Timothy J. Wallington

Evaluating rare earth element availability: a case with revolutionary demand from clean technologies.

The future availability of rare earth elements (REEs) is of concern due to monopolistic supply conditions, environmentally unsustainable mining practices, and rapid demand growth. We present an evaluation of potential future demand scenarios for REEs with a focus on the issue of comining. Many assumptions were made to simplify the analysis, but the scenarios identify some key variables that could affect future rare earth markets and market behavior. Increased use of wind energy and electric vehicles are key elements of a more sustainable future. However, since present technologies for electric vehicles and wind turbines rely heavily on dysprosium (Dy) and neodymium (Nd), in rare-earth magnets, future adoption of these technologies may result in large and disproportionate increases in the demand for these two elements. For this study, upper and lower bound usage projections for REE in these applications were developed to evaluate the state of future REE supply availability. In the absence of efficient reuse and recycling or the development of technologies which use lower amounts of Dy and Nd, following a path consistent with stabilization of atmospheric CO(2) at 450 ppm may lead to an increase of more than 700% and 2600% for Nd and Dy, respectively, over the next 25 years if the present REE needs in automotive and wind applications are representative of future needs.

Atmospheric chemistry of small organic peroxy radicals

Global atmospheric models play a key role in international assessments of the human impact on global climate and air pollution. To increase the accuracy and facilitate comparison of results from such models, it is essential they contain up-to-date chemical mechanisms. To this end, we present an evaluation of the atmospheric chemistry of the four most abundant organic peroxy radicals: CH3O2, C2H5O2, CH3C(O)O2, and CH3C(O)CH2O2. The literature data for the atmospheric reactions of these radicals are evaluated. In addition, the ultraviolet absorption cross sections for the above radicals and for HO2 have been evaluated. The absorption spectra were fitted to an analytical formula, which enabled published spectra to be screened objectively. Published kinetic and product data were reinterpreted, or in some case reanalyzed, using the new cross sections, leading to a self-consistent set of kinetic, mechanistic, and spectroscopic data. Product studies were also evaluated. A set of peroxy radical reaction rate coefficients and products are recommended for use in atmospheric modeling. A three-dimensional global chemical transport model (the Intermediate Model for the Global Evolution of Species, IMAGES) was run using both previously recommended rate coefficients and the current set to highlight the sensitivity of key atmospheric trace species to the peroxy radical chemistry used in the model.

Radiative forcing of climate by hydrochlorofluorocarbons and hydrofluorocarbons

We measure infrared absorption spectra of 18 hydrochlorofluorocarbons and hydrofluorocarbons, seven of which do not yet appear in the literature. The spectra are used in a narrowband model of the terrestrial infrared radiation to calculate radiative forcing and global warming potentials. We investigate the sensitivity of the radiative forcing to the absorption spectrum temperature dependence, halocarbon vertical profile, stratospheric adjustment, cloudiness, spectral overlap, and latitude, and we make some recommendations for the reporting of radiative forcings that would help to resolve discrepancies between assessments. We investigate simple methods of estimating instantaneous radiative forcing directly from a molecules absorption spectrum and we present a new method that agrees to within 0.3% with our narrowband model results.

Evaluated kinetic and photochemical data for atmospheric chemistry: Volume VI – heterogeneous reactions with liquid substrates

Atmospheric chemistry is the study of the complex network of thermal and photochemical processes occurring in the gas and condensed (cloud droplets, aerosol particles, ice crystals) phase as well as in multiphase processes. Chemical kinetic modeling is required to interpret observations in the field. This necessitates the availability of a robust, reliable, and regularly updated database of elementary reactions for use in chemical-radiative-transport models. Combustion chemistry and plasma processing for semiconductor applications require the same type of database.

Kinetics and mechanisms of the reactions of chlorine atoms with ethane, propane, and n-butane

Absolute (flash photolysis) and relative (FTIR-smog chamber and GC) rate techniques were used to study the gas-phase reactions of Cl atoms with C2H6 (k1), C3H8 (k3), and n-C4H10 (k2). At 297 ± 1 K the results from the two relative rate techniques can be combined to give k2/k1 = (3.76 ± 0.20) and k3/k1 = (2.42 ± 0.10). Experiments performed at 298–540 K give k2/k1 = (2.0 ± 0.1)exp((183 ± 20)/T). At 296 K the reaction of Cl atoms with C3H8 produces yields of 43 ± 3% 1-propyl and 57 ± 3% 2-propyl radicals, while the reaction of Cl atoms with n-C4H10 produces 29 ± 2% 1-butyl and 71 ± 2% 2-butyl radicals. At 298 K and 10–700 torr of N2 diluent, 1- and 2-butyl radicals were found to react with Cl2 with rate coefficients which are 3.1 ± 0.2 and 2.8 ± 0.1 times greater than the corresponding reactions with O2. A flash-photolysis technique was used to measure k1 = (5.75 ± 0.45) × 10−11 and k2 = (2.15 ± 0.15) × 10−10 cm3 molecule−1 s−1 at 298 K, giving a rate coefficient ratio k2/k1 = 3.74 ± 0.40, in excellent agreement with the relative rate studies. The present results are used to put other, relative rate measurements of the reactions of chlorine atoms with alkanes on an absolute basis. It is found that the rate of hydrogen abstraction from a methyl group is not influenced by neighboring groups. The results are used to refine empirical approaches to predicting the reactivity of Cl atoms towards hydrocarbons. Finally, relative rate methods were used to measure rate coefficients at 298 K for the reaction of Cl atoms with 1- and 2-chloropropane and 1- and 2-chlorobutane of (4.8 ± 0.3) × 10−11, (2.0 ± 0.1) × 10−10, (1.1 ± 0.2) × 10−10, and (7.0 ± 0.8) × 10−11 cm3 molecule−1 s−1, respectively.

Fourier transform infrared kinetic studies of the reaction of HONO with HNO3, NO3 and N2O5 at 295 K

The kinetics of the reaction of nitrous acid (HONO) with nitric acid (HNO3), nitrate radicals (NO3) and dinitrogen pentoxide (N2O5) have been studied using Fourier transform infrared spectroscopy. Experiments were performed at 700 torr total pressure using synthetic air or argon as diluents. From the observed decay of HONO in the presence of HNO3 a rate constant of k<7×10-19 cm3 molecule-1 s-1 was derived for the reaction of HONO with HNO3. From the observed decay of HONO in the presence of mixtures of N2O5 and NO2 we have also derived upper limits for the rate constants of the reactions of HONO with NO3 and N2O5 of 2×10-15 and 7×10-19 cm3 molecule-1 s-1, respectively. These results are discussed with respect to previous studies and to the atmospheric chemistry of HONO.

A kinetic study of the reaction of chlorine atoms with CF3CHCl2, CF3CH2F, CFCl2CH3, CF2ClCH3, CHF2CH3, CH3D, CH2D2, CHD3, CD4, and CD3Cl at 295±2 K

Abstract The relative rate technique has been used to measure the reactivity of chlorine atoms with CF 3 CHCl 2 (HCFC-123), CF 3 CH 2 F (HFC-134a), CFCl 2 CH 3 (HCFC-141b), CF 2 ClCH 3 (HCFC-142b), CHF 2 CH 3 (HFC-152a), CH 3 D, CH 2 D 2 , CHD 3 , CD 4 , and CD 3 Cl relative to methane. Using a rate constant of 1.0×10 −13 cm 3 molecule −1 s −1 for the reaction of Cl atoms with methane, the following rate constants were derived, in units of cm 3 molecule −1 s −1 : HCFC-123, (1.22±0.18)×10 −14 ; HFC-134a, (1.38±0.18)×10 −15 ; HCFC-141b, (2.04±0.22)×10 −15 ; HCFC-142b, (3.90±0.52)×10 −16 ; HFC-152a, (2.39±0.07)×10 −13 ; CH 3 D, (7.35±0.02)×10 −14 ; CH 2 D 2 , (4.57±0.22)×10 −14 ; CHD 3 , (2.32±0.05)×10 −14 ; CD 4 , (6.1±0.5)×10 −15 ; and CD 3 Cl, (8.89±0.26)×10 −14 . Quoted errors are 2σ. Experiments were performed at 295±2 K and 700 Torr total pressure of nitrogen. The results are discussed with respect to the previous literature data and to the interpretation of laboratory studies of the atmospheric chemistry of HCFC compounds.

Life-cycle energy and greenhouse gas emission benefits of lightweighting in automobiles: review and harmonization.

Replacing conventional materials (steel and iron) with lighter alternatives (e.g., aluminum, magnesium, and composites) decreases energy consumption and greenhouse gas (GHG) emissions during vehicle use but may increase energy consumption and GHG emissions during vehicle production. There have been many life cycle assessment (LCA) studies on the benefits of vehicle lightweighting, but the wide variety of assumptions used makes it difficult to compare results from the studies. To clarify the benefits of vehicle lightweighting we have reviewed the available literature (43 studies). The GHG emissions and primary energy results from 33 studies that passed a screening process were harmonized using a common set of assumptions (lifetime distance traveled, fuel-mass coefficient, secondary weight reduction factor, fuel consumption allocation, recycling rate, and energy intensity of materials). After harmonization, all studies indicate that using aluminum, glass-fiber reinforced plastic, and high strength steel to replace conventional steel decreases the vehicle life cycle energy use and GHG emissions. Given the flexibility in options implied by the variety of materials available and consensus that these materials have substantial energy and emissions benefits, it seems likely that lightweighting will be used increasingly to improve fuel economy and reduce life cycle GHG emissions from vehicles.

Fourier transform infrared studies of the reaction of Cl atoms with PAN, PPN, CH3OOH, HCOOH, CH3COCH3 and CH3COC2H5 at 295±2 K

The relative rate technique has been used to measure rate constants for the reaction of chlorine atoms with peroxyacetylnitrate (PAN), peroxypropionylnitrate (PPN), methylhydroperoxide, formic acid, acetone and butanone. Decay rates of these organic species were measured relative to one or more of the following reference compounds; ethene, ethane, chloroethane, chloromethane, and methane. Using rate constants of 9.29×10−11, 5.7×10−11, 8.04×10−12, 4.9×10−13, and 1.0×10−13 cm3 molecule−1 sec−1 for the reaction of Cl atoms with ethene, ethane, chloroethane, chloromethane, and methane respectively, the following rate constants were derived, in units of cm3 molecule−1 s−1: PAN, <7×10−15; PPN, (1.14±0.12)×10−12; HCOOH, (2.00±0.25)×10−13; CH3OOH, (5.70±0.23)×10−11; CH3COCH3, (2.37±0.12)×10−12; and CH3COC2H5, (4.13±0.57)×10−11. Quoted errors represent 2σ and do not include possible systematic errors due to errors in the reference rate constants. Experiments were performed at 295±2 K and 700 torr total pressure of nitrogen or synthetic air. The results are discussed with respect to the previous literature data and to the modelling of nonmethane hydrocarbon oxidation in the atmosphere.In recent discussions with Dr. R. A. Cox of Harwell Laboratory, UKAEA, we learnt of a preliminary value for the rate constant of the reaction of Cl with acetone of (2.5±1.0)×10−12 cm3 molecule−1 sec−1 measured by R. A. Cox, M. E. Jenkin, and G. D. Hayman using molecular modulation techniques. This value is in good agreement with our results.

Absolute rate constants for the reaction of NO with a series of peroxy radicals in the gas phase at 295 K

Abstract The rate constants for the reaction of NO with a series of peroxy radicals: CH 3 O 2 , C 2 H 5 O 2 , (CH 3 ) 3 CCH 2 O 2 , (CH 3 ) 3 CC(CH 3 ) 2 CH 2 O 2 , CH 2 FO 2 , CH 2 ClO 2 , CH 2 BrO 2 , CHF 2 O 2 , CF 2 ClO 2 , CHF 2 CF 2 O 2 , CF 3 CF 2 O 2 , CFCl 2 CH 2 O 2 and CF 2 ClCH 2 O 2 were measured at 298 K and a total pressure of 1 atm. The rate constants were obtained using the absolute technique of pulse radiolysis combined with time-resolved UVVIS spectroscopy. The results are discussed in terms of reactivity trends and the atmospheric chemistry of peroxy radicals.