Chemical Transport Research Articles

Propagations From Extreme Integrated Vapor Transport to Extreme Precipitation Events in North America

AbstractExtreme integrated vapor transport (IVT) is a crucial driving factor of extreme precipitation events (EPEs). This paper presents a complex network‐based characterization of propagations from extreme IVT to EPEs. Specifically, the propagations are tracked from extreme IVT to EPEs by event synchronization; and then the source zones of extreme IVT contributing to EPEs are identified by two‐layer complex network. A case study is devised for North America based on the daily NCEP/NCAR Reanalysis 1 from 1948 to 2021. Overall, eight communities of EPEs are identified: the west coast of United States (US) tend to receive substantial EPEs from the Pacific Ocean; the Gulf of Alaska tends to receive oceanic EPEs propagating inland; western Canada typically experiences large amount of out tendencies and the EPEs tend to accumulate in the Baffin Island and Labrador Peninsula; the southeastern US and the northern Great Plains tend to experience northward propagations from Mexico. Along the west coast of North America, the propagations from extreme IVT to EPEs typically originate from the eastern North Pacific between 160°W and 110°W, and make landfalls in 4 days. These propagations are influenced by anomalous cyclonic circulations developing over the Gulf of Alaska forced by eastward Rossby waves. The coincidence rate of these propagations with atmospheric rivers is, respectively, 85.31% in autumn, 91.35% in winter, 73.94% in spring, and 64.52% in summer. Overall, the observed propagations from extreme IVT to EPEs yield insights into the mechanism of atmospheric moisture transport and the predictability of precipitation.

Indian Ocean temperature anomalies modulate the interannual variability of springtime smoke aerosols over the Indochina Peninsula

Abstract Smoke aerosols released through frequent springtime fire activity over the Indochina Peninsula (ICP) seriously affect regional air quality, climate, and human health. However, the mechanisms driving the interannual variability of these smoke aerosols are not well understood. By analyzing multi-source historical (1980–2020) smoke aerosols and meteorological reanalysis data, we explore the response of springtime smoke aerosol changes over the ICP to the interannual variability of the Indian Ocean (IO) sea-surface temperature (SST). Our findings show a positive correlation between the variability of springtime smoke aerosol loading and the preceding winter Southeast IO (SEIO) SST anomalies. Warmer SEIO SST tends to weaken the trans-equatorial flow (TEF) and the local Hadley circulation. This weakening of the TEF impede cyclones development in the Bay of Bengal (BOB), thereby reducing southwest water vapor transport. Simultaneously, enhanced westerly winds over the northern BOB are blocked by the northwestern mountains of ICP. These winds converge and rise on the windward slopes, while descending on the leeward side with diminished humidity. Collectively, these dynamics lead to drier and hotter local meteorological conditions that favored fire-induced smoke aerosol emissions. Our findings highlight the role of the SEIO in regulating smoke aerosol variability and provide a scientific basis for developing strategies to manage smoke aerosol emissions over the ICP.

Effect of Different Doping Concentrations on the Properties of Fe2+:ZnSe and Fe2+, Cr2+:ZnSe Crystals Grown by the Chemical Vapor Transport Method.

The Fe2+:ZnSe crystal is an important material for 3-5 μm mid-infrared lasers. In this work, we have grown different doping concentrations of Fe2+:ZnSe and Fe2+, Cr2+:ZnSe by the chemical vapor transport method. The doped crystals have the same structure. The lattice constant increases slightly with a higher Fe2+ concentration, while the doped Cr2+ has a great influence on the lattice constant. Besides, with a higher Fe2+ concentration, the TO mode has no change and the LO mode presents a small blue shift. The doped ZnSe crystals all have a wide absorption peak in the range of 2.3-4.5 μm, and these absorption peaks widen with the increase of the Fe2+ doping concentration. Besides, in the range of 5-20 μm, the crystals have good transparency. The concentrations of 3, 2, and 1% Fe2+ samples are calculated to be 4.15 × 1019, 3.27 × 1019, and 3.02 × 1019 cm-3, respectively, and the Fe2+ concentration of the Fe2+, Cr2+:ZnSe sample is 3.71 × 1019 cm-3. The band gap decreases from 2.52 to 2.27 eV with a higher Fe2+ doping concentration. Therefore, we can modulate the absorption bandwidth and band gap by doping the ion concentration, which is more suitable for developing mid-infrared gain medium applications.

Contributions of Stationary and Transient Water Vapor Transports to the Extreme Precipitation Changes Over the Tibetan Plateau

AbstractThe Tibetan Plateau (TP) has experienced “south drying‐north wetting” extreme precipitation changes over the past half century. The effects of water vapor transport at different timescales on TP extreme precipitation changes remain unexplored. Here, we utilize the reanalysis data sets to quantify the contributions of stationary and transient processes of water vapor transport to the long‐term changes in the extreme precipitation (R95p) during wet season (Jun‐Jul‐Aug‐Sep) over the TP and surrounding regions. We find that the daily scale transient processes dominate the dipole trend of extreme precipitation with a contribution of 55.1% in the northern and 79.5% in the southern TP, respectively, whereas the contribution of monthly scale stationary processes is of 19.0% and 20.5%. The long‐term changes in extreme precipitation are dominated by the transient dynamic component. We identified the synoptic circulation patterns affecting the changes of R95p over the northern and southern TP by using k‐means clustering. The patterns featured with a 500 hPa trough, 200 hPa wind divergence and low transient geopotential height are identified. The frequency of the dominant circulation patterns increases in the northern TP and decreases in the southern TP, which leads to the dipolar changes of extreme precipitation over the TP and surrounding regions.

Abstract 4129036: Air pollution and Cardiovascular Disease Incidence in a Pooled Analysis of 6 U.S. Cohorts

Introduction/Background: Long term air pollution is associated with cardiovascular disease (CVD) incidence, however the effects at low levels in the US are unknown. Research Questions/Hypothesis: To assess the effect of long-term exposure to ambient air pollution CVD incidence (myocardial infarction [MI], stroke, and all CVD) in a pooled analysis of epidemiological cohorts. Materials and Methods: We harmonized data from six cohorts (Cardiovascular Health Study, Nurses’ Health Study II, Multi-Ethnic Study of Atherosclerosis, and Reasons for Geographic And Racial Differences in Stroke Study, Sister Study, and Women’s Health Initiative) with both CVD incidence data and extensive covariate information. We predicted time-varying two-year average concentrations of particulate matter <2.5 microns (PM 2.5 ) and nitrogen dioxide (NO 2 ) from 1990-2019 at participant residential addresses using validated regionalized spatio-temporal models, combining spatio-temporal universal kriging and partial least squares regression with inputs from monitoring data from regulatory and researcher-deployed networks, satellite remote-sensing data and chemical transport modeling. Cox proportional hazards regression models adjusted for individual and area-level information, including smoking status, socio-economic factors, anthropometry, blood pressure, cholesterol, and other clinical variables. Results: Our analysis included over 300,000 participants and 10,229 incident CVD events. The median residential concentration of PM 2.5 was 10.1 µg/m 3 and NO 2 was 9.3 ppb. A 5 µg/m 3 increase in PM 2.5 was not significantly associated with a higher hazard ratio for all outcomes: 1.03 (95%CI: 0.96, 1.10) for CVD incidence, 1.03 (95%CI 0.93, 1.15) for MI, and 1.00 (95%CI 0.90, 1.10) for stroke. We found that a 10ppb increase in NO 2 was associated with a 1.06 (95%CI: 1.01, 1.11) higher hazard ratio for CVD, 1.07 (95%CI: 1.01, 1.11) for MI, and 1.02 (95%CI 0.96, 1.09) for stroke. Conclusions: In this analysis of a large, pooled cohort with excellent exposure, outcome, and covariate information, we found an association of NO 2 exposure—considered a surrogate for traffic-related air pollution—with CVD incidence and MI. Associations with particulate matter were not statistically significant, but could not exclude a small increased risk. We are extending this analysis to include 6 additional cohorts and an additional 700,000 participants to allow for generation of a highly resolved concentration-response function.

Interdecadal change in the relationship between the Antarctic oscillation and autumn rainfall in the Yunnan–Guizhou plateau of Southwest China

AbstractThe interdecadal change in the relationship between the Antarctic Oscillation (AAO) and autumn rainfall in the Yunnan–Guizhou Plateau of Southwest China is investigated by using the observed autumn rainfall data at 119 stations and the National Centers for Environment Prediction/National Center for Atmospheric Research reanalysis data for the period 1961–2021. Results show the AAO correlates well with the autumn rainfall in the Yunnan–Guizhou Plateau for the second period (2002–2021) because the AAO becomes stronger. The possible influencing mechanism of AAO on autumn rainfall in the Yunnan–Guizhou Plateau during 2002–2021 is related to the meridional teleconnection pattern and associated convection over the Philippine Sea. The positive AAO can trigger a meridional teleconnection pattern in the upper troposphere to propagate from the southern Pacific to northern Pacific and cause anomalous westerly over the tropical west Pacific, which inhibits the convection over the Philippine Sea. On the one hand, the weakened convection over the Philippine Sea causes the anomalous ascending motion over the Yunnan–Guizhou Plateau; on the other hand, it results in an anomalous anticyclone over the tropical Northwest Pacific and strengthens the transport of water vapor from the tropical Pacific to the Yunnan–Guizhou Plateau.

High yield growth of centimeter-sized black phosphorus single crystal thin flakes through bidirectional vapor transport

High yield growth of centimeter-sized black phosphorus single crystal thin flakes through bidirectional vapor transport

Numerical Thermo-Hydraulic Simulation of Infiltration and Evaporation of Small-Scale Replica of Typical Dike Covers

Measurements taken on a historical dike in the Netherlands over one year showed that interaction with the atmosphere led to oscillation of the piezometric surface of about 0.7 m. The observation raised concerns about the long-term performance of similar dikes and promoted a deeper investigation of the response of the cover layer to increasing climatic stresses. An experimental and numerical study was undertaken, which included an investigation in the laboratory of the unsaturated behavior of a scaled replica of the field cover. A sample extracted from the top clayey layer in the dike was subjected to eight drying and wetting cycles in a HYPROP™ device. Data recorded during the test provide an indication of the delayed response with depth during evaporation and infiltration. The measurements taken during this continuous dynamic process were simulated by means of a finite element discretization of the time-dependent coupled thermohydraulic response. The results of the numerical simulations are affected by the way in which the environmental loads are translated into numerical boundary conditions. Here, it was chosen to model drying considering only the transport of water vapor after equilibrium with the room atmosphere, while water in the liquid phase was added upon wetting. The simulation was able to reproduce the water mass balance exchange observed during four complete drying–wetting cycles, although the simulated drying rate was faster than the observed one. The numerical curves describing suction, the amount of vapor and temperature are identical, confirming that vapor generation and its equilibrium is control the hydraulic response of the material. Vapor generation and diffusion depend on temperature; therefore, correct characterization of the thermal properties of the soil is of paramount importance when dealing with evaporation and related non-steady equilibrium states.

Landscape fire PM2.5 and hospital admissions for cause-specific cardiovascular disease in urban China

There is a growing interest in the health impacts of PM2.5 originating from landscape fires. We conducted a time-series study to investigate the association between daily exposure to landscape fire PM2.5 and hospital admissions for cardiovascular events in 184 major Chinese cities. We developed a machine learning model combining outputs from chemical transport models, meteorological information and observed air pollution data to determine daily concentrations of landscape fire PM2.5. Furthermore, we fitted quasi-Poisson regression to evaluate the link between landscape fire PM2.5 concentrations and cardiovascular hospitalizations in each city, and conducted random-effects meta-analysis to pool the city-specific estimates. Here we show that, on a national scale, a rise of 1-μg/m3 in landscape fire PM2.5 concentrations is positively related to a same-day 0.16% (95% confidence interval: 0.01%–0.32%) increase in hospital admissions for cardiovascular disease, 0.28% (0.12%–0.44%) for ischemic heart disease, and 0.25% (0.02%–0.47%) for ischemic stroke. The associations remain significant even after adjusting for other sources of PM2.5. Our findings indicate that transient elevation in landscape fire PM2.5 levels may increase risk of cardiovascular diseases.

2D-Penta-PdPS: Gate-Tunable and Thickness-Dependent Thermoelectric Transport.

Pentagonal two-dimensional (2D) materials are notable for unique properties derived from their Cairo pentagonal tiling topology. This study explores the thermoelectric potential of exfoliated penta-palladium-phosphorus-sulfur (PdPS) atomic layers, an air-stable 2D semiconductor with a puckered pentagonal low-symmetry structure, grown via chemical vapor transport (CVT). Thickness-dependent in-plane electrical conductivity (σ) and thermoelectric power factor (PF) of PdPS are investigated from 20-380 K, showing an increase in σ with thickness (11, 13, and 88-layer). Applying back-gate voltage (Vg) modulates the Fermi energy (EF), and as Vg decreases, the Seebeck coefficient (S) rises, achieving S of -700µVK-1 for 11-layer PdPS at -10V, significantly higher than the -400 µVK-1 for 88-layer PdPS. The PF increased with decreasing thickness, peaking at ≈50µW m-1K-2 for 11-layer PdPS, about twice than that of 88-layer PdPS. The high electron mobility (µe) in PdPS is confined to a narrow temperature range, peaking at 300 cm2Vs-1 at 100 K, marking the transition temperature from ionized impurity scattering to acoustic phonon scattering mechanism, consistent across all layer counts. This work highlights the significant impact of quantum confinement in ultrathin bodies in enhancing thermoelectric performance across a wide temperature range.

Dropsonde Observations of the Stable Marine Boundary Layer Beneath Atmospheric Rivers

Abstract An important source of errors in predicting landfalling atmospheric rivers (ARs), and their associated extreme precipitation and streamflow, are inaccuracies in model initial conditions in ARs offshore. These inaccuracies are particularly evident in the marine boundary layer (MBL) where the tendency of ARs to transport warm air poleward over progressively cooler SSTs generates a stable MBL (SMBL). The SMBL’s vertical structure and key modulating processes are documented using >1000 dropsondes along 99 transects of ARs from the AR Reconnaissance and CalWater field campaigns. The SMBL depth, modulated by sensible heat loss to the ocean, is typically 300–800 m in the AR core, with vertical wind shears ranging from 5–50 m s−1 km−1, representing a highly variable decoupling of the AR aloft from conditions at the ocean surface. Simulated backward air parcel trajectories originating from dropsonde locations within the AR core are used to calculate the 24-h change in SST experienced by an air parcel (DSST24) beneath each AR. The DSST24 varies from −13°C to +2°C and is directly related to the strength of the AR and its orientation relative to the SST gradient. The DSST24, therefore, distinguishes weak and strong decoupling regimes (WDR, SDR). In SDR cases, relative to WDR cases, the SMBL is characterized by greater sensible heat loss to the ocean, as well as stronger static stability, vertical wind shear, low-level jet, and horizontal water vapor transport. In SDR cases, the SMBL is deeper in the core than in adjacent warm and cold sectors.

The Different Effects of Two Types of El Niño on Eastern China’s Spring Precipitation During the Decaying Stages

El Niño is one of the most significant global climatic phenomena affecting the East Asian atmospheric circulation and climate. This study uses multi-source datasets, including observations and analyses, and statistical methods to investigate the variations and potential causes of boreal spring precipitation anomalies in eastern China under different El Niño sea surface temperature conditions, namely, the Eastern Pacific and Central Pacific (EP and CP) El Niño cases. The findings reveal that, particularly along the Yangtze–Huaihe valley, spring precipitation markedly increases in most regions of eastern China during the EP El Niño decaying stages. Conversely, during the CP El Niño decaying stages, precipitation anomalies are weak, with occurrences of weak negative anomalies in the same regions. Further analyses reveal that during the decaying spring of different El Niño cases, differences in the location and strength of the Northwest Pacific (NWP) abnormal anticyclone, which is associated with the central–eastern Pacific warm sea surface temperature anomaly (SSTA), result in distinct anomalous precipitation responses in eastern China. The SSTA center of the EP El Niño is more easterly and stronger. In the meantime, NWP abnormal anticyclones are more easterly and have a broader range, facilitating water vapor transport over eastern China. By contrast, the CP El Niño SSTA center is westward and relatively weaker, leading to a relatively weak, westward, and narrower anomalous NWP anticyclone that causes less significant water vapor transport anomalies in eastern China. This paper highlights the diverse impacts of El Niño diversity on regional atmospheric circulation and precipitation, providing valuable scientific references for studying regional climate change in East Asia.

Multiyear high-temporal-resolution measurements of submicron aerosols at 13 French urban sites: data processing and chemical composition

Abstract. This paper presents a first comprehensive analysis of long-term measurements of atmospheric aerosol components from aerosol chemical speciation monitor (ACSM) and multiwavelength Aethalometer (AE33) instruments collected between 2015 and 2021 at 13 (sub)urban sites as part of the French CARA (Chemical Characterization of Particles) program. The datasets contain the mass concentrations of major chemical species within submicron aerosols (PM1), namely organic aerosols (OAs), nitrate (NO3-), ammonium (NH4+), sulfate (SO42-), non-sea-salt chloride (Cl−), and equivalent black carbon (eBC). Rigorous quality control, technical validation, and environmental evaluation processes were applied, adhering to both guidance from the French Reference Laboratory for Air Quality Monitoring (LCSQA) and the Aerosol, Clouds, and Trace Gases Research Infrastructure (ACTRIS) standard operating procedures. Key findings include geographical differences in the aerosol chemical composition, seasonal variations, and diel patterns, which are influenced by meteorological conditions, anthropogenic activities, and proximity to emission sources. Overall, OA dominates PM1 at each site (43 %–60 % of total mass), showing distinct seasonality with higher concentrations (i) in winter, due to enhanced residential heating emissions, and (ii) in summer, due to increased photochemistry favoring secondary aerosol formation. NO3 is the second most important contributor to PM1 (15 %–30 %), peaking in late winter and early spring, especially in northern France, and playing a significant role during pollution episodes. SO4 (8 %–14 %) and eBC (5 %–11 %) complement the major fine-aerosol species, with their relative contributions strongly influenced by the origin of air masses and the stability of meteorological conditions, respectively. A comparison with the 3D chemical transport model (CTM) CHIMERE shows high correlations between simulations and measurements, albeit with an OA concentration underestimation of 46 %–76 %. Regional discrepancies in NO3 concentration levels emphasize the importance of these datasets with respect to validating air quality models and tailoring air pollution mitigation strategies. The datasets can be found at https://doi.org/10.5281/zenodo.13318298 (Chebaicheb et al., 2024).

Vapor kinetic energy for the detection and understanding of atmospheric rivers

Poleward water vapor transport in the midlatitudes mainly occurs in meandering filaments of intense water vapor transport, spanning thousands of kilometers long and hundreds of kilometers wide and moving eastward. The water vapor filaments are known as atmospheric rivers (ARs). They can cause extreme wind gusts, intense precipitation, and flooding along densely populated coastal regions. Many recent studies about ARs focused on the statistical analyses of ARs, but a process-level understanding of ARs remains elusive. Here we show that ARs are streams of air with enhanced vapor kinetic energy (VKE) and derive a governing equation for Integrated VKE to understand what contributes to the evolution of ARs. We find that ARs grow mainly because of potential energy conversion to kinetic energy, decay largely owing to condensation and turbulence, and the eastward movement is primarily due to horizontal advection of VKE. Our VKE framework complements the integrated vapor transport framework, which is popular for identifying ARs but lacks a prognostic equation for understanding the physical processes.

Electrospun Membranes of Hydrophobic Polyimide and NH2‐UiO‐66 Nanocomposite for Desalination

Hydrophobic nanofiber composite membranes comprising polyimide and metal–organic frameworks are developed for desalination via direct contact membrane distillation (DCMD). Our study demonstrates the synthesis of hydrophobic polyimides with trifluoromethyl groups, along with superhydrophobic UiO‐66 (hMOF) prepared by phenylsilane modification on the metal‐oxo nodes. These components are then combined to create nanofiber membranes with improved hydrophobicity, ensuring long‐term stability while preserving a high water flux. Integration of hMOF into the polymer matrix further increases membrane hydrophobic properties and provides additional pathways for vapor transport during MD. The resulting nanofiber composite membranes containing 20 wt% of hMOFs (PI‐1‐hMOF‐20) were able to desalinate hypersaline feed solution of up to 17 wt% NaCl solution, conditions that are beyond the capability of reverse osmosis systems. These membranes demonstrated a water flux of 68.1 kg m−2 h−1 with a rejection rate of 99.98% for a simulated seawater solution of 3.5 wt% NaCl at 70 °C, while maintaining consistent desalination performance for 250 h.

Nonlinear Radiative Response to Patterned Global Warming due to Convection Aggregation and Nonlinear Tropical Dynamics

Abstract Climate responses to global warming exhibit large dependence on the spatial pattern of sea surface temperature (SST) changes. A Green’s function (GF) approach—predicting the global climate response to a complex SST pattern change as the linear superposition of the response to finite-area SST perturbations evaluated in isolation—has been used to systematically evaluate and understand the top of atmosphere (TOA) radiation response to patterned warming. However, in general, the linear GF approach fails for TOA radiation reconstruction under future global warming scenarios in coupled models. Here, we show that the linear superposition of global mean TOA radiation responses to large SST warming perturbations at multiple patches (the GF approach prediction) overestimates the actual response to simultaneous multipatch perturbation. This is because the linear superposition overestimates tropical large-scale convection aggregation strengthening upon localized heating that enhances longwave radiative cooling, which is further explained by the overestimation of circulation response and associated horizontal water vapor transport. The nonadditivity of TOA radiation response is caused by the nonadditivity of convection aggregation, ultimately rooted in nonlinear tropical dynamics. We also demonstrate that the prediction error of the GF approach grows with decreasing patch size (equivalently, increasing patch number). We conclude that using the GF approach to predict future climate change could overestimate longwave radiative cooling and underestimate (effective) climate sensitivity. Numerical experiments may be used to identify specific perturbation patterns where the errors are smaller than the signal. Our research also highlights that an increase in the degree of large-scale convection aggregation has a nonlinear and negative feedback for mean warming.

Dominant spring precipitation anomaly modes and circulation characteristics in the Tarim Basin, Central Asia

Recently, extreme precipitation has occurred frequently in the Tarim Basin, which has a fragile ecological environment, arousing widespread concern. Using daily precipitation observations from 42 stations in the Tarim Basin during the spring of 1980–2021 and monthly circulation reanalysis data from the European Center for Medium-Range Weather Forecasts Reanalysis v5, as well as statistical analyses and physical diagnostic methods, this study investigated the abnormal modes and the evolution characteristics and differences in atmospheric circulation. The results show that the spring precipitation anomalies in the Tarim Basin can be divided into two independent precipitation modes: the first (EOF1) is a precipitation pattern that is uniform throughout the region and the second (EOF2) is an east–west inverse pattern. Thus, there are distinct differences in the atmospheric circulation characteristics responsible for abnormal spring precipitation modes in the basin. When the precipitation across the entire basin is consistently excessive, the 500 hPa geopotential height is affected by the negative phase of the North Atlantic Oscillation related circulation, and the 700 hPa wind field is controlled by abnormal southwesterly winds. Water vapor transport is mainly driven by anomalous water vapor uplift along the terrain in the middle latitudes west of the Atlantic Ocean and south of the Arabian Sea. This leaves the Tarim Basin with a net water vapor budget and abnormally high atmospheric precipitable water. The opposite situation occurs when the precipitation across the entire basin is consistently lower than normal. When there is a west-to-east precipitation gradient, The western region of the Tarim Basin is dominated by upward airflow, whereas the eastern region is dominated by downward airflow, providing dynamic conditions for the west-to-east precipitation gradient. Under the influence of anomalous water vapor transport from the southwest and water vapor convergence, water vapor conditions favorable for precipitation can occur. The net water vapor in the basin also exhibited an abnormal west-to-east transport pattern. Moreover, the atmospheric precipitable water demonstrated an inverse phase distribution under the EOF2 atmospheric precipitation mode in the Tarim Basin.

Concurrent trend turnings of drought severity across Afro-Eurasian continent since 1950

Rapidly intensifying global land drought poses severe threats to human societies, economies, and ecosystems. While previous studies have primarily investigated long-term drought trends, the frequency and concurrence of trend turnings have been largely neglected. In this study, we address this gap by employing the Running Slope Difference (RSD)-t-test to quantify trend turning frequency in Afro-Eurasian drought severity. Based on Palmer Drought Severity Index (PDSI), our analysis indicates that the PDSI trend in most parts of the Afro-Eurasian continent has experienced two turnings since 1950, although, the types of trend turnings vary regionally. The concurrence of these PDSI trending turnings is further investigated. Around 1985, a dipole pattern emerged - Eastern Europe experiences a drying trend turning, accompanied by decreased P-E and intensified drought, while Sahel exhibits a wetting trend turning, with increased P-E and mitigated drought. Around 2000, a tripole pattern is observed in Eastern Eurasia: The Russian Far East and South Asia experienced a drying trend turning, with reduced P-E and intensified drought, while Northeast Asia exhibited a further wetting trend, characterized by increased P-E and mitigated drought. We further investigate the influence of large-scale circulation changes. The enhanced Northern Hemisphere warming trend before and after 1985 contributes to increased land surface high pressure and an amplified meridional temperature gradient, favoring cross-equatorial water vapor transport. This mechanism potentially drives the dipole pattern of trend turning observed around 1985. Additionally, the North Pacific Ocean Sea Surface Temperature (SST) exhibited an enhanced North Pacific Gyre Oscillation (NPGO) pattern around 2000, which induced a tripole atmospheric circulation pattern over East Asia, corresponding to the observed tripole pattern of PDSI trend turnings. The identified dipole and tripole patterns of drought trend turnings, and their potential links to large-scale atmospheric circulation changes, provide insights into the complex dynamics of land drought variability across Afro-Eurasian.

Underappreciated roles of soil nitrogen oxide emissions on global acute health burden

The recognized importance of ambient fine particulate matter (PM2.5), ozone (O3), and nitrogen dioxide (NO2) on human health has prompted the world to enact increasingly strict regulations on anthropogenic nitrogen oxides (NOx) emissions. However, the health concerns from soil NOx, potentially driven by fertilizer input but conventionally categorized as natural sources, remain less studied. Here, we emphasize the underappreciated roles of soil NOx emissions on health burden attributable to short-term PM2.5, O3, and NO2 exposure. Globally, we quantify acute health effects using machine-learning-based daily exposure estimates and identify influences of soil NOx emissions based on chemical transport model simulations. We find that 72.3% of the globe is affected by soil NOx emissions, whose contributions to short-term PM2.5, O3, and NO2 pollution lead to 13.9 (95% Confidence Interval [CI]: 9.1-18.8), 26.0 (18.2-34.2), and 13.9 (10.3-17.5) thousand premature mortality, respectively, in 2019. With distinct variations in regions, seasons, and pollutants, soil NOx-originated air pollution poses a global health concern, particularly for developing regions and intensively agricultural areas. In response to the intensive fertilizer use, South Asia, Southern Sub-Saharan Africa, and Central Europe witness the largest soil NOx-related health burden of up to 1.6 (95% CI: 1.1-2.1) mortality per 100k population. The overall health risk peaks in May, with O3 pollution typically dominating the soil NOx-attributable health burden during warm seasons and NO2 or PM2.5 during cold months. Our study highlights the necessity of dynamically adapted agricultural strategies for health-oriented multi-pollutant control, among which the improved use of synthetic fertilizers deserves priority under the ever-changing climate.

The role of vertical grid resolution and turbulent diffusion uncertainty on chemical transport modeling

Chemical transport models (CTM) tend to perform poorly in simulating pollution processes under weak turbulent diffusion conditions. In this study, we address this issue from the perspectives of vertical grid resolution and vertical mixing schemes. Three vertical grid resolution configurations (L4, L12, L40) with the CHIMERE model are evaluated during a winter episode, which includes a heavy pollution episode (PE) in the Paris region. The results emphasize the significance of vertical grid resolution, particularly noticeable during nighttime, and consequently impacts CHIMERE simulations under nocturnal stable conditions. Consistent improvement in CTM modeling is observed with refined vertical resolutions and the first layer height based on a simple linear vertical diffusion scheme defined as the initial Kz diffusion (IKD) scheme. Compared to the other two configurations, the finest configuration (referred to as L4-IKD) demonstrates an average improvement in root mean square error of 23.26 % and 25.09 % on regular days (RD) and 62 % and 129 % during PE, respectively. However, simulations using the 1.5-order turbulence kinetic energy (TKE) based eddy diffusivity closure scheme, named the new eddy diffusion (NED), are more sensitive to the first layer height setup. Excessively fine first-layer heights can lead to inaccurate TKE calculations. Generally, models with low vertical grid resolution can reasonably predict air quality on RD or during light pollution events but struggle with heavy PEs. One straightforward enhancement strategy involves adding an extra fine first layer height in CTM simulations, resulting in an average 50.10 % improvement from L4-IKD to L12-IKD during PE. Another strategy is enhancing the model's vertical diffusion scheme, which improved the CTM modeling by 26.67 % compared with IKD during PE under identical vertical grid resolution.