Heterogeneouse Reactions of HOCL + HCL-- Cl(sub 2) + H(sub 2) and CIONO(sub 2)2 + HCL -- CL(sub 2) HNO(sub 3) on ice surfaces at polar Stratospheric Conditions
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Heterogeneous Reactions↗
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Measurements of HNO(sub 4): implications for HO(sub x)
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photochemistry of middle atmosphere↗
Reaction kinetics of OH + HNO 3 under conditions relevant to the upper troposphere/lower stratosphere
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Frank A. F. Winiberg↗
The Kinetic Nonequilibrium Processes in the Internal Flow and in the Plume of Subsonic and Supersonic Aircrafts
(1) Our results show that under combustion of thermal destruction products of n-C8H18, and other hydrocarbon fuels with air at the equivalent ratio -0.5 and less the chemical equilibrium is not realized at the exit plane of combustion chamber and in the gas turbine and nozzle for most of small components such as NO2, NO3, HNO, HNO2, HNO3, N(x)H(y), HO2, OH. The chemical equilibrium is not realized in the internal flow of ramjet hydrogen combustion engine too. So at the nozzle exit plane both of gas-turbine hydrocarbon combustion engine and of ramjet hydrogen combustion engine the relatively large values of concentration of such small components as NO3, HNO2, N2O, HNO3, HNO, NH, N2H, HO2, H2O2 may be realized. The exact definition of these component concentration as well as concentration of NO(x), OH, SO2, O, H, H2, H2O at the nozzle exit plane is very important for plume chemistry. (2) The results which were obtained for subsonic and hypersonic aircrafts indicate on the considerable change of the composition of the gas mixture along the plume. This change can be caused not only by the mixture of combustion products with the atmosphere air but by proceeding of whole complex of nonequilibrium photochemical reactions. The photodissociation processes begin to influence on the formation of the free atoms and radicals at flight altitude H greater than or equal to 18 km. Neglect of these processes can result in essential (up to 10(exp 4) times) mistakes of values gamma(sub OH), gamma(sub O), gamma(sub H), gamma(sub HSO3) and some products of CFC's disintegration. It was found that penetration of Cl-containing species from the atmosphere into the exhaust flow and its interaction with nitrogen oxides leads to essential increasing of the concentration of Cl, Cl2, ClO2, ClNO3, CH3Cl and sometimes HCl and the decreasing of ClO concentration by comparison with background values. The results of our analysis show that the plume aircraft with both hydrocarbon and hydrogen combustion engine may be source of various pollutant components such as HNO, HNO4,ClO2, CH3NO2, CH3NO3, CH2O, Cl, H2O2, but not only NO, NO2, HNO2, HNO3, N2O5, SO2, SO3, H2SO4 as it was supposed before.
Starik, Alexander M.↗
Interaction of Peroxynitric Acid with Solid H2O Ice
The uptake of peroxynitric acid (PNA), HO2NO2 or HNO4, on solid H2O ice at 193 K (-80 C) was studied using a fast flow-mass spectrometric technique. An uptake coefficient of 0.15 +/- 0.10 was measured, where the quoted uncertainty denotes 2 standard deviations. The uptake process did not result in the production of gas phase products. The composition of the condensed phase was investigated using programmed heating (3 K/min) of the substrate coupled with mass spectrometric detection of desorbed species. Significant quantities of HNO, and HNO3 desorbed from the substrates at temperatures above 225 K and 246 K, respectively. The desorbed HNO3, which was less than 9% of the desorbed HNO, and remained unchanged upon incubation of the substrate, was likely due to impurities in the HNO4 samples rather than reaction of HNO, on the substrate. The onset temperatures for HNO4 desorption increased with increasing H2O to HNO4 ratios, indicating that HNO4, like HNO3, tends to be hydrated in the presence of water. These observations suggest possible mechanisms for removal of HNO4 or repartitioning of total odd nitrogen species in the Earth's upper troposphere and stratosphere.
Li, Zhuangjie↗
M2-SCREAM: A Stratospheric Composition Reanalysis of Aura MLS Data With MERRA-2 Transport
MERRA-2 Stratospheric Composition Reanalysis of Aura Microwave Limb Sounder (M2-SCREAM) is a new reanalysis of stratospheric ozone, water vapor, hydrogen chloride (HCl), nitric acid (HNO 3 ) and nitrous oxide (N 2 O) between 2004 and the present (with a latency of several months). The assimilated fields are provided at a 50-km horizontal resolution and at a three-hourly frequency. M2-SCREAM assimilates version 4.2 Microwave Limb Sounder (MLS) profiles of the five constituents alongside total ozone column from the Ozone Monitoring Instrument. Dynamics and tropospheric water vapor are constrained by the MERRA-2 reanalysis. The assimilated species are in excellent agreement with the MLS observations, except for HNO 3 in polar night, where data are not assimilated. Comparisons against independent observations show that the reanalysis realistically captures the spatial and temporal variability of all the assimilated constituents. In particular, the standard deviations of the differences between M2-SCREAM and constituent mixing ratio data from The Atmospheric Chemistry Experiment Fourier Transform Spectrometer are much smaller than the standard deviations of the measured constituents. Evaluation of the reanalysis against aircraft data and balloon-borne frost point hygrometers indicates a faithful representation of small-scale structures in the assimilated water vapor, HNO 3 and ozone fields near the tropopause. Comparisons with independent observations and a process-based analysis of the consistency of the assimilated constituent fields with the MERRA-2 dynamics and with large-scale stratospheric processes demonstrate the utility of M2-SCREAM for scientific studies of chemical and transport variability on time scales ranging from hours to decades. Analysis uncertainties and guidelines for data usage are provided.
MERRA-2↗
Reaction of NH2 with NO and O2
Experiments were performed on the photooxidation of NH3 at room temperature and the photolysis of NH3-NO mixtures in order to determine the reaction paths of NH2 with O2. NH3 was photolyzed (NH3 + E yields NH2 + H) in the presence of O2 above 0.6 torr at 213.9 nm and 25 C, producing N2 and N2O. Only N2 and N2O were produced with any significant quantum yield, and their quantum yield was invariant with reaction conditions, which imposes a great number of constraints reducing the number of possible reactions greatly. It is argued that the N2 must be produced from the NH2O2 radical which was produced by the reaction between NH2 and O2. Subsequent reactions leading to N2 and N2O are speculative. In the photolysis of NH3 in the presence of NO and NO-O2 mixtures, the products identified were N2, H2, and N2O. Without the presence of O2, the reaction scheme after photolysis is (2) NH2 + NO yields N2 + H2O, (3) H + NO + M yields HNO + M, (4) H + HNO yields H2 + NO, and (5) 2HNO yields N2O + H2O. The average value for the ratio k3 times the square root of k5 divided by k4 was computed to be (1.6 plus or minus 0.6) times 10 to the minus 28th cm to the exponent 9/2 per square root sec. In addition, the presence of 113 mtorr of O2 had no effect on the quantum yields of N2 or H2, so it appears that it does not deactivate electronically excited NH3.
Jayanty, R. K. M.↗
Theoretical characterization of the reaction NH2 + O yields products
The potential energy surface for NH2+O has been characterized using complete active space self-consistent field (CASSCF)/derivative calculations to determine stationary point geometries and frequencies followed by internally contracted configuration interaction (ICCI) calculations to determine the energetics. The calculations predict a NO bond strength of 85.8 kcal/mol for NH2O. The barrier for isomerization of NH2O to trans-HNOH is predicted to be 48.0 kcal/mol and the barriers for H+HNO forming NH2O and NHOH are predicted to be 2.1 and 8.3 kcal/mol, respectively (all corrected for zero-point energy). The computed heats of formation for NH2O and cis- and trans-HNOH are in good agreement with the present results. The barrier for H + HNO yields H2 + NO is computed to be about 0.3 kcal/mol.
Walch, Stephen P.↗
Kinetics of the Reactions of F((sup 2)P) and Cl((sup 2)P) with HNO3
The kinetics of the reactions of HNO3 with fluorine (k(sub 1)) and Chlorine (k(sub 2)) atoms have been studied by using a time-resolved long-path laser absorption technique to monitor the appearance of product NO3 radicals following 351-nm pulsed laser photolysis of X2/HNO3/He mixtures (X = F,Cl). Absolute rate coefficients for the F((sup 2)P) + HNO reaction have been determined over the temperature range 260-373 K. Between 260 and 320 K, the data are adequately represented by the Arrhenius expression k(sub 1)(T) = (6.0 +/- 2.6) x 10(exp -12) exp[(40 +/- 120)/T]cu cm/(molecule.s). Between 335 and 373 K, the rate coefficient is found to be (2.0 +/- 0.3) x 10(exp -11)cu cm/(molecule.s) independent of temperature. The observed temperature dependence suggests that reaction proceeds via competing direct abstraction and complex pathways. No NO3 production was observed in the experiments with X equals Cl, thus establishing that k(sub 2)(298 K) is less than 2 x 10(exp -16) cu cm/(molecule.s). The Cl((sup 2)P) + HNO reaction was also investigated by using a pulsed laser photolysis-resonance fluorescence technique to monitor the decay of Cl((sup 2)P). Upper limit values for k(sub 2) obtained from these experiments, in units of 10(exp -16)cu cm/(molecule.s), are 13 at 298 K and 10 at 400 K.
Wine, P. H.↗
Application of Coupled-Cluster Methods to the Prediction and Interpretation of the Spectra of Molecules of Interest in Atmospheric Chemistry
The quality of fundamental vibrational frequencies determined using the CCSD(T) method (singles and doubles coupled-cluster theory plus a perturbational estimate of the effects of connected triple excitations) is shown to be very good, usually predicting band centers to within +/-8/cm. This approach is applied to several molecules of interest in atmospheric chemistry, including HNO, NO2(+), H2CO, and HOCl. The HNO molecule displays a large and unusual anharmonicity in the H-N stretch. For the calculation of ultraviolet (UV) spectra, the linear response CCSD (LRCCSD) approach (which is equivalent to EOM-CCSD) has been shown to yield vertical excitation energies that are accurate to approximately 0.1 eV for singly excited electronic states. This method together with more approximate methods is used to examine the UV spectra of several molecules important in stratospheric chemistry, including HOCl, Cl2O, ClOOCl, ClOOH, and HOOH.
Lee, Timothy J.↗
Ab Initio Studies of Fluorine and Chlorine Oxide and Nitrogen Oxide Species of Interest in Stratospheric Chemistry
The quality of fundamental vibrational frequencies determined using the CCSD(T) method (singles and doubles coupled-cluster theory plus a perturbational estimate of the effects of connected triple excitations) is shown to be very good, usually predicting band centers to within plus or minus 8 per centimeter. This approach is applied to several molecules of interest in atmospheric chemistry, such as HNO, cis-FONO, cis-ClONO, and ClOOH. The HNO molecule displays a large and unusual anharmonicity in the H-N stretch. For the calculation of ultraviolet (UV) spectra, the linear response CCSD (LRCCSD) approach (which is equivalent to EOM-CCSD) has been shown to yield vertical excitation energies that are accurate to approximately equal to 0.1 eV for singly excited electronic states. This method together with more approximate methods is used to examine the UV spectra of several molecules important in stratospheric chemistry, including HOCl, Cl2O, ClONO2, HONO2, ClOOCl, ClOOH, and HOOH.
Lee, Timothy J.↗
Ab Initio Potential Energy Surfaces and the Calculation of Accurate Vibrational Frequencies
Due to advances in quantum mechanical methods over the last few years, it is now possible to determine ab initio potential energy surfaces in which fundamental vibrational frequencies are accurate to within plus or minus 8 cm(exp -1) on average, and molecular bond distances are accurate to within plus or minus 0.001-0.003 Angstroms, depending on the nature of the bond. That is, the potential energy surfaces have not been scaled or empirically adjusted in any way, showing that theoretical methods have progressed to the point of being useful in analyzing spectra that are not from a tightly controlled laboratory environment, such as vibrational spectra from the interstellar medium. Some recent examples demonstrating this accuracy will be presented and discussed. These include the HNO, CH4, C2H4, and ClCN molecules. The HNO molecule is interesting due to the very large H-N anharmonicity, while ClCN has a very large Fermi resonance. The ab initio studies for the CH4 and C2H4 molecules present the first accurate full quartic force fields of any kind (i.e., whether theoretical or empirical) for a five-atom and six-atom system, respectively.
Lee, Timothy J.↗
Ab Initio Calculation of Accurate Vibrational Frequencies for Molecules of Interest in Atmospheric Chemistry
Due to advances in quantum mechanical methods over the last few years, it is now possible to determine ab initio potential energy surfaces in which fundamental vibrational frequencies are accurate to within +/- 8 cm(sup -1) on average, and molecular bond distances are accurate to within +/- 0.001-0.003 A, depending on the nature of the bond. That is, the potential energy surfaces have not been scaled or empirically adjusted in any way, showing that theoretical methods have progressed to the point of being useful in analyzing spectra that are not from a tightly controlled laboratory environment, such as rovibrational spectra from the interstellar medium. Some recent examples demonstrating this accuracy win be presented and discussed. These include the HNO, CH4, C2H4, and ClCN molecules. The HNO molecule is interesting due to the very large H-N anharmonicity, while ClCN has a very large Fermi resonance. The ab initio studies for the CH4 and C2H4 molecules present the first accurate full quartic force fields of any kind (i.e., whether theoretical or empirical) for a five-atom and six-atom system, respectively.
Lee, Timothy J.↗
Measurement of Reactive Nitrogen in the Stratosphere
We present volume mixing ratio profiles of NO, NO 2 , HNO 3 , HNO 4 , N 2 O 5 , and CINO 3 and their composite budget (NO y ), from 20 to 39 km, meassured remotely in solar occultation by the JPL MkIV Interferometer during a high-altitude ballon flight from Fort Sumner, New Mexico on 25 September 1993.
balloon↗
Candidate interstellar molecules formed from ion-molecule reactions of NO
Molecular orbital calculations using the MINDO/3 method were performed on a series of small molecules to explore reactions of NO which could lead to formation of interstellar molecules. Specifically, equilibrium geometries, isomeric energies, heats of reactions, and reaction pathways were calculated for plausible ion-molecule reactions involving NO and NO(+). The results of these calculations suggest that HNO(+) and HON(+) could be present in observable abundance in interstellar clouds. These species can be formed by the reaction of NO with H3(+) but not by NO(+) with H2. Moreover, they are stable to dissociation and do not react with H2 to re-form NO or to form isomers of HNOH(+).
Loew, G. H.↗
New interstellar molecular transitions in the 2 millimeter range
A Sgr B2 kinetic temperature of about 47 K is derived based on observations of K components of the 9K-8K transition of CH3CCH. Interstellar line emission is detected in the 2 mm wavelength region from SO, (S-34)O, SO2, CH3OH, CH3CCH, CH3CH2CN, HC3N, and nine unidentified transitions. The methylacetylene K component data combined with the derived data reduction technique, demonstrates the utility of the molecule as a temperature probe of molecular clouds when two or more rotational transitions are observed. Evidence for the existence of interstellar HNO is presented, and an attempt is made to detect sulfuric acid, formic anhydride, and the 0-18 isotopic for CO2 in interstellar clouds and in the Venusian atmosphere during inferior conjunction.
Hollis, J. M.↗
The evolution of nitrogen cycling
The energetics of nitrogen transformation reactions and the evolution of nitrogen cycling are examined. It is suggested that meteor impact-produced fixed nitrogen could have caused the entire reservoir of the earth's N2 to convert into fixed nitrogen at the end of accretion. The abiotic fixation rate on the early earth by lightning is estimated at about 1-3 X 10 to the 16th molecules of NO/J. It is found that biological nitrogen fixation may have evolved after the development of an aerobic atmosphere. It is shown that HNO could eventually become NO2(-) and NO3(-) after reaching the earth's surface. It is concluded that the evolutionary sequence for the biological transformation of nitrogen compounds is ammonification - denitrification - nitrification - nitrogen fixation.
Mancinelli, Rocco L.↗
Ammonia on the prebiotic Earth: Iron(II) reduction of nitrite
Theories for the origin of life require the availability of reduced nitrogen. In the non-reducing atmosphere suggested by geochemical evidence, production in the atmosphere and survival of NH3 against photochemical destruction are problematic. Electric discharges and impact shocks would produce NO rather than HCN or NH3. Conversion of NO to nitrous and nitric acid (by way of HNO) and precipitation in acid rain would provide a source of fixed nitrogen to the early ocean. One solution to the NH3 problem may have been the reduction of nitrite/nitrate in the ocean with aqueous ferrous iron, Fe(2+): 6Fe(+2) + 7 H2O + NO2(-) yields 3Fe2O3 + 11 H(+) + NH3. We have measured the kinetics of this reaction as a function of temperature, pH, and concentrations of salts, Fe(+2), and NO2(-). Cations (Na(+), Mg(2+), K(+)) and anions (Cl(-), Br(-), SO4(2-)) increase the rate by factors of 4 to 8. Although a competing pathway yields N2, the efficiency of the conversion of nitrite to ammonia ranges from 25% to 85%. Nitrate reduction was not consistently reproducible; however, when it was observed, its rate was slower by at least 8X than that of nitrite reduction. If the prebiotic atmosphere contained 0.2 to 10 atmospheres CO2 as suggested by Walker (1985), the Fe(+2) concentration and the rate would have been limited by siderite (FeCO3) solubility.
Summers, David P.↗