Articles de revues : « Ammoniac (NH3) »

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Nguyen, Lich Quang, Tu Cong Nguyen, Anh Tuan Ly, Thanh Phuc Tran, Pho Quoc Phan et Lam Huu Nguyen. « INVESTIGATION OF SENSITIVITY AND SELECTIVITY OF MWCNT–BASED SENSOR FOR AMMONIAC GAS DETECTION AT ROOM TEMPERATURE ». Science and Technology Development Journal 15, n^o 2 (30 juin 2012) : 62–69. http://dx.doi.org/10.32508/stdj.v15i2.1791.

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Gas sensors based on multi-walled carbon nanotube (MWCNT) for detecting gaseous molecules of ammoniac (NH3) were developed and investigated. MWCNT film was grown directly by chemical vapor deposition (CVD) method on Pt electrodes to fabricate sensor device. The CNT based – gas sensor is shown sensitively and selectively to NH3 gas at room temperature.

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Kherris, Sahraoui, Djallel Zebbar, Mohamed Makhlouf, Souhila Zebbar et Kouider Mostefa. « Etude et analyse d’une machine frigorifique à absorption-diffusion solaire NH3-H2O-H2 ». Journal of Renewable Energies 15, n^o 3 (23 octobre 2023) : 373–82. http://dx.doi.org/10.54966/jreen.v15i3.328.

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Cet article est consacré à la modélisation mathématique d’un système frigorifique solaire en vue de déterminer ses paramètres énergétiques. Le système en question est à absorption-diffusion fonctionnant avec le couple ammoniac-eau et l’hydrogène comme gaz inerte. Au cours de cette étude et pour la première fois, est utilisé dans le calcul de ce type de machine, un nouveau modèle mathématique pour le calcul des propriétés thermodynamiques du couple binaire ammoniac eau. A l’issue de cette étude, une analyse comparative des résultats a été effectuée sur la base des données de Bourseau.

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Nguyen, Thanh Phong, Joachim Clemens et Carsten Cuhls. « The effects of biofilter on the removal of greenhouse gases at anaerobic digestion plants ». Journal of Vietnamese Environment 6, n^o 1 (5 novembre 2014) : 65–68. http://dx.doi.org/10.13141/jve.vol6.no1.pp65-68.

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This study investigated the removal of gases such as methane (CH4), nitrous oxide (N2O) and ammonia (NH3) from biofilters in nine anaerobic digestion plants in Germany that treat biowaste. The treatment is in form of mechanical pre-treatment, anaerobic digestion followed by a composting with or without intensive aeration. The exhaust gases from the mechanical and anaerobic steps are treated by biofilters. In average, the biofilters removed 30% of total organic carbon (TOC), 50% of non-methane volatile organic carbon (NMVOC) and 51% NH3, whereas N2O concentrations increased by 26%. For CH4 the biofilters had only a small removal effect (6%). Nghiên cứu khảo sát sự loại bỏ những khí gây hiệu ứng nhà kính như CH4, N2O và NH3 từ những bể lọc khí sinh học ở chín nhà máy xử lý rác thải hữu cơ ở nước Đức bằng các biện pháp kỵ khí và hiếu khí. Rác hữu cơ được xử lý ở nhà máy thông qua các biện pháp như tiền xử lý bằng cơ học, kỵ khí và tiếp theo là hiếu khí với công nghệ thổi khí chủ động hoặc không thổi khí chủ động. Khí thải từ các quá trình cơ học và kỵ khí được xử lý bằng biện pháp lọc khí sinh học trước khi thải ra môi trường. Trung bình, những bể lọc khí sinh học loại bỏ 30% tổng lượng carbon hữu cơ, 50% những chất carbon hữu cơ bay hơi nhưng không phải khí methane và 51% khí ammoniac. Trong khi đó, nồng độ khí N2O tăng lên 26% sau khi qua bể lọc khí sinh học. Đối với khí methane, bể lọc khí sinh học có hiệu suất loại bỏ với loại khí này rất thấp chỉ 6%.

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Caner, Tolga, Solange Abdulnour-Nakhoul, Karen Brown, M. Toriqul Islam, L. Lee Hamm et Nazih L. Nakhoul. « Mechanisms of ammonia and ammonium transport by rhesus-associated glycoproteins ». American Journal of Physiology-Cell Physiology 309, n^o 11 (1 décembre 2015) : C747—C758. http://dx.doi.org/10.1152/ajpcell.00085.2015.

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In this study we characterized ammonia and ammonium (NH3/NH4+) transport by the rhesus-associated (Rh) glycoproteins RhAG, Rhbg, and Rhcg expressed in Xenopus oocytes. We used ion-selective microelectrodes and two-electrode voltage clamp to measure changes in intracellular pH, surface pH, and whole cell currents induced by NH3/NH4+ and methyl amine/ammonium (MA/MA+). These measurements allowed us to define signal-specific signatures to distinguish NH3 from NH4+ transport and to determine how transport of NH3 and NH4+ differs among RhAG, Rhbg, and Rhcg. Our data indicate that expression of Rh glycoproteins in oocytes generally enhanced NH3/NH4+ transport and that cellular changes induced by transport of MA/MA+ by Rh proteins were different from those induced by transport of NH3/NH4+. Our results support the following conclusions: 1) RhAG and Rhbg transport both the ionic NH4+ and neutral NH3 species; 2) transport of NH4+ is electrogenic; 3) like Rhbg, RhAG transport of NH4+ masks NH3 transport; and 4) Rhcg is likely to be a predominantly NH3 transporter, with no evidence of enhanced NH4+ transport by this transporter. The dual role of Rh proteins as NH3 and NH4+ transporters is a unique property and may be critical in understanding how transepithelial secretion of NH3/NH4+ occurs in the renal collecting duct.

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Rosso, L., et M. E. Tuckerman. « Solid-state proton conduction : An ab initio molecular dynamics investigation of ammonium perchlorate doped with neutral ammonia ». Pure and Applied Chemistry 76, n^o 1 (1 janvier 2004) : 49–61. http://dx.doi.org/10.1351/pac200476010049.

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The charge-transport mechanism in solid ammonium perchlorate crystal exposed to an ammonia-rich environment is studied using ab initio molecular dynamics. Ammonium perchlorate is an ionic crystal composed of NH4+ and ClO4- ; units that possesses an orthorhombic phase at T < 513 K and a cubic phase at T > 513 K. Exposure to an ammonia-rich atmosphere allows ammonia molecules to be absorbed into the crystal at interstitial sites. It has been proposed that these neutral ammonias can form short-lived N2H7+ complexes with the NH4+ ions allowing proton transfer between them, thereby enhancing the conductivity considerably. To date, however, there has been no direct evidence of this proposed mechanism. In this paper, ab initio molecular dynamics techniques are employed to explore this mechanism. By comparing computed infrared spectra of the pure and ammonia-doped crystals, we observe a significant broadening of the NH stretch peak into a lower frequency region, indicating through an experimentally verifiable observable, the formation of hydrogen bonds between NH3 and NH4+ units. This suggestion is confirmed by direct observation of N2H7+ complexes from the trajectory. Comparison of the diffusion constants of NH4+ in the pure and doped crystals yields a ratio that is comparable to the experimentally measured conductivity ratio and clearly shows an enhanced positive charge mobility. Finally, compelling evidence suggesting the possibility of an ammonia umbrella inversion following proton transfer from NH4+ and NH3 is obtained.

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Roßmeier, Thomas, et Nikolaus Korber. « Erstmalige Charakterisierung der Ammoniak-Proton-Komplexe [(NH3)3H]+ und [(NH3)4H]+ in den Kristallstrukturen von (NH4)3AsS4 · 5 NH3 und (NH4)3SbS4 · 8 NH3 / First Characterization of the Ammonia-Proton-Complexes [(NH3)3H]+ and [(NH3)4H]+ in the Crystal Structures of (NH4)3AsS4 · 5 NH3 and (NH4)3SbS4 · 8 NH3 ». Zeitschrift für Naturforschung B 58, n^o 7 (1 juillet 2003) : 672–77. http://dx.doi.org/10.1515/znb-2003-0711.

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The compounds (NH4)3AsS4· 5 NH3 (1) and (NH4)3SbS4· 8 NH3 (2) were prepared by the reaction of Na3AsS4 and Na3SbS4 with a proton-charged ion exchange material in liquid ammonia and characterized by low temperature single crystal X-ray structure analysis. The ammonium-ammoniates show H3N-H···N-hydrogen bonds between the ammonium ion and ammonia molecules ranging from 1.86 to 2.55 Å (DHA-angles: 145 - 173°) and H3N-H···S-bonds to the thioanions between 2.36 and 2.97 Å (DHA-angles: 130 - 176°). The former of the interactions are responsible for the formation of [(NH3)2H]+, [(NH3)3H]+ and [(NH3)4H]+-complexes, the last two of which were characterized by X-ray analysis for the first time.

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Singh, S., et U. C. Kulshrestha. « Abundance and distribution of gaseous ammonia and particulate ammonium at Delhi (India) ». Biogeosciences Discussions 9, n^o 1 (5 janvier 2012) : 191–207. http://dx.doi.org/10.5194/bgd-9-191-2012.

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Abstract. This study reports abundance and distribution of gaseous NH3 and particulate NH4+ at Delhi. Gaseous NH3 and particulate NH4+ concentrations were measured during pre monsoon, monsoon and postmonsoon seasons of the years 2010 and 2011. Average concentrations of gaseous NH3 during premonsoon, monsoon and post monsoon seasons were recorded as 26.4, 33.2 and 32.5 μg m−3, respectively. Gaseous NH3 concentrations were the highest during monsoon due to decay and decomposition of plants and other biogenic material under wet conditions which emit NH3. The results showed that particulate NH4+ was always lower than the gaseous NH3 during all the seasons. The concentrations of particulate NH4+ were recorded as 11.6, 22.9 and 8.5 μg m−3 during premonsoon, monsoon and postmonsoon seasons, respectively. The percent fraction of particulate NH4+ was noticed highest during monsoon season due to increased humidity levels. On anaverage, 33.3 % of total N-NHx was present as particulate NH4+. Higher concentrations of NH3 noticed during night time may be due to stable atmospheric conditions. Study highlighted that as compared to rural sites, urban sites showed higher concentrations of gaseous NH3 in India which may be due to higher population density, human activities and poor sanitation arrangements.

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Singh, S., et U. C. Kulshrestha. « Abundance and distribution of gaseous ammonia and particulate ammonium at Delhi, India ». Biogeosciences 9, n^o 12 (7 décembre 2012) : 5023–29. http://dx.doi.org/10.5194/bg-9-5023-2012.

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Abstract. This study reports abundance and distribution of gaseous NH3 and particulate NH4&plus; at Delhi. Gaseous NH3 and particulate NH4&plus; concentrations were measured during pre-monsoon, monsoon and post-monsoon seasons of the years 2010 and 2011. Average concentrations of gaseous NH3 during pre-monsoon, monsoon and post-monsoon seasons were recorded as 26.4, 33.2 and 32.5 μg m−3, respectively. Gaseous NH3 concentrations were the highest during monsoon, thought to be due to decay and decomposition of plants and other biogenic material under wet conditions, leading to increased NH3 emission. The results showed that particulate NH4&plus; was always lower than the gaseous NH3 during all the seasons. The concentrations of particulate NH4&plus; were recorded as 11.6, 22.9 and 8.5 μg m−3 during pre-monsoon, monsoon and post-monsoon seasons, respectively. The percent fraction of particulate NH4&plus; was noticed to be highest during the monsoon season, which is attributed to increased humidity levels favouring partitioning into the aerosol phase. On an average, 33.3% of total N-NHx was present as particulate NH4&plus;. Higher concentrations of NH3 noticed during night time may be due to stable atmospheric conditions. The study highlighted that, as compared with rural sites, urban sites showed higher concentrations of gaseous NH3 in India, which may be due to higher population density, human activities and poor sanitation arrangements.

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Flessner, M. F., R. Mejia et M. A. Knepper. « Ammonium and bicarbonate transport in isolated perfused rodent long-loop thin descending limbs ». American Journal of Physiology-Renal Physiology 264, n^o 3 (1 mars 1993) : F388—F396. http://dx.doi.org/10.1152/ajprenal.1993.264.3.f388.

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Ammonium accumulates in the renal medullas of antidiuretic mammals. The accumulation process is thought to involve countercurrent multiplication, energy-dependent recycling between the ascending and descending limbs of Henle's loop. To investigate the role of the long-loop thin descending limb (LDL) in countercurrent multiplication of ammonium, we have perfused outer medullary and inner medullary subsegments of the chinchilla LDL (and inner medullary subsegments of rat LDL) in vitro and measured the fluxes of total ammonia and total CO2. No spontaneous fluxes of total ammonia or total CO2 occurred in the absence of imposed concentration gradients. When transepithelial concentration gradients were imposed, passive total ammonia and total CO2 transport were observed in all subsegments, although the permeabilities varied with distance along the descending limb. Passive total ammonia transport occurred through a combination of NH3 and direct NH4+ permeation. The outer medullary segment was the most permeable to NH4+. The deep inner medullary segment was the most permeable to bicarbonate. Addition of carbonic anhydrase to the lumen accelerated passive NH3 entry in the outer medullary LDL, indicating that little or no luminal carbonic anhydrase is endogenously present. The passive secretion of NH4+ and NH3 into the LDL may contribute to the countercurrent multiplication of ammonium in the rodent renal medulla.

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Kriška, Tomáš, Petr Škarpa et Jiří Antošovský. « Effect of Natural Liquid Hydroabsorbents on Ammonia Emission from Liquid Nitrogen Fertilizers and Plant Growth of Maize (Zea Mays L.) under Drought Conditions ». Plants 12, n^o 4 (7 février 2023) : 728. http://dx.doi.org/10.3390/plants12040728.

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The use of mineral nitrogen (N) fertilizers is associated with significant nitrogen loss through the volatilization. Ammonia (NH3) emissions are common from fertilizers with amide (NH2) and ammonium (NH4) nitrogen forms applied to the soil surface without incorporation. The objective of the laboratory and greenhouse pot experiments was to verify the hypothesis that liquid mineral fertilizers and fertilizer solutions containing N-NH2 and N-NH4 applied to the soil surface in combination with natural hydroabsorbents (NHAs) will reduce the volatilization of nitrogen. The effect of NHAs addition to urea ammonium nitrate (UAN) fertilizer and urea, ammonium nitrate (AN) and ammonium sulphate (AS) solutions was evaluated in a laboratory experiment. The effect of the two types of NHAs (acidic and neutral) was compared with the control (UAN) and its mixture with the commercially used urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT). The proportion of volatilized NH3 of the total N from the examined fertilizers applied to the soil surface was determined by the titration method. Subsequently, the effect of fertilization with UAN and its mixture with NHAs and NBPT on the growth of maize under the drought conditions was verified in a greenhouse pot experiment. While the addition of NBPT resulted in a reduction of NH3 emission for the fertilizers containing NH2 (UAN, urea solution), a decrease in volatilization after the addition of both acidic and neutral NHA was observed especially for UAN. A reduction in ammonia emission was also observed for AS after the addition of acidic NHA. The addition of both NHAs and NBPT to UAN increased the utilization of nitrogen from the applied fertilizer, which was reflected by an increase in chlorophyll content and increased CO2 assimilation by maize plants grown under the drought stress. UAN fertilizer combined with acidic NHA and NBPT significantly increased aboveground biomass production and root system capacity of maize. Significant increases in UAN nitrogen recovery were observed for all examined additives (UI and both types of NHAs). In addition to the known effects of hydroabsorbents, especially their influence on soil physical and biological properties and soil water retention, the effect of NHAs application in combination with UAN and AS solutions on the reduction of gaseous N loss, maize plant growth and fertilizer nitrogen recovery was found.

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Sutton, M. A., Y. S. Tang, U. Dragosits, N. Fournier, A. J. Dore, R. I. Smith, K. J. Weston et D. Fowler. « A Spatial Analysis of Atmospheric Ammonia and Ammonium in the U.K. » Scientific World JOURNAL 1 (2001) : 275–86. http://dx.doi.org/10.1100/tsw.2001.313.

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As measures are implemented internationally to reduce SO2 and NOx emissions, attention is falling on the contribution of NH3 emissions to acidification, nitrogen eutrophication, and aerosol formation. In the U.K., a monitoring network has been established to measure the spatial distribution and long-term trends in atmospheric gaseous NH3 and aerosol NH4+. At the same time, an atmospheric chemistry and transport model, FRAME, has been developed with a focus on reduced nitrogen (NHx). The monitoring data are important to evaluate the model, while the model is essential for a more detailed spatial assessment. The national network is established with over 80 sampling locations. Measurements of NH3 and NH4+ (at up to 50 sites) have been made using a new low-cost denuder-filterpack system. Additionally, improved passive sampling methods for NH3 have been applied to explore local variability. The measurements confirm the high spatial variability of NH3 (annual means 0.06 to 11 mg NH3 m�3), consistent with its nature as a primary pollutant emitted from ground-level sources, while NH4+, being a slowly formed secondary product, shows much less spatial variability (0.14 to 2.4 mg NH4+ m�3). These features are reproduced in the FRAME model, which provides estimates at a 5-km level. Analysis of the underlying NH3 emission inventory shows that sheep emissions may have been underestimated and nonagricultural sources overestimated relative to emissions from cattle. The combination of model and measurements is applied to estimate spatial patterns of dry deposition to different vegetation types. The combined approach provides the basis to assess NHx responses across the U.K. to international emission controls.

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Sauerwein, Meike, et Chak Keung Chan. « Heterogeneous uptake of ammonia and dimethylamine into sulfuric and oxalic acid particles ». Atmospheric Chemistry and Physics 17, n^o 10 (23 mai 2017) : 6323–39. http://dx.doi.org/10.5194/acp-17-6323-2017.

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Abstract. Heterogeneous uptake is one of the major mechanisms governing the amounts of short-chain alkylamines and ammonia (NH3) in atmospheric particles. Molar ratios of aminium to ammonium ions detected in ambient aerosols often exceed typical gas phase ratios. The present study investigated the simultaneous uptake of dimethylamine (DMA) and NH3 into sulfuric and oxalic acid particles at gaseous DMA ∕ NH3 molar ratios of 0.1 and 0.5 at 10, 50 and 70 % relative humidity (RH). Single-gas uptake and co-uptake were conducted under identical conditions and compared. Results show that the particulate dimethyl-aminium/ammonium molar ratios (DMAH ∕ NH4) changed substantially during the uptake process, which was severely influenced by the extent of neutralisation and the particle phase state. In general, DMA uptake and NH3 uptake into concentrated H2SO4 droplets were initially similarly efficient, yielding DMAH ∕ NH4 ratios that were similar to DMA ∕ NH3 ratios. As the co-uptake continued, the DMAH ∕ NH4 gradually dropped due to a preferential uptake of NH3 into partially neutralised acidic droplets. At 50 % RH, once the sulfate droplets were neutralised, the stronger base DMA displaced some of the ammonium absorbed earlier, leading to DMAH ∕ NH4 ratios up to four times higher than the corresponding gas phase ratios. However, at 10 % RH, crystallisation of partially neutralised sulfate particles prevented further DMA uptake, while NH3 uptake continued and displaced DMAH+, forming almost pure ammonium sulfate. Displacement of DMAH+ by NH3 has also been observed in neutralised, solid oxalate particles. The results can explain why DMAH ∕ NH4 ratios in ambient liquid aerosols can be larger than DMA ∕ NH3, despite an excess of NH3 in the gas phase. An uptake of DMA to aerosols consisting of crystalline ammonium salts, however, is unlikely, even at comparable DMA and NH3 gas phase concentrations.

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Smith, CJ, JR Freney et WJ Bond. « Ammonia volatilisation from soil irrigated with urban sewage effluent ». Soil Research 34, n^o 5 (1996) : 789. http://dx.doi.org/10.1071/sr9960789.

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Losses of ammonia (NH3) following sewage effluent irrigation of pasture were measured under different climatic conditions at Wagga Wagga, New South Wales. Ammonia volatilisation was measured by the micrometeorological mass balance technique using 2 different passive samplers, and by an indirect technique based on the measurements of ammoniacal-N (NH4+ + NH3) concentration, pH, and temperature of the soil solution in the 0–3 mm soil layer, and wind speed at 1.2 m above the soil surface. Maximal NH3 emission rates were measured directly following the effluent-irrigation. There was reasonable agreement between the 2 different passive gas samplers used to measure NH3 volatilisation. The NH3 volatilised was well related to the product of wind speed and the equilibrium ammonia concentration (calculated from the soil solution measurements) as was found in other studies. In addition, NH3 flux density was strongly related to evaporation; that is, when the water (effluent) evaporated NH3 was lost to the atmosphere. Under high evaporative conditions, a maximum of 24% of the ammoniacal-N in the effluent was lost by volatilisation within 2 days of application.

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Leaist, DG. « Proton-Coupled Transport of Ammonia in Aqueous Hydrochloric Acid ». Australian Journal of Chemistry 38, n^o 2 (1985) : 249. http://dx.doi.org/10.1071/ch9850249.

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Ternary diffusion in aqueous ammonia + hydrochloric acid solutions has been measured at 25°C. It is shown that the transport coefficients can be successfully predicted from the mobilities of H+, Cl -, NH4+, and un- ionized ammonia species present in the solutions. When an ammonia concentration gradient is prepared in a solution containing excess acid, the region of the solution with the higher ammonia concentration is depleted in H+ by formation of ammonium ion: NH3+H+ ↔ NH4+. As highly mobile H+ diffuses up the ammonia gradient, there is counterflow of NH4+ in order to maintain electroneutrality . This mechanism leads to rapid diffusion of the ammonia component as NH4+. Binary diffusion coefficients of aqueous ammonia have also been measured. Extrapolation gives 2.08(�0.01) × 10-2m2 s-1 for the limiting diffusion coefficient of un-ionized ammonia, a value 6% greater than the limiting diffusion coefficient of the ammonium ion.

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Park, Junsu, Eunhye Kim, Sangmin Oh, Haeri Kim, Soontae Kim, Yong Pyo Kim et Mijung Song. « Contributions of Ammonia to High Concentrations of PM2.5 in an Urban Area ». Atmosphere 12, n^o 12 (14 décembre 2021) : 1676. http://dx.doi.org/10.3390/atmos12121676.

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Atmospheric ammonia (NH3) plays a critical role in PM2.5 pollution. Data on atmospheric NH3 are scanty; thus, the role of NH3 in the formation of ammonium ions (NH4+) in various environments is understudied. Herein, we measured concentrations of NH3, PM2.5, and its water-soluble SO42−, NO3−, and NH4+ ions (SNA) at an urban site in Jeonju, South Korea from May 2019 to April 2020. During the measurement period, the average concentrations of NH3 and PM2.5 were 10.5 ± 4.8 ppb and 24.0 ± 12.8 μg/m3, respectively, and SNA amounted to 4.3 ± 3.1, 4.4 ± 4.9, and 1.6 ± 1.8 μg/m3, respectively. A three-dimensional photochemical model analysis revealed that a major portion of NH3, more than 88%, originated from Korea. The enhancement of the ammonium-to-total ratio of NH3, NHX (NHR = [NH4+]/[NH4+] + [NH3]) was observed up to ~0.61 during the increase of PM2.5 concentration (PM2.5 ≥ 25 μg/m3) under low temperature and high relative humidity conditions, particularly in winter. The PM2.5 and SNA concentrations increased exponentially as NHR increased, indicating that NH3 contributed significantly to SNA formation by gas-to-particle conversion. Our study provided experimental evidence that atmospheric NH3 in the urban area significantly contributed to SNA formation through gas-to-particle conversion during PM2.5 pollution episodes.

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Flessner, M. F., et M. A. Knepper. « Ammonium and bicarbonate transport in isolated perfused rodent ascending limbs of the loop of Henle ». American Journal of Physiology-Renal Physiology 264, n^o 5 (1 mai 1993) : F837—F844. http://dx.doi.org/10.1152/ajprenal.1993.264.5.f837.

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Ammonium accumulates in the renal medullas of antidiuretic animals, presumably due to countercurrent multiplication, driven by NH4+ absorption from ascending loops of Henle in the outer and inner medulla. Active absorption of NH4+ occurs in the thick ascending limb (TAL). But the passive transport properties of NH3 in the TAL and the transport of ammonium or HCO3- in the ascending thin limb (ATL) have not been studied in rodents. To investigate the potential role of the ascending limb segments in medullary accumulation of ammonium, we perfused isolated subsegments of the chinchilla ATL and of the rat ATL and TAL. After imposing concentration gradients of total ammonia or total CO2 across ATL subsegments, we found very high rates of transfer of both substances, implying that at physiological flow rates the tubule luminal fluid quickly equilibrates with the interstitium. In the medullary TAL, we found a passive NH4+ permeability of 17 x 10(-5) cm/s but a relatively low NH3 permeability of < 0.003 cm/s. The low NH3 permeability prevents backleak of NH3 when NH4+ is actively transported from the lumen. We conclude that the ATL acts as an equilibrating segment and the TAL has special permeability properties that enhance net ammonium absorption and therefore enhance medullary ammonium accumulation.

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Shahgodari, Shirin, Joan Llorens et Jordi Labanda. « Viability of Total Ammoniacal Nitrogen Recovery Using a Polymeric Thin-Film Composite Forward Osmosis Membrane : Determination of Ammonia Permeability Coefficient ». Polymers 16, n^o 13 (27 juin 2024) : 1834. http://dx.doi.org/10.3390/polym16131834.

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Total ammoniacal nitrogen (TAN) occurs in various wastewaters and its recovery is vital for environmental reasons. Forward osmosis (FO), an energy-efficient technology, extracts water from a feed solution (FS) and into a draw solution (DS). Asymmetric FO membranes consist of an active layer and a support layer, leading to internal concentration polarization (ICP). In this study, we assessed TAN recovery using a polymeric thin-film composite FO membrane by determining the permeability coefficients of NH4+ and NH3. Calculations employed the solution–diffusion model, Nernst–Planck equation, and film theory, applying the acid–base equilibrium for bulk concentration corrections. Initially, model parameters were estimated using sodium salt solutions as the DS and deionized water as the FS. The NH4+ permeability coefficient was 0.45 µm/s for NH4Cl and 0.013 µm/s for (NH4)2SO4 at pH < 7. Meanwhile, the NH3 permeability coefficient was 6.18 µm/s at pH > 9 for both ammonium salts. Polymeric FO membranes can simultaneously recover ammonia and water, achieving 15% and 35% recovery at pH 11.5, respectively.

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Pfisterer, Karin, et Nikolaus Korber. « Darstellung und Strukturaufklärung von Ammonium-tetraamminlithium-amidotrithiophosphat-Ammoniak(1/1) (NH4) [Li(NH3)4] [P(NH2)S3] · NH3 ». Zeitschrift für anorganische und allgemeine Chemie 628, n^o 4 (mai 2002) : 762. http://dx.doi.org/10.1002/1521-3749(200205)628:4<762 ::aid-zaac762>3.0.co;2-q.

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Gao, Y., J. C. Cornwell, D. K. Stoecker et M. S. Owens. « Effects of cyanobacterial-driven pH increases on sediment nutrient fluxes and coupled nitrification-denitrification in a shallow fresh water estuary ». Biogeosciences Discussions 9, n^o 1 (27 janvier 2012) : 1161–98. http://dx.doi.org/10.5194/bgd-9-1161-2012.

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Abstract. Summer cyanobacterial blooms caused an elevation in pH (9 to ~10.5) that lasted for weeks in the shallow and tidal-fresh region of the Sassafras River, a tributary of Chesapeake Bay (USA). Elevated pH promoted desorption of sedimentary inorganic phosphorus and facilitated conversion of ammonium (NH4+) to ammonia (NH3). In this study, we investigated pH effects on exchangeable NH4+ desorption, nutrient pore water diffusion and flux rates of NH4+, soluble reactive phosphorus (SRP), nitrate (NO3–), nitrification, denitrification, and oxygen consumption. pH elevation enhanced the desorption of exchangeable NH4+ because of NH3 formation from both pore water and adsorbed NH4+ pools. Progressive penetration of high pH from the overlying water into sediment promoted the release of SRP and total ammonium (NH4+ and NH3) into pore water. At elevated pH, high sediment-water effluxes of SRP and total ammonium were associated with reduction in nitrification, denitrification and oxygen consumption rates. Alkaline pH and the toxicity of NH3 may inhibit nitrification in the thin aerobic zone, simultaneously constraining coupled nitrification-denitrification with limited NO3– supply and high pH penetration into the anaerobic zone. Geochemical feedbacks to pH elevation, such as enhancement of dissolved nutrient effluxes and reduction in N2 loss via denitrification, may be responsible for the persistence of cyanobacterial blooms in shallow water ecosystems.

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Gao, Y., J. C. Cornwell, D. K. Stoecker et M. S. Owens. « Effects of cyanobacterial-driven pH increases on sediment nutrient fluxes and coupled nitrification-denitrification in a shallow fresh water estuary ». Biogeosciences 9, n^o 7 (25 juillet 2012) : 2697–710. http://dx.doi.org/10.5194/bg-9-2697-2012.

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Abstract. Summer cyanobacterial blooms caused an elevation in pH (9 to ~10.5) that lasted for weeks in the shallow and tidal-fresh region of the Sassafras River, a tributary of Chesapeake Bay (USA). Elevated pH promoted desorption of sedimentary inorganic phosphorus and facilitated conversion of ammonium (NH4+) to ammonia (NH3). In this study, we investigated pH effects on exchangeable NH4+ desorption, pore water diffusion and the flux rates of NH4+, soluble reactive phosphorus (SRP) and nitrate (NO3−), nitrification, denitrification, and oxygen consumption. Elevated pH enhanced desorption of exchangeable NH4+ through NH3 formation from both pore water and adsorbed NH4+ pools. Progressive penetration of high pH from the overlying water into sediment promoted the mobility of SRP and the release of total ammonium (NH4+ and NH3) into the pore water. At elevated pH levels, high sediment-water effluxes of SRP and total ammonium were associated with reduction of nitrification, denitrification and oxygen consumption rates. Alkaline pH and the toxicity of NH3 may inhibit nitrification in the thin aerobic zone, simultaneously constraining coupled nitrification–denitrification with limited NO3− supply and high pH penetration into the anaerobic zone. Geochemical feedbacks to pH elevation, such as enhancement of dissolved nutrient effluxes and reduction in N2 loss via denitrification, may enhance the persistence of cyanobacterial blooms in shallow water ecosystems.

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21

Wen, D., J. C. Lin, L. Zhang, R. Vet et M. D. Moran. « Modeling atmospheric ammonia and ammonium using a backward-in-time stochastic Lagrangian air quality model (STILT-Chem v0.7) ». Geoscientific Model Development Discussions 5, n^o 3 (12 septembre 2012) : 2745–88. http://dx.doi.org/10.5194/gmdd-5-2745-2012.

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Abstract. A new chemistry module of atmospheric ammonia (NH3) and ammonium (NH4+) was incorporated into a backward-in-time stochastic Lagrangian air quality model (STILT-Chem) that was originally developed to simulate the concentrations of a variety of gas-phase species at receptors. STILT-Chem simulates the transport of air parcels backward in time using ensembles of fictitious particles with stochastic motions, while simulating emissions, deposition and chemical transformation forward in time along trajectories identified by the backward-in-time simulations. The incorporation of the new chemistry module allows the model to simulate not only gaseous species, but also multi-phase species involving NH3 and NH4+. The model was applied to simulate concentrations of NH3 and particulate NH4+ at six sites in the Canadian province of Ontario for a six-month period in 2006. The model-predicted concentrations of NH3 and particulate NH4+ were compared with observations, which show broad agreement between simulated concentrations and observations. Since the model is based on back trajectories, the influence of each major process such as emission, deposition and chemical conversion on the concentration of a modeled species at a receptor can be determined for every upstream location at each time step. This makes it possible to quantitatively investigate the upstream processes affecting receptor concentrations. The modeled results suggest that the concentrations of NH3 at those sites were significantly and frequently affected by southwestern Ontario, northern Ohio, and nearby areas. NH3 is mainly contributed by emission sources whereas particulate NH4+ is mainly contributed by the gas-to-aerosol chemical conversion of NH3. Dry deposition is the largest removal process for both NH3 and particulate NH4+. This study revealed the contrast between agricultural versus forest sites. Not only were emissions of NH3 higher, but removal mechanisms (especially chemical loss for NH3 and dry deposition for NH4+) were less efficient for agricultural sites. This combination explains the significantly higher concentrations of NH3 and particulate NH4+ observed at agricultural sites.

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Meng, Zhaoyang, Xiaobin Xu, Weili Lin, Baozhu Ge, Yulin Xie, Bo Song, Shihui Jia et al. « Role of ambient ammonia in particulate ammonium formation at a rural site in the North China Plain ». Atmospheric Chemistry and Physics 18, n^o 1 (8 janvier 2018) : 167–84. http://dx.doi.org/10.5194/acp-18-167-2018.

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Abstract. The real-time measurements of NH3 and trace gases were conducted, in conjunction with semi-continuous measurements of water-soluble ions in PM2.5 at a rural site in the North China Plain (NCP) from May to September 2013 in order to better understand chemical characteristics of ammonia and the impact of secondary ammonium aerosols on formation in the NCP. Extremely high NH3 and NH4+ concentrations were observed after a precipitation event within 7–10 days following urea application. Elevated NH3 levels coincided with elevated NH4+, indicating that NH3 likely influenced particulate ammonium mass. For the sampling period, the average conversion ∕ oxidation ratios for NH4+ (NHR), SO42- (SOR), and NO3- (NOR) were estimated to be 0.30, 0.64, and 0.24, respectively. The increased NH3 concentrations, mainly from agricultural activities and regional transport, coincided with the prevailing meteorological conditions. The high NH3 level with NHR of about 0.30 indicates that the emission of NH3 in the NCP is much higher than needed for aerosol acid neutralisation, and NH3 plays an important role in the formation of secondary aerosols as a key neutraliser. The hourly data obtained were used to investigate gas–aerosol partitioning characteristics using the thermodynamic equilibrium model ISORROPIA-II. Modelled SO42-, NO3-, and NH3 values agree well with the measurements, while the modelled NH4+ values largely underestimate the measurements. Our observation and modelling results indicate that strong acids in aerosol are completely neutralised. Additional NH4+ exists in aerosol, probably a result of the presence of a substantial amount of oxalic and other diacids.

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Tang, Yuk S., Christine F. Braban, Ulrike Dragosits, Anthony J. Dore, Ivan Simmons, Netty van Dijk, Janet Poskitt et al. « Drivers for spatial, temporal and long-term trends in atmospheric ammonia and ammonium in the UK ». Atmospheric Chemistry and Physics 18, n^o 2 (22 janvier 2018) : 705–33. http://dx.doi.org/10.5194/acp-18-705-2018.

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Abstract. A unique long-term dataset from the UK National Ammonia Monitoring Network (NAMN) is used here to assess spatial, seasonal and long-term variability in atmospheric ammonia (NH3: 1998–2014) and particulate ammonium (NH4+: 1999–2014) across the UK. Extensive spatial heterogeneity in NH3 concentrations is observed, with lowest annual mean concentrations at remote sites (< 0.2 µg m−3) and highest in the areas with intensive agriculture (up to 22 µg m−3), while NH4+ concentrations show less spatial variability (e.g. range of 0.14 to 1.8 µg m−3 annual mean in 2005). Temporally, NH3 concentrations are influenced by environmental conditions and local emission sources. In particular, peak NH3 concentrations are observed in summer at background sites (defined by 5 km grid average NH3 emissions < 1 kg N ha−1 yr−1) and in areas dominated by sheep farming, driven by increased volatilization of NH3 in warmer summer temperatures. In areas where cattle, pig and poultry farming is dominant, the largest NH3 concentrations are in spring and autumn, matching periods of manure application to fields. By contrast, peak concentrations of NH4+ aerosol occur in spring, associated with long-range transboundary sources. An estimated decrease in NH3 emissions by 16 % between 1998 and 2014 was reported by the UK National Atmospheric Emissions Inventory. Annually averaged NH3 data from NAMN sites operational over the same period (n = 59) show an indicative downward trend, although the reduction in NH3 concentrations is smaller and non-significant: Mann–Kendall (MK), −6.3 %; linear regression (LR), −3.1 %. In areas dominated by pig and poultry farming, a significant reduction in NH3 concentrations between 1998 and 2014 (MK: −22 %; LR: −21 %, annually averaged NH3) is consistent with, but not as large as the decrease in estimated NH3 emissions from this sector over the same period (−39 %). By contrast, in cattle-dominated areas there is a slight upward trend (non-significant) in NH3 concentrations (MK: +12 %; LR: +3.6 %, annually averaged NH3), despite the estimated decline in NH3 emissions from this sector since 1998 (−11 %). At background and sheep-dominated sites, NH3 concentrations increased over the monitoring period. These increases (non-significant) at background (MK: +17 %; LR: +13 %, annually averaged data) and sheep-dominated sites (MK: +15 %; LR: +19 %, annually averaged data) would be consistent with the concomitant reduction in SO2 emissions over the same period, leading to a longer atmospheric lifetime of NH3, thereby increasing NH3 concentrations in remote areas. The observations for NH3 concentrations not decreasing as fast as estimated emission trends are consistent with a larger downward trend in annual particulate NH4+ concentrations (1999–2014: MK: −47 %; LR: −49 %, p < 0.01, n = 23), associated with a lower formation of particulate NH4+ in the atmosphere from gas phase NH3.

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Takaya, Chibi A., Kiran R. Parmar, Louise A. Fletcher et Andrew B. Ross. « Biomass-Derived Carbonaceous Adsorbents for Trapping Ammonia ». Agriculture 9, n^o 1 (9 janvier 2019) : 16. http://dx.doi.org/10.3390/agriculture9010016.

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The preparation of low-cost carbonaceous adsorbents for nitrogen recovery is of interest from agricultural and waste management perspectives. In this study, the gaseous ammonia (NH3) and aqueous ammonium (NH4+) sorption capacities have been measured for different types of carbonaceous chars produced under different conditions. The study includes a comparison of an oak-based hydrochar produced from hydrothermal carbonisation (HTC) at 250 °C with two biochars produced from slow pyrolysis at 450 °C and 650 °C, respectively. The chars were also chemically modified with H2SO4, H3PO4, H2O2, and KOH to investigate the potential for sorption enhancement. The highest sorption capacities for NH3 were observed for the hydrochars with typical uptake capacities ranging from 18–28 mg g−1 NH3. Sorption capacity for oak biochars is significantly lower and ranges from 4–8 mg g−1 for biochars produced at 450 °C and 650 °C, respectively. Hydrochar showed a substantially higher sorption capacity for NH3 despite its lower surface area. The CaCl2 extractable NH4+ following ammonia adsorption is incomplete. Typically, only 30–40% of the N is released upon washing with CaCl2 in form of NH4+. Post chemical modification of the chars resulted in only limited enhancement of char NH3 and NH4+ sorption. H3PO4 treatment showed the greatest potential for increasing NH3/NH4+ sorption in biochars, while KOH and H2O2 treatment increased NH3 sorption in the hydrochar. As only marginal increases to char surface area were observed following char treatment, these findings suggest that char surface functionality is more influential than surface area in terms of char NH3/NH4+ sorption.

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Abdoun, Khalid, Katarina Wolf, Gisela Arndt et Holger Martens. « Effect of ammonia on Na+ transport across isolated rumen epithelium of sheep is diet dependent ». British Journal of Nutrition 90, n^o 4 (octobre 2003) : 751–58. http://dx.doi.org/10.1079/bjn2003957.

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The cellular uptake of ammonia affects the intracellular pH (pHi) of polar and non-polar cells. A predominant uptake of NH3 and its intra-cellular protonation tend to alkalinise the cytoplasm, whereas a predominant uptake of NH4+ acidifies the cytoplasm by reversing this reaction. Hence, the well-known absorption of ammonia across the rumen epithelium probably causes a change in the pHi. The magnitude and direction of this change in pHi (acid or alkaline) depends on the relative transport rates of NH3 and NH4+. Consequently, the intra-cellular availability of protons will influence the activity of the Na+-H+ exchanger, which could affect transepithelial Na+ transport. The aim of the present study has been to test this possible interaction between ruminal ammonia concentrations and Na+ transport. The term ammonia is used to designate the sum of the protonated (NH4+) and unprotonated (NH3) forms. Isolated ruminal epithelium of sheep was investigated by using the Ussing-chamber technique in vitro. The present results indicate that ammonia inhibits Na+ transport across the rumen epithelium of hay-fed sheep, probably by binding intracellular protons and thus inhibiting Na+-H+ exchange. By contrast, ammonia stimulates Na+ transport in concentrate-fed and urea-fed sheep, which develop an adaptation mechanism in the form of an increased metabolism of ammonia in the rumen mucosa and/or an increased permeability of rumen epithelium to the charged ammonium ion (NH4+). Intracellular dissociation of NH4+ increases the availability of protons, which stimulate Na+ –H+ exchange. This positive effect of ruminal ammonia on Na+ absorption may significantly contribute to the regulation of osmotic pressure of the ruminal fluid, because intraruminal ammonia concentrations up to 40 mmol/l have been reported.

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Sharylo, D., et V. Kovalenko. « Use of glucose (С6P12O6) for stimulation of heterotrophic nitrification processes in biofilters of recirculating aquaculture systems (RAS) ». Ribogospodarsʹka nauka Ukraïni., n^o 1(59) (31 mars 2022) : 45–60. http://dx.doi.org/10.15407/fsu2022.01.045.

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Purpose.Investigate the possibility of using glucose (С6Н12О6) to stimulate heterotrophic nitrification processes in biofilters and reduce the content of ammonium nitrogen in the water of recirculating aquaculture systems (RAS). Methodology. The object of research was the processes of water purification in biofilters of RAS from nitrogen compounds harmful to fish. The subject of research is the rate of heterotrophic nitrification using glucose as a source of organic carbon to accelerate nitrification processes under conditions of critical ammonium nitrogen content in process water. The research was conducted in four experimental RAS of the Fisheries Laboratory of the Department of Aquaculture of NULES of Ukraine. During the experiment, the concentrations of ammonia-ammonium in the water of aqua systems were artificially increased to 2 mg/dm3 by adding ammonium chloride solution, and 10% glucose solution was added in the proportions of 1 cm3, 5 cm3 and 10 cm3 per 100 dm3 of process water. The content of nitrogen compounds in water was determined using the Ptero Test system (NО2-, NH3/NH4+). Evaluation of the effectiveness of biofiltration in different variants of the experiment was performed on the time of excretion of NH3/NH4+ and the physical condition of sterlet fry (Acipenser ruthenus), which acted as a test object. Findings.The effectiveness of using glucose solution as a biologically active substance to stimulate the excretion of ammonia-ammonium by bacteria of the RAS biofilter has been proved. The rate of decrease of the concentration of NH3-/NH4+ to an acceptable level (below 0.1 mg/dm3) in the experimental systems with 5 and 10 сm3 of glucose per 100 dm3 of water was 5 hours versus 7 hours in the control version and in the experimental system with 1 сm3 glucose per 100 dm3 of water. Originality. A study on the use of glucose to accelerate nitrification processes in biofilters of RAS under conditions of critical ammonia-ammonium content in water was conducted for the first time. PracticalValue. The proposed method of stimulating heterotrophic nitrification solves a number of problems associated with a sharp increase of the content of NH3/NH4+ in process water. The use of this method will allow to reduce the risk of death of cultivated aquatic organisms due to a sharp increase of the concentration of ammonia-ammonium in water during the period of establishment of biological balance or in emergency situations. At the same time, it should be taken into account that heterotrophic bacteria grow much faster than nitrifying ones and may outperform the latter in the competition for substrate area in biofilters, so the use of this method is advisable for a short time, if necessary to release process water from excess ammonia-ammonium. Keywords: RAS, biofilter, glucose, heterotrophicnitrification, sterlet.

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Ali, Anwar G., et Carol J. Lovatt. « Evaluating Analytical Procedures for Quantifying Ammonium in Leaf Tissue ». Journal of the American Society for Horticultural Science 120, n^o 5 (septembre 1995) : 871–76. http://dx.doi.org/10.21273/jashs.120.5.871.

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The effects of different methods of sample preparation, extraction, and storage on the recovery of the combined pool of ammonia plus ammonium (NH3 + NH4+) from `Washington' navel orange leaves previously incubated in solutions of increasing NH4 Cl concentrations were assessed. Procedures and instruments for quantifying NH3 + NH4+ were tested for their sensitivity, reproducibility, and freedom from interference by amino acids. Reliable recoveries of NH3 + NH4+ free from amino acid interference, were obtained with oven-dried (60C) leaves ground to pass through a 40-mesh screen, extracted by homogenization in 10% TCA or by shaking in 2% acetic acid, and then filtered and analyzed on the basis of differences in electrical conductance between the sample and the reference cell. Methods measuring NH3 + NH4+ in KCl extracts by reaction with salicylate-nitroprusside in the presence of hypochlorite were compromised by significant color formation due to amino acids. Using fresh or freeze-dried leaf samples resulted in lower recoveries than use of oven-dried samples. Storage at -20C of fresh or oven-dried leaf samples in 10% TCA before or after homogenization and filtration did not alter NH3 + NH4+ levels, whereas storage of these samples at 4C increased NH3 + NH4+ levels.

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Mattsson, M., B. Herrmann, M. David, B. Loubet, M. Riedo, M. R. Theobald, M. A. Sutton, D. Bruhn, A. Neftel et J. K. Schjoerring. « Temporal variability in bioassays of the stomatal ammonia compensation point in relation to plant and soil nitrogen parameters in intensively managed grassland ». Biogeosciences 6, n^o 2 (11 février 2009) : 171–79. http://dx.doi.org/10.5194/bg-6-171-2009.

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Abstract. The exchange of ammonia between crop canopies and the atmosphere depends on a range of plant parameters and climatic conditions. However, little is known about effects of management factors. We have here investigated the stomatal ammonia compensation point in response to cutting and fertilization of a grass sward dominated by Lolium perenne. Tall grass had a very low NH3 compensation point (around 1 nmol mol−1), reflecting the fact that leaf nitrogen (N) concentration was very low. During re-growth after cutting, leaf tissue concentrations of NO3−, NH4+, soluble N and total N increased along with apoplastic NH4+ concentrations. In contrast, apoplastic pH decreased resulting in largely unaltered NH3 compensation points. Nitrogen fertilization one week after cutting caused the apoplastic NH4+ concentration of the newly emerging leaves to increase dramatically. The NH3 compensation point peaked between 15 and 25 nmol mol−1 the day after the fertiliser was applied and thereafter decreased over the following 10 days until reaching the same level as before fertilisation. Ammonium concentrations in leaf apoplast, bulk tissue and litter were positively correlated (P=0.001) throughout the experimental period. Bulk tissue NH4+ concentrations, total plant N and soil NH4+ concentrations also showed a positive correlation. A very high potential for NH3 emission was shown by the plant litter.

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Balej, Jan. « Solubility in the System (NH4)2S2O8—NH3—H2O and Mean Activity Coefficients of Saturated Solutions of (NH4)2S2O8 ». Acta Chimica Slovaca 5, n^o 1 (1 avril 2012) : 12–14. http://dx.doi.org/10.2478/v10188-012-0002-6.

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Solubility in the System (NH4)2S2O8—NH3—H2O and Mean Activity Coefficients of Saturated Solutions of (NH4)2S2O8The solubility data of ammonium peroxodisulfate in aqueous ammonia solutions at 15.5 °C have been evaluated using the relative activity coefficient expansion. Using the known value of the mean activity coefficient of saturated solution of ammonium peroxodisulfate in pure water, values of the mean activity coefficients of this salt in the saturated solutions of the given system have been calculated.

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Claros, J., E. Jiménez, L. Borrás, D. Aguado, A. Seco, J. Ferrer et J. Serralta. « Short-term effect of ammonia concentration and salinity on activity of ammonia oxidizing bacteria ». Water Science and Technology 61, n^o 12 (1 juin 2010) : 3008–16. http://dx.doi.org/10.2166/wst.2010.217.

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A continuously aerated SHARON (single reactor high activity ammonia removal over nitrite) system has been operated to achieve partial nitritation. Two sets of batch experiments were carried out to study the effect of ammonia concentration and salinity on the activity of ammonia-oxidizing bacteria (AOB). Activity of AOB raised as free ammonia concentration was increased reaching its maximum value at 4.5 mg NH3-N l−1. The half saturation constant for free ammonia was determined (KNH3 = 0.32 mg NH3-N l−1). Activity decreased at TAN (total ammonium–nitrogen) concentration over 2,000 mg NH4-N l−1. No free ammonia inhibition was detected. The effect of salinity was studied by adding different concentrations of different salts to the biomass. No significant differences were observed between the experiments carried out with a salt containing or not containing NH4. These results support that AOB are inhibited by salinity, not by free ammonia. A mathematical expression to represent this inhibition is proposed. To compare substrate affinity and salinity inhibitory effect on different AOB populations, similar experiments were carried out with biomass from a biological nutrient removal pilot plant. The AOB activity reached its maximum value at 0.008 mg NH3-N l−1 and decreased at TAN concentration over 400 mg NH4-N l−1. These differences can be explained by the different AOB predominating species: Nitrosomonas europaea and N. eutropha in the SHARON biomass and Nitrosomonas oligotropha in the pilot plant.

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Viatte, Camille, Jean-Eudes Petit, Shoma Yamanouchi, Martin Van Damme, Carole Doucerain, Emeric Germain-Piaulenne, Valérie Gros et al. « Ammonia and PM2.5 Air Pollution in Paris during the 2020 COVID Lockdown ». Atmosphere 12, n^o 2 (27 janvier 2021) : 160. http://dx.doi.org/10.3390/atmos12020160.

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During the COVID-19 pandemic, the lockdown reduced anthropogenic emissions of NO2 in Paris. NO2 concentrations recorded in 2020 were the lowest they have been in the past 5 years. Despite these low-NO2 levels, Paris experienced PM2.5 pollution episodes, which were investigated here based on multi-species and multi-platform measurements. Ammonia (NH3) measurements over Paris, derived from a mini-DOAS (differential optical absorption spectroscopy) instrument and the Infrared Atmospheric Sounding Interferometer (IASI) satellite, revealed simultaneous enhancements during the spring PM2.5 pollution episodes. Using the IASI maps and the FLEXPART model, we show that long-range transport had a statistically significant influence on the degradation of air quality in Paris. In addition, concentrations of ammonium (NH4+) and PM2.5 were strongly correlated for all episodes observed in springtime 2020, suggesting that transport of NH3 drove a large component of the PM2.5 pollution over Paris. We found that NH3 was not the limiting factor for the formation of ammonium nitrate (NH4NO3), and we suggest that the conversion of ammonia to ammonium may have been the essential driver.

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Wolff, V., I. Trebs, T. Foken et F. X. Meixner. « Exchange of reactive nitrogen compounds : concentrations and fluxes of total ammonium and total nitrate above a spruce forest canopy ». Biogeosciences Discussions 6, n^o 6 (16 novembre 2009) : 10663–706. http://dx.doi.org/10.5194/bgd-6-10663-2009.

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Abstract. Total ammonium (tot-NH4+) and total nitrate (tot-NO3−) provide a chemically conservative quantity in the measurement of exchange processes of reactive nitrogen compounds ammonia (NH3), particulate ammonium (NH4+), nitric acid (HNO3), and particulate nitrate (NO3−), using the aerodynamic gradient method. Total fluxes were derived from concentration differences of total ammonium (NH3 and NH4+) and total nitrate (HNO3 and NO3−) measured at two levels. Gaseous species and related particulate compounds were measured selectively, simultaneously and continuously above a spruce forest canopy in south-eastern Germany in summer 2007. Measurements were performed using a wet-chemical two-point gradient instrument, the GRAEGOR. Median concentrations of NH3, HNO3, NH4−, and NO3− were 0.57, 0.12, 0.76, and 0.48 μg m−3, respectively. Total ammonium and total nitrate fluxes showed large variations depending on meteorological conditions, with concentrations close to zero under humid and cool conditions and higher concentrations under dry conditions. Mean fluxes of total ammonium and total nitrate in September 2007 were directed towards the forest canopy and were −65.77 ng m−2 s−1 and −41.02 ng m−2 s−1 (in terms of nitrogen), respectively. Their deposition was controlled by aerodynamic resistances only, with very little influence of surface resistances. Including measurements of wet deposition and findings of former studies at the study site on occult deposition (fog water interception), the total N deposition in September 2007 was estimated to 5.86 kg ha−1.

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Wolff, V., I. Trebs, T. Foken et F. X. Meixner. « Exchange of reactive nitrogen compounds : concentrations and fluxes of total ammonium and total nitrate above a spruce canopy ». Biogeosciences 7, n^o 5 (25 mai 2010) : 1729–44. http://dx.doi.org/10.5194/bg-7-1729-2010.

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Abstract. Total ammonium (tot-NH4+) and total nitrate (tot-NO3−) provide chemically conservative quantities in the measurement of surface exchange of reactive nitrogen compounds ammonia (NH3), particulate ammonium (NH4+), nitric acid (HNO3), and particulate nitrate (NO3−), using the aerodynamic gradient method. Total fluxes were derived from concentration differences of total ammonium (NH3 and NH4+) and total nitrate (HNO3 and NO3−) measured at two levels. Gaseous species and related particulate compounds were measured selectively, simultaneously and continuously above a spruce forest canopy in south-eastern Germany in summer 2007. Measurements were performed using a wet-chemical two-point gradient instrument, the GRAEGOR. Median concentrations of NH3, HNO3, NH4+, and NO3− were 0.57, 0.12, 0.76, and 0.48 μg m−3, respectively. Total ammonium and total nitrate fluxes showed large variations depending on meteorological conditions, with concentrations close to zero under humid and cool conditions and higher concentrations under dry conditions. Mean fluxes of total ammonium and total nitrate in September 2007 were directed towards the forest canopy and were −65.77 ng m−2 s−1 and −41.02 ng m−2 s−1 (in terms of nitrogen), respectively. Their deposition was controlled by aerodynamic resistances only, with very little influence of surface resistances. Including measurements of wet deposition and findings of former studies on occult deposition (fog water interception) at the study site, the total N deposition in September 2007 was estimated to 5.86 kg ha−1.

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Forte, Elena, Sergey A. Siletsky et Vitaliy B. Borisov. « In Escherichia coli Ammonia Inhibits Cytochrome bo3 But Activates Cytochrome bd-I ». Antioxidants 10, n^o 1 (25 décembre 2020) : 13. http://dx.doi.org/10.3390/antiox10010013.

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Interaction of two redox enzymes of Escherichia coli, cytochrome bo3 and cytochrome bd-I, with ammonium sulfate/ammonia at pH 7.0 and 8.3 was studied using high-resolution respirometry and absorption spectroscopy. At pH 7.0, the oxygen reductase activity of none of the enzymes is affected by the ligand. At pH 8.3, cytochrome bo3 is inhibited by the ligand, with 40% maximum inhibition at 100 mM (NH4)2SO4. In contrast, the activity of cytochrome bd-I at pH 8.3 increases with increasing the ligand concentration, the largest increase (140%) is observed at 100 mM (NH4)2SO4. In both cases, the effector molecule is apparently not NH4+ but NH3. The ligand induces changes in absorption spectra of both oxidized cytochromes at pH 8.3. The magnitude of these changes increases as ammonia concentration is increased, yielding apparent dissociation constants Kdapp of 24.3 ± 2.7 mM (NH4)2SO4 (4.9 ± 0.5 mM NH3) for the Soret region in cytochrome bo3, and 35.9 ± 7.1 and 24.6 ± 12.4 mM (NH4)2SO4 (7.2 ± 1.4 and 4.9 ± 2.5 mM NH3) for the Soret and visible regions, respectively, in cytochrome bd-I. Consistently, addition of (NH4)2SO4 to cells of the E. coli mutant containing cytochrome bd-I as the only terminal oxidase at pH 8.3 accelerates the O2 consumption rate, the highest one (140%) being at 27 mM (NH4)2SO4. We discuss possible molecular mechanisms and physiological significance of modulation of the enzymatic activities by ammonia present at high concentration in the intestines, a niche occupied by E. coli.

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Flessner, M. F., S. M. Wall et M. A. Knepper. « Permeabilities of rat collecting duct segments to NH3 and NH4+ ». American Journal of Physiology-Renal Physiology 260, n^o 2 (1 février 1991) : F264—F272. http://dx.doi.org/10.1152/ajprenal.1991.260.2.f264.

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We have measured NH3 and NH4+ permeability coefficients in collecting ducts from the cortex, outer medulla, and inner medulla of the rat kidney. Isolated collecting duct segments of the rat were perfused with bicarbonate-buffered solutions containing carbonic anhydrase to eliminate any pH disequilibrium in the tubule lumen. NH3 or NH4+ concentration gradients were set up between the bath and the lumen. By measuring the total CO2 and total ammonia concentrations in the bath, the perfusate, and collected fluid, the NH3 and NH4+ concentrations were determined. Then, using the flow rate in the tubule and the tubule dimensions, we calculated the apparent permeability in each collecting duct segment for NH3 and NH4+. The NH3 permeabilities were as follows: 0.002 cm/s in the inner medullary collecting duct, 0.012 cm/s in the outer medullary collecting duct, and 0.024 cm/s in the cortical collecting duct. The NH4+ permeabilities for all segments were on the order of 10(-5) cm/s or less. The relative permeability values for the two ammonium species are consistent with the view that the secretion observed in vivo in collecting ducts is due to passive diffusion of NH3 from the interstitium to the lumen of the duct, parallel with H+ secretion.

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Fernández, B., A. Vilar, M. Ben, C. Kennes et M. C. Veiga. « Partial Nitrification of Wastewater from an Aminoplastic Resin Producing Factory ». Water Science and Technology 52, n^o 10-11 (1 novembre 2005) : 517–24. http://dx.doi.org/10.2166/wst.2005.0731.

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Nitrification via nitrite was studied in two aerobic reactors treating wastewater from an aminoplastic resin producing factory at HRT varying between 1.37–1.89 and 2.45–3.63 days. Both reactors were fed with concentrations of 366, 450, 1099 and 1899mg N-NH4+/L. In general in the reactor operated at a lower HRT, the nitritation percentage decreased from 87.2 to 21.6%, while the nitratation percentage remained always lower than 2.5% (except in the last period) when the ammonium concentration was increased. This behaviour could be due to the inhibition of the ammonium and nitrite oxidation produced by high free ammonia concentrations up to 179.3mg N-NH3/L. In the reactor operated at a higher HRT, the nitritation percentage decreased and the nitratation percentage increased from 88.6 to 39.6% and from 0.65 to 35.7%, respectively, due to an increase of the dissolved oxygen concentration from 0.76 to 1.02mg O2/L. However, when ammonium was fed at a concentration of 1898.7mg N-NH4+/L, the nitritation increased and the nitratation decreased, probably as a result of the accumulation of free ammonia up to 2.04mg N-NH3/L, meaning that nitrite oxidizers were inhibited. Nitrite build-up was observed after each modification of ammonium concentration in the feed.

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Wolff, V., I. Trebs, C. Ammann et F. X. Meixner. « Aerodynamic gradient measurements of the NH3-HNO3-NH4NO3 ; triad using a wet chemical instrument : an analysis of precision requirements and flux errors ». Atmospheric Measurement Techniques Discussions 2, n^o 5 (8 octobre 2009) : 2423–82. http://dx.doi.org/10.5194/amtd-2-2423-2009.

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Abstract. The aerodynamic gradient method is widely used for flux measurements of ammonia, nitric acid, particulate ammonium nitrate (the NH3-HNO3-NH4NO3 triad) and other water-soluble reactive trace compounds. The surface exchange flux is derived from a measured concentration difference and micrometeorological quantities (turbulent exchange coefficient). The significance of the measured concentration difference is crucial for the significant determination of surface exchange fluxes. Additionally, measurements of surface exchange fluxes of ammonia, nitric acid and ammonium nitrate are often strongly affected by phase changes between gaseous and particulate compounds of the triad, which make measurements of the four individual species (NH3, HNO3, NH4+, NO3–) necessary for a correct interpretation of the measured concentration differences. We present here a rigorous analysis of results obtained with a multi-component, wet-chemical instrument, able to simultaneously measure gradients of both gaseous and particulate trace substances. Basis for our analysis are two field experiments, conducted above contrasting ecosystems (grassland, forest). Precision requirements of the instrument as well as errors of concentration differences and micrometeorological exchange parameters have been estimated, which, in turn, allows the establishment of thorough error estimates of the derived fluxes of NH3, HNO3, NH4+, and NO3–. Derived median flux errors for the grassland and forest field experiments were: 39 and 50% (NH3), 31 and 38% (HNO3), 62 and 57% (NH4+), and 47 and 68% (NO3–), respectively. Additionally, we provide the basis for using field data to characterize the instrument performance, as well as subsequent quantification of surface exchange fluxes and underlying mechanistic processes under realistic ambient measurement conditions.

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Wolff, V., I. Trebs, C. Ammann et F. X. Meixner. « Aerodynamic gradient measurements of the NH3-HNO3-NH4NO3 ; triad using a wet chemical instrument : an analysis of precision requirements and flux errors ». Atmospheric Measurement Techniques 3, n^o 1 (10 février 2010) : 187–208. http://dx.doi.org/10.5194/amt-3-187-2010.

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Abstract. The aerodynamic gradient method is widely used for flux measurements of ammonia, nitric acid, particulate ammonium nitrate (the NH3-HNO3-NH4NO3 triad) and other water-soluble reactive trace compounds. The surface exchange flux is derived from a measured concentration difference and micrometeorological quantities (turbulent exchange coefficient). The significance of the measured concentration difference is crucial for the significant determination of surface exchange fluxes. Additionally, measurements of surface exchange fluxes of ammonia, nitric acid and ammonium nitrate are often strongly affected by phase changes between gaseous and particulate compounds of the triad, which make measurements of the four individual species (NH3, HNO3, NH4+, NO3− necessary for a correct interpretation of the measured concentration differences. We present here a rigorous analysis of results obtained with a multi-component, wet-chemical instrument, able to simultaneously measure gradients of both gaseous and particulate trace substances. Basis for our analysis are two field experiments, conducted above contrasting ecosystems (grassland, forest). Precision requirements of the instrument as well as errors of concentration differences and micrometeorological exchange parameters have been estimated, which, in turn, allows the establishment of thorough error estimates of the derived fluxes of NH3, HNO3, NH4+, and NO3−. Derived median flux errors for the grassland and forest field experiments were: 39% and 50% (NH3), 31% and 38% (HNO3), 62% and 57% (NH4+), and 47% and 68% (NO3−), respectively. Additionally, we provide the basis for using field data to characterize the instrument performance, as well as subsequent quantification of surface exchange fluxes and underlying mechanistic processes under realistic ambient measurement conditions.

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Kleydman, Yekaterina, Nigel Yarlett et Thomas E. Gorrell. « Production of ammonia by Tritrichomonas foetus and Trichomonas vaginalis ». Microbiology 150, n^o 5 (1 mai 2004) : 1139–45. http://dx.doi.org/10.1099/mic.0.26939-0.

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Production of ammonia is difficult to find among the various studies of amino acid metabolism in protozoa. Several studies suggest that catabolism of arginine to ammonium is important for the growth of trichomonads. Trichomonads are amitochondriate zooflagellates that thrive under microaerophilic and anaerobic conditions. The authors were able to detect accumulation of ammonium ions and ammonia in cultures of Tritrichomonas foetus and Trichomonas vaginalis, including those resistant to metronidazole. Ammonium ions and ammonia were detected using the indophenol colorimetric method. Cells incubated overnight under an ambient oxygen gas phase had 0·9 mM soluble ammonium (NH4 + and NH3) or a 20 % greater concentration of ammonium relative to sterile growth medium that had been incubated similarly. Production of ammonia itself was confirmed by analysis of a wick that was moistened with sulfuric acid (20 mM) and placed above the liquid in sealed cultures of a strain of Trichomonas vaginalis. The wicks from these cultures captured the equivalent of 0·048 mM volatile ammonia (NH3) from the liquid as compared to 0·021 mM volatile ammonia from sterile medium after overnight incubation. Intact trichomonads, 0·7×106 cells ml−1 equivalent to 0·7 mg protein ml−1, incubated in Doran's buffer with or without (1 mM) l-arginine produced significant amounts of soluble ammonium (0·07 mM and 0·04 mM, respectively) during 60 min. The results indicate that ammonium ions and the more irritating ammonia are significant metabolites of trichomonads. In addition, based upon end-product amounts, it appears that the rate of arginine metabolism is of the same order of magnitude as that for carbohydrate metabolism by trichomonads.

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Xiao, Hai Ping, Qin Jian Yu et Lei Huang. « Kinetics of DeNOx Process by Ammonia Injection ». Advanced Materials Research 356-360 (octobre 2011) : 2131–35. http://dx.doi.org/10.4028/www.scientific.net/amr.356-360.2131.

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In order to discover reaction mechanism between ammonia and NOx, reaction process of ammonia and NOx was simulated from the point of kinetics. As a result, NOx removal efficiency was kept in 47.23% ~98.89% at 800°C~1000°C. When NH3/NO was equal or less than 1.5, NOx removal efficiency was enhanced obviously with NH3/NO increasing. NH2 was produced as an important intermediate product in NH3 decomposition. Firstly NH2 was formed in reactions between NH3 and free radicals such as OH, H, O, M. Then NO was directly reduced to N2 by NH2.Therefore, free radicals (especially for NH2, O and H) have important influence on removal efficiency of NOx during ammonia injection.

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Menkveld, H. W. H., et E. Broeders. « Recovery of ammonium from digestate as fertilizer ». Water Practice and Technology 12, n^o 3 (1 août 2017) : 514–19. http://dx.doi.org/10.2166/wpt.2017.049.

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Ammonia inhibition can be a major problem during anaerobic digestion of manure and municipal and industrial sludges. Anaerobic digestion is sensitive to higher NH3-N concentrations, which are inhibiting and at certain levels even toxic for methanogen bacteria. The Nijhuis Ammonium Recovery (AECO-NAR) system can solve this problem and removes ammonium from digestate or other substrate for digestion. The AECO-NAR is a physical-chemical process based on stripping of ammonia. The ammonium is recovered as ammonium sulphate, which can be used as a fertilizer for agricultural purposes. The AECO-NAR was proven to be a robust process with a stable ammonium removal efficiency of 85–90% for anaerobic digested manure, municipal and other organic waste waters. The cost effectiveness mainly depends on the concentration of NH4-N in the influent, scale of the installation, the availability of residual heat and the local value and market for ammonium sulphate. Above 2 g/l NH4-N the AECO-NAR system is competitive and at higher NH4-N concentrations more cost efficient compared to other state of the art nitrogen removal technologies and ranges between 1 and 3 €/kg N.

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Wasylishen, Roderick E., et Jan O. Friedrich. « Deuterium isotope effects on nuclear shielding constants and spin–spin coupling constants in the ammonium ion, ammonia, and water ». Canadian Journal of Chemistry 65, n^o 9 (1 septembre 1987) : 2238–43. http://dx.doi.org/10.1139/v87-373.

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Deuterium isotope effects on 15N chemical shifts have been investigated for the ammonium ion, ammonia, and aniline; 1Δ15N(2/1H) equals −293.3, −622.9, and −714.6 ppb respectively. Deviations from additivity are noted for NH4−nDn+ and NH3−nDn; these deviations follow the predictions of Jameson and Osten. For ammonia, examination of the proton nuclear magnetic resonance spectrum yields 1Δ1H(15/14N) = −2.0 ± 0.4 ppb and [Formula: see text]. An accurate value of −1545 ± 5 ppb was obtained for 1Δ17O(2/1H) in water. Derivatives of the heavy atom shielding constants with respect to extensions in the equilibrium bond length have been estimated for NH4+, NH3, and H2O; these derivatives are compared with the recent calculations of Chesnut. Deuterium isotope effects on 1J (15N,H) in ammonia and aniline have been measured for the first time. For the ammonium ion, deuterium isotope effects on 1J (15N,H) are in good agreement with the less accurate values we previously observed on 1J (14N,H). In the case of water, both primary and secondary deuterium isotope effects on 1J (17O,H) are less than 2%. The isotope effects on the spin–spin coupling constants observed here are compared with those previously reported for other hydrides in the literature.

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Pfisterer, Karin, et Nikolaus Korber. « ChemInform Abstract : Synthesis and Crystal Structure of Ammonium Tetraamminelithium Amidotrithiophosphate-Ammonia(1/1) (NH4)[Li(NH3)4] [P(NH2)S3]×NH3. » ChemInform 33, n^o 28 (20 mai 2010) : no. http://dx.doi.org/10.1002/chin.200228012.

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Brennan, Brian, Ciprian Briciu-Burghina, Sean Hickey, Thomas Abadie, Sultan M. al Ma Awali, Yan Delaure, John Durkan et al. « Pilot Scale Study : First Demonstration of Hydrophobic Membranes for the Removal of Ammonia Molecules from Rendering Condensate Wastewater ». International Journal of Molecular Sciences 21, n^o 11 (30 mai 2020) : 3914. http://dx.doi.org/10.3390/ijms21113914.

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Hydrophobic membrane contactors represent a promising solution to the problem of recycling ammoniacal nitrogen (N-NH4) molecules from waste, water or wastewater resources. The process has been shown to work best with wastewater streams that present high N-NH4 concentrations, low buffering capacities and low total suspended solids. The removal of N-NH4 from rendering condensate, produced during heat treatment of waste animal tissue, was assessed in this research using a hydrophobic membrane contactor. This study investigates how the molecular composition of rendering condensate wastewater undergo changes in its chemistry in order to achieve suitability to be treated using hydrophobic membranes and form a suitable product. The main objective was to test the ammonia stripping technology using two types of hydrophobic membrane materials, polypropylene (PP) and polytetrafluoroethylene (PTFE) at pilot scale and carry out: (i) Process modification for NH3 molecule removal and (ii) product characterization from the process. The results demonstrate that PP membranes are not compatible with the condensate waste as it caused wetting. The PTFE membranes showed potential and had a longer lifetime than the PP membranes and removed up to 64% of NH3 molecules from the condensate waste. The product formed contained a 30% concentrated ammonium sulphate salt which has a potential application as a fertilizer. This is the first demonstration of hydrophobic membrane contactors for treatment of condensate wastewater.

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Mayor, Álvaro, Mònica Reig, Xanel Vecino, José Luis Cortina et César Valderrama. « Advanced Hybrid System for Ammonium Valorization as Liquid Fertilizer from Treated Urban Wastewaters : Validation of Natural Zeolites Pretreatment and Liquid-Liquid Membrane Contactors at Pilot Plant Scale ». Membranes 13, n^o 6 (2 juin 2023) : 580. http://dx.doi.org/10.3390/membranes13060580.

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This study evaluates a hybrid system combining zeolites as a sorption stage and a hollow fiber membrane contactor (HFMC) for ammonia (NH3) recovery from treated urban wastewater. Ion exchange with zeolites was selected as an advanced pretreatment and concentration step before the HFMC. The system was tested with wastewater treatment plant (WWTP) effluent (mainstream, 50 mg N-NH4/L) and anaerobic digestion centrates (sidestream, 600–800 mg N-NH4/L) from another WWTP. Natural zeolite, primarily clinoptilolite, demonstrated effective desorption of retained ammonium using a 2% NaOH solution in a closed-loop configuration, resulting in an ammonia-rich brine that enabled over 95% NH3 recovery using polypropylene HFMCs. A 1 m3/h demonstration plant processed both urban wastewaters, which were pretreated by ultrafiltration, removing over 90% of suspended solids and 60–65% of COD. The 2% NaOH regeneration brines (2.4–5.6 g N-NH4/L) were treated in a closed-loop HFMC pilot system, producing 10–15% N streams with potential use as liquid fertilizers. The resulting ammonium nitrate was free of heavy metals and organic micropollutants, making it suitable for use as liquid fertilizer. This comprehensive N management solution for urban wastewater applications can contribute to local economies while achieving reduced N discharge and circularity goals.

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Corrêa, Darlena Caroline da Cruz, Abmael da Silva Cardoso, Mariane Rodrigues Ferreira, Débora Siniscalchi, Pedro Henrique de Almeida Gonçalves, Rodolfo Nussio Lumasini, Ricardo Andrade Reis et Ana Cláudia Ruggieri. « Ammonia Volatilization, Forage Accumulation, and Nutritive Value of Marandu Palisade Grass Pastures in Different N Sources and Doses ». Atmosphere 12, n^o 9 (13 septembre 2021) : 1179. http://dx.doi.org/10.3390/atmos12091179.

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The reduction in ammonia (NH3) losses from volatilization has significant implications in forage production. The objective of this study was to evaluate the impact of N fertilizers (urea, ammonium nitrate, and ammonium sulfate) and four doses (0, 90, 180 and 270 kg N ha−1) on N losses by NH3 volatilization, accumulation, and forage chemical composition of Urochloa brizantha cv Marandu. Two field experiments were conducted to measure NH3 losses using semi-open chambers. The forage accumulation and chemical composition were evaluated in the third experiment; the response variables included forage accumulation, crude protein (CP), and neutral detergent fiber (NDF). Compared to urea, ammonium nitrate and ammonium sulfate reduced NH3 losses by 84% and 87% and increased total forage accumulation by 14% and 23%, respectively. Forage accumulation rate and CP increased linearly with the N levels, while NDF contents decreased linearly with the N levels. In both experiments, NH3 losses and forage characteristics were different according to the rainfall pattern and temperature variations. Our results indicate that the use of nitric and ammoniacal fertilizers and the application of fertilizer in the rainy season constitute an efficient fertilizer management strategy to increase forage yield and decrease losses from volatilization of NH3.

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Nakhoul, Nazih L., Solange M. Abdulnour-Nakhoul, Emile L. Boulpaep, Edd Rabon, Eric Schmidt et L. Lee Hamm. « Substrate specificity of Rhbg : ammonium and methyl ammonium transport ». American Journal of Physiology-Cell Physiology 299, n^o 3 (septembre 2010) : C695—C705. http://dx.doi.org/10.1152/ajpcell.00019.2010.

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Rhbg is a nonerythroid membrane glycoprotein belonging to the Rh antigen family. In the kidney, Rhbg is expressed at the basolateral membrane of intercalated cells of the distal nephron and is involved in NH4+ transport. We investigated the substrate specificity of Rhbg by comparing transport of NH3/NH4+ with that of methyl amine (hydrochloride) (MA/MA+), often used to replace NH3/NH4+, in oocytes expressing Rhbg. Methyl amine (HCl) in solution exists as neutral methyl amine (MA) in equilibrium with the protonated methyl ammonium (MA+). To assess transport, we used ion-selective microelectrodes and voltage-clamp experiments to measure NH3/NH4+- and MA/MA+-induced intracellular pH (pHi) changes and whole cell currents. Our data showed that in Rhbg oocytes, NH3/NH4+ caused an inward current and decrease in pHiconsistent with electrogenic NH4+ transport. These changes were significantly larger than in H2O-injected oocytes. The NH3/NH4+-induced current was not inhibited in the presence of barium or in the absence of Na+. In Rhbg oocytes, MA/MA+caused an inward current but an increase (rather than a decrease) in pHi.MA/MA+did not cause any changes in H2O-injected oocytes. The MA/MA+-induced current and pHiincrease were saturated at higher concentrations of MA/MA+. Amiloride inhibited MA/MA+-induced current and the increase in pHiin oocytes expressing Rhbg but had no effect on control oocytes. These results indicate that MA/MA+is transported by Rhbg but differently than NH3/NH4+. The protonated MA+is likely a direct substrate whose transport resembles that of NH4+. Transport of electroneutral MA is also enhanced by expression of Rhbg.

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Silvern, Rachel F., Daniel J. Jacob, Patrick S. Kim, Eloise A. Marais, Jay R. Turner, Pedro Campuzano-Jost et Jose L. Jimenez. « Inconsistency of ammonium–sulfate aerosol ratios with thermodynamic models in the eastern US : a possible role of organic aerosol ». Atmospheric Chemistry and Physics 17, n^o 8 (19 avril 2017) : 5107–18. http://dx.doi.org/10.5194/acp-17-5107-2017.

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Abstract. Thermodynamic models predict that sulfate aerosol (S(VI) ≡ H2SO4(aq) + HSO4−+ SO42−) should take up available ammonia (NH3) quantitatively as ammonium (NH4+) until the ammonium sulfate stoichiometry (NH4)2SO4 is close to being reached. This uptake of ammonia has important implications for aerosol mass, hygroscopicity, and acidity. When ammonia is in excess, the ammonium–sulfate aerosol ratio R = [NH4+] ∕ [S(VI)] should approach 2, with excess ammonia remaining in the gas phase. When ammonia is in deficit, it should be fully taken up by the aerosol as ammonium and no significant ammonia should remain in the gas phase. Here we report that sulfate aerosol in the eastern US in summer has a low ammonium–sulfate ratio despite excess ammonia, and we show that this is at odds with thermodynamic models. The ammonium–sulfate ratio averages only 1.04 ± 0.21 mol mol−1 in the Southeast, even though ammonia is in large excess, as shown by the ammonium–sulfate ratio in wet deposition and by the presence of gas-phase ammonia. It further appears that the ammonium–sulfate aerosol ratio is insensitive to the supply of ammonia, remaining low even as the wet deposition ratio exceeds 6 mol mol−1. While the ammonium–sulfate ratio in wet deposition has increased by 5.8 % yr−1 from 2003 to 2013 in the Southeast, consistent with SO2 emission controls, the ammonium–sulfate aerosol ratio decreased by 1.4–3.0 % yr−1. Thus, the aerosol is becoming more acidic even as SO2 emissions decrease and ammonia emissions stay constant; this is incompatible with simple sulfate–ammonium thermodynamics. A tentative explanation is that sulfate particles are increasingly coated by organic material, retarding the uptake of ammonia. Indeed, the ratio of organic aerosol (OA) to sulfate in the Southeast increased from 1.1 to 2.4 g g−1 over the 2003–2013 period as sulfate decreased. We implement a simple kinetic mass transfer limitation for ammonia uptake to sulfate aerosols in the GEOS-Chem chemical transport model and find that we can reproduce both the observed ammonium–sulfate aerosol ratios and the concurrent presence of gas-phase ammonia. If sulfate aerosol becomes more acidic as OA ∕ sulfate ratios increase, then controlling SO2 emissions to decrease sulfate aerosol will not have the co-benefit of suppressing acid-catalyzed secondary organic aerosol (SOA) formation.

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Wentworth, Gregory R., Jennifer G. Murphy, Katherine B. Benedict, Evelyn J. Bangs et Jeffrey L. Collett Jr. « The role of dew as a night-time reservoir and morning source for atmospheric ammonia ». Atmospheric Chemistry and Physics 16, n^o 11 (15 juin 2016) : 7435–49. http://dx.doi.org/10.5194/acp-16-7435-2016.

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Abstract. Several field studies have proposed that the volatilization of NH3 from evaporating dew is responsible for an early morning pulse of ammonia frequently observed in the atmospheric boundary layer. Laboratory studies conducted on synthetic dew showed that the fraction of ammonium (NH4+) released as gas-phase ammonia (NH3) during evaporation is dependent on the relative abundances of anions and cations in the dew. Hence, the fraction of NH3 released during dew evaporation (Frac(NH3)) can be predicted given dew composition and pH. Twelve separate ambient dew samples were collected at a remote high-elevation grassland site in Colorado from 28 May to 11 August 2015. Average [NH4+] and pH were 26 µM and 5.2 respectively and were on the lower end of dew [NH4+] and pH observations reported in the literature. Ambient dew mass (in g m−2) was monitored with a dewmeter, which continuously measured the mass of a tray containing artificial turf representative of the grass canopy to track the accumulation and evaporation of dew. Simultaneous measurements of ambient NH3 indicated that a morning increase in NH3 was coincident in time with dew evaporation and that either a plateau or decrease in NH3 occurred once the dew had completely evaporated. This morning increase in NH3 was never observed on mornings without surface wetness (neither dew nor rain, representing one-quarter of mornings during the study period). Dew composition was used to determine an average Frac(NH3) of 0.94, suggesting that nearly all NH4+ is released back to the boundary layer as NH3 during evaporation at this site. An average NH3 emission of 6.2 ng m−2 s−1 during dew evaporation was calculated using total dew volume (Vdew) and evaporation time (tevap) and represents a significant morning flux in a non-fertilized grassland. Assuming a boundary layer height of 150 m, the average mole ratio of NH4+ in dew to NH3 in the boundary layer at sunrise is roughly 1.6 ± 0.7. Furthermore, the observed loss of NH3 during nights with dew is approximately equal to the observed amount of NH4+ sequestered in dew at the onset of evaporation. Hence, there is strong evidence that dew is both a significant night-time reservoir and strong morning source of NH3. The possibility of rain evaporation as a source of NH3, as well as dew evaporation influencing species of similar water solubility (acetic acid, formic acid, and HONO), is also discussed. If release of NH3 from dew and rain evaporation is pervasive in many environments, then estimates of NH3 dry deposition and NHx ( ≡ NH3 + NH4+) wet deposition may be overestimated by models that assume that all NHx deposited in rain and dew remains at the surface.

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Bash, J. O., E. J. Cooter, R. L. Dennis, J. T. Walker et J. E. Pleim. « Evaluation of a regional air-quality model with bidirectional NH3 ; exchange coupled to an agroecosystem model ». Biogeosciences 10, n^o 3 (11 mars 2013) : 1635–45. http://dx.doi.org/10.5194/bg-10-1635-2013.

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Abstract. Atmospheric ammonia (NH3) is the primary atmospheric base and an important precursor for inorganic particulate matter and when deposited NH3 contributes to surface water eutrophication, soil acidification and decline in species biodiversity. Flux measurements indicate that the air–surface exchange of NH3 is bidirectional. However, the effects of bidirectional exchange, soil biogeochemistry and human activity are not parameterized in air quality models. The US Environmental Protection Agency's (EPA) Community Multiscale Air-Quality (CMAQ) model with bidirectional NH3 exchange has been coupled with the United States Department of Agriculture's (USDA) Environmental Policy Integrated Climate (EPIC) agroecosystem model. The coupled CMAQ-EPIC model relies on EPIC fertilization timing, rate and composition while CMAQ models the soil ammonium (NH4&plus;) pool by conserving the ammonium mass due to fertilization, evasion, deposition, and nitrification processes. This mechanistically coupled modeling system reduced the biases and error in NHx (NH3 &plus; NH4&plus;) wet deposition and in ambient aerosol concentrations in an annual 2002 Continental US (CONUS) domain simulation when compared to a 2002 annual simulation of CMAQ without bidirectional exchange. Fertilizer emissions estimated in CMAQ 5.0 with bidirectional exchange exhibits markedly different seasonal dynamics than the US EPA's National Emissions Inventory (NEI), with lower emissions in the spring and fall and higher emissions in July.

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