Earth's Atmosphere Research Articles

The Once and Future Gas: Methane's Multifunctional Roles in Earth's Evolution and Potential as a Biosignature

Methane (CH4) is a simple molecule that, due to its radiative forcing, wields an outsized impact on planetary heat balance. Methane is formed by diverse abiotic pathways across a range of pressures and temperatures. Biological methanogenesis for anaerobic respiration uses a terminal nickel-containing enzyme and is limited to the archaeal domain of life. Methane can also be produced in aerobic microbes during bacterial methylphosphonate and methylamine degradation and via nonenzymatic reactions during oxidative stress. Abiotic CH4 is produced via thermogenic reactions and during serpentinization reactions in the presence of metal catalysts. Reconstructions of methane cycling over geologic time are largely inferential. Throughout Earth's history, methane has probably been the second most important climate-forcing greenhouse gas after carbon dioxide. Biological methanogenesis has likely dominated CH4 flux to Earth's atmosphere for the past ∼3.5 billion years, during which time CH4 is thought to have generally declined as atmospheric oxygen has risen. Here we review the evolution of the CH4 cycle over Earth's history, showcasing the multifunctional roles CH4 has played in Earth's climate, prebiotic chemistry, and microbial metabolisms. We also discuss the future of Earth's atmospheric CH4, the cycling of CH4 on other planetary bodies in the Solar System (with special emphasis on Titan), and the potential of CH4 as a biosignature on Earth-like extrasolar planets. ▪ Before life arose on Earth, abundant atmospheric CH4 in Earth's early atmosphere was likely key for establishment of habitable conditions and production of organic molecules for prebiotic chemistry. ▪ Biological methanogenesis for anaerobic respiration is only known to exist in some groups of anaerobic archaea, but CH4 can also be produced via enzymatic and nonenzymatic biological pathways that are not directly coupled to energy conservation. The relative importance of each of these pathways to the global CH4 cycle is a topic of active research, but archaeal methanogenesis dominates all other biological pathways for CH4 generation. ▪ As atmospheric O2 rose over Earth history, models suggest that atmospheric CH4 declined; in the distant deoxygenated future, atmospheric CH4 is predicted to rise again. ▪ Future missions to Titan will aid in understanding the complex organic chemistry on the only other planetary body in our Solar System with an active methane cycle.

Seasonal Variations in the Strength of Sporadic Meteor Sources Observed by Meteor Radar

AbstractSporadic meteors are a significant source of metals in the Earth's atmosphere and ionosphere, and the understanding of the seasonal variations of their strengths can provide valuable insights into the origins and orbits of cosmic dust particles near Earth. This study analyzes meteor echo data collected by an all‐sky interferometric meteor radar in Ledong (LD, 18.4°N, 109.0°E) to quantify the strengths of sporadic meteor sources and their seasonal variations. The results indicate that the helion, antihelion, and apex sources are stronger than the north toroidal source, highlighting a concentration of sporadic meteors near the ecliptic plane and fewer near the ecliptic poles. Distinct seasonal variations are observed, with meteor activity peaking in April and September, likely corresponding to periods of increased meteor and dust particle density in Earth's orbit. Moreover, eight meteor showers are identified as significantly influencing the apparent radiant distributions and have comparable strengths with sporadic meteor sources. To enhance the analysis, a monthly radiant weighting system in ecliptic coordinates is developed, enabling precise calculation of source strengths and improved characterization of seasonal variations in radiant distributions. This research advances our understanding of sporadic meteors and their role in Earth's atmospheric processes, providing a foundation for future investigations into cosmic dust dynamics.

Stability of upper-tropospheric flows and the chaotic oscillation regime

In the Earth's atmosphere at the tropopause level, intense upper-tropospheric zonal flows are observed. To investigate the stability of these flows, a two-level discrete version of a surface quasigeostrophic (SQG) model is used. A nonlinear system of three differential equations for perturbation amplitudes is developed from the basic equations of this model using the Galerkin method. In the absence of Ekman friction, all solutions of the system describe a periodic regime of nonlinear oscillations or vacillations. The occurrence of such oscillations is determined by the law of conservation of the surface potential energy. In the dimensional variables, the period of oscillations is of the order of a month. This value agrees with the observed period of atmospheric oscillations in the winter period. A fundamentally new feature arises in the model taking into account the Ekman bottom friction. As in the classical Lorenz model, a regime of chaotic turbulent oscillations appears in the model with friction. This result confirms the main thesis of Lorenz – a model with three modes is sufficient to describe turbulence without involving cumbersome multi-mode models.

Cross Correlation Between Plasmaspheric Hiss Waves and Enhanced Radiation Levels at Aviation Altitudes

AbstractEnhanced radiation in the Earth's atmosphere can pose serious hazards to pilots, aircraft passengers, and commercial space travelers. Recent results have shown, statistically, that there is a strong correlation between dose rates observed by Automated Radiation Measurements for Aerospace Safety (ARMAS) instruments at aviation altitudes (>9 km) and plasmaspheric hiss wave power measured by NASA's Van Allen Probes within the inner magnetosphere. Plasmaspheric hiss waves play a very important role in removing energetic electrons from the Earth's radiation belts by precipitating them into the upper atmosphere. These relativistic electrons generally drift eastwards along closed magnetic drift shells. In this study, we use magnetic conjunction events between ARMAS and the Van Allen Probes to analyze the causality between plasmaspheric hiss waves and enhanced radiation observed at aviation altitude. We specifically study how the size of the conjunction window and a shift in L and MLT of the conjunction window affect the correlation between dose rates and plasmaspheric hiss wave power. This is to determine if the observed enhanced radiation at aviation altitude is indeed caused by the plasmaspheric hiss waves in the inner magnetosphere. The results show that the enhanced radiation levels are only correlated with plasmaspheric hiss waves within conjunction windows of −1 L 1 and 0 MLT 2. The correlation between dose rate and hiss wave power increases slightly if ARMAS is shifted approximately 1 hr in MLT to the east of the Van Allen Probes, consistent with the drift trajectory of the electrons precipitating into the atmosphere.

Diurnal and Seasonal Variations of Gravity Waves in the Lower Atmosphere of Mars as Observed by InSight

AbstractWe investigate Gravity Waves (GWs) in the lower atmosphere of Mars based on pressure timeseries acquired by the InSight lander. We compile a climatology showing that most GW activity detected at the InSight landing site takes place after the sunrise and sunset; they are almost absent during the aphelion season, and more prominent around the equinoxes, with variations during dust events and interannual variations. We find GWs with coherent phases in different sols, and a previously unnoticed coincidence of GW activity with those moments in which the diurnal cycle (of tidal origin) exhibits the fastest increases in absolute pressure. We explore the possibility that some of these GWs might actually be high‐order harmonics of thermal tides transiently interfering constructively to produce relevant meteorological patterns, and discuss other interpretations based on wind patterns. The so‐called Terminator Waves observed on Earth might also explain some of our observations.

Joost Businger—A Pioneer in Atmospheric Boundary Layer Research

Abstract This paper provides a historical review of our understanding of the workings of the atmospheric boundary layer (ABL), the part of the lower atmosphere, typically ≤1 km in depth, that directly feels the influence of Earth’s surface. It is written from the perspective of the career of Joost A. Businger (1924–2023), a pioneer in this area, who realized that the atmospheric boundary layer holds great practical importance in the sense that most of humankind’s activities take place within it and scientific importance in the sense that the boundary layer forms the interface between the free atmosphere and Earth’s surface and therefore plays a major role in our weather and climate.

Distribution of early-branching Cyanobacteriia and the potential habitats that gave rise to the earliest oxygenic phototrophs.

The evolution of oxygenic photosynthesis in the Cyanobacteria was one of the most transformative events in Earth history, eventually leading to the oxygenation of Earth's atmosphere. However, it is difficult to understand how the earliest Cyanobacteria functioned or evolved on early Earth in part because we do not understand their ecology, including the environments in which they lived. Here, we use a cutting-edge bioinformatics tool to survey nearly 500,000 metagenomes for relatives of the taxa that likely bookended the evolution of oxygenic photosynthesis to identify the modern environments in which these organisms live. Ancestral state reconstruction suggests that the common ancestors of these organisms lived in terrestrial (soil and/or freshwater) environments. This restricted distribution may have increased the lag between the evolution of oxygenic photosynthesis and the oxygenation of Earth's atmosphere.IMPORTANCECyanobacteria generate oxygen as part of their metabolism and are responsible for the rise of oxygen in Earth's atmosphere over two billion years ago. However, we do not know how long this process may have taken. To help constrain how long this process would have taken, it is necessary to understand where the earliest Cyanobacteria may have lived. Here, we use a cutting-edge bioinformatics tool called branch water to examine the environments where modern Cyanobacteria and their relatives live to constrain those inhabited by the earliest Cyanobacteria. We find that these species likely lived in non-marine environments. This indicates that the rise of oxygen may have taken longer than previously believed.

Determining an Optimal Combination of Meteorological Factors to Reduce the Intensity of Atmospheric Pollution During Prescribed Straw Burning

Currently, large-scale burning is an important straw disposal method in most developing countries. To execute prescribed burning while mitigating air pollution, it is crucial to explore the maximum possible range of meteorological changes. This study conducted a three-year monitoring program in Changchun, a core agricultural area in Northeast China severely affected by straw burning. The data included ground-level pollutant monitoring, ground-based polarized LiDAR observations, and ground meteorological factors such as planetary boundary layer height (PBLH), relative humidity (RH), and wind speed (WS). Using response surface methodology (RSM), this study analyzed key weather parameters to predict the optimal range for emission reduction effects. The results revealed that PM2.5 was the primary pollutant during the study period, particularly in the lower atmosphere from March to April, with PM2.5 rising sharply in April due to the exponential increase in fire points. Furthermore, during this phase, the average WS and PBLH increased, whereas the RH decreased. Univariate analysis confirmed that these three factors significantly impacted the PM2.5 concentration. The RSM relevance prediction model (MET-PM2.5) established a correlation equation between meteorological factors and PM2.5 levels and identified the optimal combination of meteorological indices: WS (3.00–5.03 m/s), RH (30.00–38.30%), and PBLH (0.90–1.45 km). Notably, RH (33.1%) emerged as the most significant influencing factor, while the PM2.5 value remained below 75 μg/m3 when all weather indicators varied by less than 20%. In conclusion, these findings could provide valuable meteorological screening schemes to improve planned agricultural residue burning policies, with the aim of minimizing pollution from such activities.

On the 3D transport of galactic cosmic rays in a selection of exoplanet-hosting astrospheres: the influence of stellar rotation

ABSTRACT Galactic cosmic rays (GCRs) may influence the habitability of exoplanets. The recently proposed relationship between GCR intensities at exoplanetary locations and the rotation periods of their host stars is here investigated for several M-dwarf astrospheres, namely Proxima Centauri, TRAPPIST-1, GJ 436, and LHS1140, using a three-dimensional GCR modulation code. This relation, where higher GCR intensities result from enhanced particle transport along astrospheric magnetic fields that are underwound due to longer stellar rotation periods, is found to hold for the astrospheres considered here. The influence of the stellar rotation period on GCR intensities in a Sun-like astrosphere on Earth and Mars-like atmospheres is also investigated and found to directly influence atmospheric ionization and radiation exposure.

Does total column ozone change during a solar eclipse?

Abstract. Several publications have reported that total column ozone (TCO) may oscillate with an amplitude of up to 10 DU (Dobson units) during a solar eclipse, whereas other researchers have not seen evidence that an eclipse leads to variations in TCO beyond the typical natural variability. Here, we try to resolve these contradictions by measuring short-term variations (of seconds to minutes) in TCO using “global” (Sun and sky) and direct-Sun observations in the ultraviolet (UV) range with filter radiometers (GUVis-3511 and Microtops II®). Measurements were performed during three solar eclipses: the “Great American Eclipse” of 2024, which was observed in Mazatlán, Mexico, on 8 April 2024; a partial solar eclipse that took place in the United States on 14 October 2023 and was observed at Fort Collins, Colorado (40.57° N, 105.10° W); and a total solar eclipse that occurred in Antarctica on 4 December 2021 and was observed at Union Glacier (79.76° S, 82.84° W). The upper limits of the amplitude of oscillations in TCO observed at Mazatlán, Fort Collins, and Antarctica were 0.4 %, 0.3 %, and 0.03 %, respectively. The variability at all sites was within that observed during times not affected by an eclipse. The slightly larger variability at Mazatlán is due to cirrus clouds occurring throughout the day of the eclipse and the difficulty of separating changes in the ozone layer from cloud effects. These results support the conclusion that a solar eclipse does not lead to variations in TCO of more than ± 1.2 DU and that these variations are likely much lower, drawing into question reports of much larger oscillations. In addition to calculating TCO, we also present changes in the spectral irradiance and aerosol optical depth during eclipses and compare radiation levels observed during totality. The new results augment our understanding of the effect of a solar eclipse on the Earth's upper atmosphere.

Non-linear internal waves breaking in stellar-radiation zones. Parametrisation for the transport of angular momentum: Bridging geophysical-to-stellar fluid dynamics

Internal gravity waves (IGWs) are one of the mechanisms that can play a key role in efficiently redistributing angular momentum in stars along their evolution. The study of IGWs is thus of major importance since space-based asteroseismology reveals a transport of angular momentum in stars, which is stronger by two orders of magnitude than the one predicted by stellar models ignoring their action or those of magnetic fields. IGWs trigger angular momentum transport when they are damped by heat or viscous diffusion; at this point, they meet a critical layer where their phase velocity in the azimuthal direction equals the zonal wind or when they break. Theoretical prescriptions have been derived for the transport of angular momentum induced by IGWs because of their radiative and viscous dampings and of the critical layers they encounter along their propagation. However, none have been proposed for the transport of angular momentum triggered by their non-linear breaking. In this work, we aim to derive such a physical and robust prescription, which can be implemented in stellar structure and evolution codes. We adapted an analytical saturation model -- which has been developed for IGWs' nonlinear convective breaking in the Earth's atmosphere and has been successfully compared to in situ measurements in the stratosphere -- to the case of deep spherical stellar interiors. This allowed us to derive the saturated amplitude of the velocity of IGWs breaking in stellar radiation zones through convective overturning of the stable stratification or the instability of the vertical shear of IGWs motion and of the angular momentum transport they trigger. In a first step, we neglected the modification of IGWs by the Coriolis acceleration and the Lorentz force, which are discussed and taken into account in a second step. We derive a complete semi-analytical prescription for the transport of angular momentum by IGWs that takes into account both their radiative damping and their potential nonlinear breaking because of their convective and vertical shear instabilities. We show that the deposit of angular momentum by breaking waves increases with their latitudinal degree, the ratio of the Brunt-Va"is"al"a frequency and the wave frequency; and when the density decreases or the Doppler-shifted frequency vanishes. This allows us to bring the physical prescription for the interactions between IGWs and the differential rotation to the same level of realism as the one used in global circulation models for the atmosphere.

Excitation of ULF, ELF, and VLF Resonator and Waveguide Oscillations in the Earth–Atmosphere–Ionosphere System by Lightning Current Sources Connected with Hunga Tonga Volcano Eruption

The simulations presented here are based on the observational data of lightning electric currents associated with the eruption of the Hunga Tonga volcano in January 2022. The response of the lithosphere (Earth)–atmosphere–ionosphere–magnetosphere system to unprecedented lightning currents is theoretically investigated at low frequencies, including ultra low frequency (ULF), extremely low frequency (ELF), and very low frequency (VLF) ranges. The electric current source due to lightning near the location of the Hunga Tonga volcano eruption has a wide-band frequency spectrum determined in this paper based on a data-driven approach. The spectrum is monotonous in the VLF range but has many significant details at the lower frequencies (ULF, ELF). The decreasing amplitude tendency is maintained at frequencies exceeding 0.1 Hz. The density of effective lightning current in the ULF range reaches the value of the order of 10−7 A/m2. A combined dynamic/quasi-stationary method has been developed to simulate ULF penetration through the lithosphere (Earth)–atmosphere–ionosphere–magnetosphere system. This method is suitable for the ULF range down to 10−4 Hz. The electromagnetic field is determined from the dynamics in the ionosphere and from a quasi-stationary approach in the atmosphere, considering not only the electric component but also the magnetic one. An analytical/numerical method has been developed to investigate the excitation of the global Schumann resonator and the eigenmodes of the coupled Schumann and ionospheric Alfvén resonators in the ELF range and the eigenmodes of the Earth–ionosphere waveguide in the VLF range. A complex dispersion equation for the corresponding disturbances is derived. It is shown that oscillations at the first resonance frequency in the Schumann resonator can simultaneously cause noticeable excitation of the local ionospheric Alfvén resonator, whose parameters depend on the angle between the geomagnetic field and the vertical direction. VLF propagation is possible over distances of 3000–10,000 km in the waveguide Earth–ionosphere. The results of simulations are compared with the published experimental data.

Assimilating ESA CCI land surface temperature into the ORCHIDEE land surface model: insights from a multi-site study across Europe

Abstract. Land surface temperature (LST) plays an essential role in water and energy exchanges between the Earth's surface and atmosphere. Recent advancements in high-quality satellite-derived LST data and land data assimilation systems present a unique opportunity to bridge the gap between global observational data and land surface models (LSMs) to better constrain the water and energy budgets in a changing climate. In this vein, this study focuses on the assimilation of the ESA CCI-LST product into the ORCHIDEE LSM (the continental part of the Institut Pierre-Simon Laplace Earth system model) with the aim of optimizing key parameters to improve the simulation of LST and surface energy fluxes. We use the land data assimilation system for the ORCHIDEE model (ORCHIDAS) to conduct a series of synthetic twin data assimilation experiments accounting for actual data availability and uncertainty from ESA CCI-LST to find an optimal strategy for assimilating LST. Here, we test different strategies of assimilation, notably investigating (i) two optimization methods (a random search technique and a gradient-based technique) and (ii) different ways to assimilate LST using the only raw data and/or different characteristics of the LST diurnal cycle (e.g. mean daily, daily amplitude, maximum and minimum temperatures, and morning and afternoon gradients). Upon identifying the optimal approach, we use ORCHIDAS to assimilate ESA CCI-LST data across 34 European sites provided by the Warm Winter database. Our results demonstrate the effectiveness of assimilating 3 h CCI-LST data in ORCHIDEE over a single year in 2018, thereby improving the accuracy of simulated LST and fluxes. This improvement, assessed against CCI-LST and in situ observations, reaches up to a 60 % reduction in the root-mean-square deviation, with a median decrease of 20 % over the entire validation period (2009–2020). Furthermore, we evaluate the effectiveness of optimized parameters for application at larger scales using the median of optimized parameters per vegetation type across sites. Notably, the performance for both LST and fluxes exhibits consistent stability over the years, comparable to using site-specific parameters, and indicates a significant improvement in the modelled fluxes. Future work will be focused on refining the utilization of the observation uncertainties provided by the ESA CCI-LST product (e.g. decomposed uncertainties and spatio-temporal variability) in the assimilation process.

High‐Resolution Analysis of Severe Heat Wave Dynamics and Thermal Discomfort Across India

ABSTRACTThe study explores variability and dynamical characteristics of heatwaves during March–June for 1990–2020 over India. Normalised Tmax anomaly is used to identify different heatwave spells in vulnerable regions of North‐central India (NCI) and Southeast coast of India (SECI) using India Meteorological Department (IMD, 1° × 1° resolution) observations, Indian Monsoon Data Assimilation and Analysis (IMDAA, 0.12° × 0.12°), and ECMWF Reanalysis v5 (ERA5, 0.25° × 0.25°). Results highlight that IMDAA exhibited a total 202 days (181 days) heatwaves duration in NCI (SECI) regions while ERA5 exhibited a total 132 days (89 days), respectively, compared with those of IMD (195 and 163 days). The primary heatwave periods for NCI (10 April to 20 June) and SECI region (1 May to 10 June) are well captured by IMDAA, unlike ERA5. The average length of the heatwave is 7.8, 7.5, and 7.76 days (8.15, 7.72, and 6.1 days) over NCI (SECI) in IMD, IMDAA, and ERA5, respectively. The high heat stress is more frequent in SECI than in the NCI region and is common during May–June (May only), as seen in IMDAA (ERA5). The middle to upper‐level anticyclone over NCI is stronger than SECI during heatwaves. Heat advection with stronger 850‐hPa north‐westerlies (~10 ms−1) abates sea breeze in the coastal region, aiding longer heatwaves in the SECI region. Ascending motion induced by surface heating is confined to the lower levels due to the subsidence by the upper‐level anomalous anticyclone, stagnating higher temperatures in the lower atmosphere, depicting a heat dome. The surface temperatures are slightly higher in NCI (31°C–39°C) than in SECI (30°C–37°C). However, the double moist heat dome in SECI has witnessed higher heat stress conditions than NCI. Higher relative humidity in the SECI region is contributed by maritime winds from the Bay of Bengal and Arabian Sea, soil moisture, and so forth. The study highlights the value of atmospheric moisture in differentiating the study regions for heat stress conditions.

Improvements to monoscopic analysis for imaging atmospheric Cherenkov telescopes: Application to H.E.S.S.

Imaging atmospheric Cherenkov telescopes (IACTs) detect rays by measuring the Cherenkov light emitted by secondary particles in the air shower when the rays hit the atmosphere of the Earth. Given usual distances between telescopes in IACT arrays, at low energies (lesssim 100 GeV), the limited amount of Cherenkov light produced typically implies that the event is registered by one IACT only. Such events are called monoscopic events, and their analysis is particularly difficult. Challenges include the reconstruction of the event's arrival direction, energy, and the rejection of background events due to charged cosmic rays. Here, we present a set of improvements, including a machine-learning algorithm to determine the correct orientation of the image in the camera frame, an intensity-dependent selection cut that ensures optimal performance across all energies, and a collection of new image parameters. To quantify these improvements, we make use of simulations and data from the 28-m diameter central telescope of the IACT array. Knowing the correct image orientation, which corresponds to the arrival direction of the photon in the camera frame, is especially important for the angular reconstruction, which could be improved in resolution by 57% at 100,GeV. The event selection cut, which now depends on the total measured intensity of the events, leads to a reduction of the low-energy threshold for source analyses by ∼50%. The new image parameters characterize the intensity and time distribution within the recorded images and complement the traditionally used Hillas parameters in the machine learning algorithms. We evaluate their importance to the algorithms in a systematic approach and carefully evaluate associated systematic uncertainties. We find that including subsets of the new variables in machine-learning algorithms improves the reconstruction and background rejection, resulting in a sensitivity improved by 41% at the low-energy threshold. Finally, we apply the new analysis to data from the Crab Nebula and estimate systematic uncertainties introduced by the new method.

Rain in convective downdraughts

AbstractThis study presents results from the simulation of idealised, rain‐laden downdraughts using a large‐eddy model. Each downdraught is initialised as a “cold, wet bubble”, that is, a spherical/spheroidal region of the lower atmosphere with a negative potential‐temperature perturbation and non‐zero rain mixing ratio. The bubbles are statically unstable and evolve into downdraughts. Results are compared for two‐ and three‐moment microphysics parametrisations. A tendency for larger raindrops to descend ahead of the cold air is observed, which is significant in some two‐moment runs. The effects of this are interpreted in the context of fluid‐dynamical studies of related phenomena. It is found that a drier environment has the effect of increasing cooling in the downdraught, but reduces the peak in downdraught speed. Both these effects stem from increased rain evaporation. A relatively heavy rain load leads to a narrower downdraught, through the suppression of internal (thermal‐like) circulations. Downdraughts intensify, in both cooling and vertical velocity, in correlation with the initial bubble height‐to‐width ratio, being greatest for vertically stretched bubbles.

Derivation of atmospheric reaction mechanisms for volatile organic compounds by the SAPRC mechanism generation system (MechGen)

Abstract. This paper describes the methods that are used in the SAPRC mechanism generation system, MechGen, to estimate rate constants and derive mechanisms for gas-phase reactions of volatile organic compounds (VOCs) in the lower atmosphere. Versions of this system have been used for over 20 years in the development of the SAPRC mechanisms for air quality models, but this is the first complete documentation of the scientific basis for the chemical mechanisms it derives. MechGen can be used to derive explicit gas-phase mechanisms for most compounds with C, H, O, or N atoms. Included are reactions of organic compounds with hydroxy (OH) and nitrate (NO3) radicals, O3, and O3P; photolysis or unimolecular reactions; and the reactions of the radicals they form in the presence of O2 and oxides of nitrogen (NOx) at lower-atmospheric temperatures and pressures. Measured or theoretically calculated rate constants and branching ratios are used when data are available, but in most cases rate constants and branching ratios are estimated using various structure–reactivity or other estimation methods. Types of reactions include initial reactions of organics with atmospheric oxidants or by photolysis; unimolecular and bimolecular reactions of carbon-centered, alkoxy, and peroxy radicals; and those of Criegee and other intermediates that are formed. This paper documents the methods, assignments, and estimates currently used to derive these reactions and provides examples of MechGen predictions. Many of the estimation methods discussed here have not been published previously, and others have not been used previously in developing comprehensive mechanisms. Our knowledge of atmospheric reactions of organic compounds rapidly and continuously evolves, and therefore mechanism generation systems such as MechGen also need to evolve to continue to represent the current state of the science. This paper points out areas where MechGen may need to be modified when the system is next updated. This paper concludes with a summary of the major areas of uncertainty where further experimental, theoretical, or mechanism development research is most needed to improve predictions of atmospheric reaction mechanisms of volatile organic compounds.

What we can learn about Mars from the magnetism of returned samples

The Red Planet is a magnetic planet. The Martian crust contains strong magnetization from a core dynamo that likely was active during the Noachian period when the surface may have been habitable. The evolution of the dynamo may have played a central role in the evolution of the early atmosphere and the planet's transition to the current cold and dry state. However, the nature and history of the dynamo and crustal magnetization are poorly understood given the lack of well-preserved, oriented, ancient samples with geologic context available for laboratory study. Here, we describe how magnetic measurements of returned samples could transform our understanding of six key unknowns about Mars' planetary evolution and habitability. Such measurements could i) determine the history of the Martian dynamo field's intensity; ii) determine the history of the Martian dynamo field's direction; iii) test the hypothesis that Mars experienced plate tectonics or true polar wander; iv) constrain the thermal and aqueous alteration history of the samples; v) identify sources of Martian crustal magnetization and vi) characterize sedimentary and magmatic processes on Mars. We discuss how these goals can be achieved using future laboratory analyses of samples acquired by the Perseverance rover.

Computing Accurate & Reliable Rovibrational Spectral Data for Aluminum-Bearing Molecules.

The difficulty of quantum chemically computing vibrational, rotational, and rovibrational reference data via quartic force fields (QFFs) for molecules containing aluminum appears to be alleviated herein using a hybrid approach based upon CCSD(T)-F12b/cc-pCVTZ further corrected for conventional CCSD(T) scalar relativity within the harmonic terms and simple CCSD(T)-F12b/cc-pVTZ for the cubic and quartic terms: the F12-TcCR+TZ QFF. Aluminum containing molecules are theorized to participate in significant chemical processes in both the Earth's upper atmosphere as well as within circumstellar and interstellar media. However, experimental data for the identification of these molecules are limited, showcasing the potential for quantum chemistry to contribute significant amounts of spectral reference data. Unfortunately, current methods for the computation of rovibrational spectral data have been shown previously to exhibit large errors for aluminum-containing molecules. In this work, ten different methods are benchmarked to determine a method to produce experimentally-accurate rovibrational data for theorized aluminum species. Of the benchmarked methods, the explicitly correlated, hybrid F12-TcCR+TZ QFF consistently produces the most accurate results compared to both gas-phase and Ar-matrix experimental data. This method combines the accuracy of the composite F12-TcCR energies along with the numerical stability of non-composite anharmonic terms where the non-rigid nature of aluminum bonding can be sufficiently treated.

Forecasting O3 and NO2 concentrations with spatiotemporally continuous coverage in southeastern China using a Machine learning approach.

Ozone (O3) is a significant contributor to air pollution and the main constituent ofphotochemical smog that plagues China. Nitrogen dioxide (NO2) is a significant air pollutant and a critical trace gas in the Earth's atmosphere. The presence of O3 and NO2 has detrimental effects on human health, the ecosystem, and agricultural production. Forecasting accurate ambient O3 and NO2 concentrations with full spatiotemporal coverage is pivotal for decision-makers to develop effective mitigation strategies and prevent harmful public exposure. Existing methods, including chemical transport models (CTMs) and time series at air monitoring sites, forecast O3 and NO2 concentrations either with nontrivial uncertainty or without spatiotemporally continuous coverage. In this research, we adopted a forecasting model that integrates the random forest algorithm with NASA's Goddard Earth Observing System "Composing Forecasting" (GEOS-CF) product. This approach offers spatiotemporally continuous forecasts of O3 and NO2 concentrations across southeastern China for up to five days in advance. Both overall validation and spatial cross-validation revealed that our forecast framework significantly surpassed the initial GEOS-CF model for all validation metrics, substantially reducing the errors in the GEOS-CF forecast data. Our model could provide accurate near-real-time O3 and NO2 forecasts with continuous spatiotemporal coverage.