Zoe Loh

Measurement of greenhouse gas emissions from Australian feedlot beef production using open-path spectroscopy and atmospheric dispersion modelling

Feedlot production of beef cattle results in concentrated sources of gas emissions to the atmosphere. Reported here are the preliminary results of a micrometeorological study using open-path concentration measurements to determine whole-of-feedlot emissions of methane (CH4) and ammonia (NH3). Tunable near-infrared diode lasers were used to measure line-averaged (150–400 m) open-path concentrations of CH4 and NH3. A backward Lagrangian stochastic model of atmospheric dispersion and the software package WindTrax were used to estimate greenhouse gas fluxes from the measured concentrations. We studied typical Australian beef feedlots in the north (Queensland) and south (Victoria) of the continent. The data from a campaign during summer show a range of CH4 emissions from 146 g/animal.day in Victoria to 166 g/animal.day in Queensland and NH3 emissions from 125 g/animal.day in Victoria to 253 g/animal.day Queensland.

Cl−–C6H6, Br−–C6H6, and I−–C6H6 anion complexes: Infrared spectra and ab initio calculations

Vibrational predissociation spectroscopy is used to obtain infrared spectra of the Cl−–C6H6, Br−–C6H6, and I−–C6H6 complexes in the region of the benzene CH stretch vibrations (2800–3200 cm−1). The infrared spectra of the three dimers are similar, each exhibiting several narrow bands (full width at half maximum <10 cm−1) that are only slightly redshifted from the absorptions of the free benzene molecule. Ab initio calculations predict that the most stable form of the three complexes is a planar C2v structure in which the halide is hydrogen bonded to two adjacent CH groups. The planar C2v structure in which the halide is linearly H bonded to a single CH group is predicted to be slightly less stable than the bifurcated form. Comparisons between experimental and theoretically predicted infrared spectra confirm that the bifurcated structure is indeed the most stable conformer for all three complexes. Ab initio calculations show that the electron density transfer from the halide to the benzene is not limited t...

Br−-H2 and I−-H2 anion complexes: Infrared spectra and radial intermolecular potential energy curves

Midinfrared spectra of the 81Br−-H2 and I−-H2 anion complexes are measured in the H-H stretch region by monitoring the production of halide anion photofragments. The spectra, which are assigned to complexes containing ortho H2, exhibit rotationally resolved ∑-∑ bands whose origins are redshifted from the molecular hydrogen Q1(1) transition by 110.8 cm−1 (Br−-H2) and 74.1 cm−1 (I−-H2). The complexes are deduced to possess linear equilibrium structures, with vibrationally averaged intermolecular separations between the halide anion and H2 center of mass of 3.461 A (Br−-H2) and 3.851 A (I−-H2). Vibrational excitation of the H2 subunit causes the intermolecular bond to stiffen and contract by 0.115 A (Br−-H2) and 0.112 A (I−-H2). Rydberg–Klein–Rees inversion of the spectroscopic data is used to generate effective radial potential energy curves near the potential minimum that are joined to long-range potential energy curves describing the interaction between an H2 molecule and a point negative charge. From the...

Emissions of the indirect greenhouse gases NH3 and NOx from Australian beef cattle feedlots

Emissions of indirect greenhouse gases, notably the nitrogen gases ammonia (NH3) and the odd oxides of nitrogen (NOx), play important roles in the greenhouse story. Feedlots are intense, but poorly quantified, sources of atmospheric NH3 and although production of NOx is to be expected in feedlots, rates of NOx emission are virtually unknown. In the atmosphere, these gases are involved in several transformations, but eventually return to the earth in gaseous or liquid form and can then undergo further transformations involving the formation and emission of the direct greenhouse gas nitrous oxide (N2O). The IPCC Phase II guidelines estimate that indirect N2O emissions due to atmospheric deposition of N compounds formed from NH3 and NOx could be ~14% of the direct emissions from agricultural soils or from animal production systems. IPCC recommends that these indirect emissions be accounted for in making inventory estimates of N2O emission. This paper is a preliminary report of emissions of NH3 and NOx from two Australian feedlots determined with micrometeorological techniques. Emissions of nitrogen gases from both feedlots were dominated by emissions of NH3. The average NH3 emission rate over both feedlots in winter was 46 g N/animal.day, while that of NOx was less than 1% of that rate at 0.36 g N/animal.day. It was apparent that NH3 release was governed by the wetness of the surface. Rates of emission from the feedlot with the wetter surface were almost three times those from the other. The IPCC default emission factor for the combined emission of NH3 and NOx from livestock is 0.2 kg N/kg N excreted, but in our work, the emission factor was 0.59 kg N/kg N excreted. Potential emissions of N2O due to NH3 and NOx deposition were estimated to be of the same magnitude as the direct N2O emissions, the sum of direct and potential indirect amounting to ~3 g N2O-N/animal.day. If applied nationally, this would represent a contribution of N2O from Australian feedlots of 533Gg CO2-e or 2.2% of all Australian N2O emissions.

The Cl−–CH4 anion dimer: mid infrared spectrum and ab initio calculations

Abstract The Cl − –CH 4 dimer has been investigated using infrared vibrational predissociation spectroscopy (2800–3080 cm −1 range), and through ab initio calculations at the MP2(full)/aug-cc-pVTZ level. The infrared spectrum features parallel and perpendicular bands, associated with excitation of C–H stretch vibrations localized on the CH 4 core. Spectroscopic and theoretical data are consistent with a C 3v proton-bound minimum energy configuration for the complex, although internal rotation of the CH 4 sub-unit is not completely quenched. The calculated barrier for tunneling between equivalent proton-bound minima is 603 cm −1 . Comparisons are made between the properties of the isoelectronic Cl − –H 2 O, Cl − –NH 3 , and Cl − –CH 4 complexes.

Structural and energetic properties of the Br−–C2H2 anion complex from rotationally resolved mid-infrared spectra and ab initio calculations

An infrared vibrational predissociation spectrum of the 79Br−–C2H2 anion complex has been recorded over the 2800–3400 cm−1 range. Bands are observed that correspond to excitation of bound and free C–H stretches of an acetylene molecule engaged in a linear hydrogen bond with Br−. The band associated with the bound C–H stretch displays rotationally resolved substructure. Lower J transitions are absent from the predissociation spectrum, indicating that the upper levels lie below the dissociation threshold. Analysis leads to constants for lower and upper states: v0=2981.28, B″=0.048 84, ΔB=9.3×10−4 cm−1, and a minimum J′=28 for dissociation. The rotational constants correspond to vibrationally averaged separation between Br− and the C2H2 center of mass of 4.11 A in the ground state and 4.07 A in the v3 state. A dissociation energy for Br−–C2H2 of 3020±3 cm−1 is estimated from the energy of the lowest dissociating level. The spectroscopically derived data are corroborated by ab initio calculations conducted at...

Infrared spectra of Br−-(C2H2)n complexes

Abstract Mid-infrared spectra of Br − -(C 2 H 2 ) n (1⩽ n ⩽8) complexes have been recorded using vibrational predissociation spectroscopy. Spectra of smaller clusters ( n ⩽6), feature a single relatively narrow ν 3 absorption red shifted with respect to the free molecule absorption, and are consistent with interior solvation structures containing roughly equivalent C 2 H 2 ligands bound end-on to the central Br − . Onset of the second solvation shell occurs at n =7 and is signalled by the appearance of an additional isolated band situated between the ν 3 absorptions of acetylene molecules bound directly to the Br − core and the one of free acetylene.

Structures of F − -(CH4)n and Cl − -(CH4)n (n = 1,2) Anion Clusters Elucidated through Ab Initio Calculations and Infrared Spectra

Ab initio calculations are performed at the MP2/aug-cc-pVTZ level for F−-CH4 and Cl−-CH4, to show that the dimers have C3v symmetry with the CH4 sub-unit attached to the halide anion by a single hydrogen bond. This geometry is consistent with infrared spectra of F−-CH4 and Cl−-CH4 recorded in the CH-stretch region. The calculations also indicate substantial anharmonicity in the H-bonded CH stretch of F−-CH4. Infrared spectra of the F−-(CH4)2 and Cl−-(CH4)2 trimer clusters are consistent with structures that have two equivalent CH4 sub-units H-bonded to the halide core. Additional bands in the F−-(CH4)2 spectrum are assigned as transitions to CH4 bending overtone and combination levels, gaining infrared intensity from Fermi interaction with the H-bonded CH stretch.

Gaseous Nitrogen Emissions from Australian Cattle Feedlots

At any one time, close to 700,000 beef cattle are raised intensively in Australian feedlots. This chapter describes measurements of emissions of the greenhouse gas N2O and the reactive nitrogen gases NH3 and NOx from two Australian beef cattle feedlots made over two years with open- and closed-path concentration measurement systems and backward Lagrangian stochastic dispersion modelling. Emissions of all three gases exhibited marked diurnal cycles with maxima close to mid-day and minima over night. The average emission rate for N2O was 1.3 ± 1.65 (s.d) kg N ha−1 d−1, that for NH3 was 95 ± 36 kg N ha−1 d−1, and for NOx 1.20 ± 0.58 kg N ha−1 d−1. Extrapolating these figures to all the feedlots in the country and accepting the estimate by Mosier et al. (1998) that 1 % of the NH3 and NOx would be converted to N2O after eventual deposition, the direct emissions of N2O from feedlots amount to 241 kt CO2-e year−1 and those from NH3 plus NOx to 181 kt CO2-e year−1, or 43 % of the total N2O emissions. These direct and indirect emissions are substantial, amounting to 60 % in terms of CO2-e of the CH4 emissions measured in the project.

Locating and confirming the C–H stretch bands of the halide–acetylene anion complexes using argon predissociation spectroscopy

Abstract Infrared spectra of Cl − –C 2 H 2 ·Ar, Br − –C 2 H 2 ·Ar, and I − –C 2 H 2 ·Ar are recorded in the C–H stretch region by monitoring production of X − –C 2 H 2 photofragments. Each spectrum exhibits a single band corresponding to the vibration of a hydrogen-bonded C–H unit ( ν HB =2882, 2982, 3075 cm −1 for Cl − –C 2 H 2 ·Ar, Br − –C 2 H 2 ·Ar, I − –C 2 H 2 ·Ar, respectively). Marked differences between the spectra of Cl − –C 2 H 2 ·Ar and Cl − –C 2 H 2 are attributable to the strong Cl − –HCCH bond which prevents cold Cl − –C 2 H 2 complexes from dissociating following absorption of an infrared photon. The evidence suggests that addition of the first few Ar solvent atoms has a minor influence on the C–H stretch vibrations of the halide–acetylene complexes.