Abating ammonia is more cost-effective than nitrogen oxides for mitigating PM2.5 air pollution

A novel dual-mode biosensing platform based on Au@luminol and CdSe QDs for detection of trace heavy metal ions in PM2.5

Multi-component analysis of PM2.5, especially heavy metal ions, is very important for the study of air pollution. In this work, a novel dual-mode biosensing platform based on Au@luminol and CdSe QDs luminophores was constructed to achieve simultaneous detection of trace Mn2+ and Cd2+ in PM2.5. Interestingly, Au@luminol and CdSe QDs both had excellent fluorescence (FL) and electrochemiluminescence (ECL) performance, which provided feasibility for dual-mode detection. Based on this characteristic, this platform adopted a classical magnetic bead-assisted enzyme cleavage amplification strategy to convert trace Mn2+ and Cd2+ into a large number of Au@luminol and CdSe QDs probes, respectively, producing excellent positive and negative potential ECL signals in the presence of the only co-reactant H2O2. The above two probes were introduced into a and b regions of ITO electrode by DNA hybridization to realize the ECL-spatial-potential resolution and simultaneous detection of Mn2+ and Cd2+. In addition, the above two probes could also be directly used for FL detection of Mn2+ and Cd2+, further improving the detection accuracy. In general, this work focused on heavy metal pollution in atmospheric particulates by using a cleverly designed dual-mode biosensor, which provided a new idea for simultaneous detection of multi-component samples.

Condensable particulate matter emissions regulated by flue gas desulfurization technologies in typical industrial plants

Condensable particulate matter (CPM) emissions have exceeded filterable particulate matter from industrial plants under strict emission standards. However, how CPM emission characteristics are affected by air pollution control devices (especially end-of-pipe flue gas desulfurization (FGD) systems) remains to be investigated. Here, we systematically demonstrated CPM emissions regulated by various FGD systems through field measurements of 22 typical industrial sites. Inorganic CPM (57.6 ∼ 99.5 % of CPM) predominantly consisted of water-soluble ions, whose concentrations were distinct between the inlet and outlet of FGD units. SO42- or Cl- mainly contributed to inorganic CPM before desulfurization, while SO42- and NH4+ accounted for 49.2 ∼ 96.3 % of inorganic CPM after FGD. Higher removal efficiencies for Cl- (98.1 ± 1.9 %) than SO42- (50.1 ± 23.8 %) in partial lime-gypsum-wet FGD systems could convert Cl--rich CPM into SO42--rich CPM. Ammonia-wet FGD and activated coke FGD failed to address NH3 slip issues effectively, leading to NH4+- rich (44.0 ∼ 96.0 %) CPM after desulfurization. Conversions of precursors (i.e., NH3, HCl, and SO3) before and after FGD were consistent with those of water-soluble ions. This study revealed chemical-specific transformations of CPM under different FGD processes, highlighting the control of the NH3 slip to reduce CPM emissions.

Soil health contributes to variations in crop production and nitrogen use efficiency

Soil health affects both food production and environmental quality. However, quantifying its impact poses a substantial global challenge due to the scarcity of comprehensive soil health data and the complexity of disentangling its effects from other variables. Here we integrate high-resolution global data on soil, climate and farm management practices to assess the contribution of soil health to agricultural productivity. We show that soil health is responsible for approximately 12% and 22% of global variations in crop production and nitrogen use efficiency, respectively. While the influence of climate on crop yields is comparable to that of soil health, it is substantially overshadowed by the role of agricultural management, which accounts for roughly 70% of the global yield variation. In regions such as China, India and the central United States, the influence of soil health on crop yields and nitrogen use efficiency is less pronounced due to the dominant effects of farming practices, including the intensive use of fertilizers. Enhancing global soil health could increase crop yields by 7.8 Mt while reducing nitrogen surplus by 8.1 Mt worldwide by 2050. It is crucial to achieve global sustainable development through managing soil health beyond traditional agricultural practices and climate adaptation.

Non-Precious Metal Catalysts with Gradient Oxidative Dual Sites Boost Bimolecular Activation for Catalytic Oxidation Reactions

Catalytic oxidation emerges as a highly promising and cost-effective approach for eliminating gaseous pollutants, greenhouse gases, and volatile organic compounds (VOCs) from industrial exhaust streams. However, achieving the simultaneous activation of O2 and substrate molecules at low temperatures using non-precious metal catalysts remains a significant challenge. In this study, we introduce gradient oxidative Cu─O─Ti/Cu─O─Cu dual sites that enhance bimolecular activation for catalytic oxidation reactions. The catalyst, Ti-doped CuO, is synthesized on a TiO2 support through the immobilization of Cu2⁺ on NO3⁻-grafted TiO2, followed by thermal treatment. The resulting gradient oxidative Cu─O─Ti/Cu─O─Cu sites exhibit exceptional catalytic oxidation activity for NH3 and various VOCs at low temperatures, matching the performance of precious metal-based catalysts. Notably, during NH₃ oxidation, Cu─O─Ti sites enhance the activation of both O₂ and NH₃. HNO intermediates formed on Cu─O─Ti sites react with NH intermediates on neighboring Cu─O─Cu sites-producing N₂ and H₂O via an imide mechanism-which effectively lowers the reaction barrier for catalytic NH₃ oxidation. As such, dual sites in non-precious metal catalysts show promising results for advancing future catalytic oxidation technologies.

Accounting for the uncertainty in nitrogen deposition estimates in support of policy

Deposition of reactive nitrogen (Nr) onto sensitive habitats in exceedance of Critical Load (CL) thresholds can drive biodiversity loss and affect ecosystem function. Nr deposition is a highly complex process that is difficult to measure and model, leading to large uncertainties. We assess the implications for policy development and target setting of the large range in estimates provided by different modelling approaches. We considered three UK models (UKIAM, EMEP4UK, CBED), used to inform national policy and responses to the UN-ECE Air Convention. We used a scaling method to project the range in current estimates to future scenarios, and a risk-based approach to provide a probabilistic assessment of exceedances. We considered two future scenarios, a 2040 baseline and a 2040 high ambition technological measures scenario, in relation to a 2018 baseline. The 2018 baseline CL exceedances are highly dependent on the model used - Average Accumulated Exceedance of 1.3-9.1 kg.N.ha-1.yr-1 across all habitats. The relative reduction in exceedances for future scenarios also depends on the model, with a range of 30-66 % achieved by 2040 for the high ambition scenario, posing a challenge for target setting. Despite this, it's clear that a much greater level of ambition is required to protect the majority of habitat areas. Our risk-based approach shows that implementing only technological measures is likely to leave most areas in exceedance in 2040. This uncertainty in the assessment of Nr deposition and the benefits of abatement measures poses a challenge for policy development that is not unique to the UK.

The Evolution of Global Surface Ammonia Concentrations during 2001-2019: Magnitudes, Patterns, and Drivers

Ammonia (NH3) is the most prevalent alkaline gas in the atmosphere, with its elevated concentrations posing significant adverse impacts on air quality, ecosystems, and human health across diverse spatial and temporal scales. Given the ongoing global change and intensified anthropogenic NH3 emissions, it is projected that the global surface NH3 concentration will escalate further. Here, based on ground observations, gridded data of organic and inorganic nitrogen fertilizer applications, meteorological data, and ancillary information, we estimated changes in global monthly surface NH3 concentration during 2001-2019 at a 0.1°× 0.1° resolution. A novel scale-adaptive approach, essentially an Ensemble Random Forest Model built upon Rotated Quadtree Partitioning and Box-Cox Transformation, was developed. The model well reproduced the spatial and temporal patterns of surface NH3 observations, particularly capturing peak and valley values (R2 = 0.91 and slope = 0.82 for the whole; R2 = 0.79 and slope = 0.70 for testing). The results indicate a global increase in surface NH3 concentration over 2001-2019, from 1.44 μg m-3 yr-1 in 2001 to 1.51 μg m-3 yr-1 in 2019. Notably, hotspots of elevated NH3 concentrations were located in northern South Asia, northern China, the Sahel area, southeast South America, and central United States. Decreased SO2 emissions and increased fertilizer applications dominated the increase of surface NH3 concentrations in China, while in South Asia, the increase was primarily driven by organic and inorganic nitrogen inputs. Temperature changes were identified to play an important role in affecting surface NH3 concentrations in most regions, particularly in Africa, South America, and Oceania. These findings have the potential to facilitate research on global nitrogen cycle and its environmental footprints and inform the development of locally or regionally tailored nitrogen management strategies. Furthermore, the proposed modeling algorithm showcases its capability in capturing intricate patterns and relationships within highly spatially heterogeneous data, thereby addressing up-scaling challenges associated with multimodal site observations.

Managing Ammonia for Multiple Benefits Based on Verified High-Resolution Emission Inventory in China

Atmospheric ammonia (NH3) has multiple impacts on the environment, climate change, and human health. China is the largest emitter of NH3 globally, with the dynamic inventory of NH3 emissions remaining uncertain. Here, we use the second national agricultural pollution source censuses, integrated satellite data, 15N isotope source apportionment, and multiple models to better understand those key features of NH3 emissions and its environmental impacts in China. Our results show that the total NH3 emissions were estimated to be 11.2 ± 1.1 million tonnes in 2020, with three emission peaks in April, June, and October, primarily driven by agricultural sources, which contributed 74% of the total emissions. Furthermore, employing a series of quantitative analyses, we estimated the contribution of NH3 emissions to ecosystem impacts. The NH3 emissions have contributed approximately 22% to secondary PM2.5 formation and a 16.6% increase in nitrogen loading of surface waters, while ammonium deposition led to a decrease in soil pH by 0.0032 units and an increase in the terrestrial carbon sink by 44.6 million tonnes in 2020. Reducing agricultural NH3 emissions in China would contribute to the mitigation of air and water pollution challenges, saving damage costs estimated at around 22 billion US dollars due to avoided human and ecosystem health impacts.

Reactive nitrogen emissions from cropland and their dominant driving factors in China

The environmental impacts of reactive nitrogen (Nr) emitted from fertilized cropland present significant challenges for balancing food security, air pollution and climate change mitigation. As a leading agricultural producer, China requires high-resolution Nr emissions modeling within a comprehensive processed-based framework to address these issues effectively. In this study, we applied a process-based agroecological model (FEST-C*) to estimate daily Nr emissions at 0.25° in China during 2020 and analyzed the driving factors by using Structural Equation Modeling, Random Forest, and Dominance Analysis. The hotspots of annual Nr emissions were in North China, Southeast China, and Southwest China, collectively responsible for over 80 % of the total emissions. Approximately 81 % of the total Nr emissions were from wheat, maize, and rice fields. Timing and amount of basal and topdressing fertilization under different crop rotation systems determined the monthly and seasonal variations of Nr emissions. The impacts of various factors on Nr emissions varied with NH3 being mainly driven by fertilizer consumption and other Nr species (N2O, NO, and HONO) also affected by soil temperature and water content. The spatial distributions of monthly Nr emissions calculated by FEST-C* were more realistic than currently available emission inventories compared to satellite or field observations. These findings will enable policymakers to develop effective control measures that alleviate cropland Nr emissions while sustaining crop production in China.

Sandwich-Structured ZnO/MXene Heterojunction for Sensitive and Stable Room-Temperature Ammonia Sensing

2D metal carbides/nitrides (MXenes) have attracted considerable interest in NH3 sensing due to their high electrical conductivity and abundant terminal groups. However, the strong interlayer interactions between MXene nanosheets result in challenges related to recovery and rapid response decay in MXene-based sensors. Here, a one-step hydrothermal strategy is developed that anchors Zn atoms and grows ZnO polycrystals on the Ti vacancies of Ti3C2Tx layers, forming a sandwich-structured ZnO/Ti3C2Tx heterojunction. At room temperature, the NH3 sensitivity of ZnO/Ti3C2Tx is a remarkable 45-fold higher than that of Ti3C2Tx, with a low detection limit of 138 ppb and a rapid recovery time of 39 s. Furthermore, the heterojunction exhibits exceptional long-term stability, maintaining a consistent response over 21 days. The results confirm that in situ intercalation of the ZnO polycrystals effectively solves the recovery problem in MXene substrates by completely exfoliating the Ti3C2Tx nanosheets. Meanwhile, the room-temperature sensing performance and recovery speed of the sandwich-structured ZnO/Ti3C2Tx is enhanced by rapid electron conduction. This straightforward and effective route for in situ exfoliation and intercalation of MXene layers promises the expanded use of 2D material heterojunctions in sensing applications.

Nondestructively-measured leaf ammonia emission rates can partly reflect maize growth status

A deep understanding of ammonia (NH3) emissions from cropland can promote efficient crop production. To date, little is known about leaf NH3 emissions because of the lack of rapid detection methods. We developed a method for detecting leaf NH3 emissions based on portable NH3 sensors. The study aimed to (i) determine the performance of the method in detecting leaf NH3 emissions; (ii) analyze the variation of leaf NH3 emissions with foliar rank; and (iii) elucidate the relationships between leaf NH3 emissions and other leaf parameters. Maize (Zea mays L.) was used as the tested plant. The results showed that the NH3 sensors had good repeatability, accuracy, and selectivity in detecting NH3. The response time of the method ranged 7-22 s and the NH3 reading ranged 0.078-0.463 μmol mol-1. Leaf NH3 emissions were observed mainly in daytime (negligible at night). Daytime leaf NH3 emission rates ranged 0.347-1.725 μg N cm-2 d-1. The middle leaves (near the ear) were the major contributor to plant NH3-N loss. There were significant linear relationships between leaf NH3 emission rates and other nondestructively-measured leaf parameters [e.g., SPAD (soil and plant analyzer development, which reflects the relative concentration of leaf chlorophyll), stomatal conductance, transpiration rate, and net photosynthetic rate] (p < 0.01), as well as with leaf apoplastic ammonium (NH4+) concentration and leaf total N concentration (p < 0.01). Nitrogen application increased leaf apoplastic NH4+ concentration, leaf total N concentration, and leaf NH3 emission rate. Overall, nondestructively-measured leaf NH3 emission rates can partly reflect maize growth status and provide information for N management in maize production.

Tandem Reaction on Ru/Cu-CHA Catalysts for Ammonia Elimination with Enhanced Activity and Selectivity

Ammonia emissions from vehicles and power plants cause severe environmental issues, including haze pollution and nitrogen deposition. Selective catalytic oxidation (SCO) is a promising technology for ammonia abatement, but current catalysts often struggle with insufficient activity and poor nitrogen selectivity, leading to the formation of secondary pollutants. In this study, we developed a bifunctional Ru/Cu-CHA zeolite catalyst for ammonia oxidation, incorporating both SCO sites (Ru) and selective catalytic reduction sites (SCR, Cu). Various characterizations, including HAADF-STEM, XAFS, and H2-TPR, revealed that Cu2+ cations are dispersed within the CHA zeolite, while RuOx clusters and nanoparticles are present both inside and on the surface of the zeolite. Operando DRIFTS-MS, in situ Raman spectroscopy, and DFT calculations confirmed that NH3 adsorbed on Cu2+ Lewis acid sites efficiently reduced RuO2 with a lower energy barrier, significantly enhancing the low-temperature activity of the Ru/Cu-CHA catalyst. Additionally, Cu2+ cations further facilitated the elimination of byproducts (NOx) via the tandem SCR reaction, thus greatly improving the nitrogen selectivity. This synergistic effect contributed to high catalytic activity (>94% at 200 °C) and excellent nitrogen selectivity (>90% even at high temperatures above 325 °C) for Ru2.5/Cu-CHA during practical ammonia elimination in the presence of NOx and water vapor.

Warming Promotes Nitrogen and Carbon Cycles in Global Grassland

Grasslands, standing as one of Earth's major ecosystems, offer numerous services vital to human well-being. The productivity of grasslands hinges on the availability of soil reactive nitrogen, which is highly sensitive to climatic variations. Using an extensive synthesis of 1242 experimental observations, reinforced by multiple models, we show that warming as a single driver of climate change intensifies nitrogen dynamics in grasslands. This could lead to increases in net primary productivity of 1% to 9% and escalate nitrogen leakage into the environment by 22% to 141%. Under the warming SSP2-4.5 scenario, we foresee an annual boost of 17 million tons per year (Tg yr-1) of nitrogen inputs, predominantly via biological nitrogen fixation, compared to the baseline scenario by 2050. Total nitrogen harvest is projected to climb by 12 Tg yr-1. However, the nitrogen surplus surge is expected to increase by 5 Tg yr-1, potentially intensifying nitrogen pollution. To counter this, adaptation measures must aim at curtailing reactive nitrogen losses while preserving increased nitrogen harvest. This could reduce nitrogen input and surplus by 10 and 20 Tg yr-1, respectively, while boosting nitrogen harvest by 10 Tg yr-1, potentially yielding economic gains of up to 121 billion USD by 2050. In shaping climate change adaptation policies, it is critical to balance the potential benefits and drawbacks of forging effective management approaches.

Catalytic Advancements in NH3 Selective Catalytic Oxidation: The Impact of Cu-Induced Lattice Distortion in TiO2 Crystal Structure

A series of x Cu-TiO2 obtained from the sol-gel method were tested for NH3 selective catalytic oxidation (NH3-SCO). Its performance was higher than that of supported Cu/TiO2-Im and solvent-free Cu/TiO2-SF. The catalyst exhibits better water resistance at 300 °C. XRD, Raman, and H2-TPR proved that the crystal lattice of TiO2 was deformed by Cu doping, which increased the specific surface area of the catalyst. The dispersion of the Cu component is further enhanced. The enhancement of redox potential was the key to improving catalytic activity. The NH3-TPD results prove that more acidic sites promote more active NH3 species being adsorbed and dissociated on the catalyst surface. The in-situ DRIFTs results certify that the NH3 species adsorbed on the Lewis acid sites were easier to consume than those on the Brønsted acid sites. The DFT theoretical calculation demonstrates that the doped Cu promotes the TiO2 conduction band to move closer to the Fermi level and enhances the redox performance of the catalyst. The results suggest that the Cu-TiO2 catalyst was a potential catalyst under actual working conditions, which would provide a technological reserve for the development and diffusion of ammonia slip for both mobile and fixed sources.

Adsorption removal of mercury from flue gas by metal selenide: A review

Mercury (Hg) pollution has been a global concern in recent decades, posing a significant threat to entire ecosystems and human health due to its cumulative toxicity, persistence, and transport in the atmosphere. The intense interaction between mercury and selenium has opened up a new field for studying mercury removal from industrial flue gas pollutants. Besides the advantages of good Hg° capture performance and low secondary pollution of the mineral selenium compounds, the most noteworthy is the relatively low regeneration temperature, allowing adsorbent regeneration with low energy consumption, thus reducing the utilization cost and enabling recovery of mercury resources. This paper reviews the recent progress of mineral selenium compounds in flue gas mercury removal, introduces in detail the different types of mineral selenium compounds studied in the field of mercury removal, reviews the adsorption performance of various mineral selenium compounds adsorbents on mercury and the influence of flue gas components, such as reaction temperature, air velocity, and other factors, and summarizes the adsorption mechanism of different fugitive forms of selenium species. Based on the current research progress, future studies should focus on the economic performance and the performance of different carriers and sizes of adsorbents for the removal of Hg0 and the correlation between the gas-particle flow characteristics and gas phase mass transfer with the performance of Hg0 removal in practical industrial applications. In addition, it remains a challenge to distinguish the oxidation and adsorption of Hg0 quantitatively.

Protective Effects of Resveratrol Against Perfluorooctanoic Acid-Induced Testicular and Epididymal Toxicity in Adult Rats Exposed During Their Prepubertal Period

The antioxidant properties of resveratrol (RES) against oxidative toxicity induced by testicular toxicants are well documented. The current study aimed to investigate the probable beneficial role of RES on male reproduction in adult rats following prepubertal exposure to perfluorooctanoic acid (PFOA). Healthy rats of the Wistar strain (23 days old) were allocated into four groups. Rats in group I did not receive any treatment, while rats in groups II, III, and IV received RES, PFOA, and RES + PFOA, respectively, between days 23 and 56 and were monitored for up to 90 days. Exposure to PFOA resulted in a significant reduction in spermiogram parameters, testicular 3β- and 17β-HSD activity levels, and circulatory levels of testosterone. A significant elevation in LPx, PCs, H2O2, and O2-, associated with a concomitant reduction in SOD, CAT, GPx, GR, and GSH, was noticed in the testes, as well as region-specific changes in pro- and antioxidants in the epididymides of exposed rats compared to controls. A significant increase in serum FSH and LH, testicular cholesterol levels, and caspase-3 activity was observed in PFOA-exposed rats compared to controls. Histological analysis revealed that the integrity of the testes was deteriorated in PFOA-exposed rats. Transcriptomic profiling of the testes and epididymides revealed 98 and 611 altered genes, respectively. In the testes, apoptosis and glutathione pathways were disrupted, while in the epididymides, glutathione and bile secretion pathways were altered in PFOA-exposed rats. PFOA exposure resulted in the down-regulation in the testes of 17β-HSD, StAR, nfe2l2, ar, Lhcgr, and mRNA levels, associated with the up-regulation of casp3 mRNA, and down-regulation of alpha 1 adrenoceptor, muscarinic choline receptor 3, and androgen receptor in the epididymides of exposed rats compared to the controls. These events might lead to male infertility in PFOA-exposed rats. In contrast, restoration of selected reproductive variables was observed in RES plus PFOA-exposed rats compared to rats exposed to PFOA alone. Taken together, we postulate that prepubertal exposure to PFOA triggered oxidative damage and altered genes in the testes and epididymides, leading to suppressed male reproductive health in adult rats, while RES, with its steroidogenic, antiapoptotic, and antioxidant effects, restored PFOA-induced fertility potential in rats.

Polyoxometalates-Mediated Selectivity in Pt Single-Atoms on Ceria for Environmental Catalysis

Optimizing the reactivity and selectivity of single-atom catalysts (SACs) remains a crucial yet challenging issue in heterogeneous catalysis. This study demonstrates selective catalysis facilitated by a polyoxometalates-mediated electronic interaction (PMEI) in a Pt single-atom catalyst supported on CeO2 modified with Keggin-type phosphotungstate acid (HPW), labeled as Pt1/CeO2-HPW. The PMEI effect originates from the unique arrangement of isolated Pt atoms and HPW clusters on the CeO2 support. Electrons are transferred from the ceria support to the electrophilic tungsten in HPW clusters, and subsequently, Pt atoms donate electrons to the now electron-deficient ceria. This phenomenon enhances the positive charge of Pt atoms, moderating O2 activation and limiting lattice oxygen mobility compared to the conventional Pt1/CeO2 catalyst. The resulting electronic structure of Pt combined with the strong and local acidic environment of HPW on Pt1/CeO2-HPW leads to improved efficiency and N2 selectivity in the degradation of NH3 and NO, as well as increased CO2 yield when inputting volatile organic compounds. This study sheds the light on the design of SACs with balanced reactivity and selectivity for environmental catalysis.

Enhanced Nonagricultural Emissions of Ammonia Influence Aerosol Ammonium in an Urban Atmosphere: Evidence from Kinetic Versus Equilibrium Isotope Fractionation Controls on Nitrogen

Aerosol ammonium (NH4+) is a critical component of particulate matter that affects air pollution, climate, and human health. Isotope-based source apportionment of NH4+ is essential for ammonia (NH3) mitigation but the role of kinetic vs equilibrium controls on nitrogen isotope (δ15N) fractionation between NH3 and NH4+ remains unresolved. Based on concurrent measurements of NH3 and NH4+ in winter Beijing, we observed that the difference of δ15N between NH3 and NH4+ on clean days (3.3 ± 13.3‰) was significantly lower than that during polluted periods (30.2 ± 11.8‰). This difference signified incomplete equilibrium fractionation and that kinetic fractionation may have occurred between NH3 and NH4+, especially during clean days. Assuming that kinetic and equilibrium fractionation occurred successively, the contribution of nonagricultural emissions to NH4+ was apportioned to 60.3 ± 12.8%, higher than that of 50.4 ± 17.7% considering only equilibrium fractionation. These results indicate that the source apportionment of NH4+ considering only equilibrium fractionation in the conventional scenario would underestimate the contribution of nonagricultural emissions by 16.4% (up to 33.1% on clean days). Our analysis highlighted the importance in considering both kinetic and equilibrium fractionation scenarios to improve the precision of NH4+ source apportionment by using nitrogen isotopes.

Changing patterns of global nitrogen deposition driven by socio-economic development

Advances in manufacturing and trade have reshaped global nitrogen deposition patterns, yet their dynamics and drivers remain unclear. Here, we compile a comprehensive global nitrogen deposition database spanning 1977-2021, aggregating 52,671 site-years of data from observation networks and published articles. This database show that global nitrogen deposition to land is 92.7 Tg N in 2020. Total nitrogen deposition increases initially, stabilizing after peaking in 2015. Developing countries at low and middle latitudes emerge as new hotspots. The gross domestic product per capita is found to be highly and non-linearly correlated with global nitrogen deposition dynamic evolution, and reduced nitrogen deposition peaks higher and earlier than oxidized nitrogen deposition. Our findings underscore the need for policies that align agricultural and industrial progress to facilitate the peak shift or reduction of nitrogen deposition in developing countries and to strengthen measures to address NH3 emission hotspots in developed countries.

Sources of PM2.5 exposure and health benefits of clean air actions in Shanghai

Estimating PM2.5 exposure and its health impacts in cities involves large uncertainty due to the limitations of model resolutions. Consequently, attributing the sources of PM2.5-related health impacts at the city level remains challenging. We characterize the health impacts associated with chronic PM2.5 exposure and anthropogenic emissions in Shanghai using a chemical transport model (GEOS-Chem) and its adjoint. By incorporating high-resolution satellited-derived PM2.5 estimates into the calculation, we investigate the response of PM2.5 exposure and its related health impacts in Shanghai to changes in anthropogenic emissions from each individual region, species, sector, and month. We estimate that a 10% decrease in anthropogenic emissions throughout China avoids over 752 (506-1,044) PM2.5-related premature deaths in Shanghai, with changes in local emissions potentially saving 241 (161-334) lives. Ammonia (NH3) emissions are identified as the marginal dominant contributor to the health impacts due to the NH3-limited PM2.5 formation within the city, thus controlling NH3 emissions at both the local and regional scales are effective at reducing the population's exposure to PM2.5. A negative response of the PM2.5 exposure to local nitrogen oxides (NOx) emission changes is detected in winter. Even so, controlling NOx emissions is still justified since the negative impacts decrease as anthropogenic emissions decline and NOx emission reductions benefit the public health on average. The anthropogenic emission changes due to Clean Air Actions helped avoid 3,132 (2,108-4,346) PM2.5-related premature deaths in 2019 relative to 2013, most of which are associated with emission reductions in the agricultural and industrial sectors.

Response of South Asia PM2.5 pollution to ammonia emission changes and associated impacts on human health

Countries in South Asia are suffering severe PM2.5 pollution with rapid economic development, impacting human health and the environment. Whilst much attention has been given to understanding the contribution of primary emissions, the contribution of agriculture to PM2.5 concentrations, especially from agricultural ammonia (NH3) emissions, remains less explored. Using an advanced regional atmospheric chemistry and transport modelling system (WRF-EMEP) with a new estimate of anthropogenic NH3 emissions inputs, we estimate the influence of agricultural NH3 emissions on surface PM2.5 in South Asia and evaluate the health impacts and the economic losses attributable to PM2.5 in 2018. Results show that WRF-EMEP can reproduce magnitudes and variations of PM2.5 well, with a high annual mean PM2.5 concentration that exceeds 120 µg/m2 and mainly appeared in the Indo-Gangetic Plain. We estimate 2,228,000 (95 % Confidence Interval: 2,052,000-2,400,000) premature deaths and US$ 596,000 (95 % CI: 549,000-642,000) million in economic losses are attributable to total ambient PM2.5 under the current emissions. We calculate that NH3 emissions are associated with 11 % of the annual average PM2.5 concentrations across South Asia. Changes in PM2.5 concentrations follow a non-linear response to NH3 emissions reductions, highlighting increased efficiency with 70 %-100 % reductions in NH3 emissions reductions. We estimate that 247,000 (227,000-265,000) premature deaths and US$ 66,000 (61,000-71,000) million economic losses through this pathway can be attributed to NH3 emissions. These findings confirm that in the current NH3-rich chemical environment of South Asia, the efficiency of PM2.5 reduction is only moderately sensitive to the reduction in intensity of NH3 emissions until emissions are cut very severely. Thus, SO2, NOx and NH3 emissions controls need to be considered jointly for greater mitigation of ambient secondary PM2.5 in South Asia.

Duckweed (Lemna minor L.) as a natural-based solution completely offsets the increase in ammonia volatilization induced by soil drying and wetting cycles in irrigated paddies

One of the primary pathways of nitrogen loss in rice fields, ammonia (NH3) volatilization resulting in low nitrogen use efficiency and contributes significantly to near-surface atmospheric pollution. Duckweed (Lemna minor L.), a common small floating plant in rice fields, often completely covers the water surface. However, the extent to which this biotic cover affects ammonia flux remains unclear. A three-year field experiment was conducted to investigate the effects of duckweed cover on NH3 volatilization in rice fields under two different irrigation management practices (Flooding irrigation vs. alternate wetting and drying irrigation). In the duckweed-free paddies, alternate wetting and drying irrigation significantly increased the cumulative ammonia emissions over the full observation period by 16.6 %, 22.5 % and 7.8 % in 2020, 2021, and 2022, respectively, compared to flooding irrigation. Compared to the duckweed-free paddies, the presence of duckweed significantly mitigated cumulative NH3 volatilization in rice fields, regardless of the irrigation regimes. Under flooding irrigation, the reduction in NH3 volatilization with duckweed cover reached 6.3 %, 33.2 % and 37.6 % over three consecutive years. The reduction was 23.3 %, 48.2 % and 41.8 % under alternate wetting and drying irrigation, demonstrating that duckweed achieved greater reductions in NH3 volatilization under alternate wetting and drying irrigation than flooding irrigation. An independent incubation experiment revealed that physical coverage, ammonium ion absorption and surface water temperature reduction were primary factors contributing to duckweed-induced NH3 emission mitigation, accounting for 50.9 %, 28.4 %, and 20.7 %, respectively. The present study indicates that duckweed might prove a promising nature-based solution for mitigating the potential environmental risks of excessive reactive nitrogen outputs from rice paddies, and for promoting the broader application of alternating wet and dry irrigation.

Review of health effects driven by aerosol acidity: Occurrence and implications for air pollution control

Acidity, generally expressed as pH, plays a crucial role in atmospheric processes and ecosystem evolution. Atmospheric acidic aerosol, triggering severe air pollution in the industrialization process (e.g., London Great Smoke in 1952), has detrimental effects on human health. Despite global endeavors to mitigate air pollution, the variation of aerosol acidity remains unclear and further restricts the knowledge of the acidity-driven toxicity of fine particles (PM2.5) in the atmosphere. Here, we summarize the toxicological effects and mechanisms of inhalable acidic aerosol and its response to air pollution control. The acidity could adjust toxic components (e.g., metals, quinones, and organic peroxides) bonded in aerosol and synergize with oxidant gaseous pollutants (e.g., O3 and NO2) in epithelial lining fluid to induce oxidative stress and inflammation. The inhaled aerosol from the ambient air with higher acidity might elevate airway responsiveness and cause worse pulmonary dysfunction. Furthermore, historical observation data and model simulation indicate that PM2.5 can retain its acidic property despite considerable reductions in acidifying gaseous pollutants (e.g., SO2 and NOx) from anthropogenic emissions, suggesting its continuing adverse impacts on human health. The study highlights that aerosol acidity could partially offset the health benefits of emission reduction, indicating that acidity-related health effects should be considered for future air pollution control policies.

Evidence for global increases in urban ammonia pollution and their drivers

Ammonia (NH3) affects air quality, human health, and life expectancy through its important role in forming fine particulate matter. However, the spatial patterns and trends of NH3 concentrations in the urban environment remain unknown worldwide. Here we use satellite measurements to produce a global distribution of NH3 at fine resolution, and then identify, categorize and quantify NH3 air concentrations in urban clusters throughout the world, as well as explore associated trends and drivers. Based on satellite records, a significant increase is evident in global urban NH3 concentrations between 2008 and 2019, with an annual increase of 1.2 % yr-1. Our results show that the decline of acidic gas (NOx/SO2) explains the largest part of the increasing NH3 concentrations (42 %), exceeding the contribution of local NH3 emissions. Our results also show that increasing temperature can explain 20 % of the increase in urban NH3 concentrations implying that efforts to reduce NH3 emissions need to be greatly strengthened to compensate for increases in urban NH3 pollution induced by global warming and so improve the urban environment.

Exploring the chemistry of waste eggshells and its diverse applications

The large-scale production of chicken eggs results in a substantial amount of eggshell (ES) residue, often considered as waste. These discarded shells naturally decompose in soil approximately within a year. Eggshells (ES), comparatively contribute lesser towards environmental pollution, contain a remarkable amount of calcium, which can be converted into various valuable products that finds applications in industries, pharmaceuticals, and medicine. Among the diverse applications of ES, most effective and promising applications are removal of heavy metals (Cd, Cr, Pb, Zn, and Cu) ∼93-99 % metal adsorption capacity and capturing of flue gases (CO2 and SO2) from the environment. With ES having a maximum CO2 sorption capacity of 92 % as compared to other sources, and SO2 adsorption capacity of Calcined ES∼11.68 mg/g. The abundance, low cost and easy availability of CaO from ES makes them sustainable and eco-friendly. Additionally, its versatility extends beyond environmental prospects, as it is widely used in various industries as a catalyst, sorbent, fertilizer, and calcium supplement in food for individuals, plants and animals, among other diverse fields of study. Owing to its versatile applications, current review focuses on structure, chemical composition, treatment methods, and valorization pathways for diverse applications, aiming to reduce the eggshells waste and mitigate environmental pollution.

Variation pattern, influential factors, and prediction models of PM2.5 concentrations in typical urban functional zones of northeast China

This study investigated the spatial and temporal variations of PM2.5 concentrations in Harbin, China, under the influence of meteorological parameters and gaseous pollutants. The complex relationship between meteorological parameters and pollutants was explored using Pearson correlation analysis and interaction effect analysis. Using the correlation analysis and interaction analysis methods, four mechanical learning models, PCC-Is-CNN, PCC-Is-LSTM, PCC-Is-CNN-LSTM and PCC-Is-BP neural network, were developed for predicting PM2.5 concentration in different time scales by combining the long-term and short-term data with the basic mechanical learning models. The results show that the PCC-Is-CNN-LSTM model has superior prediction performance, especially when integrating short-term and long-term historical data. Meanwhile, applying the model to cities in other climatic zones, the results show that the model performs well in the Dwa climatic zone, while the prediction performance is lower in the CWa climatic zone. This suggests that although the model is well adapted in regions with a similar climate to Harbin, model performance may be limited in areas with complex climatic conditions and diverse pollutant sources. This study emphasizes the importance of considering meteorological and pollutant interactions to improve the accuracy of PM2.5 predictions, providing valuable insights into air quality management in cold regions.

Understanding the spatial patterns of atmospheric ammonia trends in South Asia

Ammonia (NH3) is the most abundant alkaline gas in the atmosphere, mainly emitted by agricultural activities. NH3 readily reacts with other atmospheric acidic pollutants, such as the oxidation products of sulfur dioxide (SO2) and nitrogen oxides (NOₓ), to create fine particulate matter, which has far-reaching effects on human health and ecosystems. Here, we investigated long-term atmospheric NH3 trends in South Asia (SA) using satellite observations from the Infrared Atmospheric Sounding Interferometer (IASI). We analyzed 15 years (2008-2022) of IASI-NH3 retrievals against climate, biophysical, and chemical variables using an ensemble of multivariate statistical methods to identify the major factors driving the observed patterns in the region. Trend analysis of IASI-NH3 data reveals a significant rise in atmospheric NH3 over 51 % of SA plains, but a downward trend over 31 % of the region. Spatial correlation analysis reveals that biophysical factors, representing cropland expansion and agriculture intensification, have the highest positive correlation over 56 % of SA plains experiencing positive NH3 trends. However, our results reveal that the chemical conversion of NH3 to ammonium compounds, driven by the positive trends in NOₓ and SO2 pollution, is driving the apparently declining trend of NH3 in the other regions. Our results provide important insights into the NH3 trends detected by satellite data and can better inform the policy design aimed at reducing NH3 emissions and improving air quality for developing regions of the world.

Enhancing Environmental and Human Health Management Through the Integration of Advanced Revitalization Technologies Utilizing Artificial Intelligence

Pollution can be broadly defined as the presence of contaminants or energy sources detrimental to ecosystems and human health. The human organism serves as a valuable indicator of ecosystem contamination. However, understanding physiological disorders and correlating specific contaminants with disease development is a complex and arduous task, necessitating extensive scientific research spanning years or even decades. To facilitate a more rapid and precise understanding of the physiological impairments induced by various contaminants, a comprehensive approach is indispensable. This review proposes a model for such an approach, which involves the systematic collection and analysis of data from ecosystem contamination monitoring, integrated with biomedical data on compromised physiological conditions in humans across different temporal and spatial scales. Given the complexity and sheer volume of data, alongside the imperative for strategic decision-making, this model leverages the capabilities of artificial intelligence (AI) tools. Although this paper exemplifies the model by investigating the effects of contaminants on the human organism, the model is adaptable to all ecosystem components, thereby supporting the conservation of plant and animal species.

Trade optimality and micro-nutrient productivity: Assessing the impact of crop trade on nitrogen fertiliser use efficiency

Intensification of agricultural practices has been pivotal in meeting the nutritional demands of a burgeoning global population. However, the widespread application of nitrogen (N) fertilisers has contributed to environmental pollution. In this study, we quantitatively assessed the role of international crop trade in optimising the productivity of micro-nutrients and its implications for N fertiliser use. Using a comprehensive dataset spanning from 1961 to 2019, we analysed the trade flows of seven key micro-nutrients-vitamin C (VC), vitamin B3 (VB3), vitamin B6 (VB6), calcium (Ca), magnesium (Mg), iron (Fe), and zinc (Zn)-embedded in agricultural products. We developed a novel framework to evaluate trade optimality and functionality based on the concentration-weighted productivity of micro-nutrients per kilogram of N fertiliser. Our findings reveal that while international trade has generally contributed to enhancing micro-nutrient productivity per unit of N fertiliser, trade optimality has shown a decreasing trend. High-productivity countries tend to export less relative to their potential, whereas countries with lower productivity import a larger share of crops. This decoupling suggests the need to re-evaluate trade policies to ensure that they align with sustainable agricultural practices and environmental conservation goals. We also identified potential savings in N fertiliser use through optimised trade practices, with estimated savings of 15-45 Tg of N per year. This could mitigate the negative agricultural impact and demonstrates the significant role that trade can play in achieving global sustainability targets. Overall, our research underscores the importance of aligning international crop trade with sustainable N management strategies to enhance micro-nutrient availability, improve environmental outcomes, and contribute to global efforts in achieving the Sustainable Development Goals.

Whole-chain intensification of pig and chicken farming could lower emissions with economic and food production benefits

Intensified monogastric livestock management could conserve feed inputs and mitigate some of the environmental and climate challenges associated with animal production. In this study, we used data from 166 countries to model the environmental, climate and economic impacts of pig and chicken intensification. We found that whole-chain intensification could reduce annual nitrogen and greenhouse gas emissions by 49% (4.6 Tg) and 68% (554 Tg CO2-equivalent), respectively. These changes translate to 5.0 Tg lower nitrogen fertilizer input for feed production, resulting in an overall benefit of US$93 billion. Integrated crop-livestock optimization under intensive management could release 27 Mha of cropland and provide additional food for 310 million people. A judicious promotion of intensification could alleviate global pressures related to food security, environment and climate change.

Inequality in agricultural greenhouse gas emissions intensity has risen in rural China from 1993 to 2020

Reducing greenhouse gas (GHG) emissions in crop production while ensuring emission equity is crucial for sustainable agriculture in China, yet long-term large-scale data on GHG emissions intensity (GEI) are limited. Using an extensive dataset based on surveyed farm households (n > 430,000 households) from 1993 to 2020, we reveal that 2015 was a turning point for GEI levels, which dropped 16% in 2020, while inequality-measured as average GHG emissions per unit planted area-increased 13%. The key driving forces behind such trends included farmland input, all other inputs, agricultural labour input and total factor productivity but not capital input. Notably, farmland input and all other inputs contributed to 80% of the inequality, while contribution of total factor productivity gradually declined and was replaced by migration-induced agricultural labour input differences. Reducing GEI levels and guarding against widening inequality require optimizing production factor inputs.

Quantitative assessment of benefits and losses from the influence of atmospheric nitrogen deposition on cropland ecosystems in China

China is facing severe atmospheric nitrogen (N) deposition. Assessing the economic benefits and damage costs induced by N deposition can help to develop effective mitigation strategies for N emissions. A net economic benefit method was used to assess the economic impact of N deposition in cropland ecosystems in China in 2020. The results showed that atmospheric N deposition gained an economic benefit of $4896.0 million through increased yields of major grain crops and a climate benefit of $1259.3 million through cooling effects. On the other hand, N deposition induced economic losses of $6257.1 and $1063.4 million, respectively to human health and ecosystem health; excessive N deposition induced damages of $137.8 million due to reduced crop yields and $168.4 million due to the increased greenhouse gas emissions. In general, the net economic benefit was -$1471.5 million (-$5324.7 ∼ $921.4 million), indicating that China is suffering economic losses due to N deposition in cropland ecosystems. These results would provide scientific data for the government to enact efficient measures to reduce N pollution.

Tracking Carbon and Ammonia Emission Flows of China's Nitrogen Fertilizer System: Implications for Domestic and International Trade

China is the world's largest producer, consumer, and exporter of synthetic nitrogen (N) fertilizer. To assess the impact of domestic demand and international exports, we quantified the life-cycle CO2eq and ammonia (NH3) emissions by tracking carbon (C) and nitrogen (N) flows from coal/gas mining through ammonia production to N fertilizer production, application, and export. In 2020, China's N fertilizer system emitted 496.04 Tg of CO2eq and 3.74 Tg of NH3, with ammonia production and N fertilizer application processes contributing 36 and 85% of the life-cycle CO2eq and NH3 emissions, respectively. As the largest importers of N fertilizer, India, Myanmar, South Korea, Malaysia, and the Philippines collectively shifted 112.41 Tg of CO2eq. For every ton of N fertilizer produced and used in China, 16 t of CO2eq and 0.18 t of NH3 were emitted, compared to 9.7 t of CO2eq and 0.13 t of NH3 in Europe. By adopting currently available technologies, improving N fertilizer utilization efficiency and employing nitrification inhibitors could synergistically reduce CO2eq emissions by 20% and NH3 emissions by 75%, while energy transformation efforts would primarily reduce CO2eq emissions by 59%. The production of ammonia using green electricity or green hydrogen could significantly enhance the decarbonization of China's N fertilizer system.

Unlocking nitrogen management potential via large-scale farming for air quality and substantial co-benefits

China's sustained air quality improvement is hindered by unregulated ammonia (NH3) emissions from inefficient nitrogen management in smallholder farming. Although the Chinese government is promoting a policy shift to large-scale farming, the benefits of this, when integrated with nitrogen management, remain unclear. Here we fill this gap using an integrated assessment, by combining geostatistical analysis, high-resolution emission inventories, farm surveys and air quality modeling. Smallholder-dominated farming allows only 13%-31% NH3 reduction, leading to limited PM2.5 decreases nationally due to non-linear PM2.5 chemistry. Conversely, large-scale farming would double nitrogen management adoption rates, increasing NH3 reduction potential to 48%-58% and decreasing PM2.5 by 9.4-14.0 μg·m-3 in polluted regions. The estimated PM2.5 reduction is conservative due to localized NH3-rich conditions under large-scale livestock farming. This strategy could prevent over 300 000 premature deaths and achieve a net benefit of US $68.4-86.8 billion annually, unlocking immense benefits for air quality and agricultural sustainability.

Substantial nitrogen abatement accompanying decarbonization suppresses terrestrial carbon sinks in China

China faces challenges in reaching its carbon neutrality goal by the year 2060 to meet the Paris Agreement and improving air quality simultaneously. Dramatic nitrogen emission reductions will be brought by this ambitious target, yet their impact on the natural ecosystem is not clear. Here, by combining two atmospheric chemistry models and two process-based terrestrial ecosystem models constrained using nationwide measurements, we show that atmospheric nitrogen deposition in China's terrestrial land will decrease by 44-57% following two emission control scenarios including one aiming at carbon neutrality. They consequently result in a pronounced shrinkage in terrestrial net ecosystem production, by 11-20% depending on models and emission scenarios. Our results indicate that the nitrogen emission reductions accompanying decarbonization would undermine natural carbon sinks and in turn set back progress toward carbon neutrality. This unintended impact calls for great concern about the trade-offs between nitrogen management and carbon neutrality.

Aspirational nitrogen interventions accelerate air pollution abatement and ecosystem protection

Although reactive nitrogen (Nr) emissions from food and energy production contribute to multi-dimensional environmental damages, integrated management of Nr is still lacking owing to unclear future mitigation potentials and benefits. Here, we find that by 2050, high-ambition compared to low-ambition N interventions reduce global ammonia and nitrogen oxide emissions by 21 and 22 TgN/a, respectively, equivalent to 40 and 52% of their 2015 levels. This would mitigate population-weighted PM2.5 by 6 g/m3 and avoid premature deaths by 817 k (16%), mitigate ozone by 4 ppbv, avoid premature deaths by 252k (34%) and crop yield losses by 122 million tons (4.3%), and decrease terrestrial ecosystem areas exceeding critical load by 420 Mha (69%). Without nitrogen interventions, most environmental damages examined will deteriorate between 2015 and 2050; Africa and Asia are the most vulnerable but also benefit the most from interventions. Nitrogen interventions support sustainable development goals related to air, health, and ecosystems.

Air Quality, Health, and Equity Benefits of Carbon Neutrality and Clean Air Pathways in China

In the pursuit of carbon neutrality, China's 2060 targets have been largely anchored in reducing greenhouse gas emissions, with less emphasis on the consequential benefits for air quality and public health. This study pivots to this critical nexus, exploring how China's carbon neutrality aligns with the World Health Organization's air quality guidelines (WHO AQG) regarding fine particulate matter (PM2.5) exposure. Coupling a technology-rich integrated assessment model, an emission-concentration response surface model, and exposure and health assessment, we find that decarbonization reduces sulfur dioxide (SO2), nitrogen oxides (NOx), and PM2.5 emissions by more than 90%; reduces nonmethane volatile organic compounds (NMVOCs) by more than 50%; and simultaneously reduces the disparities across regions. Critically, our analysis reveals that further targeted reductions in air pollutants, notably NH3 and non-energy-related NMVOCs, could bring most Chinese cities into attainment of WHO AQG for PM2.5 5 to 10 years earlier than the pathway focused solely on carbon neutrality. Thus, the integration of air pollution control measures into carbon neutrality strategies will present a significant opportunity for China to attain health and environmental equality.

Green manuring alters reactive N losses and N pools in arable soils: A meta-regression study

Green manuring is a conservation agricultural practice that improves soil quality and crop yield. However, increasing the active nitrogen (N) and carbon (C) pools during green manure (GM) amendment may accelerate soil N transformation and stimulate N loss. Previous studies have reported the effects of cover crop incorporation on N2O emission; however, the driving mechanisms and other N losses remain unclear. Therefore, we conducted a comprehensive meta-analysis of 109 published articles (517 paired observations) to clarify the effects of GM amendment on soil reactive N (Nr) losses (N2O emissions, NH3 volatilization, and N leaching and runoff), N pools, and N cycling functional gene abundance. The results showed that green manuring increased soil microbial biomass N (MBN) and NO3--N concentrations and stimulated N2O emission but significantly lowered N leaching and yield-scaled NH3 volatilization. Practices of green manuring made a dominant contribution to the variation in N2O emissions and NH3 volatilization after GM application. Furthermore, applying legume-based GM, using N derived from GM (GMN) as an additional input, and short-term GM amendment each stimulated N2O emissions. In contrast, adopting non-legume GM, using GMN to partially substitute mineral N, and applying GM to the soil surface or paddy field mitigated NH3 loss during GM amendment. Additionally, the variation in NH3 volatilization was positively related to soil pH and N application rate (NAR) but had a negative relationship with mean annual precipitation (MAP). This study highlighted the marked effects of green manuring on soil N retention and loss. Agricultural operations that adopt GM amendment should select suitable GM species and optimize mineral N inputs to minimize N loss.

Role of gas-particle conversion of ammonia in haze pollution under ammonia-rich environment in Northern China and prospects of effective emission reduction

As an important precursor of secondary inorganic aerosols (SIAs), ammonia (NH3) plays a key role in fine particulate matter (PM2.5) formation. In order to investigate its impacts on haze formation in the North China Plain (NCP) during winter, NH3 concentrations were observed at a high-temporal resolution of 1 min by using the SP-DOAS in Tai'an from December 2021 to February 2022. During the observation period, the average NH3 concentration was 11.84 ± 5.9 ppbv, and it was determined as an ammonia-rich environment during different air quality conditions. Furthermore, the average concentrations of sulfate (SO42-), nitrate (NO3-) and ammonium (NH4+) were 9.54 ± 5.97 μg/m3, 19.09 ± 14.18 μg/m3 and 10.72 ± 6.53 μg/m3, respectively. Under the nitrate-dominated atmospheric environment, aerosol liquid water content (ALWC) was crucial for NH3 particle transformation during haze aggravation, and the gas-particle partitioning of ammonia played an important role in the SIAs formation. The reconstruction of the molecular composition further indicated that ammonium nitrate (NH4NO3) plays a dominant role in the increase of PM2.5 during haze events. Consequently, future efforts to mitigate fine particulate pollution in this region should focus on controlling NH4NO3 levels. In ammonia-rich environments, NO3- formation is more dependent on the concentration of nitric acid (HNO3). The sensitive analysis of TNO3 (HNO3 + NO3-) and NHX (NH3 + NH4+) reduction using the thermodynamic model suggested that the NO3- concentration decreases linearly with the reduction of TNO3. And the concentration of NO3- decreases rapidly only when NHX is reduced by 50-60 %. Reducing NOX emissions is the most effective way to alleviate nitrate pollution in this region.

Understanding Reductions of PM2.5 Concentration and Its Chemical Composition in the United States: Implications for Mitigation Strategies

Motivated by the recent tightening of the US annual standard of fine particulate matter (PM2.5) concentrations from 12 to 9 μg/m3, there is a need to understand the spatial variation and drivers of historical PM2.5 reductions. We evaluate and interpret the variability of PM2.5 reductions across the contiguous US using high-resolution estimates of PM2.5 and its chemical composition over 1998-2019, inferred from satellite observations, air quality modeling, and ground-based measurements. We separated the 3092 counties into four characteristic regions sorted by PM2.5 trends. Region 1 (primarily Central Atlantic states, 25.9% population) exhibits the strongest population-weighted annual PM2.5 reduction (-3.6 ± 0.4%/yr) versus Region 2 (primarily rest of the eastern US, -3.0 ± 0.3%/yr, 39.7% population), Region 3 (primarily western Midwest, -1.9 ± 0.3%/yr, 25.6% population), and Region 4 (primarily the Mountain West, -0.4 ± 0.5%/yr, 8.9% population). Decomposition of these changes by chemical composition elucidates that sulfate exhibits the fastest reductions among all components in 2720 counties (76% of population), mostly over Regions 1-3, with the 1998-2019 mean sulfate mass fraction in PM2.5 decreasing from Region 1 (29.5%) to Region 4 (11.8%). Complete elimination of the remaining sulfate may be insufficient to meet the new standard for many regions in exceedance. Additional measures are needed to reduce other PM2.5 sources and components for further progress.

Unraveling the Mechanistic Origin of High N2 Selectivity in Ammonia Selective Catalytic Oxidation on CuO-Based Catalyst

NH3 emissions from industrial sources and possibly future energy production constitute a threat to human health because of their toxicity and participation in PM2.5 formation. Ammonia selective catalytic oxidation to N2 (NH3-SCO) is a promising route for NH3 emission control, but the mechanistic origin of achieving high N2 selectivity remains elusive. Here we constructed a highly N2-selective CuO/TiO2 catalyst and proposed a CuOx dimer active site based on the observation of a quadratic dependence of NH3-SCO reaction rate on CuOx loading, ac-STEM, and ab initio thermodynamic analysis. Combining this with the identification of a critical N2H4 intermediate by in situ DRIFTS characterization, a comprehensive N2H4-mediated reaction pathway was proposed by DFT calculations. The high N2 selectivity originated from the preference for NH2 coupling to generate N2H4 over NH2 dehydrogenation on the CuOx dimer active site. This work could pave the way for the rational design of efficient NH3-SCO catalysts.

Regime shift in secondary inorganic aerosol formation and nitrogen deposition in the rural United States

Secondary inorganic aerosols play an important role in air pollution and climate change, and their formation modulates the atmospheric deposition of reactive nitrogen (including oxidized and reduced nitrogen), thus impacting the nitrogen cycle. Large-scale and long-term analyses of secondary inorganic aerosol formation based on model simulations have substantial uncertainties. Here we improve constraints on secondary inorganic aerosol formation using decade-long in situ observations of aerosol composition and gaseous precursors from multiple monitoring networks across the United States. We reveal a shift in the secondary inorganic aerosol formation regime in the rural United States between 2011 and 2020, making rural areas less sensitive to changes in ammonia concentrations and shortening the effective atmospheric lifetime of reduced forms of reactive nitrogen. This leads to potential increases in reactive nitrogen deposition near ammonia emission hotspots, with ecosystem impacts warranting further investigation. Ammonia (NH3), a critical but not directly regulated precursor of fine particulate matter in the United States, has been increasingly scrutinized to improve air quality. Our findings, however, show that controlling NH3 became significantly less effective for mitigating fine particulate matter in the rural United States. We highlight the need for more collocated aerosol and precursor observations for better characterization of secondary inorganic aerosols formation in urban areas.

Asymmetric Coordination of Single-Atom Ru Sites Achieves Efficient N(sp3)-H Dehydrogenation Catalysis for Ammonia Oxidation

Ruthenium single-atom catalysts have great potential in ammonia-selective catalytic oxidation (NH3-SCO); however, the stable sp3 hybrid orbital of NH3 molecules makes N(sp3)-H dissociation a challenge for conventional symmetrical metallic oxide catalysts. Herein, we propose a heterogeneous interface reverse atom capture strategy to construct Ru with unique asymmetric Ru1N2O1 coordination. Ru1N2O1/CeO2 exhibits intrinsic low-temperature conversion (T100 at 160 °C) compared to symmetric coordinated Ru-based (280 °C), Ir-based (220 °C), and Pt-based (200 °C) catalysts, and the TOF is 65.4 times that of Ag-based catalysts. The experimental and theoretical studies show that there is a strong d-p orbital interaction between Ru and N atoms, which not only enhances the adsorption of ammonia at the Ru1N2O1 position but also optimizes the electronic configuration of Ru. Furthermore, the affinity of Ru1N2O1/CeO2 to water is significantly weaker than that of conventional catalysts (the binding energy of the Pd3Au1 catalyst is -1.19 eV, but it is -0.39 eV for our material), so it has excellent water resistance. Finally, the N(sp3)-H activation of NH3 requires the assistance of surface reactive oxygen species, but we found that asymmetric Ru1N2O1 can directly activate the N(sp3)-H bond without the involvement of surface reactive oxygen species. This study provides a novel principle for the rational design of the proximal coordination of active sites to achieve its optimal catalytic activity in single-atom catalysis.

Combined short-term and long-term emission controls improve air quality sustainably in China

The effectiveness of national policies for air pollution control has been demonstrated, but the relative effectiveness of short-term emission reduction measures in comparison with national policies has not. Here we show that short-term abatement measures during important international events substantially reduced PM2.5 concentrations, but air quality rebounded to pre-event levels after the measures ceased. Long-term adherence to strict emission reduction policies led to successful decreases of 54% in PM2.5 concentrations in Beijing, and 23% in atmospheric nitrogen deposition in China from 2012 to 2020. Incentivized by "blue skies" type campaigns, economic development and reactive nitrogen pollution are quickly decoupled, showing that a combination of inspiring but aggressive short-term measures and effective but durable long-term policies delivers sustainable air quality improvement. However, increased ammonia concentrations, transboundary pollutant flows, and the complexity to achieving reduction targets under climate change scenarios, underscore the need for the synergistic control of multiple pollutants and inter-regional action.

Evidence and causes of recent decreases in nitrogen deposition in temperate forests in Northeast China

High reactive nitrogen (N) emissions due to anthropogenic activities in China have led to an increase in N deposition and ecosystem degradation. The Chinese government has strictly regulated reactive N emissions since 2010, however, determining whether N deposition has reduced requires long-term monitoring. Here, we report the patterns of N deposition at a rural forest site (Qingyuan) in northeastern China over the last decade. We collected 456 daily precipitation samples from 2014 to 2022 and analysed the temporal dynamics of N deposition. NH4+-N, NO3--N, and total inorganic N (TIN) deposition ranged from 10.5 ± 3.5 (mean ± SD), 6.1 ± 1.6, and 16.6 ± 4.7 kg N ha-1 year-1, respectively. Over the measurement period, TIN deposition at Qingyuan decreased by 55 %, whereas that in comparable sites in East Asia declined by 14-34 %. We used a random forest model to determine factors influencing the deposition of NH4+-N, NO3--N, and TIN during the study period. NH4+-N deposition decreased by 60 % because of decreased agricultural NH3 emissions. Furthermore, NO3--N deposition decreased by 42 %, due to reduced NOx emissions from agricultural soil and fossil fuel combustion. The steep decline in N deposition in northeastern China was attributed to reduced coal consumption, improved emission controls on automobiles, and shifts in agricultural practices. Long-term monitoring is needed to assess regional air quality and the impact of N emission control regulations.

Inorganic PM2.5 reduction in Kanto, Japan: The role of ammonia and its emission sources control strategies

Ammonia (NH3) is attracting attention as a carbon-free energy source and a significant precursor to inorganic PM2.5 (hereafter PM2.5), aside from NOx and SOx. Since the emission of NH3 has often been overlooked compared to NOx and SOx, this study aims to reveal the role of NH3 and its emission control on PM2.5 in Kanto, Japan. With the aid of gas ratio (GR) quantitatively defining the stoichiometry between the three precursors to PM2.5, and the aid of atmospheric modeling software ADMER-PRO, coupled with thermodynamics calculations, the spatiotemporal distribution along with PM2.5 reduction under different NH3 emission cutoff strategies in Kanto had been revealed for the first time. The cutoff of NH3 emission could effectively reduce the PM2.5 concentration, with sources originated from agriculture, human/pet activities, and vehicle sources, overall giving a 93.32% PM2.5 reduction. Different cutoff strategies lead to distinct reduction efficiencies of the overall and local PM2.5 concentrations, with GR as a crucial factor. The regions with GR ∼1, are sensitive to the NH3 concentration for forming PM2.5, at which the NH3 reduction strategies should be applied with high priority. On the other hand, installing a new NH3 emission source should be avoided in the region with GR < 1, suppressing the so-yielded PM2.5 pollution. The future PM2.5 pollution control related to the NH3 emission control strategies based on GR, which is stoichiometry-based and applicable to regions other than Kanto, has been discussed.

Mitigating air pollution benefits multiple sustainable development goals in China

Achieving the United nations 2030 Sustainable Development Goals (SDGs) remains a significant challenge, necessitating urgent and prioritized strategies. Among the various challenges, air pollution continues to pose one of the most substantial threats to the SDGs due to its widespread adverse effects on human health and ecosystems. However, the connections between air pollution and the SDGs have often been overlooked. This study reveals that out of the 169 SDG targets, 71 are adversely impacted by air pollution, while only 6 show potential positive effects. In China, two major atmospheric nitrogen pollutants, ammonia and nitrogen oxides, resulted in an economic loss of 400 billion United States Dollar (USD) in 2020, which could be reduced by 33% and 34% by 2030, respectively. It would enhance the progress towards SDGs in China by 14%, directly contributing to the achievement of SDGs 1 to 6 and 11 to 15. This improvement is estimated to yield overall benefits totaling 119 billion USD, exceeded the total implementation cost of 82 billion USD with ammonia as the preferential mitigation target. This study underscores the importance of robust scientific evidence in integrated policies aimed at aligning improvements in environmental quality with the priorities of sustainable development.

Microscopic Mechanism for Further NO Heterogeneous Reduction by Potassium-Doped Biochar: A DFT Study

Biomass reburning is an efficient and low-cost way to control nitric oxide (NO), and the abundant potassium (K) element in biomass affects the heterogeneous reaction between NO and biochar. Due to the incomplete simulation of the NO heterogeneous reduction reaction pathway at the molecular level and the unclear catalytic effect of K element in biochar, further research is needed on the possible next reaction and the influencing mechanism of the element. After the products of the existing reaction pathways are referenced, two reasonably simplified biochar structural models are selected as the basic reactants to study the microscopic mechanism for further NO heterogeneous reduction on the biochar surface before and after doping with the K atom based on density functional theory. In studying the two further NO heterogeneous reduction reaction pathways, we find that the carbon monoxide (CO) molecule fragment protrudes from the surface of biochar models with the desorption of N2 at the TS4 transition state, and the two edge types of biochar product models obtained by simulation calculation are Klein edge and ac56 edge observed in the experiment. In studying the catalytic effect of potassium in biochar, we find that the presence of K increases the heat release of adsorption of NO molecules, reduces the energy barrier of the rate-determining step in the nitrogen (N2) generation and desorption process (by 50.88 and 69.97%), and hinders the CO molecule from desorbing from the biochar model surface. Thermodynamic and kinetic analyses also confirm its influence. The study proves that the heterogeneous reduction reaction of four NO molecules on the surface of biochar completes the whole reaction process and provides a basic theoretical basis for the emission of nitrogen oxides (NOx) during biomass reburning.

Engineering surface framework TiO6 single sites for unprecedented deep oxidative desulfurization

Catalytic oxidative desulfurization (ODS) using titanium silicate catalysts has emerged as an efficient technique for the complete removal of organosulfur compounds from automotive fuels. However, the precise control of highly accessible and stable-framework Ti active sites remains highly challenging. Here we reveal for the first time by using density functional theory calculations that framework hexa-coordinated Ti (TiO6) species of mesoporous titanium silicates are the most active sites for ODS and lead to a lower-energy pathway of ODS. A novel method to achieve highly accessible and homogeneously distributed framework TiO6 active single sites at the mesoporous surface has been developed. Such surface framework TiO6 species exhibit an exceptional ODS performance. A removal of 920 ppm of benzothiophene is achieved at 60°C in 60 min, which is 1.67 times that of the best catalyst reported so far. For bulky molecules such as 4,6-dimethyldibenzothiophene (DMDBT), it takes only 3 min to remove 500 ppm of DMDBT at 60°C with our catalyst, which is five times faster than that with the current best catalyst. Such a catalyst can be easily upscaled and could be used for concrete industrial application in the ODS of bulky organosulfur compounds with minimized energy consumption and high reaction efficiency.

Influencing factors on ammonia emissions from gasoline vehicles: A systematic review and meta-analysis

Ammonia, a significant precursor for secondary inorganic aerosols, plays a pivotal role in new particle formation. Inventories and source apportionment studies have identified vehicular exhaust as a primary source of atmospheric ammonia in urban regions. Existing research on the factors influencing ammonia emissions from gasoline vehicles exhibits substantial inconsistencies in both test results and analyses. The lack of a uniform pattern in ammonia emissions across different standard vehicles and the significant overlap in test results across diverse operational conditions highlight the complexities in this field of study. While individual results can be interpreted through a mechanistic lens, disparate studies often lack a common explanatory framework. To address this gap, our study leverages the robust and comprehensive approach of meta-analysis to reconcile these inconsistencies and provide a more precise understanding of the factors influencing ammonia emissions from gasoline vehicles. A large number (N = 537) of ammonia emission factors were extracted after screening >1628 publications. The combined ammonia emission factor was 23.57 ± 24.94 mg/km. Emission standards, engine type, ambient temperatures, mileage, vehicle speed, and engine displacement have a significant impact on ammonia emission factors, explaining the ammonia emission factor by up to 50.63 %, with speed being the most significant factor. All these factors are attributed to the interplay of catalyst properties, lambda, and residence time (space velocity). In the current fleet, ammonia emission control is relatively insufficient under low-speed and ultra-high speed, low temperature, and ultra-high mileage conditions. Since ammonia emission factors do not monotonically decrease with the upgrading of motor vehicle emission standards, it is called for the addition of ammonia emission factors indicators in motor vehicle emission standards, and stipulation of targeted testing procedures and testing instruments.

Updated loss factors and high-resolution spatial variations for reactive nitrogen losses from Chinese rice paddies

Anthropogenic reactive nitrogen (Nr) loss has been a critical environmental issue. However, due to the limitations of data availability and appropriate methods, the estimation of Nr loss from rice paddies and associated spatial patterns at a fine scale remain unclear. Here, we estimated the background Nr loss (BNL, i.e., Nr loss from soils without fertilization) and the loss factors (the percentage of Nr loss from synthetic fertilizer, LFs) for five loss pathways in rice paddies and identified the national 1 × 1 km spatial variations using data-driven models combined with multi-source data. Based on established machine learning models, an average of 23.4% (15.3-34.6%, 95% confidence interval) of the synthetic N fertilizer was lost to the environment, in the forms of NH3 (17.4%, 10.9-26.7%), N2O (0.5%, 0.3-0.8%), NO (0.2%, 0.1-0.4%), N leaching (3.1%, 0.8-5.7%), and runoff (2.3%, 0.6-4.5%). The total Nr loss from Chinese rice paddies was estimated to be 1.92 ± 0.52 Tg N yr-1 in 2021, in which synthetic fertilizer-induced Nr loss accounted for 69% and BNL accounted for the other 31%. The hotspots of Nr loss were concentrated in the middle and lower regions of the Yangtze River, an area with extensive rice cultivation. This study improved the estimation accuracy of Nr losses and identified the hotspots, which could provide updated insights for policymakers to set the priorities and strategies for Nr loss mitigation.