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Summary: Recent studies have suggested that in certain environments, tree stems emit methane (CH4). This study explored the mechanism of CH4 emission from the stem surfaces of Alnus japonica in a riparian wetland. Stem CH4 emission rates and sap flux were monitored year‐round, and fine‐root anatomy was investigated.CH4 emission rates were estimated using a closed‐chamber method. Sap flux was measured using Granier‐type thermal dissipation probes. Root anatomy was studied using both optical and cryo‐scanning electron microscopy.CH4 emissions during the leafy season exhibited a diurnally changing component superimposed upon an underlying continuum in which the diurnal variation was in phase with sap flux. We propose a model in which stem CH4 emission involves at least two processes: a sap flux‐dependent component responsible for the diurnal changes, and a sap flux‐independent component responsible for the background continuum. The contribution ratios of the two processes are season‐dependent.The background continuum possibly resulted from the diffusive transport of gaseous CH4 from the roots to the upper trunk. Root anatomy analysis indicated that the intercellular space of the cortex and empty xylem cells in fine roots could serve as a passageway for transport of gaseous CH4. [ABSTRACT FROM AUTHOR]

Tree‐mediated methane (CH4) emissions represent an uncertain pathway of the total CH4 flux released from forested ecosystems. We measured the stem CH4 fluxes from Alnus japonica in a riparian wetland of a temperate forest for a year from 2017 to 2018, using automated chambers. The stem CH4 fluxes varied seasonally, showing summertime maxima and wintertime minima. Medians of stem CH4 fluxes were 12.9, 0.5, 0.4, and 13.4 nmol m−2 s−1 during autumn, winter, spring, and summer, respectively. Dissolved CH4 concentration in groundwater beneath the trees was the major controlling factor of the stem CH4 fluxes. Temporal variations in soil environmental conditions (temperature and groundwater level) controlled dissolved CH4 concentrations in groundwater, and accordingly, stem CH4 fluxes. In addition, stem CH4 emissions were observed when the sap flux diminished during the defoliation period. These results indicate that CH4 in the rhizosphere is mainly transported in the gaseous form through intercellular space in trees. Intense rainfall occasionally caused a transient increase in the stem CH4 emissions, which was attributed to the temporal changes in the groundwater flow paths by rainfall affecting the belowground CH4 concentrations. Our findings highlight the need for continuous stem CH4 flux measurements for improved understanding of the controlling factors and future response of CH4 dynamics in forests, with regards to climate change. Plain Language Summary: Methane (CH4) is an important greenhouse gas. Aerated forest soils are assumed to be an atmospheric CH4 sink. However, the results of recent experimental and field studies suggest that tree‐mediated CH4 emissions have the potential to offset the soil CH4 sink and may convert the forest from a net sink to a net source. Tree‐mediated CH4 emissions represent an uncertain pathway of the total CH4 flux from forested ecosystems. In this study, we conducted continuous field measurements for a year, on the stem CH4 fluxes from Alnus japonica standing in a riparian wetland. We found that the seasonal variation in the stem CH4 fluxes is controlled by seasonal variations of the dissolved CH4 concentrations in the groundwater. Temporal changes in soil environmental conditions (temperature and groundwater level) controlled dissolved CH4 concentrations in groundwater. It was also found that intense rainfall causes a transient increase in the stem CH4 emissions. At the study site, changes in the groundwater flow paths by rainfall affect the dissolved CH4 concentrations in the rhizosphere and the stem CH4 flux. Understanding these mechanisms will contribute to the development of models used to estimate the CH4 emissions from forest ecosystems and predict their response to environmental changes. Key Points: The stem CH4 fluxes from Alnus japonica seasonally vary and increase during and after intense rainfallDissolved CH4 concentration in groundwater is a major factor controlling stem CH4 flux as shown by path analysisRhizospheric CH4 is mainly transported in the gaseous form through intercellular space in trees and partly by the transpiration stream [ABSTRACT FROM AUTHOR]

Potential energy curves of triplet states for collinear O-O[sub 2] were calculated by ab initio CASSCF and MRSDCI methods. We found a pseudocrossing between 1 ³Σ[sup -] (6 ³A″) and 2 ³Σ[sup -] (7 ³A″) states at long O-O[sub 2] separation. The electronic quenching reaction, O(¹D)+O[sub 2](X ³Σ[sup -, sub g])→O(³P) + O[sub 2](b ¹&Sigma[sup +, sub g]), is dominated by the nonadiabatic transition via the pseudocrossing. The collision energy dependence of the quenching reaction probability, which is evaluated by Zhu and Nakamura's formula, is found to be in good agreement with experiment. [ABSTRACT FROM AUTHOR]

Determines the heat of formation of oxygen using vacuum ultraviolet laser-induced fluorescence spectroscopy and two-dimensional product imaging techniques. Photofragment excitation spectrum for oxygen products; Value of the bond dissociation energy; Standard heat formation of oxygen.

Examines wavelength and temperature dependence of the absolute O1D production yield from ozone photodissociation through laser induced fluorescence. Background of ozone photochemistry study; Determination of the wavelength and temperature dependence; Analysis of photodissociation process model.

Examines the photofragment excitation spectrum for oxygen production from the photolysis of ozone under supersonic free-jet conditions. Bond dissociation energy; Cut-off wavelength for vibrationally hot band excitation to the dissociative continuum of oxygen; Sharp peaks corresponding to vibrational bands in the Huggins system.

The photofragment excitation spectra for O(1D) production from the 317–327 nm photolysis of ozone under supersonic free-jet and low-temperature flow conditions show structure superimposed on an underlying continuum. Doppler profiles of the nascent O(1D) photofragments confirm that the O(1D) formed by photolysis at the wavelengths of the peaks in the photofragment excitation spectrum arises from the hitherto unobserved spin-forbidden predissociation to O(1D)+O2(X 3Σg-) products. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The phenomenon of interference of the amplitude for absorption of one photon of frequency 3ω and the amplitude for absorption of three photons of frequency ω was theoretically predicted by Shapiro, Hepburn, and Brumer. The interference was demonstrated experimentally by varying the relative phase between the tripled frequency photon and three photons with the fundamental frequency by the groups of Elliott and Gordon in atoms and small molecules. In order to see how general this phenomenon is, five compounds were studied, ammonia, trimethylamine, triethylamine, cyclooctatetraene, and 1,1-dimethylhydrazine. CH3I was used as the tripling gas for light in the range 604–600 nm. Interference was observed in all cases. The last four compounds have low ionization potentials and interference was observed between a 3+1 and a 1+1 ionization process with a maximum modulation of 22%. NH3 with a higher ionization potential requires absorption of 3+2 or 1+2 photons and exhibits a maximum modulation of 33%. We conclude that molecular size is no obstacle and that as long as a molecule has sufficiently strong absorption at the tripled frequency, and sufficient vapor pressure, and the laser fundamental beam is very strong, phase control of interference is observable. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Methane ( $${\mathrm {CH}}_{4}$$ ) fluxes observed with the eddy-covariance technique using an open-path $${\mathrm {CH}}_{4}$$ analyzer and a closed-path $${\mathrm {CH}}_{4}$$ analyzer in a rice paddy field were evaluated with an emphasis on the flux correction methodology. A comparison of the fluxes obtained by the analyzers revealed that both the open-path and closed-path techniques were reliable, provided that appropriate corrections were applied. For the open-path approach, the influence of fluctuations in air density and the line shape variation in laser absorption spectroscopy (hereafter, spectroscopic effect) was significant, and the relative importance of these corrections would increase when observing small $${\mathrm {CH}}_{4}$$ fluxes. A new procedure proposed by Li-Cor Inc. enabled us to accurately adjust for these effects. The high-frequency loss of the open-path $${\mathrm {CH}}_{4}$$ analyzer was relatively large (11 % of the uncorrected covariance) at an observation height of 2.5 m above the canopy owing to its longer physical path length, and this correction should be carefully applied before correcting for the influence of fluctuations in air density and the spectroscopic effect. Uncorrected $${\mathrm {CH}}_{4}$$ fluxes observed with the closed-path analyzer were substantially underestimated (37 %) due to high-frequency loss because an undersized pump was used in the observation. Both the bandpass and transfer function approaches successfully corrected this flux loss. Careful determination of the bandpass frequency range or the transfer function and the cospectral model is required for the accurate calculation of $${\mathrm {CH}}_{4}$$ fluxes with the closed-path technique. [ABSTRACT FROM AUTHOR]

Very few studies have conducted long-term observations of methane (CH) flux over forest canopies. In this study, we continuously measured CH fluxes over an evergreen coniferous (Japanese cypress) forest canopy throughout 1 year, using a micrometeorological relaxed eddy accumulation (REA) system with tuneable diode laser spectroscopy (TDLS) detection. The Japanese cypress forest, which is a common forest type in warm-temperate Asian monsoon regions with a wet summer, switched seasonally between a sink and source of CH probably because of competition by methanogens and methanotrophs, which are both influenced by soil conditions (e.g., soil temperature and soil moisture). At hourly to daily timescales, the CH fluxes were sensitive to rainfall, probably because CH emission increased and/or absorption decreased during and after rainfall. The observed canopy-scale fluxes showed complex behaviours beyond those expected from previous plot-scale measurements and the CH fluxes changed from sink to source and vice versa. [ABSTRACT FROM AUTHOR]

Measurements of the local distribution of atmospheric nitrogen dioxide (NO2) by long-path pulsed differential optical absorption spectroscopy (LP-PDOAS) in Tokyo during August 2008 are presented. Two LP-PDOAS systems simultaneously measured average NO2 temporal mixing ratios along two different paths from a single observation point. Two flashing aviation obstruction lights, located 7.0 km north and 6.3 km east from the observation point, were used as light sources, allowing spatiotemporal variations of NO2 in Tokyo to be inferred. The LP-PDOAS data were compared with ground-based data measured using chemiluminescence. Surface wind data indicated that large inhomogeneities were present in the spatial NO2 distributions under southerly wind conditions, while northerly wind conditions displayed greater homogeneity between the two systems. The higher correlation in the NO2 mixing ratio between the two LP-PDOAS systems was observed under northerly wind conditions with a correlation factor R2 = 0.88. We demonstrated that the combined deployment of two LP-PDOAS systems oriented in different directions provides detailed information on the spatial distribution of NO2. [ABSTRACT FROM AUTHOR]

Particle mass spectrometers of two types-a time-of-flight aerosol mass spectrometer (AMS) of Aerodyne Research Inc. and a laser desorption/ionization single particle aerosol mass spectrometer (LISPA-MS) developed at Nagoya University-were deployed to characterize aerosol particles in the Tokyo metropolitan area during the summer of 2008. Based on the ensemble measurements by AMS, equivalent mass concentration of organic aerosol, traced by mass-to-charge ratio (m/z) 44, showed a closer correlation with particulate nitrate and gas-phase odd oxygen, [O3+NO2], whereas equivalent mass concentration of organic aerosol, traced by m/z 57, did not. On a particle-by-particle basis, the relative signal peak area of various target species in the LISPA-MS spectra, which was calculated as the ion-signal fraction of the species relative to the total signal peak area summed over all the ion peaks in each spectrum, was used as a measure of the relative amount of the species. A rough qualitative agreement was obtained between the temporal variation observed in the LISPA-MS RCOO- signal and that in the AMS m/z 44, but not the AMS m/z 57, in which the LISPA-MS RCOO- signal was defined as the sum of the relative signal peak areas of 17 different negative-ion mass peaks used as markers of oxygenated organics. Analysis of the LISPA-MS spectra also showed that approximately 95% of the oxygen-containing organic particles contained nitrate, which is expected to be responsible in part for the correlation between AMS m/z 44 and AMS nitrate. [ABSTRACT FROM AUTHOR]

Smog chamber relative rate techniques were used to measure rate coefficients of (5.00 ± 0.54) × 10-11, (5.87 ± 0.63) × 10-11, and (6.49 ± 0.82) × 10-11 cm3 molecule-1 s-1 in 700 Torr air at 296 ± 1 K for reactions of OH radicals with allyl alcohol, 1-buten-3-ol, and 2-methyl-3-buten-2-ol, respectively; the quoted uncertainties encompass the extremes of determinations using two different reference compounds. The OH-initiated oxidation of allyl alcohol in the presence of NOx gives glycolaldehyde in a molar yield of 0.85 ± 0.08; the quoted uncertainty is two standard deviations. Oxidation of 2-methyl-3-buten-2-ol gives acetone and glycolaldehyde in molar yields of 0.66 ± 0.06 and 0.56 ± 0.05, respectively. The reaction of OH radicals with allyl alcohol, 1-buten-3-ol, and 2-methyl-3-buten-2-ol proceeds predominately via addition to the >C&dbond;CH2 double bond with most of the addition occurring to the terminal carbon. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 151–158, 2010 [ABSTRACT FROM AUTHOR]

The thermal decomposition rate of N2O5 in 760 Torr of air as a function of temperature between 314 and 348 K has been investigated using the technique of pulsed laser cavity ring-down spectroscopy (CRDS) detection of NO3 radicals at 662 nm. The Arrhenius expression of the thermal decomposition rates determined by the CRDS experiments, which is incorporated with literature values down to 263 K, is given by 1.36 × 1015 exp{(-11300 ± 200)/T} s-1 over the temperature range 263–348 K. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 679–684, 2008 [ABSTRACT FROM AUTHOR]

Pulsed laser photolysis/vacuum ultraviolet laser-induced fluorescence techniques were used to measure rate coefficients for Cl atom reactions with a series of fluoroalkenes (CxF2x+1CH&dbond;CH2, x = 1,2,4,6,8) in 6–10 Torr of CF4 diluent at 295 ± 2 K. Rate coefficients (units of 10-11 cm3 molecule-1s-1) of 4.49 ± 0.64, 6.58 ± 0.59, 8.91 ± 0.58, 9.27 ± 0.64, and 9.00 ± 0.87 were determined for CxF2x+1CH&dbond;CH2 with x = 1,2,4,6, and 8, respectively. In 6–10 Torr of CF4 diluent, the kinetics of the title reactions are at, or near, the high-pressure limit for x = 4, 6, and 8, approximately 30% below the high-pressure limit for x = 2, and approximately 50% below the high-pressure limit for x = 1. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 328–332, 2007 [ABSTRACT FROM AUTHOR]

The isotopic ratio of molecules often provides valuable information about past or presently occurring processes in the atmosphere because chemical and physical processes may give rise to isotope fractionation of molecular species. However, there are so far no published satellite measurements on the spatial and temporal variations of ozone isotopes in the stratosphere. Spectroscopic remote sensing methods can theoretically be used to observe ozone isotope fractionation on a global scale, but sufficient accuracy has not yet been achieved. A new generation of submillimeter-wave receivers employing sensitive superconductor-insulator-superconductor (SIS) detector technology will provide new opportunities for precise remote sensing measurements of ozone isotopes on a global scale. We have estimated the observation capabilities of two different SIS instruments, namely the space-station-borne Japanese Experimental Module/Sub-Millimeter-wave Limb Emission Sounder (JEM/SMILES) instrument, currently planned for launch in 2008, as well as the airborne Submillimeter wave Atmospheric Sounder/Airborne Submillimeter SIS Radiometer (SUMAS/ASUR) sensor. Measurements of the airborne sensor, conducted in 1996, are presented in order to demonstrate the detection of normal-O3 and asymmetric-18-O3 in the SMILES frequency bands. In the ideal case, JEM/SMILES has the capability to measure the ozone isotope enrichment (δMO3) in the middle stratosphere with a precision of ∼12‰∼11‰, and ∼9‰, for asymmetric-18-O3, symmetric-17-O3, asymmetric-17-O3, respectively, for a daily zonal mean product with resolution of 10° in latitude. The systematic error, including contributions of all instrumental and spectroscopic uncertainties, is estimated to be of the order of 100‰ to 200‰ and should be reduced by prelaunch laboratory measurements and in-flight calibrations. A remaining bias in the SMILES measurements will have to be quantified by dedicated validation campaigns. JEM/SMILES should then be capable to provide valuable information on the global distribution and seasonal variation of ozone isotope fractionation in the stratosphere. This new technology will allow us to shed new light on this still open issue in atmospheric sciences. [ABSTRACT FROM AUTHOR]

A high-sensitive technique to detect O(1S) atoms using vacuum ultraviolet laser-induced fluorescence (VUV-LIF) spectroscopy has been applied to study the O(1S) production process from the UV photodissociation of O3, N2O, and H2O2. The quantum yields for O(1S) formation from O3 photolysis at 215 and 220 nm are determined to be (1.4 ± 0.4) × 10−4 and (5 ± 3) × 10−5, respectively. Based on thermochemical considerations, the O(1S) formation from O3 photolysis at 215 and 220 nm is attributed to a spin-forbidden process of O(1S)+O2(X3Σg −). Analysis of the Doppler profile of O(1S) produced from O3 photolysis at 193 nm also indicates that the O(1S) atoms are produced from the spin-forbidden process. In the photolysis of N2O and H2O2 at 193 nm, no discernible signal of O(1S) atoms has been detected. The upper limit values of the quantum yields for O(1S) production from N2O and H2O2 photolysis at 193 nm are estimated to be 8 × 10−5 and 3 × 10−5, respectively. Using the experimental results, the impact of the O(1S) formation from O3 photolysis on the atmospheric OH radical formation through the reaction of O(1S)+H2O has been estimated. The calculated results show that the contribution of the O(1S)+H2O reaction to the OH production rate is ∼2% of that of the O(1D)+H2O reaction at 30 km altitude in mid-latitude. Implications of the present laboratory experimental results for the terrestrial airglow of O(1S) at 557.7 nm have also been discussed. [ABSTRACT FROM AUTHOR]

Photodissociation processes of H2O2 in the range 193–240 nm have been studied by pulsed laser photolysis and laser-induced fluorescence detection of H atom fragments at 121.56 nm. The quantum yield values for H atom formation at 295 ± 2 K have been determined to be 0.20 ± 0.03, 0.038 ± 0.008, 0.029 ± 0.003, 0.015 ± 0.006, 0.007 ± 0.002 at 193, 207, 210, 220, and 230 nm, respectively. At 240 nm, only the upper limit value of <0.002 has been obtained. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 751–754, 2005 [ABSTRACT FROM AUTHOR]