evidence indicate substantial lead exposure during antiquity that potentially impacted human health. Although lead exposure routes were many and included the use of glazed tablewares, paints, cosmetics, and even intentional ingestion, the most significant for the nonelite, rural majority of the population may have been through background air pollution from mining and smelting of silver and lead ores that underpinned the Roman economy. Here, we determined potential health effects of this air pollution using Arctic ice core measurements of Roman-era lead pollution, atmospheric modeling, and modern epidemiology-based relationships between air concentrations, blood lead levels (BLLs), and cognitive decline. Findings suggest air lead concentrations exceeded 150 ng/m 3 near metallurgical emission sources, with average enhancements of >1.0 ng/m 3 over Europe during the Pax Romana apogee of the Roman Empire. The result was blood lead enhancements in young children of about 2.4 µg/dl above an estimated Neolithic background of 1.0 µg/dl, leading to widespread cognitive decline including a 2.5-to-3 point reduction in intelligence quotient throughout the Roman Empire.

Here we will look at how the air moves into the up area and how it’s moves have changed over the last two times four ten years. We know that the up area air is not alone, but it is a part of the whole sky air. We can see that in the early year when not clean air is moved from areas more down to the up area and the air in the up area is becoming less nice.For our work we use a computer to add up the time how long air parts stay in the up area and to follow air parts to see where they come from and where they go to. So we can also find out where the not clean air comes from. Maybe the areas where the not clean air comes from has changed over time?Our computer tells us that air parts usually stay in the up area for around one week in month one of the year and around two weeks in month seven of the year. However, this is not the same in the whole up area and it has changed in the last two times four ten years. It has changed most in month four of the year, when the air parts stay shorter in the up area now than they used to.

Abstract Rapid warming and human exploitation threaten boreal forests. Understanding links among vegetation, climate, and people in this vast biome requires highly resolved long‐term records that integrate regional inputs. We developed an 850‐year pollen‐based record of supraregional vegetation change using a southern Greenland ice core and atmospheric modeling that identified the boreal and mixed‐conifer forests of eastern Canada as the dominant pollen source regions. Conifer pollen increased ∼1400 CE at the onset of the cooler and drier Little Ice Age. A subsequent decline began ∼1650 CE and a statistically significant pollen change after 1760 CE suggests ecological consequences of the Little Ice Age cooling and initial human exploitation that persisted until recent decades. These supraregional changes are broadly consistent with local records and demonstrate intensification of human impacts on northern forests, suggesting a shift from a climate‐modulated to an increasingly human‐controlled system during recent centuries.

We determine the global emission distribution of the potent greenhouse gas sulfur hexafluoride (SF6) for the period 2005-2021 using inverse modelling. The inversion is based on 50 d backward simulations with the Lagrangian particle dispersion model (LPDM) FLEXPART and on a comprehensive observation data set of SF6 mole fractions in which we combine continuous with flask measurements sampled at fixed surface locations and observations from aircraft and ship campaigns. We use a global-distribution-based (GDB) approach to determine baseline mole fractions directly from global SF6 mole fraction fields at the termination points of the backward trajectories. We compute these fields by performing an atmospheric SF6 re-analysis, assimilating global SF6 observations into modelled global three-dimensional mole fraction fields. Our inversion results are in excellent agreement with several regional inversion studies in the USA, Europe, and China. We find that (1) annual US SF6 emissions strongly decreased from 1.25 Gg in 2005 to 0.48 Gg in 2021; however, they were on average twice as high as the reported emissions to the United Nations. (2) SF6 emissions from EU countries show an average decreasing trend of -0.006 Gg yr-1 during the period 2005 to 2021, including a substantial drop in 2018. This drop is likely a direct result of the EU's F-gas regulation 517/2014, which bans the use of SF6 for recycling magnesium die-casting alloys as of 2018 and requires leak detection systems for electrical switch gear. (3) Chinese annual emissions grew from 1.28 Gg in 2005 to 5.16 Gg in 2021, with a trend of 0.21 Gg yr-1, which is even higher than the average global total emission trend of 0.20 Gg yr-1. (4) National reports for the USA, Europe, and China all underestimated their SF6 emissions. (5) Our results indicate increasing emissions in poorly monitored areas (e.g. India, Africa, and South America); however, these results are uncertain due to weak observational constraints, highlighting the need for enhanced monitoring in these areas. (6) Global total SF6 emissions are comparable to estimates in previous studies but are sensitive to a priori estimates due to the low network sensitivity in poorly monitored regions. (7) Monthly inversions indicate that SF6 emissions in the Northern Hemisphere were on average higher in summer than in winter throughout the study period.

Numerical methods and simulation codes are essential for the advancement of our understanding of complex atmospheric processes. As technology and computer hardware continue to evolve, the development of sophisticated code is vital for accurate and efficient simulations. In this paper, we present the recent advancements made in the FLEXible PARTicle dispersion model (FLEXPART), a Lagrangian particle dispersion model, which has been used in a wide range of atmospheric transport studies over the past 3 decades, extending from tracing radionuclides from the Fukushima nuclear disaster, to inverse modelling of greenhouse gases, and to the study of atmospheric moisture cycles.This version of FLEXPART includes notable improvements in accuracy and computational efficiency. (1) By leveraging the native vertical coordinates of European Centre for Medium Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS) instead of interpolating to terrain-following coordinates, we achieved an improvement in trajectory accuracy, leading to a similar to 8 %-10 % reduction in conservation errors for quasi-conservative quantities like potential vorticity. (2) The shape of aerosol particles is now accounted for in the gravitational settling and dry-deposition calculation, increasing the simulation accuracy for non-spherical aerosol particles such as microplastic fibres. (3) Wet deposition has been improved by the introduction of a new below-cloud scheme, by a new cloud identification scheme, and by improving the interpolation of precipitation. (4) Functionality from a separate version of FLEXPART, the FLEXPART CTM (chemical transport model), is implemented, which includes linear chemical reactions. Additionally, the incorporation of Open Multi-Processing parallelisation makes the model better suited for handling large input data. Furthermore, we introduced novel methods for the input and output of particle properties and distributions. Users now have the option to run FLEXPART with more flexible particle input data, providing greater adaptability for specific research scenarios (e.g. effective backward simulations corresponding to satellite retrievals). Finally, a new user manual (https://flexpart.img.univie.ac.at/docs/, last access: 11 September 2024) and restructuring of the source code into modules will serve as a basis for further development.

Abstract. To investigate the historical levels of atmospheric ammonia (NH3) pollution in south-eastern Europe, a 182 m long ice core was extracted from Mount Elbrus in the Caucasus, Russia. This ice core contains a record of ammonium (NH4+) levels from ~1750 CE (Common Era) to 2009 CE. The NH4+ ice core record indicates a 3.5-fold increase of annual concentrations from 34 ± 7 ng g-1 (~1750–1830) to 117 ± 23 ng g-1 over the recent decades (1980–2009). The increase remained moderate until 1950 CE (mean concentration of 49 ± 14 ng g-1 over the 1830–1950 period), and then accelerated to reach a maximum close to 120 ng g-1 in 1989. This ice core trend is compared to estimated past anthropogenic NH3 emissions in Europe by using state-of-the-art atmospheric transport modeling of submicron aerosols (FLEXPART model driven with 0.5° x 0.5° ERA5 reanalysis data). It is shown that in summer, when both vertical atmospheric mixing and agricultural NH3 emissions are strengthened, the NH4+ ice core trend is in good agreement with the course of estimated NH3 emissions from south-eastern Europe since ~1750 with a main contribution from south European Russia, Turkey, Georgia, and Ukraine. Examination of Mount Elbrus ice deposited over the second half of the 18th century when agricultural activities were less than 10% of those during the 1990s, suggest a pre-1750 annual NH4+ ice concentration related to natural emissions of 25 ng g-1. This pre-1750 natural level mainly related to natural soil emissions represents ~20% of the 1980–2009 NH4+ level, a level mainly related to current agricultural emissions that almost completely outweigh biogenic emissions from natural soils.

Black carbon emitted from incomplete combustion of biomass and fossil fuel burning is an important aerosol; however, available long-term black carbon data are limited to remote polar and high-alpine ice cores from few geographic regions. Black carbon records from lake sediments fill geographic gaps but such records are still scarce, particularly in the Southern Hemisphere. We applied a new incandescence-based methodology to develop Holocene refractory black carbon (rBC) records from four lake-sediment archives in New Zealand and compare these with macroscopic charcoal records. Our rBC records suggest periods with substantial rBC deposition during the Holocene before human arrival in the 13th century reflecting long-range transport and possibly local wetland fires. With Polynesian settlement, rBC deposition increased on the South Island in agreement with macroscopic charcoal records, and it is this period of burning that is proposed as the source of rBC increases evident in Antarctic ice cores. However, sites on the North Island show no contemporaneous rBC increase suggesting regional differences in biomass burning patterns between the North and South islands. None of the New Zealand records show an increase in rBC from fossil fuel sources during the Industrial Era post-1850 CE.

<p>Atmospheric transport modeling with the Lagrangian Particle Dispersion Model (LPDM) FLEXPART has been used for the interpretation of ice core records in several studies in the recent past. Here we present (1) the methodology and results of a study looking into the historical black carbon (BC) emissions based on inverse modeling of ice core records, (2) discuss preliminary results and further plans for a similar study looking into the historical sulphur dioxide (SO<sub>2</sub>) emissions, (3) and give a short overview of other ice core studies using FLEXPART simulations.</p> <p>Both, BC and SO<sub>2</sub> emissions, are caused by anthropogenic as well as natural processes, e.g., (incomplete) combustion of fossil fuels / biomass and volcanic eruptions. And, both negatively influence our health and environment, e.g., causing premature mortality, lowering surface albedo, producing acid rain. However, both species also act as climate forcers, and therefore an accurate knowledge of past BC/SO<sub>2</sub> emissions is essential to quantify and model associated global climate forcing. Nowadays, commonly used bottom-up BC/SO<sub>2</sub> emission inventories for historical Earth System Modeling (ESM), e.g., for the Coupled Model Intercomparison Project Phase 5 / Phase 6 (CMIP5/CMIP6) are poorly constrained by observations prior to the late 20<sup>th </sup>century.</p> <p>In a recent study, we revisit and evaluate these historical 1850 to 2000 BC emission inventories used for ESM simulations, based on an array of deposition ice core records, Lagrangian atmospheric modeling with the FLEXPART model, and an objective inversion technique in order to bring the spatial-temporal patterns of emission inventories in accordance with observed deposition at the ice core sites. We find substantial discrepancies between our reconstructed BC emissions and the existing bottom-up inventories which do not fully capture the complex spatial-temporal BC emission patterns. Our findings imply changes to existing historical BC radiative forcing estimates are necessary, with potential implications for observation-constrained climate sensitivity.</p>

Phosphorus (P) is a key nutrient for many organisms but its global atmospheric budget is largely unconstrained. Estimates of major emissions sources such as fossil-fuel combustion range from similar to 0.02 to 1.1 Tg yr(-1), and primary biogenic emissions range from 0.16 to 1.0 Tg yr(-1). Here we used detailed measurements of phosphorus in Alpine ice cores extracted from the Col du D & ocirc;me (CDD) glacier located near the Mont Blanc summit and atmospheric model simulations to evaluate changes in western European emissions from pre-industrial (PI) to modern times. The ice-core records show that P concentrations during the PI were about 0.9 ng g(-1), of which one third was of crustal origin and two thirds the result of primary biogenic emissions. Concentrations were higher throughout the 20th century, reaching 2.5 ng g(-1) in the 1980s. Analysis of source tracers measured in the same ice, commodity productions statistics, and other information suggest that the increase in P throughout the 20th century was caused by enhanced emissions from natural and anthropogenic sources. Coal burning and steel industry represented the main anthropogenic sources during the first and second half of the century, respectively. After 1950, the increase in P was also caused by enhanced dust emissions, with increased biogenic emissions caused by recent changes of use-land also contributing. These findings provide important constraints on the atmospheric P budget at the scale of western Europe during the recent centuries.