Eric A. Betterton

Henry's law constants of some environmentally important aldehydes

The Henry’s law constants of seven aldehydes have been determined as a function of temperature by bubble-column and by head-space techniques. The compounds were chosen for their potential importance in the polluted troposphere and to allow structure-reactivity patterns to be investigated. The results (at 25 oC) are as follows (in units of M atm^(-1)): chloral, 3.44 X 10^5; glyoxal, ≥ 13 X 10^5; methylglyoxal, 3.71 X 10^3; formaldehyde, 2.97 X 10^3; benzaldehyde, 3.74 X 10^1; hydroxyacetaldehyde, 4.14 X 10^4; acetaldehyde, 1.14 X 10^1. A plot of Taft’s parameter, ∑σ^*, vs log H^* (the apparent Henry’s law constant) gives a straight line with a slope of 1.72. H^* for formaldehyde is anomalously high, as expected, but the extremely high value for hydroxyacetaldehyde was unexpected and may indicate that α-hydroxy-substituted aldehydes could have an unusually high affinity for the aqueous phase. The intrinsic Henry’s law constants, H, corrected for hydration, do not show a clear structure-reactivity pattern for this series of aldehydes.

A review on the importance of metals and metalloids in atmospheric dust and aerosol from mining operations

Contaminants can be transported rapidly and over relatively long distances by atmospheric dust and aerosol relative to other media such as water, soil and biota; yet few studies have explicitly evaluated the environmental implications of this pathway, making it a fundamental but understudied transport mechanism. Although there are numerous natural and anthropogenic activities that can increase dust and aerosol emissions and contaminant levels in the environment, mining operations are notable with respect to the quantity of particulates generated, the global extent of area impacted, and the toxicity of contaminants associated with the emissions. Here we review (i) the environmental fate and transport of metals and metalloids in dust and aerosol from mining operations, (ii) current methodologies used to assess contaminant concentrations and particulate emissions, and (iii) the potential health and environmental risks associated with airborne contaminants from mining operations. The review evaluates future research priorities based on the available literature and suggest that there is a particular need to measure and understand the generation, fate and transport of airborne particulates from mining operations, specifically the finer particle fraction. More generally, our findings suggest that mining operations play an important but underappreciated role in the generation of contaminated atmospheric dust and aerosol and the transport of metal and metalloid contaminants, and highlight the need for further research in this area. The role of mining activities in the fate and transport of environmental contaminants may become increasingly important in the coming decades, as climate change and land use are projected to intensify, both of which can substantially increase the potential for dust emissions and transport.

Electrolytic oxidation of trichloroethylene using a ceramic anode

Trichloroethylene (TCE) was transformed to CO2, CO, Cl− and ClO3− at the anode of a two-chambered electrolytic cell. The working electrode was constructed from Ebonex®, an electrically conductive ceramic (Ti4O7). Under our experimental conditions (anode potential Ea = 2.5 to 4.3 V vs SSCE), the disappearance of TCE was first order in TCE concentration. The transformation rate was independent of pH in the range 1.6 < pH < 11. TCE oxidation occurred only on the anodic surface and was limited by mass transport at high potentials (Ea > 4.0V). The maximum (transport-limited), surface-area-normalized rate constant was about 0.002 43cms−1. Carbon-containing products included CO2 primarily with traces of CO. At neutral and alkaline pHs, the only chlorine-containing products were Cl− and ClO3−. Hydroxyl radicals were detected in the anodic compartment using a spin trap (4-POBN). A kinetic model was successfully correlated with experimental results.

Kinetics and mechanism of reductive dehalogenation of carbon tetrachloride using zero-valence metals

Abstract Elemental iron and zinc reduced part-per-thousand levels of aqueous-phase carbon tetrachloride to chloroform in a few hours. Free metal ions, chloride ion and hydrogen gas were produced in the reaction; protons were consumed. Process kinetics were dependent on solution pH, surface area of the elemental metal, carbon tetrachloride concentration, buffer selection and solvent composition (volume fraction 2-propanol). Reaction rate was first-order with respect to carbon tetrachloride at concentrations less than 7.5 mM. This class of reactions offers promise as a means for initiating the destruction of heavily halogenated organic compounds.

An aerosol climatology for a rapidly growing arid region (southern Arizona): Major aerosol species and remotely sensed aerosol properties

This study reports a comprehensive characterization of atmospheric aerosol particle properties in relation to meteorological and back trajectory data in the southern Arizona region, which includes two of the fastest growing metropolitan areas in the United States (Phoenix and Tucson). Multiple data sets (MODIS, AERONET, OMI/TOMS, MISR, GOCART, ground-based aerosol measurements) are used to examine monthly trends in aerosol composition, aerosol optical depth (AOD), and aerosol size. Fine soil, sulfate, and organics dominate PM2.5 mass in the region. Dust strongly influences the region between March and July owing to the dry and hot meteorological conditions and back trajectory patterns. Because monsoon precipitation begins typically in July, dust levels decrease, while AOD, sulfate, and organic aerosol reach their maximum levels because of summertime photochemistry and monsoon moisture. Evidence points to biogenic volatile organic compounds being a significant source of secondary organic aerosol in this region. Biomass burning also is shown to be a major contributor to the carbonaceous aerosol budget in the region, leading to enhanced organic and elemental carbon levels aloft at a sky-island site north of Tucson (Mt. Lemmon). Phoenix exhibits different monthly trends for aerosol components in comparison with the other sites owing to the strong influence of fossil carbon and anthropogenic dust. Trend analyses between 1988 and 2009 indicate that the strongest statistically significant trends are reductions in sulfate, elemental carbon, and organic carbon, and increases in fine soil during the spring (March-May) at select sites. These results can be explained by population growth, land-use changes, and improved source controls.

Henry's law coefficients of formic and acetic acids

The Henrys law constants, KH, of dilute aqueous formic and acetic acids were determined experimentally as a function of concentration and temperature using a new counterflow packed-column technique. KH was found to be (8.9±1.3)×103 and (4.1±0.4)×103 M atm-1 at 25°C for HCOOH and CH3COOH, respectively. The reaction enthalpies, ΔH, were found to be −51±2 kJ mol-1 and −52±1 kJ mol-1 for formic and acetic acid, respectively. These are in good agreement with calculated thermochemical values.Whereas the KH values are in reasonably good agreement with certain other experimentally determined values, KH (HCOOH) is two to three times higher than calculated thermochemical values while KH (CH3COOH) is lower than the two calculated values.The ‘best’ experimental values appear to be (11±2)×103 M atm-1 and (7±3)×103 M atm-1 for HCOOH and CH3COOH, respectively.

Hygroscopic and Chemical Properties of Aerosols collected near a Copper Smelter: Implications for Public and Environmental Health

Particulate matter emissions near active copper smelters and mine tailings in the southwestern United States pose a potential threat to nearby environments owing to toxic species that can be inhaled and deposited in various regions of the body depending on the composition and size of the particles, which are linked by particle hygroscopic properties. This study reports the first simultaneous measurements of size-resolved chemical and hygroscopic properties of particles next to an active copper smelter and mine tailings by the towns of Hayden and Winkelman in southern Arizona. Size-resolved particulate matter samples were examined with inductively coupled plasma mass spectrometry, ion chromatography, and a humidified tandem differential mobility analyzer. Aerosol particles collected at the measurement site are enriched in metals and metalloids (e.g., arsenic, lead, and cadmium) and water-uptake measurements of aqueous extracts of collected samples indicate that the particle diameter range of particles most enriched with these species (0.18-0.55 μm) overlaps with the most hygroscopic mode at a relative humidity of 90% (0.10-0.32 μm). These measurements have implications for public health, microphysical effects of aerosols, and regional impacts owing to the transport and deposition of contaminated aerosol particles.

Electrolytic reduction of trichloroethylene and chloroform at a Pt- or Pd-coated ceramic cathode

Trichloroethylene (TCE) and chloroform (CF) were electrolytically dechlorinated in a two-compartment cell in which the working electrode (cathode) consisted of an Ebonex ceramic sheet plated with platinum (Pt) or palladium (Pd). The halogenated targets were not reduced using a cathode of untreated Ebonex. Under typical experimental conditions (e.g., cathode potentials EC = −0.3 V to −1.4 V vs SHE, pH 7.0), transformations were first order in TCE and CF. Reaction kinetics were mass transport limited at EC < −1.4 V. Transport-limited rate constants were 0.45 cm min−1 for TCE reduction and 0.42 cm min−1 for CF. The primary products of CF reduction were methane and hydrochloric acid. For TCE reduction, major products were ethane, ethylene and hydrochloric acid. Carbon and chlorine mass balances were within 5–10%. Current efficiencies ranged from nearly 100% at EC = −0.5 V (both reactants) to 24.4% for TCE and 16.6% for CF at EC = −1.4 V. Rate constants for TCE and CF transformations were inversely related to pH in the range 2 < pH < 11. Pt–Ebonex resisted sulfate and chloride poisoning. The Pd–Ebonex electrode quickly lost activity (50% loss in 5–10 min) in 0.1 M K2SO4 electrolyte (cathode potential, EC = −1.15 to −1.4 V vs SHE).

Effect of Wind Speed and Relative Humidity on Atmospheric Dust Concentrations in Semi-Arid Climates

Atmospheric particulate have deleterious impacts on human health. Predicting dust and aerosol emission and transport would be helpful to reduce harmful impacts but, despite numerous studies, prediction of dust events and contaminant transport in dust remains challenging. In this work, we show that relative humidity and wind speed are both determinants in atmospheric dust concentration. Observations of atmospheric dust concentrations in Green Valley, AZ, USA, and Juárez, Chihuahua, México, show that PM10 concentrations are not directly correlated with wind speed or relative humidity separately. However, selecting the data for high wind speeds (>4m/s at 10 m elevation), a definite trend is observed between dust concentration and relative humidity: dust concentration increases with relative humidity, reaching a maximum around 25% and it subsequently decreases with relative humidity. Models for dust storm forecasting may be improved by utilizing atmospheric humidity and wind speed as main drivers for dust generation and transport.

Environmental Fate of Sodium Azide Derived from Automobile Airbags

The environmental fate of sodium azide (NaN3) is of considerable interest given the recent surge in production to satisfy demand for automobile air bag inflators, where it serves as the principal active ingredient. Since the mid-1990s, demand for sodium azide has exceeded 5 million kg per year and most passenger vehicles sold in the United States now contain approximately 300 g (≈0.7 lb) of sodium azide. This has greatly increased the potential for accidental environmental releases and for human exposure to this highly toxic, broad-spectrum biocide. It can be argued that a new environmental threat has developed because not only are millions of kilograms of sodium azide now transported to and processed at air bag inflator factories, but also this substance is now widely distributed throughout the developed world in automobiles. Even if sodium azide were to be replaced by a more benign propellant in the future, the problem of safely disposing of large quantities of azide will remain as the vehicle fleet ages and is retired to scrap yards and shredders. Unfortunately, the environmental fate of sodium azide is unknown so it is difficult to effectively manage releases. The problem is compounded by the fact that aqueous sodium azide is readily hydrolyzed to yield hydrazoic acid (HN3), a volatile substance that partitions strongly to the gas phase.