NO2 Photolysis Research Articles

Measuring Air Pollutant Uptake by Plants: Nitrogen Dioxide

AbstractDirect kinetic determinations of the uptake of nitrogen dioxide (NO2) by selected plant species under various conditions were made using continuous stirred tank reactor (CSTR) techniques. Second‐order rate constants with respect to exposure concentration and leaf area were obtained for corn [Zea mays (L.) ‘Pioneer Brand 3369A’], soybean [Glycine max (L.) Merr. ‘Davis’], loblolly pine (Pinus taeda L.), and white oak (Quercus alba L.). Mean rate constants in units of 10−3 dm−2 min−1 were: corn, 9.3; soybean, 13.6; loblolly pine, 13.7; and white oak, 2.8. On a mass basis, rates would be 3.5, 5.1, 5.2, and 1.1 × 10−2 µg dm−2 min−1 pphm−1 (pphm = parts per hundred million), respectively. Uptake rate constants remained the same over 5‐hour exposure periods within the exposure concentration range of 0 to 58 pphm. The NO2 uptake increased as the level of photosynthetically active radiation (PAR) increased. This effect of light was linearly correlated with the inverse of total diffusive resistance. Varying the level of tissue nitrogen (N) did not influence NO2 uptake even though the leaves were smaller and chlorotic at the lower levels of tissue N. Photolysis of NO2 occurred in controlled environment rooms under artificial light; the mean k1 for photolysis was 0.03 min−1.

Determination of the spectral dependences of the absolute quantum yields of O(1S) by the XeO* luminescence method. I. Photolysis of CO2and N2O

A method is proposed for measuring the spectral distribution of the absolute quantum yield of O(1S) in the photolysis of oxygen-containing compounds (RO). This involves investigating the luminescence excitation spectra of XeO* excimers formed in the O(1S)+Xe+XeXeO*+Xe reaction. The measurements were made in a following RO?Xe mixture of accurately known composition in a system with differential evacuation. The spectral dependences of the quantum yield of O(1S) in the photolysis of N2O (?=170?102 nm) and CO2 (?=128?102 nm) were obtained. The absorption spectra of these compounds and the excitation spectra of RO, corresponding to the transitions to states which dissociated forming O(1S), were determined. The mechanism for excitation and dissociation of CO2 and N2O in these spectral ranges was discussed in the light of the experimental results and the published data. Transfer of the excitation energy from the Xe atoms, formed by absorption of radiation in the spectral range ? < 120 nm, to N2O molecules was observed, resulting in the dissociation of N2O to give and O(1S) or in the formation of N2 and XeO*.

Fluorescence and thermoluminescence of N2O, CO, and CO2 in an argon matrix at low temperature

The photolysis of N2O in an argon matrix at 7 °K by 8.4 eV energy photons leads to the emission of the Vegard–Kaplan system of N2 (A 3Σ+→X 1Σ+g) and to the atomic emissions O(1S) →O(1D) and N(2D) →N(4S). The thermoluminescence which accompanies an increase of the matrix temperature is due to O2 (A 3Σ+u→X 3Σ−g). In the presence of CO, the atomic oxygen emission disappears and the CO (a 3Π→X 1Σ) Cameron System is detected. The thermoluminescence in this case is a continuum (3800–5000 Å) apparently due to CO2 (3B2→X 1Σ+g) showing that ground state oxygen atoms, O(3P), react with CO at cryogenic temperatures: CO (X 1Σ+)+O(3P) →CO2(3B2), CO2(3B2) →CO2(X 1Σ+g)+hν.

The NO Yield of O(1D) + N2O as Function of Kinetic Energy

AbstractThe photolysis of pure N2O and of N2O in a large excess of He at 184.9 nm and at 206.2 nm was used as a source of O(1D) atoms, to study the branching ratio of reactions (2a) N2O + O(1D) → N2 + O2 and (2b) N2O + O(1D) → NO + NO, as function of kinetic energy of O(1D). The mole fraction b = k2b/(k2a + k2b) of O(1D) atoms reacting with N2O via (2b) governs the source strength of NO in the stratosphere. The products N2, O2, and NO were measured every 3 minutes by automated gas chromatography, and continuously by a chemi‐luminescence detector as function of time during the photolysis of N2O. Back extrapolation of the product ratios to zero conversion yielded the correct stoichiometry. The value of b derived from initial product ratios was b = 0.617 ± 0.015, independent of kinetic energy in the range 11.3 to 184 kJ/mol. The result is in excellent agreement with a theoretical model of reaction (2) proposed by Tully. The new value of b = 0.617 increases the source strength of NO in the stratosphere by 23% relative to current model calculations based on b = 0.50.

Product Quantum Yields from the Photolysis of NO2 at 366 nm in the Presence of Ethylene. ‐ The Role of NO3*

AbstractNitrogen dioxide (1.3 · 10−4, 4.0 · 10−4, and 7.2 · 10−4 mol/l) has been photolysed (λ = 366 nm) at room temperature in the presence of ethylene (3.7 · 10−2 mol/l). Quantum yields of N2O, NO, CO, CO2, O2, CH2O, (CH2)2O, CH3CHO, CH3ONO, CH3ONO2, CH3NO2, C2H5ONO2, and C2H5NO2 were determined (NO2 actinometry). Satisfactory N, O, and H material balances were obtained. ‐ The O atoms from the photolysis of NO2 react with NO2 to give NO3*, as well as with ethylene to yield C2H4O*. It is concluded that the excited NO3*, rather than being deactivated to thermal NO3, essentially reacts chemically with ethylene. The excited C2H4O* may either become collisionally deactivated into (CH2)O and CH3CHO, or decay to CHO and CH3 radicals. The observed products can be explained via subsequent reactions of these radicals. A number of rate constants and ratios of rate constants pertinent to this system have been estimated.

Reaction Mechanism of the Photooxidation of the Toluene–NO2–O2–N2 System in the Gas Phase

Abstract Photooxidation of the toluene (34 ppm)–NO2(8–207 ppm)–N2 and/or O2(1 atm) system has been studied in a 67 dm3 reaction chamber. The reaction was initiated by O(3P) atoms formed in the photolysis of NO2. The main products were benzaldehyde, cresols, benzyl nitrate, m-nitrotoluene, 6-nitro-o-cresol, and 2-nitro-p-cresol. Their relative yields were studied as functions of reactant concentrations. The formation mechanisms of the products were proposed on the basis of the reactions of O(3P) and OH radicals with toluene in the presence of NO2 and O2.

Determination of the Absolute Rate of Solar Photolysis of NO2

Improvements made on the direct NO2 photolysis actinometer developed by J. O. Jackson have produced more precise data. A plot of measured values of the photolysis rate J1 vs Eppley uv photometer readings produces a curved rather than the straight line correlation previously reported. This curvature arises from the Eppley and NO2 absorption spectrum overlap, backround surface albedoes, the Ep-pley's cosine response and inherent errors in the chemical equation used. New J1 measurement vs Eppley data is shown, and a procedure for calculating instantaneous J-i values from an Eppley output is suggested.

Sunrise measurements of stratospheric nitric oxide

The chemiluminescence technique has been used to measure the growth of stratospheric nitric oxide from before sunrise until about 2 h prior to local noon at a constant altitude of 26.5 km at 33.1 °N. The instrument has sufficient time resolution to record the rapid growth of NO due to photolysis of NO2 during ultraviolet sunrise. As well, NO was observed to increase slowly throughout the remainder of the experiment. This slow growth is tentatively assigned to the release of NO2 and NO3 and subsequently NO from the photolysis of N2O5 formed during the night. A time dependent computer simulation of diurnal measurements is used to investigate the sensitivity of the computed NO growth curves to O3, total NOx, and the photolysis coefficient of N2O5.

Experiments on 558-nm argon oxide laser system

Vacuum ultraviolet (VUV) photolysis of N2O immersed in high-pressure Ar has been used to produce O(1S0) at high density. A two-chamber apparatus was used to prevent the effects of electron and ion collision in the experimental volume, thereby providing a much clearer kinetic situation. The gain profile and stimulated emission cross section near 558 nm and the upper-state lifetime were determined for ArO.

The reaction of OH with CO

AbstractHydroxyl radicals were prepared from the photolysis of N2O at 213.9 nm in the presence of excess H2. The O(1D) produced in the primary photolytic act reacts with H2 to produce OH radicals. If CO is also present, then OH can react either with H2 or CO: equation image The competition between reactions (1) and (2) was measured by measuring the CO2 yield at various values of the ratio [CO]/[H2] at 217–298°K. At 298°K the ratio of the rate coefficients k1/k2 increased with pressure from a low‐pressure limiting value of 14 to a high‐pressure limiting value of 50. The low‐pressure limiting value agrees well with the low‐pressure values found by others. At lower temperatures our high‐pressure values of k1/k2 were larger than deduced from the accepted low‐pressure Arrhenius expression and could be fitted to the expression The mechanism which seems to fit the results best is equation image with k1° = kakb/k‐a and k1∞ = ka.

The reaction of OH with NO

AbstractMixtures of N2O, CO, and NO in excess H2 were photolyzed at 213.9 nm and 298°K. The initially formed O(1D) atoms from the photolysis of N2O abstract an H atom from H2 permitting a study of the competition: equation image From the CO2 yield the relative rate coefficient k1/k2 is obtained. It is found to be slightly dependent on pressure for total pressures (mainly H2) of 95.5 to 768 torr. However, the values are near the high‐pressure limiting value which is found by extrapolation to give k1∞ = 1.2 × 10−11 cm3/sec based on k2∞ = 3.55 × 10−13 cm3/sec.

Experiments on the formation of particles by chemical reactions in the dark and under influence of light.

Some experiments concerning the photochemical production of condensation nuclei are described. Preliminary measurements of filtered atomospheric air, initially free of particles yielded high concentrations of particles by reactions in the dark when the air was previously irradiated by sunlight. In further investigations a definite composition of pure gases was used. The formation of nitric acid particles from NO2 in pure nitrogen of different relative humidities in the dark and under influence of light was investigated. No particle formation was found which could be correlated to any production of nitric acid nuclei. Even within a spectral region in which photolysis of NO2 takes place no HNO3-nucleation could be found. The particles detected under certain conditions of irradiation originate from impurities in the walls of the reaction chamber. Particle growth in an irradiated mixture of N2 and NO2 with benzene is demonstrated and the mean radius of particles is calculated from measurement with a diffusion battery.

ChemInform Abstract: REACTION OF OXYGEN ATOMS WITH SATURATED HYDROCARBONS IN THE LIQUID STATE

AbstractGesättigte Kohlenwaserstoffe reagieren mit Distickstoffmonoxid bei Belichtung hauptsächlich zu Alkoholen.

Evidence for the formation of CO2 in the photolyses of N2O and CO2 in the presence of CO

The photolysis of CO2 at 1633 Å in the presence of 13CO has been found to give an appreciable yield of 13CO2. The photolysis of N2O at 1633 Å conducted in the presence of CO and a large excess of N2 has also been found to lead to CO2 formation. The experimental conditions for both photolyses are such that O 1D atoms generated in the photolysis would be efficiently deactivated to O 3P atoms and the product CO2 is believed to arise from reactions involving the latter. A radical-chain mechanism has been proposed for the formation of CO2, but the possibility of a surface reaction mechanism has not been ruled out.

The Role of Excess Kinetic Energy in the Reactions of O(1D) Atoms

The effect of the excess kinetic energy of O(1D) atoms on their reactions with some gaseous compounds was investigated using two different experimental methods. O(1D) atoms with maximum excess kinetic energies of 41 ± 5 and 31 kcal/mol respectively, were produced by flash photolysis of N2O (1800–2300 Å) and by photolysis of N2O at 2139 Å, in the presence and absence of He which is a deactivator of kinetic energy. In the first method the competition between N2O and one of CO2, Xe, CO, and N2 for O(1D) atoms was measured and it was found that the relative rate constants [Formula: see text] and [Formula: see text] are not affected by the excess kinetic energy of the O(1D) atoms.In the second method the competition between neopentane and one of CO2, Xe, CO, and N2 for O(1D) atoms was measured. The results of the second study were not entirely conclusive. However, they also indicate no effect or at best only a very small effect of excess kinetic energy.

Direct NO2 photolysis rate monitor.

An optically thin actinometer is described which measures the rate of photolysis of NO2 in air. Operating details of the device are reported together with a test in downtown Detroit. The result was that the instrument was more accurate than some of the other test parameters in the range 0–0.5 min−1. Applications to photochemical smog and stratospheric pollution problems are discussed.

On the mechanism of M+O3− and M+NO2− formation by photolysis of matrix samples at 15 K

The species M+O3− and M+NO2− have been produced in matrix samples of alkali atoms, N2O and O2 or NO by mercury arc photolysis. In similar studies, Milligan and Jacox proposed a mechanism involving the diffusion and reaction of the O− anion. We believe that the observations are better explained by photolysis of N2O in the presence of M+O2− with oxygen atom transfer to give M+O3− and the analogous reaction with M+NO− to give M+NO2−.

Primary Processes in the Photolysis of NO2

AbstractThe quantum yield of the photolysis of NO2 (6 Torr) under continuous irradiation has been measured in the presence of N2 in the pressure range 0 ≤ P(N2) ≤ 1000 atm at temperatures 296 ≤ T ≤ 428 K and wavelengths 313 ≤ λ ≤ 416 nm. The primary quantum yield is separated from the contribution of secondary reactions. The dependence of the primary quantum yield on pressure, temperature and wavelength is analyzed in terms of the specific rate constants k(E) for photolysis and detailed rate constants for collisonal energy transfer.

Reaction of oxygen atoms with saturated hydrocarbons in the liquid state

Photolysis of N2O in saturated hydrocarbon solution results mainly in alcohols whose distribution ratios indicate reactions of both excited O(1D) and ground state O(3P) atoms; the competitive reactions of O(1D) and O(3P) atoms were studied by photolysis of N2O dissolved in mixtures of hydrocarbons.

Vacuum ultra-violet photolysis of nitrous oxide. Energy disposal in the reaction O(21 D)+ N2O ? 2NO

The vacuum u.v. photolysis of N2O has been studied at 170 nm, and (140–155) nm. Energy disposal in the reaction O(21D)+ N2O → 2NO has been investigated at the longer wavelengths and the distribution over vibrational states found to be consistent with a ‘complex’ mechanism. At the shorter wavelengths experiments with 15NNO indicate formation of NO via reaction of O(21D), N2(Atilde;3Σ+u) and possibly O(21S) with N2O, though the majority of O(21S) atoms are physically deactivated to the 21D state.