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The conversion of atmospheric nitrogen (N2) into ammonia (NH3), known as nitrogen fixation, plays a crucial role in sustaining life on Earth, facing innovation with electrocatalytic and photocatalytic methods. These approaches promise gentler conversions from atmospheric nitrogen to ammonia, diverging from the energy‐intensive Haber‐Bosch process, which requires complex plant infrastructure. Vitality lies in eco‐friendly, cost‐effective, and energy‐efficient pathways. The challenge is that electrocatalysts and photocatalysts for nitrogen reduction have shown low Faraday efficiency, hampered by hydrogen evolution. This work delves into recent strides in electro/photo‐catalytic nitrogen fixation/reduction, deciphering mechanisms, catalysts, and prospects. By unveiling the core principles steering these processes, it dissects efficiency drivers. Experimental and theoretical studies, ranging from density functional calculations/simulations to machine learning‐based catalyst screening, mark the path toward highly efficient catalysts, including single/multi‐atom catalysts embedded in 2D materials. The journey explores diverse catalysts, assessing their performance, spotlighting emerging nanomaterials, heterostructures, and co‐catalyst techniques. Perspectives on future directions and potential applications of electro/photo‐catalytic nitrogen fixation/reduction are offered, by emphasizing their role in sustainable nitrogen management and their implications for global agriculture and environmental sustainability. [ABSTRACT FROM AUTHOR]

The In-O-Mo bond-modulated In 2 O 3 /Bi 2 MoO 6 S-scheme heterostructure was synthesized using the static electron assembly method. At the heterostructure interface, the formation of In-O-Mo bonds serves as an essential pathway for rapid carrier transfer/transport, resulting in carrier-oriented accumulation and significantly improving PNRR performance. [Display omitted] • In 2 O 3 /Bi 2 MoO 6 photocatalysts were synthesized using a mild electrostatic assembly method. • The formation of In-O-Mo bond at the heterogeneous interface was critical for rapid charge-carrier transportation and carrier oriented accumulation. • The carrier-oriented accumulation of carriers can trigger PNRR and OER half-reactions, facilitating efficient photocatalytic N 2 -to-NH 3 conversion. • 3 % In/BMO-based S-scheme heterostructure realized a nitrogen fixation rate of 150.9 μmol·g cat −1·h−1, demonstrating a significant performance improvement. Photocatalytic nitrogen fixation presents an eco-friendly approach to converting atmospheric nitrogen into ammonia (NH 3), but the process faces challenges due to rapid interface charge recombination. Here, we report an innovative charge transfer and oriented accumulation strategy using an In-O-Mo bond-modulated S-scheme heterostructure composed of In 2 O 3 /Bi 2 MoO 6 (In/BMO) synthesized using a simple electrostatic assembly. The unique interfacial arrangement with optimal photocatalyst configuration (3 % In/BMO) enabled enhanced photogenerated electron separation and transfer, leading to a remarkable nitrogen fixation rate of approximately 150.9 μmol·g cat −1·h−1 under visible light irradiation. The performance of the photocatalyst was 9-fold and 27-fold higher than that of its pristine components, Bi 2 MoO 6 and In 2 O 3 , respectively. The experimental and theoretical evaluation deemed interfacial In-O-Mo bonds crucial for rapid transfer and charge-oriented accumulation. Whereas the generated internal electric field drove the spatial separation and transfer of photo-generated electrons and holes, significantly enhancing the photocatalytic N 2 -to-NH 3 conversion efficiency. The proposed work lays the foundation for designing S-scheme heterostructures with highly efficient interfacial bonds, offering a promising avenue for substantial improvements in photocatalytic nitrogen fixation. [ABSTRACT FROM AUTHOR]

Wurtzite-type aluminum nitride (AlN) thin films exhibiting high thermal conductivity, large grain size, and low surface roughness are desired for both bulk acoustic wave and surface acoustic wave resonators. In this work, we use ammonia (NH3) assisted reactive sputter deposition of AlN to significantly improve these properties. The study shows a systematic change in the structural, thermal, and morphological properties of AlN grown in nitrogen (N2) and N2 + NH3 atmosphere. The study demonstrates that NH3 assisted AlN sputtering facilitates 2D growth. In addition, the study presents a growth model relating the 2D growth to improve the mobility of aluminum (Al) and nitrogen (N) ad-atoms in NH3 atmosphere. Consequently, the thermal conductivity and roughness improve by ≈ 76%, and ≈ 35%, while the grain size increases by ≈ 78%. [ABSTRACT FROM AUTHOR]

Nitrogen deposition is an important means of exogenous nitrogen input in reservoir water. Agricultural activities around the reservoir lead to a sharp increase in the concentration of ammonia in the atmosphere, which poses a threat to the reservoir water body. Clarifying the contribution of agricultural ammonia release to atmospheric NH x (gaseous NH 3 and particulate NH 4 +), in the reservoir area can provide a theoretical foundation for local reactive nitrogen control. We collected atmospheric NH 3 and NH 4 + samples during the agricultural periods and analyzed the isotopic characteristics of atmospheric NH x and the contribution rates of different ammonia sources in the Xichuan area of the Danjiangkou Reservoir. The results showed that the initial δ15N values of NH 3 (–30.0‰ to –7.2‰) and particulate NH 4 +(–33‰ to +4.9‰ for finer and coarser particles, respectively) are different, and their contribution ratios from dissimilar ammonia sources are also different, among which NH 4 + is more susceptible to meteorological factors. However, since the atmospheric NH x in the Xichuan area is mainly gaseous NH 3 , the final sources of atmospheric ammonia nitrogen source depend on gaseous NH 3. Agricultural sources (59%-74%) were the main NH 3 sources in this area. Among them, the fertilizer use emission was dominant; it had the highest contribution rate in summer during the agricultural period and a more prominent impact in areas with less human interference. Reasonable regulation of the application of high-ammonia releasing fertilizer, especially during the agricultural period in summer, is an effective way to reduce the threat of atmospheric ammonia to water health. [Display omitted] [ABSTRACT FROM AUTHOR]

The development of solar-driven transfer of atmospheric nitrogen into ammonia is one of the green and sustainable strategies in industrial ammonia production. Nickel-titanium-layered double hydroxide (NiTi-LDH) was synthesised using the soft-chemical process for atmospheric nitrogen fixation application under photocatalysis in an aqueous system. NiTi-LDH was investigated using advanced characterisation techniques and confirmed the potential oxygen vacancies and/or surface defects owing to better photocatalytic activity under the solar spectrum. It also exhibited a bandgap of 2.8 eV that revealed its promising visible-light catalytic activities. A maximum of 33.52 µmol L−1 aqueous NH3 was obtained by continuous nitrogen (99.9% purity) supply into the photoreactor under an LED light source. Atmospheric nitrogen supply (≈78%) yielded 14.67 µmol L−1 aqueous NH3 within 60 min but gradually reduced to 3.6 µmol L−1 at 330 min. Interestingly, in weak acidic pH, 20.90 µmol L−1 NH3 was produced compared to 11.51 µmol L−1 NH3 in basic pH. The application of NiTi-LDH for visible-light harvesting capability and photoreduction of atmospheric N2 into NH3 thereby opens a new horizon of eco-friendly NH3 production using natural sunlight as alternative driving energy. [ABSTRACT FROM AUTHOR]

The Arctic Ocean is particularly affected by climate change with unknown consequences for primary productivity. Diazotrophs—prokaryotes capable of converting atmospheric nitrogen to ammonia—have been detected in the often nitrogen-limited Arctic Ocean but distribution and community composition dynamics are largely unknown. We performed amplicon sequencing of the diazotroph marker gene nifH from glacial rivers, coastal, and open ocean regions and identified regionally distinct Arctic communities. Proteobacterial diazotrophs dominated all seasons, epi- to mesopelagic depths and rivers to open waters and, surprisingly, Cyanobacteria were only sporadically identified in coastal and freshwaters. The upstream environment of glacial rivers influenced diazotroph diversity, and in marine samples putative anaerobic sulphate-reducers showed seasonal succession with highest prevalence in summer to polar night. Betaproteobacteria (Burkholderiales, Nitrosomonadales, and Rhodocyclales) were typically found in rivers and freshwater-influenced waters, and Delta- (Desulfuromonadales, Desulfobacterales, and Desulfovibrionales) and Gammaproteobacteria in marine waters. The identified community composition dynamics, likely driven by runoff, inorganic nutrients, particulate organic carbon, and seasonality, imply diazotrophy a phenotype of ecological relevance with expected responsiveness to ongoing climate change. Our study largely expands baseline knowledge of Arctic diazotrophs—a prerequisite to understand underpinning of nitrogen fixation—and supports nitrogen fixation as a contributor of new nitrogen in the rapidly changing Arctic Ocean. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive technical and economic assessment of potential green hydrogen and ammonia production plants in different locations in Iran with strong wind and solar resources. The study was organized in five steps. First, regarding the wind density and solar PV potential data, three locations in Iran were chosen with the highest wind power, solar radiation, and a combination of both wind/solar energy. All these locations are inland spots, but since the produced ammonia is planned to be exported, it must be transported to the export harbor in the South of Iran. For comparison, a base case was also considered next to the export harbor with normal solar and wind potential, but no distance from the export harbor. In the second step, a similar large-scale hydrogen production facility with proton exchange membrane electrolyzers was modeled for all these locations using the HOMER Pro simulation platform. In the next step, the produced hydrogen and the nitrogen obtained from an air separation unit are supplied to a Haber-Bosch process to synthesize ammonia as a hydrogen carrier. Since water electrolysis requires a considerable amount of water with specific quality and because Iran suffers from water scarcity, this paper, unlike many similar research studies, addresses the challenges associated with the water supply system in the hydrogen production process. In this regard, in the fourth step of this study, it is assumed that seawater from the nearest sea is treated in a desalination plant and sent to the site locations. Finally, since this study intends to evaluate the possibility of green hydrogen export from Iran, a detailed piping model for the transportation of water, hydrogen, and ammonia from/to the production site and the export harbor is created in the last step, which considers the real routs using satellite images, and takes into account all pump/compression stations required to transport these media. This study provides a realistic cost of green hydrogen/ammonia production in Iran, which is ready to be exported, considering all related processes involved in the hydrogen supply chain. • The minimum cost of green H2 in Iran was calculated to be between 2.94 and 3.32 USD/kgH 2. • The minimum cost of green NH3 in Iran was obtained between 580 and 641 USD/tNH 3. • H2 transportation via pipelines to the export harbor is the costliest scenario. • More than two-thirds of the cost of NH3 is caused by the power generation system. • Integrating green electricity into the Iranian grid is better than the P2A route. [ABSTRACT FROM AUTHOR]

Dry deposition of ammonia (NH 3) is the largest contributor to the nitrogen deposition from the atmosphere to soil and vegetation in the Netherlands, causing eutrophication and loss of biodiversity; however, data sets of NH 3 fluxes are sparse and in general have monthly resolution at best. An important reason for this is that measurement of the NH 3 flux under dry conditions is notoriously difficult. There is no technique that can be considered as the gold standard for these measurements, which complicates the testing of new techniques. Here, we present the results of an intercomparison of two novel measurement set-ups aimed at measuring dry deposition of NH 3 at half hourly resolution. Over a 5-week period, we operated two novel optical open-path techniques side by side at the Ruisdael station in Cabauw, the Netherlands: the RIVM-miniDOAS 2.2D using the aerodynamic gradient technique, and the commercial Healthy Photon HT8700E using the eddy covariance technique. These instruments are widely different in their measurement principle and approach to derive deposition values from measured concentrations; however, both techniques showed very similar results (r=0.87) and small differences in cumulative fluxes (∼ 10 %) as long as the upwind terrain was homogeneous and free of nearby obstacles. The observed fluxes varied from ∼ -80 to ∼ + 140 ng NH 3 m -2 s -1. Both the absolute flux values and the temporal patterns were highly similar, which substantiates that both instruments were able to measure NH 3 fluxes at high temporal resolution. However, for wind directions with obstacles nearby, the correlations between the two techniques were weaker. The uptime of the miniDOAS system reached 100 % once operational, but regular intercalibration of the system was applied in this campaign (35 % of the 7-week uptime). Conversely, the HT8700E did not measure during and shortly after rain, and the coating of its mirrors tended to degrade (21 % data loss during the 5-week uptime). In addition, the NH 3 concentrations measured by the HT8700E proved sensitive to air temperature, causing substantial differences (range: -15 to +6 µ g m -3) between the two systems. To conclude, the miniDOAS system appears ready for long-term hands-off monitoring. The current HT8700E system, on the other hand, had a limited stand-alone operational time under the prevailing weather conditions. However, under relatively dry and low-dust conditions, the system can provide sound results, opening good prospects for future versions, also for monitoring applications. The new high temporal resolution data from these instruments can facilitate the study of processes behind NH 3 dry deposition, allowing an improved understanding of these processes and better parameterisation in chemical transport models. [ABSTRACT FROM AUTHOR]

Rhizobia form nodules on the roots of legumes and fix atmospheric nitrogen into ammonia, thus supplying it to host legumes. In return, plants supply photosynthetic products to maintain rhizobial activities. In most cases, rhizobial Nod factors (NFs) and their leguminous receptors (NFRs) are essential for the establishment of symbiosis. However, recent studies have discovered a novel symbiotic pathway in which rhizobia utilize the type III effectors (T3Es) similar to the pathogenic bacteria to induce nodulation. The T3Es of rhizobia are thought to be evolved from the pathogen, but they have a unique structure distinct from the pathogen, suggesting that it might be customized for symbiotic purposes. This review will focus on the recent findings from the study of rhizobial T3Es, discussing their features on a symbiont and pathogen, and the future perspectives on the role of rhizobial T3Es in symbiosis control technology. [ABSTRACT FROM AUTHOR]

Atmospheric ammonia (NH3) and ammonium (NH4+) can substantially influence air quality, ecosystems, and climate. NH3 volatilization from fertilizers and wastes (v-NH3) has long been assumed to be the primary NH3 source, but the contribution of combustion-related NH3 (c-NH3, mainly fossil fuels and biomass burning) remains unconstrained. Here, we collated nitrogen isotopes of atmospheric NH3 and NH4+ and established a robust method to differentiate v-NH3 and c-NH3. We found that the relative contribution of the c-NH3 in the total NH3 emissions reached up to 40 ± 21% (6.6 ± 3.4 Tg N yr−1), 49 ± 16% (2.8 ± 0.9 Tg N yr−1), and 44 ± 19% (2.8 ± 1.3 Tg N yr−1) in East Asia, North America, and Europe, respectively, though its fractions and amounts in these regions generally decreased over the past decades. Given its importance, c-NH3 emission should be considered in making emission inventories, dispersion modeling, mitigation strategies, budgeting deposition fluxes, and evaluating the ecological effects of atmospheric NH3 loading. By integrating nitrogen isotope systematics of ammonia emissions and transformations in the atmosphere, this study quantified the combustion-related ammonia emission and uncovered its importance for mitigating strategies of ammonia pollution. [ABSTRACT FROM AUTHOR]

Summary: Legume nodules are symbiotic structures formed as a result of the interaction with rhizobia. Nodules fix atmospheric nitrogen into ammonia that is assimilated by the plant and this process requires strict metabolic regulation and signaling. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are involved as signal molecules at all stages of symbiosis, from rhizobial infection to nodule senescence. Also, reactive sulfur species (RSS) are emerging as important signals for an efficient symbiosis. Homeostasis of reactive molecules is mainly accomplished by antioxidant enzymes and metabolites and is essential to allow redox signaling while preventing oxidative damage. Here, we examine the metabolic pathways of reactive molecules and antioxidants with an emphasis on their functions in signaling and protection of symbiosis. In addition to providing an update of recent findings while paying tribute to original studies, we identify several key questions. These include the need of new methodologies to detect and quantify ROS, RNS, and RSS, avoiding potential artifacts due to their short lifetimes and tissue manipulation; the regulation of redox‐active proteins by post‐translational modification; the production and exchange of reactive molecules in plastids, peroxisomes, nuclei, and bacteroids; and the unknown but expected crosstalk between ROS, RNS, and RSS in nodules. [ABSTRACT FROM AUTHOR]

Rhizobia are soil bacteria that can establish a symbiotic association with legumes. As a result, plant nodules are formed on the roots of the host plants where rhizobia differentiate to bacteroids capable of fixing atmospheric nitrogen into ammonia. This ammonia is transferred to the plant in exchange of a carbon source and an appropriate environment for bacterial survival. This process is subjected to a tight regulation with several checkpoints to allow the progression of the infection or its restriction. The type 3 secretion system (T3SS) is a secretory system that injects proteins, called effectors (T3E), directly into the cytoplasm of the host cell, altering host pathways or suppressing host defense responses. This secretion system is not present in all rhizobia but its role in symbiosis is crucial for some symbiotic associations, showing two possible faces as Dr. Jekyll and Mr. Hyde: it can be completely necessary for the formation of nodules, or it can block nodulation in different legume species/cultivars. In this review, we compile all the information currently available about the effects of different rhizobial effectors on plant symbiotic phenotypes. These phenotypes are diverse and highlight the importance of the T3SS in certain rhizobium–legume symbioses. [ABSTRACT FROM AUTHOR]

The enzyme nitrogenase performs the process of biological nitrogen fixation (BNF), converting atmospheric dinitrogen gas into the biologically accessible ammonia, which is rapidly protonated at physiological pH to yield ammonium. The reduction of dinitrogen requires both ATP and electrons. Azotobacter vinelandii is an aerobic nitrogen-fixing microbe that is a model organism for the study of BNF. Previous reports have described strains of A. vinelandii that are partially deregulated for BNF, resulting in the release of large quantities of ammonium into the growth medium. Determining the source of the electrons required to drive BNF is complicated by the existence of several protein complexes in A. vinelandii that have been linked to BNF in other species. In this work, we used the high-ammonium-accumulating strains of A. vinelandii to probe the source of electrons to nitrogenase by disrupting the Rnf1 and Fix complexes. The results of this work demonstrate the potential of these strains to be used as a tool to investigate the contributions of other enzymes or complexes in the process of BNF. These results provide strong evidence that the Rnf1 complex of A. vinelandii is the primary source of electrons delivered to the nitrogenase enzyme in this partially deregulated strain. The Fix complex under native regulation was unable to provide sufficient electrons to accumulate extracellular ammonium in the absence of the Rnf1 complex. Increased ammonium accumulation could be attained in a strain lacking the Rnf1 complex if the genes of the Fix protein complex were relocated behind the strong promoter of the S-layer protein but still failed to achieve the levels found with just the Rnf1 complex by itself. Key points: • The Rnf1 complex is integral to ammonium accumulation in A. vinelandii. • The Fix complex can be deleted and still achieve ammonium accumulation in A. vinelandii. • A. vinelandii can be engineered to increase the contribution of the Fix complex to ammonium accumulation. [ABSTRACT FROM AUTHOR]

Dry deposition of ammonia (NH3) is the largest contributor to the nitrogen deposition from the atmosphere to soil and vegetation in the Netherlands, causing eutrophication and loss of biodiversity. Yet, data sets of NH3 fluxes are sparse and in general have monthly resolution at best. An important reason for this is that measurement of the NH3 flux under dry conditions is notoriously difficult. There is no technique that can be considered the golden standard for these measurements, which complicates testing of new techniques and judging their quality. Here, we present the results of an intercomparison of two novel measurement setups aimed at measuring dry deposition of NH3 at half-hourly resolution. In a five-week comparison period, we operated two optical open-path techniques side by side at the Ruisdael station in Cabauw, the Netherlands: the novel RIVM-miniDOAS 2.2D using the aerodynamic gradient technique, and the novel commercial Healthy Photon HT8700E using the eddy covariance technique. Both are open-path optical instruments, leaving NH3 in the air during measurement. Otherwise, they are widely different in their measurement principle and approach to derive deposition values from measured concentrations. The two different techniques showed very similar results when the upwind terrain was both homogeneous and free of nearby obstacles (r = 0.87). The observed fluxes varied from a deposition of ~80 ng NH3 m-2 s-1 to an emission of ~140 ng NH3 m-2 s-1. We obtained similar results from two widely different techniques, both in absolute flux values as in their temporal pattern, which substantiated that both instruments were able to measure NH3 fluxes at high temporal resolution for a consecutive period of at least several weeks. However, for wind directions with nearby obstacles, the correlations between the two techniques were weaker. Moreover, the technical performance (e.g., uptime, precision) and practical limitations of both systems were discussed. The uptime of the miniDOAS system reached 100% once operational, but regular intercalibration of the two instruments was applied in this campaign (35% of the 7-week uptime). Conversely, the HT8700E did not measure during, and shortly after, rain, and the coating of its mirrors tended to degrade (21% data loss during the 5-week uptime). In addition, the HT8700E measured NH3 concentrations proved sensitive to air temperature, causing substantial differences (range: -15 to + 6 µg m-3) between the two systems. To conclude, the miniDOAS system appeared ready for long-term hands-off monitoring. The current HT8700E system, on the other hand, had a limited stand-alone operational time under the prevailing weather conditions. However, under the right circumstances, the system can provide sound results, opening good prospects for future versions, also for monitoring applications. The new high temporal resolution data from these instruments can facilitate the study of processes behind NH3 dry deposition, allowing improved understanding of these processes and better parametrization in chemical transport models. [ABSTRACT FROM AUTHOR]

Delhi, the capital city of India, experiences severe air pollution and suffers from its adverse effects on human health and ecosystems. This pollution is characterized by high levels of pollutants, including atmospheric nitrogen in both the gaseous and particulate phases. However, there is a lack of simultaneous measurement of chemical composition, tracers and 15N data in aerosols to understand the influence of different sources on N aerosols over Delhi. Here, we measured total nitrogen (TN), water-soluble total nitrogen (WSTN), water-soluble inorganic nitrogen (WSIN), and N stable isotope compositions (δ15N) in PM 2.5 samples covering the post-monsoon, winter, and summer periods of the year 2018–19. NH 4 +-N was the major N species, accounting for an average 58% of TN and 68% of WSIN. The temporal variations of TN, WSTN, NH 4 +-N, NO 3 −-N, and WSON showed peaks in the post-monsoon and winter seasons, exhibiting seasonality similar to PM 2.5 and levoglucosan (a biomass-burning tracer) indicating their co-genetic sources. Based on the correlation analysis between δ15N and N-species, we identified two distinct secondary chemical processes: i) in an NH 4 +-poor atmosphere, the gas-to-particle (NH 3 → NH 4 +) conversion and subsequent formation of NH 4 HSO 4 was the main process controlling the 15N and nitrogen enrichments in PM 2.5 ; whereas ii) under NH 4 +-rich conditions, the formation and dissociation of NH 4 NO 3 dominated. The coupled HYSPLIT and PSCF analyses highlighted the transport and contributions of open biomass burning emissions under a northwesterly atmospheric flow during post-monsoon as well as from local biomass combustion (from cooking and heating) during winter in the city and its vicinity. Our results suggested that i) both NH 4 +-N and NO 3 −-N were mainly impacted by biomass combustion during post-monsoon and winter seasons, and ii) NO 3 −-N resulted of dust transport from the Thar Desert in the summer season, but not NH 4 +-N. Finally, we recommend that future research focuses on the study of the seasonality of atmospheric nitrogen composition using 15N data from their different sources to design tailor-made measures and policies regarding the different potential sources, combining them within a comprehensive framework to ultimately improve air quality and the living environment in Delhi. • NH 4 +-N was the major N species, accounting for an average of 58% of TN. • NH 3 to NH 4 +conversion and formation of NH 4 HSO 4 dominated in NH 4 +-poor atmosphere. • Under NH 4 +-rich conditions, the formation and dissociation of NH 4 NO 3 dominated. • NH 4 +-N was mainly impacted by biomass combustions. • NO 3 −-N was related to both biomass burning and dust transport. [ABSTRACT FROM AUTHOR]

[Display omitted] • A creek within a coastal wetland was a strong N 2 O emitter. • N 2 O distributions were influenced by N substrate and salinity gradients. • Nitrite reduction and ammonia oxidation appeared to outpace N 2 O reduction. • High-resolution sampling is required to characterize N 2 O contribution from coastal creeks. Increased anthropogenic input of nitrogen into coastal creeks make them potential hotspots for N 2 O production and emission, but they are often excluded from regional and global N 2 O budget, and high-resolution sampling is required to characterize the strong spatiotemporal heterogeneity within the creeks. In this study, we analyzed the N 2 O concentration and diffusive N 2 O flux within a coastal creek in the Shanyutan Wetland in southeastern China in high spatial resolution across four seasons. Ancillary hydrographical variables and N 2 O-related functional gene abundances were also measured. Results showed that the creek was consistently oversaturated in N 2 O, at a seasonal average of 5.6–14.2 nmol/L, relative to the overlying atmosphere. The spatial distribution of N 2 O followed the gradient of nitrogenous substrate but was inversely related to the salinity gradient, and the coefficient of spatial variation of N 2 O flux ranged from 66.3 % to 116.5 %. Nitrite reduction (based on nirK and nirS gene abundances) and ammonia oxidation (AOA amoA and AOB amoA) appeared to outpace N 2 O reduction (nosZ I and nosZ II), and these were the main microbial processes that determined N 2 O concentration and flux. Both N 2 O concentration and flux were substantially higher in autumn than those in the other seasons, but that did not appear to be related to precipitation. N 2 O diffusive flux from the creek averaged 322.2 nmol m−2 h−1, which was over 2 times higher than the global average for lakes and reservoirs. Our results highlight that coastal creeks are strong atmospheric N 2 O sources with high spatiotemporal variability. [ABSTRACT FROM AUTHOR]

Unprecedented nitrogen (N) inputs into terrestrial ecosystems have profoundly altered soil N cycling. Ammonia oxidizers and denitrifiers are the main producers of nitrous oxide (N2O), but it remains unclear how ammonia oxidizer and denitrifier abundances will respond to N loading and whether their responses can predict N‐induced changes in soil N2O emission. By synthesizing 101 field studies worldwide, we showed that N loading significantly increased ammonia oxidizer abundance by 107% and denitrifier abundance by 45%. The increases in both ammonia oxidizer and denitrifier abundances were primarily explained by N loading form, and more specifically, organic N loading had stronger effects on their abundances than mineral N loading. Nitrogen loading increased soil N2O emission by 261%, whereas there was no clear relationship between changes in soil N2O emission and shifts in ammonia oxidizer and denitrifier abundances. Our field‐based results challenge the laboratory‐based hypothesis that increased ammonia oxidizer and denitrifier abundances by N loading would directly cause higher soil N2O emission. Instead, key abiotic factors (mean annual precipitation, soil pH, soil C:N ratio, and ecosystem type) explained N‐induced changes in soil N2O emission. Altogether, these findings highlight the need for considering the roles of key abiotic factors in regulating soil N transformations under N loading to better understand the microbially mediated soil N2O emission. [ABSTRACT FROM AUTHOR]

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Atmospheric reactive nitrogen (Nr) pollution leads to enhanced Nr deposition. There still big gaps in understanding atmospheric nitrogen deposition because of limited monitoring sites in arid land ecosystems of Central Asia. To determine Nr concentrations and deposition in the study area, we have set up 20 monitoring sites to collect gaseous, particulate, and precipitation samples and measure their Nr components since 2009. Nr concentrations in air showed large spatial variations. Based on the Nr concentrations, dry deposition was calculated using the monthly average Nr concentrations by the corresponding deposition velocities modeled, which was varied between 3.15 and 27.92 kg N ha-1 yr-1 across desert, grassland, desert-grassland, forest, farmland, and city/suburb ecosystems. Ammonia N deposition varied between 0.50 asnd 8.66 kg N ha-1 yr-1, and nitrate N deposition c varied between 0.67 and 4.22 kg N ha-1 yr-1, respectively, in precipitation. Annual N deposition is following the order of desert (4.0) < grassland (6.0) < desert-grassland (7.6) < forest (16.1) < farmland (18.4) < city/suburb (35.4) ecosystems. Dry deposition contributed 52.7, 53.8, 100, 68.2, 73.7, and 78.9% of total N deposition in grassland, desert-grassland, desert, forest, farmland and city/suburb ecosystems, respectively. Reduced nitrogen deposition accounted for 62% of total N deposition in the arid area. Dry NH3 deposition made an important contribution (on average 40%) to total N deposition. Therefore, understanding the characteristics of Nr pollution especially NH3 emission is indispensable to atmospheric pollution control in arid region. [ABSTRACT FROM AUTHOR]

Under nitrogen-limiting conditions, symbiotic nodulation promotes the growth of legume plants via the fixation of atmospheric nitrogen to ammonia by rhizobia in root nodules. The rhizobial Nod factor (NF) and type III secretion system (T3SS) are two key signaling pathways for establishing the legume–rhizobium symbiosis. However, whether NF signaling is involved in the nodulation of Robinia pseudoacacia and Mesorhizobium amorphae CCNWGS0123, and its symbiotic differences compared with T3SS signaling remain unclear. Therefore, to elucidate the function of NF signaling in nodulation, we mutated nodC in M. amorphae CCNWGS0123, which aborted NF synthesis. Compared with the plants inoculated with the wild type strain, the plants inoculated with the NF-deficient strain exhibited shorter shoots with etiolated leaves. These phenotypic characteristics were similar to those of the plants inoculated with the T3SS-deficient strain, which served as a Nod− (non-effective nodulation) control. The plants inoculated with both the NF- and T3SS-deficient strains formed massive root hair swellings, but no normal infection threads were detected. Sections of the nodules showed that inoculation with the NF- and T3SS-deficient strains induced small, white bumps without any rhizobia inside. Analyzing the accumulation of 6 plant hormones and the expression of 10 plant genes indicated that the NF- and T3SS-deficient strains activated plant defense reactions while suppressing plant symbiotic signaling during the perception and nodulation processes. The requirement for NF signaling appeared to be conserved in two other leguminous trees that can establish symbiosis with M. amorphae CCNWGS0123. In contrast, the function of the T3SS might differ among species, even within the same subfamily (Faboideae). Overall, this work demonstrated that nodulation of R. pseudoacacia and M. amorphae CCNWGS0123 was both NF and T3SS dependent. [ABSTRACT FROM AUTHOR]

Ammonia (NH3) is an important agent involved in atmospheric chemistry and nitrogen cycling. Current estimates of NH3 emissions from biomass burning (BB) differ by more than a factor of 2, impeding a reliable assessment of their environmental consequences. Combining high-resolution satellite observations of NH3 columns with network measurements of the concentration and stable nitrogen isotope composition (δ15N) of NH3 , we present coherent estimates of the amount of NH3 derived from BB in the heartland of Southeast Asia, a tropical monsoon environment. Our results reveal a strong variability in atmospheric NH3 levels in time and space across different landscapes. All of the evidence on hand suggests that anthropogenic activities are the most important modulating control with respect to the observed patterns of NH3 distribution in the study area. N-isotope balance considerations revealed that during the intensive fire period, the atmospheric input from BB accounts for no more than 21±5 % (1σ) of the ambient NH3 , even at the rural sites and in the proximity of burning areas. Our N-isotope-based assessment of the variation in the relative contribution of BB-derived NH3 is further validated independently through the measurements of particulate K+ , a chemical tracer of BB. Our findings underscore that BB-induced NH3 emissions in tropical monsoon environments can be much lower than previously anticipated, with important implications for future modeling studies to better constrain the climate and air quality effects of wildfires. [ABSTRACT FROM AUTHOR]

Long-term observational data for the size distributions and particulate chemical components have been summarized to understand the past and current particulate conditions in Osaka City. The positive matrix factorization (PMF) method was also applied to estimate the source changes. The observational data obtained using Andersen cascade impactors reveals that for the 40 years from fiscal year (FY) 1976 to 2015, there was a 70% reduction in PMfine (less than 2.1 µm of the aerodynamic diameter) and 76% reduction in PMcoarse (over 2.1 µm). These correspond to a 71% and 74% reduction in PM2.5 (particulate matter less than 2.5 µm in diameter) and PM10-2.5, respectively. From the continuous chemical measurements made in this study, we observed a more than 50% reduction in coarse particulate elemental carbon (EC), SO42-, NH4 +, Zn, Pb, and Cd, commonly in residential and roadside areas, over the last 20 years. Similarly, the level of the fine particulate EC, Ca2+, Cl-, Zn, Mg2+, Pb, and Cd was reduced by more than 50%. Notably, the results of the particulate component analysis of ECfine show a typical reduction of 73%-79% for 20 years, and this is the main component contributing to the reduction of atmospheric particulate concentration. However, there seems to have been no apparent reduction of Vfine concentrations, SO42- fine showed a relatively low reduction of 19% to 26%, and NH4+ fine levels fell by 14% to 21% in 20 years. Since fine sulfate and ammonium have similar behaviors, ammonium sulfate is considered to be a secondary particle aerosol because of long-range transportation. The PMF analysis still estimates a high contribution rate of secondary particles, which is one of the current problems. In contrast, although vanadium is a minor element, it is likely to be generated from harbor areas with ships because they are susceptible to the prevailing sea breeze in summer. Therefore, in the future, it will be necessary to scrutinize and take countermeasures not only for long-range transportation but also for domestic sources. [ABSTRACT FROM AUTHOR]

The production of ammonia from atmospheric nitrogen and water using sunlight is an important way to obtain ammonia as an energy carrier and is a new paradigm for achieving a low‐carbon and sustainable‐energy society. In this study, we attempted to enhance the ammonia photosynthesis efficiency both by increasing the electron supply using a novel photoanode composed of Au film, TiO2, and Au‐NPs (ATA) with hybrid energy states due to modal strong coupling and by increasing the surface area of the Zr cathode. We investigated the key properties of this hybrid mode‐assisted NH3 photosynthesis using two‐electrode systems combining photoanodes and cathodes by performing photoelectrochemical measurements and product analysis. We found that the ATA structure has high absorptivity and enhances the quantum efficiency of ammonia photosynthesis and the surface area available to adsorb N2 on the Zr cathode is a critical factor for enhancing the reaction rate. [ABSTRACT FROM AUTHOR]

Under nitrogen starvation, most legume plants form a nitrogen-fixing symbiosis with Rhizobium bacteria. The bacteria induce the formation of a novel organ called the nodule in which rhizobia reside as intracellular symbionts and convert atmospheric nitrogen into ammonia. During this symbiosis, miRNAs are essential for coordinating the various plant processes required for nodule formation and function. miRNAs are non-coding, endogenous RNA molecules, typically 20–24 nucleotides long, that negatively regulate the expression of their target mRNAs. Some miRNAs can move systemically within plant tissues through the vascular system, which mediates, for example, communication between the stem/leaf tissues and the roots. In this review, we summarize the growing number of miRNAs that function during legume nodulation focusing on two model legumes, Lotus japonicus and Medicago truncatula , and two important legume crops, soybean (Glycine max) and common bean (Phaseolus vulgaris). This regulation impacts a variety of physiological processes including hormone signaling and spatial regulation of gene expression. The role of mobile miRNAs in regulating legume nodule number is also highlighted. [ABSTRACT FROM AUTHOR]

As a common gaseous pollutant in atmospheric environment, ammonia (NH 3) not only contributes to the formation of haze, but also disturb the nitrogen balance in ecosystem through atmospheric nitrogen deposition. Therefore, the control of NH 3 emission has important environmental significance. Adsorption is the most commonly used technology for NH 3 purification in practice, and efficient adsorbents are the key to adsorption method. Herein, a core-shell structured HC@MnO 2 adsorbent was constructed by in-situ growth of layered δ-MnO 2 on hydrochar (HC) surface, and its surface acidic sites were further strengthened. The enhancement of surface acidic sites significantly improved the adsorption performance of HC@MnO 2 for NH 3 , reaching 34.49 mg NH 3 /g, which was superior to commercial carbon-based materials (whose adsorption capacity was 8.47 times that of Coal-based activated carbon, 14.25 times that of Coconut shell activated carbon, and 12.77 times that of Bamboo charcoal). Moreover, the operating parameters and adsorption kinetics were detailly investigated. The adsorption of HC@MnO 2 on NH 3 was in accordance with pseudo-second-order adsorption kinetics model. Large surface area of core-shell structure and abundant surface acidic sites of δ-MnO 2 are the decisive reasons for the excellent adsorption performance of HC@MnO 2. Importantly, the enhancement of surface stronger Brønsted acidic sites is the key to improve NH 3 adsorption performance of HC@MnO 2. Finally, the thermal regeneration and recycling performance of HC@MnO 2 –H were also investigated. This study provides a suggestive for further research on low-cost composite materials with excellent NH 3 adsorption performance. [Display omitted] • Core-shell structured HC@MnO 2 was constructed by in-situ growth of δ-MnO 2 on hydrochar. • Enhancing of acidic sites significantly improves the adsorption performance for NH 3. • The operating parameters and adsorption kinetics were detailly investigated. • Adsorption sites and adsorption mechanism of NH 3 were further revealed. [ABSTRACT FROM AUTHOR]

Atmospheric ammonia (NH3) is a precursor to fine particulate matter formation and contributes to nitrogen (N) deposition, with potential implications for the health of humans and ecosystems. Agricultural soils and animal excreta are the primary source of atmospheric NH3, but natural soils can also be an important emitter. In regions with distinct dry and wet seasons such as the Sahel, the start of the rainy season triggers a pulse of biogeochemical activity in surface soils known as the Birch effect, which is often accompanied by emissions of microbially produced gases such as carbon dioxide and nitric oxide. Field and lab studies have sometimes, but not always, observed pulses of NH3 after the wetting of dry soils; however, the potential regional importance of these emissions remains poorly constrained. Here we use satellite retrievals of atmospheric NH3 using the Infrared Atmospheric Sounding Interferometer (IASI) regridded at 0.25° resolution, in combination with satellite-based observations of precipitation, surface soil moisture, and nitrogen dioxide concentrations, to reveal substantial precipitationinduced pulses of NH3 across the Sahel at the onset of the rainy season in 2008. The highest concentrations of NH3 occur in pulses during March and April when NH3 biomass burning emissions estimated for the region are low. For the region of the Sahel spanning 10 to 16° N and 0 to 30° E, changes in NH3 concentrations are weakly but significantly correlated with changes in soil moisture during the period from mid-March through April when the peak NH3 concentrations occur (r = 0:28, p = 0:02). The correlation is also present when evaluated on an individual pixel basis during April (r = 0:16, p < 0:001). Average emissions for the entire Sahel from a simple box model are estimated to be between 2 and 6 mgNH3 m-2 d-1 during peaks of the observed pulses, depending on the assumed effective NH3 lifetime. These early season pulses are consistent with surface observations of monthly concentrations, which show an uptick in NH3 concentration at the start of the rainy season for sites in the Sahel. The NH3 concentrations in April are also correlated with increasing tropospheric NO2 concentrations observed by the Ozone Monitoring Instrument (r = 0:78, p < 0:0001), which have previously been attributed to the Birch effect. Box model results suggest that pulses occurring over a 35-day period in March and April are responsible for roughly one-fifth of annual emissions of NH3-N from the Sahel. We conclude that precipitation early in the rainy season is responsible for substantial NH3 emissions in the Sahel, likely representing the largest instantaneous fluxes of gas-phase N from the region during the year. [ABSTRACT FROM AUTHOR]

The UK Acid Gases and Aerosol Monitoring Network (AGANet) was established in 1999 (12 sites, increased to 30 sites from 2006), to provide long-term national monitoring of acid gases (HNO3, SO2, HCl) and aerosol components (NO-3, SO2- 4, Cl-, Na+, Ca2+, Mg2+). An extension of a low-cost denuder-filter pack system (DELTA) that is used to measure NH3 and NH+ 4 in the UK National Ammonia Monitoring Network (NAMN) provides additional monthly speciated measurements for the AGANet. A comparison of the monthly DELTA measurement with averaged daily results from an annular denuder system showed close agreement, while the sum of HNO3 and NO-3 and the sum of NH3 and NH+ 4 from the DELTA are also consistent with previous filter pack determination of total inorganic nitrogen and total inorganic ammonium, respectively. With the exception of SO2 and SO2-4, the AGANet provides, for the first time, the UK concentration fields and seasonal cycles for each of the other measured species. The largest concentrations of HNO3, SO2, and aerosol NO-3 and SO2- 4 are found in southern and eastern England and smallest in western Scotland and Northern Ireland, whereas HCl are highest in southeastern, south-western, and central England, that may be attributed to dual contribution from anthropogenic (coal combustion) and marine sources (reaction of sea salt with acid gases to form HCl). Na+ and Cl- are spatially correlated, with largest concentrations at coastal sites, reflecting a contribution from sea salt. Temporally, peak concentrations in HNO3 occurred in late winter and early spring attributed to photochemical processes. NO-3 and SO2- 4 have a spring maxima that coincides with the peak in concentrations of NH3 and NH+ 4, and are therefore likely attributable to formation of NH4NO3 and .NH4/2SO4 from reaction with higher concentrations of NH3 in spring. By contrast, peak concentrations of SO2, Na+, and Cl- during winter are consistent with combustion sources for SO2 and marine sources in winter for sea salt aerosol. Key pollutant events were captured by the AGANet. In 2003, a spring episode with elevated concentrations of HNO3 and NO-3 was driven by meteorology and transboundary transport of NH4NO3 from Europe. A second, but smaller episode occurred in September 2014, with elevated concentrations of SO2, HNO3, SO2- 4, NO-3, and NH+ 4 that was shown to be from the Icelandic Holuhraun volcanic eruptions. Since 1999, AGANet has shown substantial decrease in SO2 concentrations relative to HNO3 and NH3, consistent with estimated decline in UK emissions. At the same time, large reductions and changes in the aerosol components provide evidence of a shift in the particulate phase from .NH4/2SO4 to NH4NO3. The potential for NH4NO3 to release NH3 and HNO3 in warm weather, together with the surfeit of NH3 also means that a larger fraction of the reduced and oxidized N is remaining in the gas phase as NH3 and HNO3 as indicated by the increasing trend in ratios of NH3 V NH+ 4 and HNO3 V NO-3 over the 16-year period. Due to different removal rates of the component species by wet and dry deposition, this change is expected to affect spatial patterns of pollutant deposition with consequences for sensitive habitats with exceedance of critical loads of acidity and eutrophication. The changes are also relevant for human health effects assessment, particularly in urban areas as NH4NO3 constitutes a significant fraction of fine particulate matter (< 2:5 μm) that are linked to increased mortality from respiratory and cardiopulmonary diseases. [ABSTRACT FROM AUTHOR]

Five-year (2011-2015) measurements of gaseous NH3, NO2, and HNO3 and particulate NH4+ and NO3- in air and/or precipitation were conducted at 27 sites in the Nationwide Nitrogen Deposition Monitoring Network (NNDMN) to better understand spatial and temporal (seasonal and annual) characteristics of reactive nitrogen (Nr) concentrations and deposition in eastern China. Our observations reveal annual average concentrations (16.4-32.6 µgN m-3), dry deposition fluxes (15.8-31.7 kg N ha-1 yr-1), and wet/bulk deposition fluxes (18.4-28.0 kg N ha-1 yr-1) based on land use, ranked as urban > rural > background sites. Annual concentrations and dry deposition fluxes of each Nr species in air were comparable at urban and background sites in northern and southern regions, but were significantly higher at northern rural sites. These results, together with good agreement between spatial distributions of NH3 and NO2 concentrations determined from ground measurements and satellite observations, demonstrate that atmospheric Nr pollution is heavier in the northern region than in the southern region. No significant inter-annual trends were found in the annual Nr dry and wet/bulk N deposition at almost all of the selected sites. A lack of significant changes in annual averages between the 2013-2015 and 2011-2012 periods for all land use types suggests that any effects of current emission controls are not yet apparent in Nr pollution and deposition in the region. Ambient concentrations of total Nr exhibited non-significant seasonal variation at all land use types, although significant seasonal variations were found for individual Nr species (e.g. NH3, NO2, and pNO3-) in most cases. In contrast, dry deposition of total Nr exhibited a consistent and significant seasonal variation at all land use types, with the highest fluxes in summer and the lowest in winter. Based on sensitivity tests by the GEOS-Chem model, we found that NH3 emissions from fertilizer use (including chemical and organic fertilizers) were the largest contributor (36 %) to total inorganic Nr deposition over eastern China. Our results not only improve the understanding of spatial--temporal variations of Nr concentrations and deposition in this pollution hotspot, but also provide useful information for policy-makers that mitigation of NH3 emissions should be a priority to tackle serious N deposition in eastern China. [ABSTRACT FROM AUTHOR]

The stomatal compensation point of ammonia (χ s ) is a key factor controlling plant-atmosphere NH 3 exchange, which is dependent on the nitrogen (N) supply and varies among plant species. However, knowledge gaps remain concerning the effects of elevated atmospheric N deposition and ozone (O 3 ) on χ s for forest species, resulting in large uncertainties in the parameterizations of NH 3 incorporated into atmospheric chemistry and transport models (CTMs). Here, we present leaf-scale measurements of χ s for hybrid poplar clone ‘546’ ( Populusdeltoides cv. 55/56 x P. deltoides cv. Imperial ) growing in two N treatments (N0, no N added; N50, 50 kg N ha −1 yr −1 urea fertilizer added) and two O 3 treatments (CF, charcoal-filtered air; E-O 3 , non-filtered air plus 40 ppb) for 105 days. Our results showed that χ s was significantly reduced by E-O 3 (41%) and elevated N (19%). The interaction of N and O 3 was significant, and N can mitigate the negative effects of O 3 on χ s . Elevated O 3 significantly reduced the light-saturated photosynthetic rate ( A sat ) and chlorophyll (Chl) content and significantly increased intercellular CO 2 concentrations ( C i), but had no significant effect on stomatal conductance ( g s ). By contrast, elevated N did not significantly affect all measured photosynthetic parameters. Overall, χ s was significantly and positively correlated with A sat , g s and Chl, whereas a significant and negative relationship was observed between χ s and C i. Our results suggest that O 3 -induced changes in A sat , C i and Chl may affect χ s . Our findings provide a scientific basis for optimizing parameterizations of χ s in CTMs in response to environmental change factors (i.e., elevated N deposition and/or O 3 ) in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • The axial fifth ligands X (X = O, OH, F, Cl, Br, and I) enhance the eNO 3 RR -to- NH 3 activity of Fe- N 4 -C significantly. • The catalytic activity is closely related to the NO 3 - and NO adsorption strength modulated by axial ligands. • The configurations of * NO 3 and *NO are orbital-dependent. Single Fe atom coordinated with four planar nitrogen atoms codoped graphene layer (Fe- N 4 -C) has emerged as one of the promising single atom electrocatalyst (eSAC) for the remediation of nitrate ( NO 3 -). Herein, based on density functional theory (DFT) calculations, it is found that the ligands X (X = O, OH, F, Cl, Br, and I) axially ligated to the Fe center of Fe- N 4 -C can significantly improve its catalytic activity toward electrocatalytic nitrate reduction (eNO 3 RR) to ammonia (NH 3) with limiting potentials (U L) of 0, −0.36, −0.28, −0.41, −0.25, and − 0.19 eV, respectively. The remarkable catalytic activity should be associated with the well-matched orbitals of the F e 3 d xz / F e 3 d yz and NO π ∗ , together with moderate NO ∗ adsorption free energy (Δ G NO ∗). Although e N O 3 R R on O - F e - N 4 is highly energy favorable, extremely low Δ G NO ∗ (-0.02 eV) may lead to inferior selectivity toward NH 3 product. These findings highlight the role of axial ligand for the e N O 3 R R properties of F e - N 4 - C. [ABSTRACT FROM AUTHOR]

Forest fragmentation can increase dry deposition of atmospheric ammonia (NH 3) volatilized from agricultural areas, and consequently increase spatial variability of Nr deposition within the forest ("elevated reactive nitrogen (Nr) deposition"). However, little is known about this effect and its impact on forest production in a deciduous broad-leaved forest in Asian countries. Here, we performed the field observations of atmospheric concentration and deposition of inorganic Nr gases and particles in a Japanese fragmented forest from May 2018 to April 2019. Leaf traits and growth of Japanese oak tree and understory vegetation were also measured. Atmospheric concentration and deposition of dissolved inorganic Nr (DIN) to tree canopies were measured via filter sampling and throughfall methods, respectively. Canopy retention/exchange was also estimated as a part of dry deposition using the canopy budget model. The results demonstrated that annual dry deposition of NH 3 to tree canopies (4.4 kgN ha−1 y−1) was dominant in the annual total DIN deposition (7.1 kgN ha−1 y−1) at the forest edge, including the elevated Nr deposition of approximately 2 kgN ha−1 y−1. Additionally, agricultural activities such as fertilization in the area surrounding the forest likely enhanced the potential of canopy retention of NH 4 +, readily absorbed by tree canopy. The growth rates of tree and understory vegetation (dwarf bamboo) were higher at the edge than that at the interior, emphasizing a need for further investigation to quantify the effect of low Nr deposition (<3–5 kgN ha−1 y−1) on forest production, along with the conventional experimental studies under a high Nr deposition. • Field observations were conducted in a Japanese cool-temperate fragmented forest. • Canopy retention was estimated using the canopy budget model. • The edge effect of NH 3 dry deposition was about 2 kgN ha−1 y−1. • Agricultural activities surrounding the forest enhanced the NH 3 canopy retention. • Growth rates of tree and dwarf bamboo may be enhanced due to the edge effect. [ABSTRACT FROM AUTHOR]

The chemical breakdown of marine derived reactive nitrogen transported to the land as seabird guano represents a significant source of ammonia (NH 3 ) in areas far from other NH 3 sources. Measurements made at tropical and temperate seabird colonies indicate substantial NH 3 emissions, with emission rates larger than many anthropogenic point sources. However, several studies indicate that thermodynamic processes limit the amount of NH 3 emitted from guano, suggesting that the percentage of guano volatilizing as NH 3 may be considerably lower in colder climates. This study undertook high resolution temporal ammonia measurements in the field and coupled results with modelling to estimate NH 3 emissions at a temperate puffin colony and two sub-polar penguin colonies (Signy Island, South Orkney Islands and Bird Island, South Georgia) during the breeding season. These emission rates are then compared with NH 3 volatilization rates from other climates. Ammonia emissions were calculated using a Lagrangian atmospheric dispersion model, resulting in mean emissions of 5 μg m −2 s −1 at the Isle of May, 12 μg m −2 s −1 at Signy Island and 9 μg m −2 s −1 at Bird Island. The estimated percentage of total guano nitrogen volatilized was 5% on the Isle of May, 3% on Signy and 2% on Bird Island. These values are much smaller than the percentage of guano nitrogen volatilized in tropical contexts (31–65%). The study confirmed temperature, wind speed and water availability have a significant influence on the magnitude of NH 3 emissions, which has implications for reactive nitrogen in both modern remote regions and pre-industrial atmospheric composition and ecosystem interactions. [ABSTRACT FROM AUTHOR]

As a class of brown carbon, organonitrogen compounds originating from the heterogeneous uptake of NH3 by secondary organic aerosol (SOA) have received significant attention recently. In the current work, particulate organonitrogen formation during the ozonolysis of a-pinene and the OH oxidation of m-xylene in the presence of ammonia (34-125 ppb) was studied in a smog chamber equipped with a high resolution time-of-flight aerosol mass spectrometer and a quantum cascade laser instrument. A large diversity of nitrogen-containing organic (NOC) fragments was observed which were consistent with the reactions between ammonia and carbonyl-containing SOA. Ammonia uptake coefficients onto SOA which led to organonitrogen compounds were reported for the first time, and were in the range of ~ 10-3-10-2, decreasing significantly to < 10-5 after 6 h of reaction. At the end of experiments (~ 6 h) the NOC mass contributed 8.9 ± 1.7 and 31.5 ± 4.4 wt % to the total α-pinene- and m-xylene-derived SOA, respectively, and 4-15 wt % of the total nitrogen in the system. Uptake coefficients were also found to be positively correlated with particle acidity and negatively correlated with NH3 concentration, indicating that heterogeneous reactions were responsible for the observed NOC mass, possibly limited by liquid phase diffusion. Under these conditions, the data also indicate that the formation of NOC can compete kinetically with inorganic acid neutralization. The formation of NOC in this study suggests that a significant portion of the ambient particle associated N may be derived from NH3 heterogeneous reactions with SOA. NOC from such a mechanism may be an important and unaccounted for source of PM associated nitrogen. This mechanism may also contribute to the medium or long-range transport and wet/dry deposition of atmospheric nitrogen. [ABSTRACT FROM AUTHOR]

Animal feeding operations are primary contributors of anthropogenic ammonia (NH3) emissions in North America and Europe. Mathematical modeling of NH3 volatilization from each stage of livestock manure management allows comprehensive quantitative estimates of emission sources and nutrient losses. A regionally-specific mass balance model based on total ammoniacal nitrogen (TAN) content in animal manure was developed for estimating NH3 emissions from beef farming operations in western Canada. Total N excretion in urine and feces was estimated from animal diet composition, feed dry matter intake and N utilization for beef cattle categories and production stages. Mineralization of organic N, immobilization of TAN, nitrification, and denitrification of N compounds in manure, were incorporated into the model to account for quantities of TAN at each stage of manure handling. Ammonia emission factors were specified for different animal housing (feedlots, barns), grazing, manure storage (including composting and stockpiling) and land spreading (tilled and untilled land), and were modified for temperature. The model computed NH3 emissions from all beef cattle sub-classes including cows, calves, breeding bulls, steers for slaughter, and heifers for slaughter and replacement. Estimated NH3 emissions were about 1.11 × 105 Mg NH3 in Alberta in 2006, with a mean of 18.5 kg animal−1 yr−1 (15.2 kg NH3–N animal−1 yr−1) which is 23.5% of the annual N intake of beef cattle (64.7 kg animal−1 yr−1). The percentage of N intake volatilized as NH3–N was 50% for steers and heifers for slaughter, and between 11 and 14% for all other categories. Steers and heifers for slaughter were the two largest contributors (3.5 × 104 and 3.9 × 104 Mg, respectively) at 31.5 and 32.7% of total NH3 emissions because most growing animals were finished in feedlots. Animal housing and grazing contributed roughly 63% of the total NH3 emissions (feedlots, barns and pastures contributed 54.4, 0.2 and 8.1% of total emissions, respectively.). Manure storage (composting and stockpiling) and land spreading contributed 23 and 14% of the total emissions, respectively. Parameters from this TAN-based mass balance model will be incorporated into the HOLOS model – a farm-level greenhouse gas calculator. [ABSTRACT FROM AUTHOR]

Nitrogen (N) deposition has been considered as one of the important factors contributing to the critical impacts on nature, including eutrophication and biodiversity loss. To understand the effect of anthropogenic N emissions on urban-scale dry and wet N depositions, an investigation using a chemical transport model coupled with a sensitivity analysis solver was conducted in the domains that hold large megacities in Japan, the Tokyo metropolitan area, and Osaka, in the whole year of 2017. The validation results from the comparison of the modeling results to the observed results of N depositions showed that the overall calculated results replicated the observed results in the same order of magnitude. The results of the whole year calculation showed that both dry and wet N depositions were higher in spring and summer, mainly due to the higher emission of ammonia (NH 3) due to the higher temperatures in those seasons. The results of the sensitivity analysis showed that NH 3 was the most critical anthropogenic emission to the urban-scale N depositions, revealing the importance of the strategy to mitigate NH 3 reduction. The findings of this study provide a basic understanding of urban-scale N deposition in terms of atmospheric chemistry and anthropogenic emission of N compounds. [Display omitted] • An urban-scale analysis of nitrogen (N) deposition in Japan was conducted using CMAQ. • Calculated N depositions replicate the observed data in the same order of magnitude. • N deposition was high in spring and summer because of the high volatility of NH 3. • The sensitivity of NH 3 emissions to N depositions was 100 times higher than that of NO x. • NH 3 reduction is the key approach to mitigate urban-scale N deposition in Japan. [ABSTRACT FROM AUTHOR]

Abstract: Local agricultural emissions contribute significantly to the atmospheric reactive nitrogen loads of Danish terrestrial ecosystems. In the vicinity of the sources this may be up to 6–8kgNha−1 yr−1 depending on location and ecosystem type. This contribution arises from dry deposition of gas phase ammonia derived from local livestock production. Long-range transport, however, often constitutes the largest contribution to the overall atmospheric terrestrial reactive nitrogen loadings in Denmark. This is often in the range 10–15kgNha−1 yr−1 and consists mainly of aerosol phase nitrate and ammonium (reaction products of nitrogen oxides and ammonia), but also dry deposition of other reactive nitrogen compounds (mainly nitrogen oxides in the form of gas phase nitric acid and nitrogen dioxide). In Denmark’s environmental management of the sensitive terrestrial ecosystems modelling tools are required that account for both the local and the long-range transported contributions. This motivated development of the Danish Ammonia MOdelling System (DAMOS) that has been successfully applied to the assessment of atmospheric nitrogen loadings to sensitive Danish ecosystems. We present here three different examples of such assessments. Our results show that ecosystems located in Western Denmark (Case 1) receive the highest loads of atmospheric nitrogen depositions which generally exceed the critical load. This part of the country has the highest livestock density. In the Eastern part of the country, the atmospheric loadings are often below or close to the lower end of the interval for critical load values. These lower loads in Eastern Denmark (Case 2) are due to lower density of agricultural activities, as well as, lower precipitation rates, which leads to less wet deposition of reactive nitrogen. In general there is a gradient in atmospheric deposition over the country, with the highest depositions in the South-Western part of Denmark (Case 3) due to long-range transport contributions from North-Western Europe, but also due to local ammonia deposition associated with the high local emission from the high density livestock farming in this area. [Copyright &y& Elsevier]

Abstract. We use in situ observations from the Interagency Monitoring of PROtected Visual Environments (IMPROVE) network, the Midwest Ammonia Monitoring Project, 11 surface site campaigns as well as Infrared Atmospheric Sounding Interferometer (IASI) satellite measurements with the GEOS-Chem model to investigate inorganic aerosol loading and atmospheric ammonia concentrations over the United States. IASI observations suggest that current ammonia emissions are underestimated in California and in the spring-time in the Midwest. In California this underestimate likely drives the underestimate in nitrate formation in the GEOS-Chem model. However in the remaining continental United States we find that the nitrate simulation is biased high (normalized mean bias > = 1.0) year-round, except in Spring (due to the underestimate in ammonia in this season). None of the uncertainties in precursor emissions, the uptake efficiency of N2O5 on aerosols, OH concentrations, the reaction rate for the formation of nitric acid, or the dry deposition velocity of nitric acid are able to explain this bias. We find that reducing nitric acid concentrations to 75% of their simulated values corrects the bias in nitrate (as well as ammonium) in the US. However the mechanism for this potential reduction is unclear and may be a combination of errors in chemistry, deposition and sub-grid near-surface gradients. This "updated" simulation reproduces PM and ammonia loading and captures the strong seasonal and spatial gradients in gas-particle partitioning across the United States. We estimate that nitrogen makes up 15-35% of inorganic fine PM mass over the US, and that this fraction is likely to increase in the coming decade, both with decreases in sulfur emissions and increases in ammonia emissions. [ABSTRACT FROM AUTHOR]

Human activities have intensely altered the global nitrogen cycle and produced nitrogenous gases of environmental significance, especially in China where the most serious atmospheric nitrogen pollution worldwide exists. We present a comprehensive assessment of ammonia (NH3), nitrogen oxides (NOx), and nitrous oxide (N2O) emissions in China based on a full cycle analysis. Total reactive nitrogen (Nr) emission more than doubled over the past three decades, during which the trend of increase slowed for NH3 emissions after 2000, while the trend of increase continued to accelerate for NOx and N2O emissions. Several hotspots were identified, and their Nr emissions were about 10 times higher than others. Agricultural sources take 95% of total NH3 emission; fossil fuel combustion accounts for 96% of total NOx emission; agricultural (51%) and natural sources (forest and surface water, 39%) both contribute to the N2O emission in China. Total atmospheric Nr emissions related health damage in 2008 in China reached US$19-62 billion, accounting for 0.4-1.4% of China's gross domestic product, of which 52-60% were from NH3 emission and 39-47% were from NOx emission. These findings provide policy makers an integrated view of Nr sources and health damage to address the significant challenges associated with the reduction of air pollution. [ABSTRACT FROM AUTHOR]

Nitrogen (N) has emerged in recent years as a key factor associated with global changes, with impacts on biodiversity, ecosystems functioning and human health. In order to ameliorate the effects of excessive N, safety thresholds have been established, such as critical loads (deposition fluxes) and levels (concentrations). For Mediterranean ecosystems, few studies have been carried out to assess these parameters. Our objective was therefore to determine the critical loads of N deposition and long-term critical levels of atmospheric ammonia for Mediterranean evergreen woodlands. For that we have considered changes in epiphytic lichen communities, which have been shown to be one of the most sensitive to excessive N. Based on a classification of lichen species according to their tolerance to N we grouped species into response functional groups, which we used as a tool to determine the critical loads and levels. This was done under Mediterranean climate, in evergreen cork-oak woodlands, by sampling lichen functional diversity and annual atmospheric ammonia concentrations and modelling N deposition downwind from a reduced N source (a cattle barn). By modelling the highly significant relationship between lichen functional groups and N deposition, the critical load was estimated to be below 26 kg (N) ha-1 yr-1, which is within the upper range established for other semi-natural ecosystems. By modelling the highly significant relationship of lichen functional groups with annual atmospheric ammonia concentration, the critical level was estimated to be below 1.9 µg m-3, in agreement with recent studies for other ecosystems. Taking into account the high sensitivity of lichen communities to excessive N, these values should be taken into account in policies that aim at protecting Mediterranean woodlands from the initial effects of excessive N. [ABSTRACT FROM AUTHOR]

Himalayan forests are biodiverse and support the cultural and economic livelihoods of their human communities. They are bounded to the south by the Indo-Gangetic Plain, which has among the highest concentrations of atmospheric ammonia globally. This source of excess nitrogen pushes northwards into the Himalaya, generating concern that Himalayan forests will be impacted. To estimate the extent to which atmospheric nitrogen is impacting Himalayan forests we focussed on lichen epiphytes, which are a well-established bioindicator for atmospheric nitrogen pollution. First, we reviewed published literature describing nitrogen thresholds (critical levels and loads) at which lichen epiphytes are affected, identifying a mean and confidence intervals based on previous research conducted across a diverse set of biogeographic and ecological settings. Second, we used estimates from previously published atmospheric chemistry models (EMEP-WRF and UKCA-CLASSIC) projected to the Himalaya with contrasting spatial resolution and timescales to characterise model variability. Comparing the lichen epiphyte critical levels and loads with the atmospheric chemistry model projections, we created preliminary estimates of the extent to which Himalayan forests are impacted by excess nitrogen; this equated to c. 80–85% and c. 95–98% with respect to ammonia and total nitrogen deposition, respectively. Recognising that lichens are one of the most sensitive bioindicators for atmospheric nitrogen pollution, our new synthesis of previous studies on this topic generated concern that most Himalayan forests are at risk from excess nitrogen. This is a desk-based study that now requires verification through biological surveillance, for which we provide key recommendations. • We reviewed nitrogen critical levels and loads for lichen biodindicators. • These thresholds were applied to Himalayan forests based on modelled nitrogen. • Over 80% of Himalayan forests exceeded critical levels and loads. • Lichen bioindicators signal potential for widespread negative effects associated with atmospheric nitrogen pollution. [ABSTRACT FROM AUTHOR]

In this work, four types of torrefaction atmosphere (N 2 , 14% O 2 , CO 2 , and NH 3) were employed during torrefaction pretreatment to regular the element distribution of biomass, then the effect of torrefaction pretreatment on subsequent pyrolysis behaviors was investigated. After torrefaction pretreatment, the content of carbon increased, while the content of oxygen sharply decreased. CO 2 atmosphere resulted in highest content of carbon, and NH 3 atmosphere resulted in lowest content of oxygen and highest content of nitrogen. The residual mass in TG curve increased after torrefaction pretreatment, resulting in lower mass loss rate at the DTG peaks. Meanwhile, the release amounts of H 2 O, CH 4 , CO 2 , and CO were highly related to the element distribution in torrefied biomass. As the increase of torrefaction temperature, the contents of ketones and acids decreased, while the content of phenols increased. Compared to other three types of torrefaction atmospheres (N 2 , CO 2 , and 14%O 2), NH 3 atmosphere resulted in lowest content of acids because of the Maillard reactions where majority of carbonyl group in the biomass was replaced by the NH 2 */NH* radicals. Thus, some nitrogen-containing components was detected after the NH 3 torrefaction pretreatment because of the incorporation of nitrogen element in torrefied biomass. • Four torrefaction atmospheres were employed in biomass torrefaction process. • CO 2 atmosphere resulted in highest carbon content. • NH 3 atmosphere resulted in lowest oxygen content and highest nitrogen content. • Torrefaction favored the formation of phenols, while hinder acids and ketones in bio-oil. • NH 3 atmosphere resulted in lowest content of acids in bio-oil, while highest content of N-containing chemicals. [ABSTRACT FROM AUTHOR]

With growing global demand for food, the agriculture sector worldwide is under pressure to intensify and expand, risking acceleration of existing negative biodiversity impacts. Agriculture is the dominant source of ammonia (NH 3) emissions, which can impact biodiversity directly through dry deposition as NH 3 and by wet deposition following conversion to ammonium (NH 4) in the atmosphere. Nitrogen deposition is one of the leading causes of global decline in biodiversity alongside changing land use and climate. Natura 2000 sites which are intended to protect important habitats and species across Europe, require strict levels of protection to ensure designated features achieve favourable conservation status. Many of these sites are nitrogen-limited, and/or contain sensitive species such as lichens or mosses. This project carried out ambient NH 3 monitoring on selected Irish Natura 2000 sites, in order to establish potential impacts from agricultural NH 3. Monitoring on twelve Natura 2000 sites observed concentrations ranging from 0.47 to 4.59 μg NH 3 m−3, from which dry deposition was calculated to be 1.22–11.92 kg N ha−1 yr−1. European Monitoring and Evaluation Programme (EMEP) was used to quantify wet deposited NH 4 and nitrogen oxides (NOx), in addition to dry deposited NOx on monitored sites. Estimated total nitrogen deposition ranged between 5.93 and 17.78 kg N ha−1 yr−1. On average across all monitored sites, deposition was comprised of 50.4%, 31.7%, 7.5%, and 10.3% dry NH 3 , wet NH 4 , dry NOx and wet NOx respectively. Implications for Irish agriculture are discussed in the light of both this monitoring and the European Commission Dutch Nitrogen Case (C 293/17 & C 294/17), highlighting a number of recommendations to aid compliance with the EU Habitats Directive (92/43/EEC). [Display omitted] • Ambient ammonia across twelve Natura 2000 sites was 0.47–4.59 μg NH 3 m−3. • Nitrogen deposition across twelve Natura 2000 sites was 5.93–17.78 kg N ha−1 yr−1. • Average nitrogen deposition comprised of 50.4% dry NH 3 & 31.7% wet NH 4. • Average nitrogen deposition comprised of 7.5% dry NOx & 10.3% wet NOx. • Agriculture is the primary source of biodiversity impacts from the more harmful NH 3. [ABSTRACT FROM AUTHOR]

The conversion of atmospheric nitrogen (N 2) to ammonia (NH 3) under mild conditions is quite challenging due to high stability of the triple covalent bond. Here we report that Bi-decorated BiOBr microspheres with plentiful oxygen vacancies (OVs) were successfully fabricated by one-step solvothermal strategy and used as effective photocatalysts for nitrogen fixation. The metallic Bi was reduced in-situ by glycerol and deposited on the surface of BiOBr microspheres. The synchronously generated OVs can serve as the activation center for nitrogen. Compared to pure BiOBr, Bi@BiOBr hetero-structured microspheres have higher specific surface area, superior visible-light utilization, more effective separation of photoexcited charge carriers, thus exhibiting more pronounced visible light photocatalytic N 2 fixation performance. Specifically, the N 2 reduction rate of the Bi@BiOBr-2 is 1350 μmol g−1 h−1, which is 11.8 times higher than pure BiOBr (114 μmol g−1 h−1). This study provides a simple and low energy consumption method for effective and stable photocatalytic N 2 fixation. A simple one-step hydrothermal strategy was applied to prepare the metallic Bi-decorated BiOBr microspheres with plentiful oxygen vacancies that is proved to be an effective photocatalyst to yield ammonia under visible light without any organic scavengers or noble-metal cocatalysts. [Display omitted] • A simple one-step hydrothermal strategy was used to prepare the Bi@BiOBr with OVs. • The Bi and OVs increase the light absorbance and decrease the charge recombination. • The Bi@BiOBr-OVs shows effective and stable photocatalytic N 2 fixation property. [ABSTRACT FROM AUTHOR]

• Mixed dimensional C3N4/MoS2/Mn3O4 composite with broadening optical window for effective light harvesting. • Sandwich Structure enhanced charge transport, as well as large contact area for fast interfacial charge separation and photochemical reactions. • C3N4/MoS2/Mn3O4 catalyst can capture and activate N2, providing an alternative pathway to overcome the limitations at room temperature for N2 reduction. C 3 N 4 /MoS 2 /Mn 3 O 4 composite with mixed dimension was synthesized, and its properties of broadening optical window and large contact area could improve the light harvesting, charge transport and interfacial charge separation properties in photochemical reactions, which promise the ability to capture and activate N 2 , providing an alternative pathway to overcome the limitations at room temperature for N 2 reduction. The composite with suitable absorption edge and increased exposed surface sites are favourable for furnishing sufficient visible light-induced electrons to realize excellent and stable photoreduction of atmospheric N 2 into NH 3. The decoration of Mn 3 O 4 on C 3 N 4 /MoS 2 can not only consume part of hole for OER, but also inhabits the HER property of the composite and utilizes more electrons for N 2 reduction. The NH 3 generation rate is as high as 185 μmol h−1 g−1. The results presented herein provide new insights into rational design and engineering for the creation of highly active catalysts with visible light sensitive activity toward efficient, stable, and sustainable visible light N 2 fixation in mild conditions. [ABSTRACT FROM AUTHOR]

With atmospheric reactive nitrogen (Nr) emissions increasing globally, research into Nr deposition has attracted increasing attention, especially in remote environments. These ecosystems are very sensitive to global change, especially enhanced Nr deposition. Forest environments, in particular, are highlighted because of their important ecological function. We quantified atmospheric Nr concentrations and deposition over four years of continuous monitoring in a southeast Tibetan boreal forest ecosystem, an ecosystem in which forest biomass and carbon density are high around the world. Average annual bulk Nr deposition was 3.00 kg N ha−1 y−1, with those of reduced and oxidized species estimated at 1.60 and 1.40 kg N ha−1 y−1, respectively. Bulk deposition of both NH4+ and NO3− were controlled by precipitation amount: both Nr deposition and precipitation were highest in summer and lowest in winter. Dry deposition of NH3 and NO2 were 1.18 and 0.05 kg N ha−1 y−1, respectively. Atmospheric NH3 concentrations were in the range 1.15–3.53 mg N L−1, highest in summer and lowest in winter. In contrast, no clear trend in seasonal NO2 concentrations was observed. Monthly NO2 concentrations were 0.79–1.13 mg N L−1. Total Nr deposition (bulk plus dry) was 4.23 (3.00 + 1.23) kg N ha−1 y−1 in the forest. Reduced nitrogen was the dominant species. In conclusion, Nr deposition was in the range at which forest net productivity and carbon sequestration are sensitive to any variation in nitrogen input, so quantification of Nr deposition should continue and with greater detail. [ABSTRACT FROM AUTHOR]

The trends and variability of atmospheric nitrogen deposition in the Pearl River Delta (PRD) region for the period 2008–2017 were investigated by integrating ground- and satellite-based observations and a chemical transport model, in order to gauge the effects of emission reductions and meteorological variability. We show that dry deposition observation of oxidized nitrogen decreased at the rate of 2.4% yr−1 for a moderate reduction in NO x emissions by 27% in the past decade, while reduced nitrogen presented an increase at the rate of 2.3% yr−1 despite no regulated interventions for NH 3 emissions, which is likely related to changes in atmospheric gas-particle partitioning of NH 3 as reductions in SO 2 and NO x emissions. These results coincide with the trends in ground-level concentrations of oxidized and reduced nitrogen compounds in the atmosphere during 2008–2017. The changes in annual deposition fluxes of total oxidized and reduced nitrogen are not statistically significant trends and largely related with the inter-annual variability in their corresponding wet depositions, which reflects combined effects of variability in precipitation amount, and changes in atmospheric nitrogen compounds which dominates wet deposition of the oxidized and reduced forms. The meteorological conditions can mask 34% and 25% decrease in total oxidized and reduced nitrogen deposition on the decadal timescale, respectively. We conclude that meteorology-driven variability probably have masked the full response of oxidized nitrogen deposition to NO x emissions reduction. Our results also imply that persistent and integrated emission control strategies on NO x and NH 3 are needed to effectively reduce total nitrogen deposition fluxes towards the critical limit in the PRD region. Image 1 • Dry deposition of oxidized N decreased, whereas reduced forms showed an increase. • No detectable trend in wet deposition of oxidized and reduced N forms. • Meteorological variations masked decrease in oxidized N deposition. Meteorological variations can offset a 34% decrease in oxidized N deposition, and have masked the benefits from local NO x emission reduction on the decadal timescale. [ABSTRACT FROM AUTHOR]

Nitrogenase, a bacteria-based enzyme, is the sole enzyme that is able to generate ammonia by atmospheric nitrogen fixation. Thus, improved understanding of its utilization and developing methods to artificially activate it may contribute to basic research, as well as to the design of future artificial systems. Here, we present methods to artificially activate nitrogenase using photoinduced reactions. Two nitrogenase variants originating from Azotobacter vinelandii were examined using photoactivated CdS nanoparticles (NPs) capped with thioglycolic acid (TGA) or 2-mercaptoethanol (ME) ligands. The effect of methyl viologen (MV) as a redox mediator of hydrogen and ammonia generation was tested and analyzed. We further determined the NPs conductive band edges and their effect on the nitrogenase photoactivation. The nano-biohybrid systems comprising CdS NPs and nitrogenase were further imaged by transmission electron microscopy, visualizing their formation for the first time. Our results show that the ME-capped CdS NPs–nitrogenase enzyme biohybrid system with added MV as a redox mediator leads to a five-fold increase in the production of ammonia compared with the non-mediated biohybrid system; nevertheless, it stills lag behind the natural process rate. On the contrary, a maximal hydrogen generation amount was achieved by the αL158C MoFe-P and the ME-capped CdS NPs. [ABSTRACT FROM AUTHOR]