Joel D. Burley

Translational energy dependence of O+(4S) + H2(D2, HD) → OH+(OD+) + H(D) from thermal energies to 30 eV c.m.

Abstract Guided ion beam mass spectrometry is used to examine the kinetic energy dependences of the reactions of ground-state atomic oxygen ion with molecular hydrogen and its isotopic variants. At interaction energies below 0.3 eV, the total reaction cross-sections for all three systems are in excellent agreement with those predicted by the Langevin-Gioumousis-Stevenson model for exothermic ion/molecule reactions. At energies above 0.3 eV, the reaction efficiency declines. Phase space theory calculations are used to show that this behavior is due partly to angular momentum constraints. Above 6 eV, dissociation of the product ion is evident. For reaction with HD, the intramolecular isotope branching ratio oscillates several times over the energy range examined. This result is explained by comparison with phase space theory calculations and with several dynamical models.

Laboratory investigation of the catalytic reduction technique for measurement of atmospheric NOy

We report laboratory studies of the detection scheme employed for in situ measurement of NOy in the atmosphere. In this technique, an air stream is passed over a hot metal (usually 24 karat (k) Au) catalyst in the presence of a reducing agent (usually CO), which converts the NOx compounds to NOx Using the NOy species NO, NO2, HNO3, and isopropyl nitrate and the potential interferences HCN, CH3CN, NH3, and N2O, we investigated: (1) conversion efficiencies as a function of pressure and catalyst temperature; (2) conversion efficiencies as a function of reducing-agent concentration with both H2 and CO; (3) the effect of humidity and O3 on conversion efficiency; (4) loss of NO in the catalyst; and (5) the efficacy and suitability as catalytic converters (or inlets) of several metals (24 k Au, 18k Au, Au with 1% Co, Ag, Pt, stainless steel) and quartz. The most significant results are the discovery of a gas-phase process that contributes to the conversion of HNO3 to NO and the identification of conditions under which HCN, CH3CN, and NH3 are converted to NO with high efficiency. We discuss the implications of these results for in situ measurement of atmospheric NOy.

Translational energy dependence of O+(4S)+N2→NO++N from thermal energies to 30 eV c.m.

Guided ion beam mass spectrometry is used to examine the kinetic energy dependence of the reaction of ground state atomic oxygen ion with molecular nitrogen. An O+(4S) source which produces less than 0.06% excited states is described. Cross sections for the NO++N product channel decrease with increasing energy below 0.25 eV but increase with energy at higher energies. Analysis of the region above 0.25 eV finds an effective barrier of 0.33±0.08 eV which previous theoretical work suggests is on the N2O+(1 4A‘) hypersurface. Below this barrier, ground state products can only be formed via a spin‐forbidden surface transition. The magnitude and energy dependence of the probability for this transition are in reasonable agreement with a Landau–Zener formalism. These results are compared to previous ion beam, flowing afterglow (FA), and flow/drift tube (FD) studies. Apparent disagreement between the present data and previous FA and FD measurement is shown to be caused primarily by differences in the ion energy di...

Ionic mechanisms for heterogeneous stratospheric reactions and ultraviolet photoabsorption cross sections for NO2+, HNO3, AND NO3− in sulfuric acid

We present room temperature photo-absorption cross sections between 180 and 340 nm for potassium nitrate dissolved in sulfuric acid-water solutions of 0, 80, and 96% sulfuric acid by mass. Other investigators have obtained ultraviolet absorption spectra for similar solutions above 220 nm, and there is a large literature on the spectra, species, and nitration reactions in sulfuric acid solutions. The predominant nitrogen-containing species are the nitrate anion (NO3−) in pure water or dilute sulfuric acid solutions, molecular nitric acid (HNO3) in 80% sulfuric acid, and the nitronium ion (NO2+) in 96% sulfuric acid. Upon reviewing the literature involving these species, we consider elementary ionic and molecular reactions in mechanisms of stratospheric heterogeneous catalysis. We formulate a general mechanism for acid catalyzed reactions, with examples that convert inactive HCl and ClNO3 into photochemically active ClNO2, ClNO, Cl2, HOCl, and ClO, and we show that reactions forming all of these products are thermodynamically allowed.

Nitrosyl sulfuric acid and stratospheric aerosols

From information found in the atmospheric and chemical literature, we propose that nitrosyl sulfuric acid (NSA), NOHSO4, may play an important role in stratospheric chemistry. In one study, NSA was observed as a slurry of crystals in about a third of the aerosol particles collected between 15 and 20 km. From the chemical literature, we find that NSA is formed from several reactions between NOy species (averaging +3 oxidation state) and sulfuric acid, if the acid is above 70 wt % at room temperature and above 60 % at stratospheric temperatures. NSA is a non-volatile ionic solid (NO+HSO4−), melting at 346 K and boiling with decomposition at 633 K. Over time, it could accumulate as a solution in the liquid aerosol, and upon reaching solubility saturation (about 3 % under lower stratospheric conditions) precipitate out as solid crystals, which permits further accumulation. At room temperature, HCl gas reacts with NSA, either the solid or in sulfuric acid solution, to form gaseous nitrosyl chloride, ClNO, which is rapidly photolyzed in the atmosphere to form nitric oxide and atomic chlorine. The overall catalytic cycle for this process can be written in a number of ways, depending upon the NOy species responsible for NSA formation; with NSA production from HONO, the cycle is The net reaction is thermodynamically favorable for at least three modes of NSA formation. If the reaction probability of forming NSA per collision of NO with a sulfuric acid aerosol is 10−3, 1% of the sulfuric acid would be converted to NSA within 1 day at 20 km altitude. If NSA in the sulfate aerosols is 1% of the sulfuric acid and if the second order rate constant for (HCl + NOHSO4 = H2SO4 + ClNO) in sulfuric acid solution is greater than 10−18 cm3 molec.−1 s−1 under conditions at 20 km altitude, the rate of HCl + NSA is faster than the rate of HO + HCl. In this case, this heterogeneous catalysis is expected to affect the balance of NOy, Cly, and ozone in the lower stratosphere.

Balloon‐borne measurements of CLO, NO, and O3 in a volcanic cloud: An analysis of heterogeneous chemistry between 20 and 30 km

Balloon profiles of chlorine monoxide (ClO), nitric oxide (NO), and ozone (O3) were measured on March 11, 1992 from 100 to 10 mb over Greenland (67.0°N, 50.6°W). Measurements from SAGE II indicate that the aerosol surface area in the region was enhanced by sulfur from the eruption of Mt. Pinatubo, reaching 50 times background near 20 km. Concentrations of ClO were enhanced and concentrations of NO were suppressed relative to low aerosol conditions consistent with the effects of hydrolysis of N2O5 on the surface of sulfuric acid aerosols. The data are consistent with a value of 2×10−4 for the reaction probability of the heterogeneous hydrolysis of ClONO2, indicating a minor role for this reaction at a temperature of 220 K. At these temperatures, we find no evidence for the catastrophic loss of ozone predicted to occur under conditions of enhanced aerosol surface area.

The Nevada Rural Ozone Initiative (NVROI): Insights to understanding air pollution in complex terrain

The Nevada Rural Ozone Initiative (NVROI) was established to better understand O3 concentrations in the Western United States (US). The major working hypothesis for development of the sampling network was that the sources of O3 to Nevada are regional and global. Within the framework of this overarching hypothesis, we specifically address two conceptual meteorological hypotheses: (1) The high elevation, complex terrain, and deep convective mixing that characterize Nevada, make this state ideally located to intercept polluted parcels of air transported into the US from the free troposphere; and (2) site specific terrain features will influence O3 concentrations observed at surface sites. Here, the impact of complex terrain and site location on observations are discussed. Data collected in Nevada at 6 sites (1385 to 2082 m above sea level (asl)) are compared with that collected at high elevation sites in Yosemite National Park and the White Mountains, California. Average daily maximum 1-hour concentrations of O3 during the first year of the NVROI ranged from 58 to 69 ppbv (spring), 53 to 62 ppbv (summer), 44 to 49 ppbv (fall), and 37 to 45 ppbv (winter). These were similar to those measured at 3 sites in Yosemite National Park (2022 to 3031 m asl), and at 4 sites in the White Mountains (1237 to 4342 m asl) (58 to 67 ppbv (summer) and 47 to 58 ppbv (fall)). Results show, that in complex terrain, collection of data should occur at high and low elevation sites to capture surface impacts, and site location with respect to topography should be considered. Additionally, concentrations measured are above the threshold reported for causing a reduction in growth and visible injury for plants (40 ppbv), and sustained exposure at high elevation locations in the Western USA may be detrimental for ecosystems.

Variability and sources of surface ozone at rural sites in Nevada, USA: Results from two years of the Nevada Rural Ozone Initiative.

Ozone (O3) has been measured at Great Basin National Park (GBNP) since September 1993. GBNP is located in a remote, rural area of eastern Nevada. Data indicate that GBNP will not comply with a more stringent National Ambient Air Quality Standard (NAAQS) for O3, which is based upon the 3-year average of the annual 4th highest Maximum Daily 8-h Average (MDA8) concentration. Trend analyses for GBNP data collected from 1993 to 2013 indicate that MDA8 O3 increased significantly for November to February, and May. The greatest increase was for May at 0.38, 0.35, and 0.46 ppb yr(-1) for the 95th, 50th, and 5th percentiles of MDA8 O3 values, respectively. With the exception of GBNP, continuous O3 monitoring in Nevada has been limited to the greater metropolitan areas. Due to the limited spatial detail of O3 measurements in rural Nevada, a network of rural monitoring sites was established beginning in July 2011. For a period ranging from July 2011 to June 2013, maximum MDA8 O3 at 6 sites occurred in the spring and summer, and ranged from 68 to 80ppb. Our analyses indicate that GBNP, in particular, is ideally positioned to intercept air containing elevated O3 derived from regional and global sources. For the 2 year period considered here, MDA8 O3 at GBNP was an average of 3.1 to 12.6 ppb higher than at other rural Nevada sites. Measured MDA8 O3 at GBNP exceeded the current regulatory threshold of 75 ppb on 7 occasions. Analyses of synoptic conditions, model tracers, and air mass back-trajectories on these days indicate that stratospheric intrusions, interstate pollution transport, wildfires, and Asian pollution contributed to elevated O3 observed at GBNP. We suggest that regional and global sources of ozone may pose challenges to achieving a more stringent O3 NAAQS in rural Nevada.

Kinetic energy dependence of C+(2P) + O2 from thermal energies to 35 eV c.m.

Abstract Guided ion beam mass spectrometry is used to examine the kinetic energy dependence of the reaction of ground-state atomic carbon ion with molecular oxygen. At the lowest energy examined, 0.05 eV, the magnitude of the total cross-section approaches to within 75% of the prediction of the Langevin—Gioumousis—Stevenson (LGS) model. The branching ratio at this energy is 60% (O + + CO) and 40% (CO + + O). These results are in good agreement with previous studies at thermal energies. As the energy is increased, σ total falls more rapidly than the LGS model and the fraction of O + formed declines steadily such that, above 0.14 eV, CO + + O is the preferred product channel. There is no indication of direct competition between these two reaction channels. Results of phase space calculations indicate that the formation of CO + is largely statistical but production of O + is highly non-statistical. The endothermic charge transfer channel, O + 2 + C, is also observed at elevated energies. Analysis of the cross-section data for this product yields a threshold energy of 0.82 eV, in excellent agreement with the known thermochemistry. The mechanism of these reactions is discussed in the context of qualitative potential energy surfaces.

Kinetic‐energy dependence of the reactions of C+(2P)+N2 from threshold to 28 eV CM

Guided‐ion‐beam mass spectrometry is used to examine the kinetic‐energy dependence of the reaction of ground‐state atomic carbon ion with molecular nitrogen. Integral reaction cross sections are measured for the three possible product channels: N2+ + C, CN+ + N, and N+ + CN, all strongly endothermic. Thresholds for all three channels are found to be consistent with literature thermochemistry, although formation of N2+ is inefficient near threshold. The observed behavior suggests that the 3Π state of CN+ is either the ground state or within 0.14 eV of the ground state, and that N2+ is formed primarily in its A 2Πu first excited state rather than the X 2Σg+ ground state. The thermochemistry measured here finds ΔfH00(CN)=102±3 kcal/mol, D00(CN)=7.82±0.14 eV, and IE(CN)=14.02±0.14 eV. The reaction mechanism for this system is explored by examination of the electronic state correlations and by phase‐space calculations.