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Meteoritic materials within sulfate aerosol particles in the troposphere are detected with transmission electron microscopy

Abstract

When meteorites impact the Earth’s atmosphere, they fractionalize and ablate, generating aerosol particles containing extraplanetary materials. Meteoritic materials have been identified among aerosol particles using elemental markers (iron and magnesium); however, their shapes and mixing states are largely unknown. Here we demonstrate the presence of meteoritic materials collected by a research aircraft from the troposphere over the western Pacific using transmission electron microscopy. The distribution of meteoritic elements within individual particles coincided with sulfur, indicating that they were in forms of sulfates, i.e., water-soluble. Enhanced number fractions of sulfate particles with meteoritic materials were observed during tropopause-folding events, suggesting that they originated from the stratosphere. We also estimated the potential contributions of the Chelyabinsk meteorite event, which occurred 5 months prior to the sampling and represents the largest meteorite event in the past century. This study provides unique observational evidence for the linkage between extraplanetary materials and tropospheric aerosols.

Introduction

Meteorites from various cosmic sources provide mineralogical and geochemical footprints during the formation and evolution of the early solar system1. Historically, large meteorite and asteroid impacts have caused several mass extinctions2. In addition to such large-impact events, small but numerous meteorites frequently collide with the Earth’s atmosphere. These small meteorites add considerable amounts of meteoritic materials to the mesosphere and stratosphere and potentially influence the Earth’s climate3. Estimates of the input amount of interplanetary dust particles (IDP) to the Earth ranged from 5 to 300 tons per day, depending on the estimation methods (e.g., models and observations)3. A study4 estimated the amount of meteorites falling to the Earth to be 43 ± 14 tons per day and that of ablating meteoritic materials as 8 tons per day. These meteoritic materials mainly occur as meteoritic vapor, smoke particles, or unablated microparticles5.

Meteoritic materials are a source of aerosol particles in the upper atmosphere, where anthropogenic aerosols are extremely rare. Some studies have detected the traces of meteoritic materials from aerosol particles in the stratosphere (>15 km)6,7,8. Small aerosol particles with meteoritic materials could suspend in the atmosphere for several months to years and eventually descend to the troposphere, primarily in the form of internal mixtures with sulfates5,6. When suspended in the atmosphere, they act as cloud condensation nuclei (CCN) and ice nucleating particles (INPs)3. Furthermore, a study3 demonstrated the potential for precipitation containing soluble Fe from meteoritic materials to act as an important nutrient source for phytoplankton in the Southern Ocean, where Fe limits the growth of phytoplankton that uptake atmospheric CO2, subsequent carbon delivery to the deep ocean9,10.

Technical limitations pose challenges to the measurements of aerosol particles in the stratosphere and mesosphere, such as the limitations of available research platforms and the low abundance of aerosol particles. Nevertheless, several attempts have been made to identify meteoritic materials in aerosol particles collected in the stratosphere. For example, NASA routinely collects IDPs in the stratosphere with sizes of several micrometers or larger using specially designed aircraft and collectors11,12. Remote sensing from satellite observations and in situ measurements by single-particle mass spectrometers (SPMS), such as the Particle Analysis by Laser Mass Spectrometry (PALMS), aircraft-based laser ablation aerosol mass spectrometer, and European Research council Instrument for Chemical composition of Aerosols have revealed the presence of meteoritic materials in the mesosphere, stratosphere, and troposphere by identifying elements such as Na, Fe, and Mg6,7,8,13,14,15. In addition to SPMS measurements, Ebert et al.16 found grains containing Fe, Al, Cr, Mn, Ni, and Zn with diameters of several hundred nanometers or larger from refractory stratospheric aerosol particles and suggested that meteoritic materials could be a possible source of these refractory materials. Although meteoritic materials are recognized as important aerosol components in the stratosphere, they constitute a relatively small number fraction in the troposphere (<5%)6,7 because of the dominant aerosol contributions from anthropogenic, marine, and terrestrial sources. Thus, the occurrences and fate of meteoritic materials in the troposphere are not well understood.

In this study, we collected aerosol particles at altitudes <8 km in the troposphere and the vicinity of a tropopause fold over the western Pacific in July 2013 onboard a research aircraft during the Aerosol Radiative Forcing in East Asia 2013 Summer (A-FORCE2013S) campaign (Supplementary Fig. 1). The composition and mixing state of individual particles from 135 samples (ten flights) were analyzed using transmission electron microscopy (TEM) (Table 1). We encountered many sulfate particles involving Fe and Mg, which are characteristic elements of meteorites with a specific ratio between Mg and Fe, in samples from several flights. This study characterizes these particles and discusses their origin, climatological implications, and the linkage with the Chelyabinsk meteorite event, the largest meteorite event in the past century.

Table 1 Information for the research flights used in this study.

Results and discussion

Identification, characterization, and abundance of sulfate particles with meteoritic materials

The elemental markers of meteoritic materials used in the SPMS analyses6,17, mainly Fe and Mg, were detected in our collected particles (Fig. 1 and Supplementary Fig. 2). Based on the elemental compositions, we first classified aerosol particles into mineral dust, sea salt, sulfate, or carbonaceous particles using scanning TEM analysis combined with energy-dispersive X-ray spectroscopy (STEM-EDS) (Supplementary Fig. 3). The overall number fractions of sulfate, sea salt, carbonaceous, and dust particles were 85.7%, 10.9%, 2.5%, and 0.4%, respectively, and the distribution of particle types exhibited a dependence on altitude, particularly for sea salt particles (Fig. 2). Next, we subclassified the sulfate particles with detectable amounts of Fe and Mg (>0.3 wt%) as sulfate particles with meteoritic materials, which constituted a number fraction of 2.8% of the measured particles. Although sea salt and mineral dust particles can contain Fe and Mg, we considered only particles associated with sulfates and excluded those mixed with sea salt and mineral dust particles. Anthropogenic Fe-bearing particles can also be a source of Fe; however, their contribution to the sulfate particles with meteoritic materials is limited in the current samples because the current samples were collected from the air with a negligible anthropogenic influence, as we discuss later, and Mg is commonly absent in anthropogenic Fe-bearing particles18,19. Additionally, Fe and Mg concentrations in the sulfate particles were well correlated (R2 = 0.6 with a linear regression slope of 0.14) (Fig. 3) and had a Mg/Fe ratio similar to that of stratospheric aerosol particles containing meteoritic material (0.2–0.3)20. These results suggest that meteoritic materials are the primary source of Fe and Mg in these sulfate particles. The major proportion of sulfate particles with meteoritic materials had area-equivalent diameters ranging from 630 to 1000 nm. These sulfate particles were systematically larger than other sulfate-containing particles (Supplementary Fig. 4). Note that the original meteoritic materials could be much smaller than the hosting sulfate particles, as the former occupy only a small portion of the latter, which is apparent from the average wt% of Fe and Mg of 3.8 ± 3.1 within the sulfate particles.

Fig. 1: TEM images of sulfate particles with and without meteoritic material and the corresponding elemental maps.
figure 1

Sulfate particles containing meteoritic material have S, Mg, and Fe, as well as Al, Cr, and Ni (particle c). These sulfate particles are surrounded by satellite structures, indicating that they were less neutralized and had a low viscosity when collected. Although these particles are mixtures of various elements, they were defined as sulfate based on (1) the abundance of S, (2) the round shapes and crystal structures, and (3) the beam sensitivity, all of which are consistent with sulfate particle properties reported in previous studies53, 54. The TEM samples were collected on a 5:21 UTC, July 17, 2013, b 5:24 UTC, July 18, 2013, and c 3:53 UTC, July 7, 2013.

Fig. 2: Fractions of major aerosol species and sulfate particles with meteoritic materials along with sampling altitudes.
figure 2

Errors are shown in a 90% confidence interval. The numbers of samples analyzed by TEM were 63, 44, 22, and 6 for altitude ranges of 0–2, 2–4, 4–6, and 6–8 km, respectively.

Fig. 3: Relationship between Fe and Mg within sulfate particles with meteoritic materials measured using STEM-EDS.
figure 3

The plots contain 23,376 data points representing all particles and sulfate particles with meteoritic materials are represented by a 571 (all Mg values) and b 560 (Mg < 3 wt%) data points. Top: all particles. Bottom: only sulfate particles with meteoritic materials and Mg < 3 wt% are shown. The linear fitting was calculated using a York regression55.

In addition to Fe and Mg, meteoritic materials from aerosol particles are known to contain various elements, including Na, Al, K, Ca, Cr, and Ni17. Although the concentrations of these elements were mostly below the detection limits of our measurements (<0.1 wt%), they were occasionally detected along with Fe and Mg in sulfate particles. To evaluate the abundance of these elements in the meteoritic materials, we compared their average wt% in sulfate particles with and without meteoritic materials (Fig. 4). The results indicate that sulfate particles with meteoritic materials contained Mg, Al, Ca, Fe, and Ni (wt%) more than three times higher than those without meteoritic materials, consistent with the results of previous studies17,21. In our study, Cr was slightly enriched in meteoritic materials (1.9 times more abundant than in sulfate particles without meteoritic material), although Na and K did not show notable differences (1.1 and 0.9 times, respectively). Because our samples were collected in the troposphere, those non-meteoritic sulfates can have taken up Na and K from sea salt and biomass burning particles, respectively, in non-meteoritic particles, resulting in the absence of apparent enhancement due to meteoritic materials.

Fig. 4: Ratios of average sulfate particle compositions with and without meteoritic material.
figure 4

The ratios are shown on a logarithmic scale. Errors are shown at the 95% confidence interval. The number of sulfate particles with and without meteoritic material was 571 and 19,253, respectively. Dashed lines indicate ratios of 3 and 1.

Sulfate particles were decomposed and vaporized by exposure to intensive electron beams during the STEM-EDS measurements, leaving sulfate residuals. The elemental analysis of sulfate particles with meteoritic materials showed that the distributions of Fe and Mg in particles coincided with sulfate residuals, suggesting that they were in the form of sulfate salts and were, therefore, water-soluble (Fig. 1 and Supplementary Fig. 2). Earlier studies have shown that Fe and Mg in meteoritic materials become water-soluble via reaction with H2SO4 in the upper troposphere and stratosphere22,23. Some particles also contain Ni, Cr, or Al with similar distributions of Fe and Mg (Fig. 1c). Si was occasionally detected in nanosized grains in sulfate particles with meteoritic materials (Supplementary Fig. 2e, f). The occurrence of Fe, Mg, and Si within meteoritic materials is consistent with the PALMS results of Murphy et al.7, who interpreted their mass spectrometry results by taking Fe and Mg in solution and Si and Al as insoluble oxides. In our study, Al occurred either homogeneously within host particles or as grains, suggesting that it can present as both solution and insoluble oxides.

The number fraction of sulfate particles with meteoritic materials among the total particles varied from 0 to 35% (Table 1), where samples collected at high altitudes have high number fractions (Figs. 2 and 5). Five-day back trajectories of the observed air parcels indicate that all samples with a meteoritic material number fraction of >5% originated from altitudes higher than the sampling points. For example, on July 17 and 18, when the meteoritic fractions were relatively high, the air parcels were transported downward from the stratosphere to troposphere through a tropopause-folding event, as indicated by low relative humidity (<25% RH) and the descent of air parcels with potential vorticity unit (PVU) > 2, which typically represents the stratosphere6,24 (Fig. 6 and Supplementary Figs. 5 and 6). The air parcels were unlikely influenced by anthropogenic sources considering the low concentrations of black carbon (BC) particles (Fig. 5). These results indicate that the tropopause-folding events play an important role in transferring meteoritic materials from the stratosphere to the troposphere.

Fig. 5: Relationship between the number fraction of sulfate particles with meteoritic materials and observed parameters.
figure 5

Observed parameters are a altitude, b relative humidity (RH), and c black carbon (BC) concentrations (particle number per cm3 at standard temperature and pressure) at the sampling points. Plot colors and symbols indicate different flight (F) numbers. The numbers of samples from each flight used for TEM were 11, 12, 10, 11, 6, 20, 13, 18, 17, and 17 for F4, F5, F6, F7, F8, F10, F12, F13, F14, and F15, respectively. Errors for Y-axes are shown at the 95% confidence interval, and those for number fractions are based on Poisson statistics.

Fig. 6: Vertical distribution of number fractions of sulfate particles with meteoritic materials and relative humidity.
figure 6

The number fractions of sulfate particles with meteoritic materials (circles), relative humidity (RH; color bar is shown at the bottom), and vertical wind velocity (m s−1; vectors with scaling near the lower right corner) are shown as a function of pressure and latitude for flights on a 17 July (145°E) and b 18 July (147.5°E). Dry air represented in purple, and downward motion between 400 and 700 hPa indicates tropopause-folding events. Plots of all flights are shown in the Supplementary Information (Supplementary Fig. 5). The meteorological data were obtained from the Japanese 55-year reanalysis data. Vertical wind velocities (m s−1) were calculated from omega-velocities (Pa s−1) in the data. Only wind vectors with magnitudes greater than 0.015 m s−1 were plotted.

Potential impact of the Chelyabinsk meteorite

The maximum number fractions of meteoritic materials in our study were mostly higher than that reported in previous studies6,7 when comparing data sampled at similar altitudes (<8 km) or PVU <2 (Supplementary Fig. 6). In addition to the influence of the tropopause-folding events described above as well as differences in measurement techniques (SPMS vs. TEM), we hypothesized that the Chelyabinsk meteorite event in Russia on February 15, 201325, 5 months before the campaign, could have influenced our samples.

The Chelyabinsk meteorite was the largest meteorite impact event since the Tunguska event in 190825. The meteorite was originally ~18–20 m in diameter with an estimated weight of 11,000–13,000 tons when entering the Earth’s atmosphere25. Fragmentation began at an altitude of ~83 km and peaked at ~30 km before exploding at ~27 km25,26. As a result, 76% of the meteorite mass evaporated, and most of the remaining masses became micrometer- and nanometer-sized dust particles in the mesosphere and stratosphere25. The input of Chelyabinsk meteoritic materials was evaluated to be ~70–83% of the average annual mass input by meteorites (15,700 ± 5000 tons per year4). The Chelyabinsk meteorite plume was observed by the Ozone Mapping Profiler Suite Limb Profiler (OMPS/LP) satellite in a high-altitude polar belt26 and the Optical Spectrograph and Infrared Imaging System on the Odin satellite near 35 km altitude between 50°N and 70°N for several months27. In May 2013, the plume was observed descending to the Junge layer with a deposition speed of ~90 m per day26, suggesting that a large fraction of the mass from the Chelyabinsk meteorite remained in the atmosphere during our sampling.

The recovered Chelyabinsk meteorite had a composition consistent with an ordinary chondrite LL5 with a bulk composition of Fe (20.3%), Mg (16.0%), Ca (1.7%), Al (1.2%), and Ni (1.2%) along with oxygen and various trace elements25. These major element abundances were similar to those found in our samples, although the quantitative weight percent values showed some discrepancies. For example, the ratio of Mg to Fe wt% in an unablated Chelyabinsk meteorite (Mg/Fe: 0.79) was higher than that in our aerosol particles (a median Mg/Fe ratio of 0.25 among all measured meteoritic materials, or a value of 0.14 from the slope in Fig. 3). When meteorites ablate in the atmosphere, their evaporation temperatures may depend on their elemental compositions28. Thus, ablated meteoritic materials can have atomic ratios different from their original ones. Cziczo et al.20 reported that Fe ablates about two times more than Mg, yielding Mg/Fe ratios in stratospheric aerosols (Mg/Fe: 0.2–0.3 in wt% ratio) that are about half that of the original meteorite compositions.

To further verify the hypothesis that meteoritic materials from the Chelyabinsk meteorite were present in the area and at the time of our sampling campaign, we conducted model calculations to simulate the global distribution of meteoritic materials derived from the ablation of the Chelyabinsk meteorite event, assuming three initial mass inputs (100, 1000, and 10,000 tons) of ablated meteoritic materials with radii between 0.1 and 1 µm. The initial input mass of 100 tons estimated by ref. 26 corresponds to 1% of the original Chelyabinsk meteorite, whereas the 1000 tons input corresponds to the ablation mass estimated by ref. 25 and that of 10,000 tons corresponds to nearly the entire initial mass of the meteorite. We used the estimate of 10,000 tons to evaluate the upper limit of the impact, recognizing that the estimate may be unrealistic as the Chelyabinsk meteorite did not fully ablate, and the sulfur mass in the stratosphere may not be enough to condense all these meteoritic materials.

In July 2013, horizontal distributions of the column-integrated mass concentration of the meteoritic material displayed widespread occurrence throughout the northern hemisphere, with high concentrations at high latitudes (Supplementary Fig. 7). The vertical distributions over the sampling area (140°–148°E, 35°–45°N) along the elapsed time showed that most meteoritic materials remained concentrated at high altitudes (<100 hPa) and were seasonally transported downward over the following 4 years. Most of the meteorite mass reached the planetary boundary layer in the spring of 2014, ~1 year after the impact. Thus, the model results suggested that at the time of sample collection during the observation period, most meteoritic materials remained in the stratosphere. The deposition mass fluxes of the Chelyabinsk meteorite over the sampling area (140°–148°E, 35°–45°N) in July 2013 were estimated to be ~0.6, 6.2, and 60.4 kg per day for the initial meteorite mass assumptions of 100, 1000, and 10,000 tons, respectively (Supplementary Fig. 8). These deposition estimates correspond to ~3, 34, and 333% of the average deposition of ablated small meteorites that frequently impact the Earth over the same area (8 tons per day over the Earth4), assuming that the averaged meteorite depositions are uniformly distributed across the globe and that the meteorite input and deposition masses are equivalent. Thus, despite uncertainties of multiple orders of magnitude in the initial mass estimate, some contributions from the Chelyabinsk meteorite in our samples is possible.

The model simulations showed that during the sampling period, several tropopause-folding events carried meteoritic materials from the Chelyabinsk meteorite in dry air descending from the stratosphere, consistent with our observations, i.e., dry air contained relatively high number fractions of sulfate particles with meteoritic materials (e.g., 7, 17, and 18 July), where modeled meteoritic material concentrations were also high (Fig. 7). Note that the horizontal distributions of meteoritic materials from the Chelyabinsk event (Supplementary Fig. 7) indicate that they were distributed throughout the northern hemisphere, suggesting that they could have been mixed with background meteoritic materials. Thus, although our model simulations considered only the concentrations of meteoritic material from the Chelyabinsk meteorite, such tropopause-folding events can also deliver stratospheric meteoritic materials from other small meteorites. Overall, the model results support the hypothesis that Fe and Mg in sulfate particles measured using TEM originated from meteoritic materials and were transported from the upper atmosphere by a tropopause-folding event. The magnitude of the Chelyabinsk meteorite contribution largely depends on the initial mass estimates of aerosol particles and assumptions used in the model (e.g., mixing states, sizes, and microphysical processes), and a further modeling study is recommended to address condensation of sulfuric acid onto meteoritic materials. Nevertheless, at least the spatial distributions and deposition patterns of the Chelyabinsk meteorite suggest that this meteorite was one of the possible meteorite sources for our samples.

Fig. 7: Simulated vertical distributions of meteoritic materials from the Chelyabinsk meteorite event and observed number fractions of sulfate particles with meteoritic materials.
figure 7

The simulated concentrations (pg m−3, colored as indicated near the bottom) at the sampling locations and observed number fractions of sulfate particles with meteoritic materials (red circles) at the sampling altitudes are plotted for initial inputs of a simulated meteorite mass of a 100, b 1000, and c 10,000 tons. Black lines indicate a relative humidity (RH) of 25%. During the tropopause-folding events (e.g., on 7, 17, and 18 July), RH values were <25% around the 400–700 hPa levels, at which the number fractions of sulfate particles with meteoritic materials were relatively high.

Summary and the possible fate of meteoritic material

We proved the mixing states and shapes of meteoritic materials within sulfate particles in the troposphere using TEM. These particles may have originated from the Chelyabinsk meteorite and other relatively small meteorites that frequently collide with the Earth. Such meteorites are ablated and fragmented into the Earth’s atmosphere and become meteorite dust and smoke containing Fe and Mg (Fig. 8). They may either coagulate with pre-existing sulfate particles or act as nuclei for sulfate condensation in the stratosphere and upper troposphere, accelerating sulfate formation. Within the sulfate particles, Fe and Mg dissolve in the hosting particles. After suspending in the stratosphere for months or years, they are slowly removed from the stratosphere by sedimentation, and some are transferred to the troposphere more quickly by tropopause folding, as we encountered during the sampling. Upon being transported to the troposphere, sulfate particles with meteoritic materials serve as CCN and INPs29 and are removed from the atmosphere by precipitation.

Fig. 8: Schematic illustrating of the fate of meteoritic materials.
figure 8

Gray, purple, and blue spheres indicate meteoritic materials, sulfate particles with meteoritic materials, and sulfate particles without meteoritic materials, respectively.

The amount of meteoritic materials observed in the current study is small compared to the abundance of other types of tropospheric aerosol particles. However, their relative abundance increased at high altitudes, where anthropogenic particles are rare. It is also possible that their relative abundance increases following collision with large or high numbers of meteorites with the Earth. Thus, we recommend that meteoritic materials be regarded as a source of aerosol particles with the potential to influence climate in the upper troposphere and stratosphere.

Methods

A-FORCE2013S campaign

The A-FORCE2013S aircraft campaign was conducted during July 2013 using a Beechcraft King Air vessel operated by Diamond Air Service Inc. (Table 1 and Supplementary Fig. 1). This campaign was conducted over the Pacific Ocean northeast of Japan and based at Sendai Airport (38.14°N, 140.93°E) from July 1 to July 11 and at Memanbetsu Airport (43.88°N, 144.16°E) from July 11 to July 21, 2013. The main goal of this campaign was to measure aerosol-cloud interactions over the western edge of the North Pacific. Prior to the current campaign, companion campaigns were carried out over the Yellow Sea, the East China Sea, and the western Pacific Ocean in spring 2009 (A-FORCE200930) and winter 2013 (A-FORCE2013W31). A-FORCE2013S used the same instruments as in A-FORCE2013W31.

Measurements

Aerosol particles for TEM measurements were collected on TEM grids coated with collodion carbon substrates using a custom-made aerosol sampler32. The 50% cutoff sizes correspond to aerodynamic diameters of 100 and 700 nm at the small and large ends, respectively, with a flow rate of 2 l min−1. Samples were collected every 12 min. Because TEM analyzes only nonvolatile aerosol particles, volatile and semi-volatile aerosol particles, such as semi-volatile organic aerosol particles that constitute ~10–30% of all aerosol mass33, will be lost before or during the TEM measurements.

A 120-kV transmission electron microscope (JEM-1400, JEOL) equipped with an energy-dispersive X-ray spectrometer (X-max, Oxford Instruments) was used in both TEM and STEM mode34,35,36. On average, we analyzed 177 particles per TEM grid sample using the STEM-EDS system. Measured particles containing >100 pixels at the measured magnifications (e.g., ×6000) were distinguished from the substrates using appropriate threshold values in dark-field STEM images37. Particle compositions and shapes were measured using a 20 s EDS acquisition time, and TEM images were acquired before and after EDS measurements. The compositions were normalized among C, N, O, Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Zn, and Pb with a one sigma peak intensity detection limit (~0.1 wt%). Elemental maps were also collected for selected particles using STEM-EDS.

Particles were first classified based on their major components: mineral dust (Al > 1 wt% and Fe > 1 wt%), sea salt (Na > 1 wt%), sulfate (S > 1 wt%), carbonaceous (C + O > 90 wt%), and others (Supplementary Fig. 3). Sulfate particles were then subdivided into those with and without meteoritic material, the former of which was defined as those containing both Fe > 0.3 wt% and Mg > 0.3 wt%. Although these threshold wt% values are close to the detection limits, the particles with compositions above the threshold wt% yielded clear signals (>10 net-area peak intensities) for these elements in the EDS spectra. These minimum threshold values were chosen in consideration of the small fraction of meteoritic material found in most host sulfate particles. For example, a threshold value of 1.0 wt% reduced the number fraction of sulfate particles with meteoritic materials to ~20% of that for a threshold of 0.3 wt%.

BC concentrations were measured using a single-particle soot photometer (SP2)31,38, which measured BC with volume equivalent diameters between 75 and 850 nm. Relative humidity was measured with the AIMMS-20 probe (Aventech Research Inc., Ontario, US) (0.1% resolution and 2% accuracy)39. Five-day kinematic back trajectories40 of air parcels measured onboard the aircraft were calculated every minute using six‐hourly meteorological data from the final operational global analysis of the National Centers for Environmental Prediction.

Model calculations

We used the Meteorological Research Institute Earth System Model version 2 (MRI-ESM241,42) to estimate the global spatial and temporal distributions of meteoritic material originating from the Chelyabinsk meteorite event. The original model consists of an atmospheric general circulation model with land processes (MRI-AGCM3.5), an ocean–sea-ice general circulation model (OGCM), an aerosol chemical transport model, and an atmospheric chemistry model. In this study, we coupled all component models except the OGCM. The aerosol component model was the Model of Aerosol Species in the Global Atmosphere mark-2 revision 4-climate (MASINGAR mk-2r4c43,44,45), which treats non-sea-salt sulfate, BC, organic carbon, mineral dust, sea salt, and aerosol precursor gases and assumes external mixing for all aerosol species. Mineral dust and sea salt were categorized into ten discrete size bins to resolve their size distribution (e.g., due to size-dependent gravitational settling), while the other aerosols were represented by lognormal size distributions. MRI-ESM2 uses different horizontal resolutions in each component model corresponding to ~120 km (TL159), 180 km (TL95), and 280 km (T42) for MRI-AGCM3.5, the aerosol chemical transport model, and the atmospheric chemistry model, respectively. All models employed 80 vertical layers (from the surface to the top of the model at 0.01 hPa) in a hybrid sigma-pressure coordinate system. The current model simulations followed the procedures of the Atmospheric Model Intercomparison Project (AMIP) experiment in the Coupled Model Intercomparison Project phase 6 (CMIP6)46, which uses the prescribed observed sea surface temperature and sea-ice concentration data47.

We performed three types of MRI-ESM2 simulations with the Chelyabinsk meteoritic material (cases for 100, 1000, and 10,000 tons of meteoritic material) from January 2013 to December 2020 after a 33-year spin-up run from January 1980. In these simulations, horizontal wind fields were nudged toward the 6-hourly Japanese 55-year reanalysis data48 to reproduce realistic meteorological fields. We used the historical anthropogenic emission dataset from the Community Emissions Data System49 and the biomass burning emission dataset50 developed for CMIP6. In this study, the dust component in the model was used as a proxy for meteoritic material by assuming the same physical and chemical properties for meteoritic material as for mineral dust25. Meteoritic material was placed into one column of the model grid box over Chelyabinsk (54.8°N, 61.1°E) between 3:00 UTC and 4:00 UTC on February 15, 2013. We generally used the initial settings of the meteorite material input provided by ref. 26. In total, 5%, 90%, and 5% of the meteoritic material were vertically distributed over the 15–30, 30–45, and 45–60 km altitude ranges, respectively, and the total meteoritic material mass was distributed among the five smallest size bins: 26.7%, 26.7%, 26.7%, 10%, and 10% of the mass was assigned to the size bins with radius ranges of 0.10–0.16, 0.16–0.25, 0.25–0.40, 0.40–0.63, and 0.63–1.00 µm, respectively. The current model simulation focused on material from the Chelyabinsk meteorite without considering background meteoric material from other relatively small meteorite events.

Data availability

STEM-EDS data, sampling parameters, and model data used in Fig. 7 and Supplementary Figs. 7 and 8 are available at https://doi.org/10.5281/zenodo.572846251. Information on the meteorological data used in Fig. 6 and Supplementary Figs. 5 and 6 are available at https://jra.kishou.go.jp/JRA-55/index_en.html52.

Code availability

Access to the MRI-ESM2 code is available under a collaboration framework with Meteorological Research Institute.

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Acknowledgements

We are indebted to all A-FORCE2013S participants for their cooperation and support. The authors also acknowledge the pilots and flight staff of Diamond Air Service Inc. This work was supported by the Environment Research and Technology Development Fund (JPMEERF20205001, JPMEERF20202003, JPMEERF20215003, and JPMEERF20172003) of the Environmental Restoration and Conservation Agency of Japan; the Global Environmental Research Coordination System of the Ministry of the Environment of Japan (MLIT1753); the Arctic Challenge for Sustainability ArCS II project (JPMXD1420318865) of the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan; and the Japan Society for the Promotion of Science (JSPS) KAKENHI (grant numbers JP26701004, JP16K16188, JP16H01772, JP18H04134, JP18H03363, JP18H05292, JP19H01972, JP19H04236, JP19K21905, JP19H04259, and JP21H03582). The trajectory calculation program used in this study was developed by Y. Tomikawa at the National Institute of Polar Research and K. Sato at the University of Tokyo, Japan.

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K.A. conducted TEM analyses and data processing. K.A., N.M., and M.K. collected the TEM samples. N.O. conducted the model calculations and analyses. N.T. and M.K. prepared and designed the aircraft measurements. N.M. obtained the BC data. M.K. supervised the campaign. K.A. prepared the first draft. All authors agreed to the final version of the manuscript.

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Correspondence to Kouji Adachi.

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Communications Earth & Environment thanks Johannes Schneider and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editors: Kerstin Schepanski, Joe Aslin, and Clare Davis. Peer reviewer reports are available.

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Adachi, K., Oshima, N., Takegawa, N. et al. Meteoritic materials within sulfate aerosol particles in the troposphere are detected with transmission electron microscopy. Commun Earth Environ 3, 134 (2022). https://doi.org/10.1038/s43247-022-00469-8

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