Atmospheric transmittance modeling for spaceborne oceanic lidar: Global assessment and distribution characteristics at the Fraunhofer line of 486.1 nm

Atmospheric transport and deposition of potentially toxic elements along a South-North altitudinal transect (2-3650m a.s.l.): Assessing spatiotemporal patterns, sources, orographic control, and public health implications.

The key role of Mediterranean and North Atlantic sea surface temperatures on the 2024 record-breaking Valencia precipitation event

The impact of trade activities on the balance between interregional environmental and socio-economic development is critical for sustainable regional cooperation. This study integrates a nested multiregional input-output (MRIO) model with an atmospheric chemical transport model (WRF-CAMx) to quantify the complex impacts of embodied emission transfers on PM2.5 concentrations under significant interregional differences in energy consumption and emission intensity, enabling a regionally development status-aligned assessment of environmental benefits; furthermore, by coupling environmental (PM2.5 concentration), social (employment opportunity), and economic (value-added) benefits, a regional multidimensional balance index (RESI) was constructed. Results indicate that in 2017, trade between China and its 33 neighboring countries was generally balanced (RESI values close to zero), suggesting relatively equitable exchanges of environmental and socio-economic impacts. The path of China's sustainable development has played a positive role in promoting mutually beneficial and win-win regional cooperation. At the provincial level, developed coastal regions gained economic benefits while outsourcing pollution, whereas less-developed inland regions bore environmental burdens without receiving corresponding socio-economic returns. Incorporating PM2.5 concentration and employment factors alters inequality assessments for some regions, providing a more realistic evaluation. This study provides a scientific basis for improving cross-regional environmental compensation and promoting more balanced and sustainable development.

Hydroxymethyl hydroperoxide (HMHP, HOCH2OOH) is one of the most abundant organic peroxides (POs) in the atmosphere. Owing to its extremely high solubility, HMHP readily partitions into cloudwater and aerosol liquid water, where it hydrolyzes to hydrogen peroxide (H2O2) and formaldehyde (HCHO). However, previous studies were conducted in dilute solutions and did not adequately account for the high-salinity characteristic of deliquesced aerosol particles. Here, we systematically investigate the combined effects of pH (0-6), temperature (277-313 K), ionic strength (0-10 M), and ion identity (NH4+, Na+, SO42-, and Cl-) on the hydrolysis kinetics of HMHP. For the first time, a parametrization formula describing the dependence of the hydrolysis rate constant on ionic strength is established, demonstrating that ionic strength exerts only a limited influence on HMHP hydrolysis. However, it is found that in highly concentrated ammonium salt solutions, HMHP undergoes a previously unrecognized NH3-driven reaction pathway. This new pathway competes with hydrolysis, accelerating the apparent transformation rate of HMHP by more than an order of magnitude while significantly reducing the yield of H2O2 and HCHO. Our findings highlight that future atmospheric chemical models should fully account for the NH3-driven pathway in aqueous-phase reactions of POs, thereby enabling a more accurate assessment of the role of POs in atmospheric oxidant cycling and secondary particulate matter formation.

Abstract. Some global atmospheric chemistry modeling applications assume that intra-month variability in anthropogenic emissions averages out at monthly timescales. To systematically quantify the impacts of resolving daily and hourly emissions, we use a global model with a refined ∼ 14 km resolution over the contiguous United States (CONUS; MUSICAv0) and a regional CONUS inventory for July 2018. Switching from daily to hourly nitric oxide (NO) emissions (typically higher during the day and lower at night) yields contrasting spatial responses in nitrogen oxides (NOx≡ NO+ nitrogen dioxide (NO2)) and ozone (O3) concentrations in the western versus eastern CONUS and in urban versus rural areas. Neglecting hourly variations in CONUS NO emissions leads to grid-cell level discrepancies in monthly mean surface O3 concentrations of −22 % to +11 % (−7 to +5 ppb) and surface NO2 of −49 % to +86 % (−1 to +8 ppb), with tropospheric NO2 columns showing similar spatial patterns (−12 % to +56 %). While comparable in magnitude to a uniform 30 % NO emission reduction (grid-cell level surface O3 differences of −12 % to +9 %, −7 to +3 ppb), the spatial response patterns differ with location-specific timing of emissions and meteorology. For example, Los Angeles shows higher morning NOx concentrations and stronger NOx-saturated O3 suppression relative to New York City. A simple scaling analysis suggests that neglecting hourly emissions variability can bias NOx emissions inferred from monthly mean tropospheric NO2 columns, with absolute relative differences ranging from ∼ 1 % to ∼ 56 % within individual model grid cells.

Abstract Cloud feedback remains the main source of uncertainty in climate sensitivity estimated by global climate models (GCMs), largely because subgrid cloud responses are parameterized in GCMs due to their coarse resolution. This study examines cloud feedback in the global 3.25-km Simple Cloud-Resolving Energy Exascale Earth System Model (E3SM) Atmosphere Model (SCREAM 3 km) through a pair of 1-yr atmosphere-only simulations with control and +4-K sea surface temperature perturbations. SCREAM 3 km produces a positive cloud feedback that falls within but at the upper end of the range of Coupled Model Intercomparison Project phase 5 (CMIP5) and CMIP phase 6 (CMIP6) models and expert judgment. The positive cloud feedback arises from positive contributions from both high- and low-level clouds, with increases in high-cloud altitude and decreases in low-cloud amount and optical depth playing key roles. The stronger-than-CMIP-average feedback is mainly attributable to the high-cloud altitude feedback, owing to cloud tops rising nearly isothermally in SCREAM 3 km. The positive low-cloud amount feedback is weaker in SCREAM than in GCMs because estimated inversion strength (EIS) increases more dramatically with warming. A coarser 12-km resolution version of SCREAM exhibits a weaker positive cloud feedback than SCREAM 3 km, mainly because its low-cloud-radiative flux is more sensitive to EIS, leading to a stronger negative low-cloud amount feedback. With this process-level assessment of cloud feedback, this study reveals where SCREAM aligns with and diverges from conventional GCMs and expert assessment, providing insights to inform further model improvement and future expert assessment.

Abstract This study investigates the relative contributions of large-scale thermodynamic and dynamic processes to decadal and multidecadal changes in Atlantic tropical cyclone (TC) activity, spanning the historical record since the late nineteenth century, and extending to 2100 projections. We employ a framework that decomposes TC counts into precursor disturbances that transition into fully developed storms, applied to multiensemble simulations of two TC-permitting atmospheric models. Using these models, we conduct controlled experiments with distinct SST forcings that isolate the influence of SST spatial patterns from that of global-mean warming on Atlantic TC activity. Our results show that decadal and multidecadal changes in TC frequency are primarily governed by two thermodynamic variables: potential intensity and moist entropy deficit. In the historical record, these variables reinforced one another, producing more robust trends in TC activity. In contrast, future projections suggest opposing influences, with one variable (potential intensity) becoming more favorable for TCs while the other (moist entropy deficit) becomes less favorable, leading to increased uncertainty in TC projections. We trace this shift to differences in relative warming between the tropical Atlantic and the broader tropics, underscoring that regional SST patterns, rather than the global-mean warming rate, control both past variability and projected future changes in TC activity. Constraining future projected patterns of warming is therefore essential for improving the reliability of TC projections.

Declining nitrogen oxide (NOx = NO + NO2) emissions have transformed oxidation pathways in urban atmospheres, with implications for air quality. Organic peroxy radicals (RO2), key intermediates in volatile organic compound oxidation, typically react with NO to form ozone (O3). Under lower-NO conditions, alternative RO2 fates, including isomerization forming highly oxidized organic molecules (HOMs), can enhance secondary organic aerosol (SOA) production. We combine aircraft observations over four major North American cities with geostationary satellite data to characterize isoprene-derived RO2 fate across urban environments. We infer RO2 bimolecular lifetimes (τbi) as a proxy for isomerization potential, finding longer τbi (17 ± 11 seconds) in New York, Chicago, and Toronto compared to Los Angeles (7 ± 6 seconds). Satellite measurements reveal that long τbi is widespread across urban North America, suggesting that declining NOx is likely to lead to greater HOM formation in urban regions. These findings indicate that atmospheric models omitting RO2 isomerization chemistry may incorrectly simulate organic oxidation and the subsequent oxidation state of volatile organic compounds and SOA.

NASA's Goddard Earth Observing System (GEOS) infrastructure was used to couple a cloud-admitting (7-km grid, 72 levels) configuration of the GEOS atmospheric model with a mesoscale-resolving (2-4-km grid, 90 levels) Estimating the Circulation and Climate of the Ocean (ECCO) configuration of the Massachusetts Institute of Technology general circulation model (MITgcm), and to conduct a 14-month "nature" simulation initialized with January 20, 2020, 21Z conditions. The output of this simulation is contained in the dataset described here. The NASA GEOS/ECCO Coupled Nature Run includes astronomical tidal forcing in the ocean component of the simulation, an interactive aerosol component and aerosol-cloud interactions in the atmosphere, and the storage of copious amounts of model output. The inclusion of tidal forcing permits a more realistic representation of vertical mixing in the ocean and of high-frequency variability that is aliased in satellite observations. All of the above make this simulation well suited as a nature run in Observing System Simulation Experiments (OSSEs) and for the study of high frequency/wavenumber coupled processes in weather and climate.

Atmospheric microplastics and nanoplastics (MNPs), particularly fibers, are emerging contaminants with complex deposition dynamics that remain poorly understood. Here, a mechanistic dry deposition model is developed for MNP fibers, integrating gravitational settling, Brownian diffusion, impaction, and interception. The model incorporates fiber-specific drag corrections and shape-dependent diffusivity to estimate total deposition velocity across a range of particle lengths and aspect ratios. Results show that total deposition velocity deviates significantly from gravitational settling alone, especially for submicron fibers. Global simulations reveal strong spatial and seasonal variability driven by land cover and turbulence. Atmospheric lifetime estimates based on dry deposition indicate that micro - nano transition fibers (∼ 1 μm) persist longest in the boundary layer, with dry-deposition lifetimes exceeding four months (∼ 2,900 h). This framework supports the integration of MNP fibers into existing aerosol dry-deposition schemes in regional and global atmospheric models and improves predictions of their environmental fate.

This study presents an integrated methodological framework that couples a physical protection system (PPS) performance assessment with atmospheric dispersion consequence modeling for a hypothetical sabotage scenario involving a spent nuclear fuel pool. The framework has two objectives: (1) to estimate the probability of adversary success using the design and evaluation process outline (DEPO) methodology and (2) to quantify off-site external dose consequences using the worldwide version of the system for prediction of environmental emergency dose information (WSPEEDI). Two U.S. nuclear power plants (South Texas Project and Comanche Peak) are examined as comparative case studies. A one-year meteorological and dispersion database (8760 simulations per site) is used to characterize the variability in the plume transport and deposition and to identify high-consequence scenarios. The results indicate that plausible variations in the PPS response parameters yield adversary success probabilities on the order of 10−1, while meteorological variability produces order-of-magnitude differences in the 4-day integrated external dose, as illustrated by the selected high-consequence realizations. These findings demonstrate that integrating protection effectiveness with consequence modeling provides a structured basis for comparative risk-informed assessments of spent fuel pool security vulnerabilities.

Nitrous acid (HONO) is a key precursor to hydroxyl radicals (OH) and a reservoir of reactive nitrogen. Here, we identify abiotic photodecomposition of marine algae as a previously unrecognized HONO source. During Ulva prolifera green tides, daytime HONO levels closely followed tidal cycles, peaking at low tide, contrasting with typical inland nocturnal peaks. Chamber experiments confirm that common algae (e.g., U. prolifera and Sargassum) emit HONO under irradiation, with fluxes increasing with light intensity and algal surface area. This light-driven, abiotic process is mechanistically distinct from microbial soil HONO production. Measured fluxes (1.08×10-7 to 2.31×10-6 mole per square meter per hour) are comparable to soil HONO emissions and exceed marine NO fluxes by two to three orders of magnitude. Incorporating this source into atmospheric models substantially elevated HONO concentrations, enhancing OH and ozone production and oxidation of climate-relevant gases. With intensifying global algal blooms driven by eutrophication and climate warming, this process is expected to become increasingly important.

OH-Initiated Oxidation of N-Methyl-2-Pyrrolidone: Kinetics, Environmental Fate, and Implications for Biological Interactions.

The westerlies moisture transport underpins water security for over two billion people dependent on the Asian water towers (AWTs). However, the mechanisms by which large-scale westerlies-advected moisture is integrated into the AWTs' atmospheric water budget remain poorly understood due to observational gaps. Here, we combine three-dimensional observations of atmospheric water vapor stable isotopes with isotope-enabled modeling. We identify the conveyor mechanism that regulates the vertical moisture transport under calm conditions during the winter-spring period when the westerlies are dominant. Sharp vertical isotopic gradients show that large-scale westerlies-advected moisture is predominantly confined aloft, while local residual moisture persists near the surface. Our results show the interplay of the westerlies' subsidence at night with thermodynamically distinct local residual air, yielding thermal inversions and condensation that suppresses vertical mixing and decouples moisture between the free troposphere and the atmospheric boundary layer. This process constitutes a primary pathway for integrating westerlies-advected moisture into the local moisture budget without precipitation, sustaining near-surface moisture accumulation. Our results provide critical benchmarks for improving atmospheric models, refining climate projections of the intensifying water cycle over the AWTs, and advancing interpretations of isotopic records in regional climatic archives.

Abstract We report the discovery of an SX Phe-type pulsating star LSST-AP-DO-313893022856118297 from the Rubin Observatory Legacy Survey of Space and Time (LSST) alerts, which is located within one of the Deep Drilling Fields (DDFs), the Euclid Deep Field South. From LSST and our own observations, its pulsation period is determined as 0.04638(1) day. The Southern African Large Telescope optical spectrum with the deep absorption lines of the Balmer series is well-fitted by a stellar atmosphere model with effective temperature T eff = 7650 ± 200 K, surface gravity log g ( cm s − 2 ) = 4.6 ± 0.2 , and metallicity [Fe/H] = −1.4 ± 0.2. Together with its high Galactic latitude ( b = − 49 . ° 3535 ), these characteristics are consistent with the general properties of SX Phe stars. This result emphasizes the importance of the DDF even for Galactic science cases.

Abstract. Nitrogen dioxide (NO2) is a critical air pollutant with significant environmental and human health impacts, yet global and long-term NO2 datasets with daily continuity and fine spatial resolution remain limited. In this study, we construct a continuous global daily NO2 concentration (https://doi.org/10.5281/zenodo.13842191, Mu and Tao, 2025) spanning from 2005 to 2023 at a 0.1° resolution using the advanced Air Transformer deep learning framework that integrates satellite observations, ground-based measurements, meteorological reanalysis, land-use information, and auxiliary geophysical variables. The resulting dataset shows robust performance across diverse regions and pollution regimes, with improved spatial consistency and reduced biases relative to existing global products. Based on this dataset, we characterize the spatiotemporal evolution of global NO2 concentrations over the past two decades. Global annual mean NO2 increased from 2005 to 2015, followed by a moderate decline during 2016–2019, a pronounced decrease in 2020 associated with COVID-19-related reductions in economic activity and transportation, and a partial rebound thereafter, reaching 3.38 ppbv in 2023. The Northern Hemisphere and tropical regions largely followed the global trend, whereas the Southern Hemisphere exhibited distinct behaviour, with relatively stable or declining NO2 levels prior to 2015, a sharp decrease in 2020, and a stronger post-pandemic rebound during 2021–2023. As one of the global, multi-decadal NO2 datasets with daily resolution, this dataset provides a valuable resource for air quality assessment, exposure analysis, and atmospheric model evaluation.

Abstract We present a multiwavelength analysis of the nearby millisecond pulsar PSR J0437–4715, combining Hubble Space Telescope (HST) far-ultraviolet, ROSAT soft X-ray, and XMM-Newton X-ray data, to model its broadband emission and energy-resolved pulse profiles and infer key stellar parameters via Bayesian inference. The broadband emission includes cold thermal, hot thermal, and nonthermal components: cold bulk surface emission is modeled with a nonmagnetized partially ionized hydrogen atmosphere; hot-spot emission adopts the pulse profile modeling technique with a nonmagnetized fully ionized hydrogen atmosphere model; and nonthermal emission is included as a phase-invariant power-law component. By adopting an informative prior on the hot-spot geometry informed by radio polarization position angle measurements, the joint multi-instrument analysis yields a statistically viable and radio-consistent solution with a gravitational mass of 1.38 ± 0.03 M ⊙ and an equatorial circumferential radius of 13.25 − 0.35 + 0.34 km (68% confidence intervals). The hot-spot geometry consists of two spherical caps with uniform temperature distributions: the primary hot spot is situated at a colatitude of ≈130°, and the secondary hot spot lies at a colatitude of ≈9°, close to the north pole. It yields tighter radius constraints than HST+ROSAT fits and shifts the radius posterior distribution to larger values relative to NICER-only fits. This work demonstrates the importance of multiwavelength data in refining neutron star mass–radius measurements and resolving geometric degeneracies.

Abstract We present a study of the effect of metallicity on the determination of the effective temperature and surface gravity of A and B type horizontal-branch stars using the spectroscopic method based on fitting the Balmer line profiles. We used synthetic spectra derived from chemically homogeneous atmospheric models calculated with PHOENIX in the LTE mode at various metallicities [M/H] between −1.5 and +0.5 dex solar. Stars from globular clusters M3 and M13 known to have a low metallicity ([Fe/H] ≃ 1.5 dex solar), observed at the Calar Alto 3.5 m telescope, are used for this purpose. For each star, we determined the atmospheric parameters considering various metallicity values. For stars cooler than 11,500 K and model metallicities between −1.5 and −1.0 dex, the effective temperature and surface gravity differ by a maximum of 200 K and 0.1 dex, respectively. For stars hotter than 11,500 K, considering that their atmospheric metallicities are broadly enhanced due to atomic diffusion, metallicities at ±0.5 dex from solar are of more interest. In this low metallicity range, atmospheric parameters increase, with increasing metallicity, to a maximum of 500 K in effective temperature and 0.25 dex in surface gravity.

Estimation of aqueous solubility and hygroscopicity in poly- and perfluoroalkyl substances with COSMOtherm.