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Ozone produced by discharge or photolysis of oxygen has unusually heavy isotopic composition (18O/16O and 17O/16O ratio) which does not follow normal mass fractionation rule: S17O ~ 0.52*δ18O, expressed as an anomaly Δ17O = δ17O - 0.52*δ18O. Ozone molecule being an open isosceles triangle can have the heavy isotope located either in its apex or symmetric (s) position or the base or asymmetric (as) position. Correspondingly, one can define positional isotopic enrichment, written as δ18O (s) or δ18O (as) (and similarly for δ17O) as well as position dependent isotope anomaly Δ17O (s) and Δ17O (as). Marcus and co-workers have proposed a semi-empirical model based in principle on the RRKM model of uni-molecular dissociation but with slight modification (departure from statistical randomness assumption for symmetrical molecules) which explains many features of ozone isotopic enrichment. This model predicts that the bulk isotope anomaly is contained wholly in the asymmetric position and the Δ17O (s) is zero. Consequently, Δ17O (as) = 1.5 * Δ17O (bulk) (named here simply as the "1.5 rule") which has been experimentally confirmed over a range of isotopic enrichment. We now show that a critical re-analysis of the earlier experimental data demonstrates a small but significant departure from this 1.5 rule at the highest and lowest levels of enrichments. This departure provides the first experimental proof that the dynamics of ozone formation differs from a statistical model constrained only by restriction of symmetry. We speculate over some possible causes for the departure. [ABSTRACT FROM AUTHOR]

We have measured the rovibronic densities of four symmetric (C2v) and two asymmetric (Cs) isotopologues of nitrogen dioxide just below their photodissociation threshold. At dissociation threshold and under jet conditions the laser-induced fluorescence abruptly disappears because the dissociation into NO(2Π1/2)+O(3P2) is much faster than the radiative decay. As a consequence, in a narrow energy range below D0, the highest bound rovibronic energy levels of J=1/2 and J=3/2 can be observed and sorted. A statistical analysis of the corresponding rovibronic density, energy spacing, and rovibronic transition intensities has been made. The observed intensity distributions are in agreement with the Porter-Thomas distribution. This distribution allows one to estimate the number of missing levels, and therefore to determine and compare the rovibronic and the vibronic densities. The four symmetric NO2 isotopologues, 16O14N16O, 18O14N18O, 16O15N16O, and 18O15N18O, have, respectively, a sum of J=1/2 and J=3/2 rovibronic densities of 18±0.8, 18.3±1.4, 18.4±2.7, and 19.8±3.5/cm-1, while for the two asymmetric isotopologues, 18O14N16O and 18O15N16O, the corresponding densities are 20.9±4.5 and 23.6±5.6/cm-1. The corresponding vibronic densities are in agreement only if we include both the merging of symmetry species (from those of C2v to those of Cs) and the contribution of the long-range tail(s) of the potential-energy surface along the dissociation coordinate. The effects of isotopic substitution on dissociation rates and the possible relation to mass-independent isotopic fractionation are discussed. [ABSTRACT FROM AUTHOR]

We have measured the rotationless photodissociation threshold of six isotopologues of NO2 containing 14N, 15N, 16O, and 18O isotopes using laser induced fluorescence detection and jet cooled NO2 (to avoid rotational congestion). For each isotopologue, the spectrum is very dense below the dissociation energy while fluorescence disappears abruptly above it. The six dissociation energies ranged from 25 128.56 cm-1 for 14N16O2 to 25 171.80 cm-1 for 15N18O2. The zero point energy for the NO2 isotopologues was determined from experimental vibrational energies, application of the Dunham expansion, and from canonical perturbation theory using several potential energy surfaces. Using the experimentally determined dissociation energies and the calculated zero point energies of the parent NO2 isotopologue and of the NO product(s) we determined that there is a common De=26 051.17±0.70 cm-1 using the Born-Oppenheimer approximation. The canonical perturbation theory was then used to calculate the zero point energy of all stable isotopologues of SO2, CO2, and O3, which are compared with previous determinations. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The oxygen isotope composition of nitrogen oxides (NOx) in the atmosphere is a useful tool for understanding the oxidation of NOx into nitric acid / nitrate in the atmosphere. A set of experiments was conducted to examine change in isotopic composition of NOx due to NOx-O2- O3 photochemical cycling. At low NOx /O2 mixing ratios, NOx became progressively and nearly equally enriched in 17O and 18O over time until it reached a steady state with Δ17O values of 39.3±1.9‰and δ18O values of 84.2±4 ‰, relative to the isotopic composition of the initial O2 gas. As the mixing ratios were increased, the isotopic enrichments were suppressed by isotopic exchange between O atoms, O2, and NOx. A kinetic model was developed to simulate the observed data and it showed that the isotope effects occurring during O3 formation play a dominant role in controlling NOx isotopes and, in addition, secondary kinetic isotope effects or isotope exchange reactions are also important during NOx cycling. The data and model were consistent with previous studies which showed that the NO + O3 reactions occur mainly via the transfer of the terminal atoms of O3. The model predicts that under tropospheric concentrations of NOx and O3, the timescale of NOx-O3 isotopic equilibrium ranges from hours (for ppbv NOx /O2 mixing ratios) to days (for pptv mixing ratios) and yields steady state Δ17O and δ18O values of 45‰ and 117‰ respectively (relative to Vienna Standard Mean Ocean Water (VSMOW)) in both cases. Under atmospheric conditions when O3 has high concentrations, the equilibrium between NOx and O3 should occur rapidly (h) but this equilibrium cannot be reached during polar winters and/or nights if the NOx conversion to HNO3 is faster. The experimentally derived rate coefficients can be used to model the major NOx-O3 isotopologue reactions at various pressures and in isotope modeling of tropospheric nitrate. [ABSTRACT FROM AUTHOR]

The oxygen isotope composition of nitrogen oxides (NOx) in the atmosphere may be a useful tool for understanding the oxidation of NOx into nitric acid/nitrate in the atmosphere. A set of experiments were conducted to examine changes in isotopic composition of NOx due to O3-NOx photochemical cycling. At low NO2/O2 mixing ratios, NO2 becomes progressively and nearly equally enriched in 17O and 18O over time until it reaches a steady state with Δ17O values of 40.6±1.9‰ and δ18O values of 84.2 ± 4 ‰, relative to the isotopic composition of the O2 gas. As the mixing ratio increases, isotopic exchange between O atoms and O2 and NOx suppresses the isotopic enrichments. A kinetic model simulating the observed data shows that the isotope effects during ozone formation play a more dominant role compared to kinetic isotope effects during NO oxidation or exchange of NO2. The model results are consistent with the data when the NO + O3 reaction occurs mainly via the transfer of the terminal atom of O3. The model predicts that under tropospheric concentrations of the three reactants, the timescale of NOx isotopic equilibrium ranges from hours (ppbv mixing ratios) to days/weeks (pptv) and yields steady state Δ17O and δ18O values of 46 ‰ and 115 ‰ respectively with respect to Vienna Standard Mean Ocean Water. Interpretation of tropospheric nitrate isotope data can now be done with the derived rate coefficients of the major isotopologue reactions at various pressures. [ABSTRACT FROM AUTHOR]

Here we present ISO-RACM, an isotope mass balance model that utilizes the Regional Atmospheric Chemistry Mechanism to predict Δ17O values in atmospheric nitrate. A large number of simulations were carried out that varied atmospheric parameters that are 5 important in altering the magnitude and range of Δ17O values generated in photochemically produce nitrate. These parameters included temperature, relative humidity, actinic flux, aerosol surface area and chemical speciation, and three different N2O5 uptake parameterizations. Trace gas mixing ratios were also varied including CH4, CO, NOx, O3, volatile organic compounds and biogenic organic compounds. The model 10 predicts that there are seasonal, latitudinal and diurnal variations in Δ17O values due to changes in actinic flux with lower values corresponding to higher actinic fluxes. There was also a minor positive correlation between higher Δ17O values and increased temperature. There were distinct differences in Δ17O depending on which N2O5 parameterization was used, mostly the result of changing relative humidity being a factor in 15 two of the parameterization schemes. Changing CO and CH4 mixing ratios had negligible impact on Δ17O values but significant variation in magnitude and range were predicted with NOx, O3, and organic loading. High NOx and O3 generated high Δ17O with a narrow (10‰) range, while high organics led to low Δ17O values and a wider range of possible values. Implications for using Δ17O to evaluate NOx-NOy chemistry 20 and aerosol formation processes are discussed, as is needed future research. [ABSTRACT FROM AUTHOR]

The basic financial purpose of the firm is maximization of its value. A inventory management should also contribute to realization of this basic aim. Many current assets management models which we can find in the literature relating to financial management were constructed with the assumption of book profit maximization as basic aim. These models could lacking what relates to another aim, i.e., maximization of enterprise value. This article presents the value based inventory management model modification.

The basic financial purpose of an enterprise is maximization of its value Trade credit management should also contribute to realization of this fundamental aim. Many of the current asset management models that are found in financial management literature assume book profit maximization as the basic financial purpose. These book profit-based models could be lacking in what relates to maximization of enterprise value. The enterprise value maximization strategy is executed with a focus on risk and uncertainty. This article presents the consequences that can result from operating risk that is related to purchasers using payment postponement for goods and/or services. The present article offers a method that uses portfolio management theory to determine the level of accounts receivable in a firm.

Nitrate as an important water pollutant, causing eutrophication was analyzed in Pakistan at different water sources (hand pump (HP), bore hole (BH) and tube well (TW)) to assess the contamination level caused by NO 3 - . NO 3 - concentrations in the HP water samples were 31 mg L -1 to 59 mg L -1 , in BH 20 mg L -1 to 79 mg L -1 while in TW water samples it was between 29 to 55 mg L -1 . The association of NO 3 - with other selected parameter in groundwater can be determined by using statistical approaches. Different physicochemical parameters (pH, electrical conductivity (EC), temperature and dissolved oxygen (DO)) were studied in groundwater samples of the research district. The Pearson correlation coefficient (r) for groundwater characteristics were calculated. Hierarchical Cluster Analysis (HCA) was used to categorize samples based on their groundwater quality similarities and to find links between groundwater quality factors. The key relationship of the groundwater for HP samples on EC and TDS ( r  = 1) had a great correlation, while all other parameters correlations were lower ( r  = 0.40), BH's parameters on WT and WSD ( r  = 0.57), WT and pH ( r  = 0.57), EC and DO ( r  = 0.50), DO and TDS (0.50), EC and TDS ( r  = 1) had a quite high correlation, while all other parameters correlations were less than ( r  = 0.40), on the other hand, tube well parameters on TDS and EC ( r  = 1) had a perfect correlation, DO and pH ( r  = 0.75) parameters correlations were less than ( r  = 0.40).

Atmospheric ammonia (NH 3 ) and ammonium (NH 4 + ) can substantially influence air quality, ecosystems, and climate. NH 3 volatilization from fertilizers and wastes (v-NH 3 ) has long been assumed to be the primary NH 3 source, but the contribution of combustion-related NH 3 (c-NH 3 , mainly fossil fuels and biomass burning) remains unconstrained. Here, we collated nitrogen isotopes of atmospheric NH 3 and NH 4 + and established a robust method to differentiate v-NH 3 and c-NH 3 . We found that the relative contribution of the c-NH 3 in the total NH 3 emissions reached up to 40 ± 21% (6.6 ± 3.4 Tg N yr -1 ), 49 ± 16% (2.8 ± 0.9 Tg N yr -1 ), and 44 ± 19% (2.8 ± 1.3 Tg N yr -1 ) in East Asia, North America, and Europe, respectively, though its fractions and amounts in these regions generally decreased over the past decades. Given its importance, c-NH 3 emission should be considered in making emission inventories, dispersion modeling, mitigation strategies, budgeting deposition fluxes, and evaluating the ecological effects of atmospheric NH 3 loading., (© 2022. The Author(s).)

Formation pathways and sources of atmosphere nitrate (NO 3 - ) have attracted much attention as NO 3 - had detrimental effects on Earth's ecosystem and climate change. Here, we measured nitrogen (δ 15 N-NO 3 - ) and oxygen (δ 18 O-NO 3 - and Δ 17 O-NO 3 - ) isotope compositions in nitrate aerosols at the Qomolangma station (QOMS) over the Himalayan-Tibetan Plateau (HTP) to quantify the formation mechanisms and emission sources of nitrate at the background site. At QOMS, the enhanced NO 3 - concentrations were observed in the springtime. The average δ 15 N-NO 3 - , δ 18 O-NO 3 - , and Δ 17 O-NO 3 - values were 0.4 ± 4.9, 64.7 ± 11.5 and 27.6 ± 6.9‰, respectively. Seasonal variations of isotope ratios at QOMS can be explained by the different emissions and formation pathways to nitrate. The average fractions of NO 2 + OH and N 2 O 5 + H 2 O to nitrate production were estimated to be 43 and 52%, respectively, when the NO 3 + hydrocarbon (HC)/dimethyl sulfide (DMS) (NO 3 + HC/DMS) pathway was assumed to be 5%. Using stable isotope analysis in the R (SIAR) model, the relative contributions of biomass burning (BB), biogenic soil emission, traffic, and coal combustion to nitrate were estimated to be 28, 25, 24, and 23%, respectively, on yearly basis. By FLEXible PARTicle (FLEXPART) dispersion model, we highlighted that NO x from BB emission over South Asia that had undergone N 2 O 5 + H 2 O processes enhanced the nitrate concentrations in the springtime over the HTP region.

Oral mucositis (OM) is a treatment-limiting adverse side effect of radiation and chemotherapy. Approximately 80% of patients undergoing radiotherapy (RT) for head and neck cancers (HNC) develop OM, representing a major unmet medical condition. Our understanding of the immunopathogenesis of OM is limited, due in part to the surprising paucity of information regarding healing mechanisms in the oral mucosa. RNAseq of oral tissue in a murine model that closely mimics human OM, showed elevated expression of IL-17 and related immune pathways in response to head and neck irradiation (HNI). Strikingly, mice lacking the IL-17 receptor (IL-17RA) exhibited markedly more severe OM. Restoration of the oral mucosa was compromised in Il17ra -/- mice and components associated with healing, including matrix metalloproteinase 3, 10 and IL-24 were diminished. IL-17 is typically associated with recruitment of neutrophils to mucosal sites following oral infections. Unexpectedly, in OM the absence of IL-17RA resulted in excessive neutrophil recruitment and immunopathology. Instead, neutrophil activation was IL-1R-driven in Il17ra -/- mice. Blockade of IL-1R and depletion of neutrophils lessened the severity of damage in these mice. Overall, we show IL-17 is protective in OM through multiple mechanisms including restoration of the damaged epithelia and control of the neutrophil response. We also present a clinically relevant murine model of human OM to improve mechanistic understanding and develop rational translational therapeutics., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Saul-McBeth, Dillon, Lee, Launder, Kratch, Abutaha, Williamson, Schroering, Michalski, Biswas, Conti, Shetty, McCracken, Bruno, Parsai and Conti.)

Since the industrial revolution, it has been assumed that fossil-fuel combustions dominate increasing nitrogen oxide (NO x ) emissions. However, it remains uncertain to the actual contribution of the non-fossil fuel NO x to total NO x emissions. Natural N isotopes of NO 3 - in precipitation (δ 15 N w-NO3- ) have been widely employed for tracing atmospheric NO x sources. Here, we compiled global δ 15 N w-NO3- observations to evaluate the relative importance of fossil and non-fossil fuel NO x emissions. We found that regional differences in human activities directly influenced spatial-temporal patterns of δ 15 N w-NO3- variations. Further, isotope mass-balance and bottom-up calculations suggest that the non-fossil fuel NO x accounts for 55 ± 7% of total NO x emissions, reaching up to 21.6 ± 16.6Mt yr -1 in East Asia, 7.4 ± 5.5Mt yr -1 in Europe, and 21.8 ± 18.5Mt yr -1 in North America, respectively. These results reveal the importance of non-fossil fuel NO x emissions and provide direct evidence for making strategies on mitigating atmospheric NO x pollution.

Nitrification is a crucial step in ecosystem nitrogen (N) cycling, but scaling up from plot-based measurements of gross nitrification to catchments is difficult. Here, we employed a newly developed method in which the oxygen isotope anomaly (Δ 17 O) of nitrate (NO 3 - ) is used as a natural tracer to quantify in situ catchment-scale gross nitrification rate (GNR) for a temperate forest from 2014 to 2017 in northeastern China. The annual GNR ranged from 71 to 120 kg N ha -1 yr -1 (average 94 ± 10 kg N ha -1 yr -1 ) over the 4 years in this forest. This result and high stream NO 3 - loss (4.2-8.9 kg N ha -1 yr -1 ) suggest that the forested catchment may have been N-saturated. At the catchment scale, the total N output of 10.7 kg N ha -1 yr -1 , via leaching and gaseous losses, accounts for 56% of the N input from bulk precipitation (19.2 kg N ha -1 yr -1 ). This result indicates that the forested catchment is still retaining a large fraction of N from atmospheric deposition. Our study suggests that estimating in situ catchment-scale GNR over several years when combined with other conventional flux estimates can facilitate the understanding of N biogeochemical cycling and changes in the ecosystem N status.

Secondary sulfate aerosols played an important role in aerosol formation and aging processes, especially during haze episodes in China. Secondary sulfate was formed via atmospheric oxidation of SO 2 by OH, O 3 , H 2 O 2 , and transition-metal-catalyzed (TMI) O 2 . However, the relative importance of these oxidants in haze episodes was strongly debated. Here, we use stable sulfur isotopes (δ 34 S) of sulfate aerosols and a Rayleigh distillation model to quantify the contributions of each oxidant during a haze episode in Nanjing, a megacity in China. The observed δ 34 S values of sulfate aerosols showed a negative correlation with sulfur oxidation ratios, which was attributed to the sulfur isotopic fractionations during the sulfate formation processes. Using the average fractionation factor calculated from our observations and zero-dimensional (0-D) atmospheric chemistry modeling estimations, we suggest that OH oxidation was trivial during the haze episode, while the TMI pathway contributed 49 ± 10% of the total sulfate production and O 3 /H 2 O 2 oxidations accounted for the rest. Our results displayed good agreement with several atmospheric chemistry models that carry aqueous and heterogeneous TMI oxidation pathways, suggesting the role of the TMI pathway was significant during haze episodes.

Nitrate source identification in river systems is important for water quality management. Recently, the oxygen isotopic anomaly of nitrate in atmospheric deposition (Δ 17 O atm ) is used to identify unprocessed atmospheric nitrate in river systems to reduce the uncertainty caused by the wide range of δ 18 O. In high-elevation regions, such as the Qinghai-Tibetan Plateau (QTP) featured with lower temperature and pressure as well as strong radiation, the Δ 17 O atm might be different from that in low-elevation regions, but no relevant studies have been reported. In this work, Δ 17 O atm in the QTP was studied, and the fingerprints of nitrate isotopes in synthetic fertilizer, livestock manure, domestic sewage, and soil organic nitrogen (SON) were identified and used to quantify various source contributions to riverine nitrate in the Yellow River and Changjiang River source regions located in the QTP during 2016-2017. The results showed that the average of Δ 17 O atm in the QTP was 16.4‰, lower than the range (19-30‰) reported for the low-elevation regions. The possible mechanism is decreased O 3 as well as increased hydroxyl and peroxy radical levels in the troposphere caused by the climate condition and ozone valley in the QTP will affect the production pathways of atmospheric nitrate. By combining the sewage discharge data with the output results of the SIAR (stable isotope analysis in R) model based on the stable isotope data, manure was determined to be one of the major sources to riverine nitrate for both rivers. The contributions of various sources to riverine nitrate were 47 ± 10% for manure, 30 ± 5% for SON, 10 ± 4% for atmospheric precipitation, 9 ± 2% for synthetic fertilizer, and 4 ± 0% for sewage in the Yellow River source region. This study indicates that the unique atmospheric conditions in the QTP have led to a lower Δ 17 O atm value, and atmospheric source makes a considerable contribution to riverine nitrate in the QTP., (Copyright © 2019 Elsevier B.V. All rights reserved.)