Evolution of vehicle exhaust particles in the atmosphere

Aerosol mass spectrometer (AMS) measurements are used to characterize the evolution of exhaust particulate matter (PM) properties near and downwind of vehicle sources. The AMS provides time-resolved chemically speciated mass loadings and mass-weighted size distributions of nonrefractory PM smaller than 1 microm (NRPM1). Source measurements of aircraft PM show that black carbon particles inhibit nucleation by serving as condensation sinks for the volatile and semi-volatile exhaust gases. Real-world source measurements of ground vehicle PM are obtained by deploying an AMS aboard a mobile laboratory. Characteristic features of the exhaust PM chemical composition and size distribution are discussed. PM mass and number concentrations are used with above-background gas-phase carbon dioxide (CO2) concentrations to calculate on-road emission factors for individual vehicles. Highly variable ratios between particle number and mass concentrations are observed for individual vehicles. NRPM1 mass emission factors measured for on-road diesel vehicles are approximately 50% lower than those from dynamometer studies. Factor analysis of AMS data (FA-AMS) is applied for the first time to map variations in exhaust PM mass downwind of a highway. In this study, above-background vehicle PM concentrations are highest close to the highway and decrease by a factor of 2 by 200 m away from the highway. Comparison with the gas-phase CO2 concentrations indicates that these vehicle PM mass gradients are largely driven by dilution. Secondary aerosol species do not show a similar gradient in absolute mass concentrations; thus, their relative contribution to total ambient PM mass concentrations increases as a function of distance from the highway. FA-AMS of single particle and ensemble data at an urban receptor site shows that condensation of these secondary aerosol species onto vehicle exhaust particles results in spatial and temporal evolution of the size and composition of vehicle exhaust PM on urban and regional scales.     

Externalization of employment in a service environment: the role of organizational and customer identification

This study investigates the impact of employment externalization (in the form of limited‐term vs. permanent employment status) on customer‐oriented service behavior, and how identification processes may help to resolve the ‘paradox of externalization’ (i.e., organizations relying more on potentially disenfranchised employees to maintain strong connections with their customers). Survey data were obtained from 369 sales, service, and technical support personnel from the Canadian subsidiary of a large international service organization in the high technology sector. Organizational and customer identification fully mediate the relationship between employment status and customer‐oriented service behavior. Additionally, the perceived external image of the organization and the visibility of one's affiliation with the organization moderate the relationships between employment status and organizational and customer identification. Copyright © 2007 John Wiley & Sons, Ltd.     

Cell preparation methods influence Escherichia coli D21g surface chemistry and transport in saturated sand

The effect of cell preparation methods on the surface chemistry and retention of Escherichia coli D21 g was investigated over a range of ionic strength conditions. The cell preparation methods that were considered included filtration and centrifugation (at various speeds and for different durations). For a given ionic strength condition, it was found that cells prepared by filtration were more negatively charged and hydrophobic than cells prepared by centrifugation. Increasing the centrifugation speed (force imposed) or duration produced cells with a higher zeta potential (less negative) and a lower hydrophobicity. Column transport experiments for E. coli D21 g were also conducted with ultra pure quartz sand and the same solution chemistries. The first-order retention rate coefficient for E. coli D21 g increased with increasing speed and duration of centrifugation, and was lowest in the case of filtered cells. Moreover, the influence of cell preparation method was more pronounced in lower ionic strength solutions.     

A Systematic Review of Wild Burro Grazing Effects on Mojave Desert Vegetation,USA

Wild burros (Equus asinus), protected by the 1971 Wild Free-Roaming Horse and Burro Act on some federal lands but exotic animals many ecologists and resource mangers view as damaging to native ecosystems, represent one of the most contentious environmental management problems in American Southwest arid lands. This review synthesizes the scattered literature about burro effects on plant communities of the Mojave Desert, a center of burro management contentions. I classified 24 documents meeting selection criteria for this review into five categories of research: (i) diet analyses directly determining which plant species burros consume, (ii) utilization studies of individual species, (iii) control-impact comparisons, (iv) exclosure studies, and (v) forage analyses examining chemical characteristics of forage plants. Ten diet studies recorded 175 total species that burros consumed. However, these studies and two exclosure studies suggested that burros preferentially eat graminoid and forb groups over shrubs. One study in Death Valley National Park, for example, found that Achnatherum hymenoides (Indian ricegrass) was 11 times more abundant in burro diets than expected based on its availability. Utilization studies revealed that burros also exhibit preferences within the shrub group. Eighty-three percent of reviewed documents were produced in a 12-year period, from 1972 to 1983, with the most recent document produced in 1988. Because burros remain abundant on many federal lands and grazing may interact with other management concerns (e.g., desert wildfires fueled by exotic grasses), rejuvenating grazing research to better understand both past and present burro effects could help guide revegetation and grazing management scenarios.     

Toxicity and metal speciation characterisation of waste water from an abandoned gold mine in tropical northern Australia

The decommissioned Mount Todd gold mine, located in the wet-dry tropics of northern Australia, consists of a large waste water inventory and an acid rock drainage problem, which has the potential to impact upon freshwater ecosystems of the Edith River catchment. The toxicity of retention pond 1 (RP1) water was determined using six local freshwater species (duckweed, alga, cladoceran, snail, hydra and a fish). RP1 water was very toxic to all species, with the percentage dilution of RP1 water inhibiting 10% of organism response (IC(10)), or lethal to 5% of individuals (LC(5)), ranging from 0.007 to 0.088%. The percentage dilution of RP1 water inhibiting 50% of organism response (IC(50)), or lethal to 50% of individuals (LC(50)), ranged from 0.051% to 0.58%. Based on chemical analyses and geochemical speciation modelling of the test waters, Cu, Zn and Al were the most likely toxic components at acidic dilutions (i.e. 1%), while Cu and Zn were the most likely toxic components at 0.1% RP1 water, where pH was 6.5. Species sensitivity distributions (SSDs) were used to predict dilutions of RP1 water that would protect or unacceptably affect the downstream aquatic ecosystems. A dilution ratio of 1 part RP1 water to 20000 parts Edith River water (0.005% RP1 water) was calculated to be required for the protection of at least 95% of species. This information can be used in conjunction with field chemical and biological data to better predict the ecological risks of RP1 waste water downstream of the Mount Todd mine.     

Influence of fipronil compounds and rice-cultivation land-use intensity on macroinvertebrate communities in streams of southwestern Louisiana, USA

Laboratory tests of fipronil and its degradation products have revealed acute lethal toxicity at very low concentrations (LC50) of <0.5 microg/L to selected aquatic macroinvertebrates. In streams draining basins with intensive rice cultivation in southwestern Louisiana, USA, concentrations of fipronil compounds were an order of magnitude larger than the LC50. The abundance (rho=-0.64; p=0.015) and taxa richness (r2=0.515, p<0.005) of macroinvertebrate communities declined significantly with increases in concentrations of fipronil compounds and rice-cultivation land-use intensity. Macroinvertebrate community tolerance scores increased linearly (r2=0.442, p<0.005) with increases in the percentage of rice cultivation in the basins, indicating increasingly degraded stream conditions. Similarly, macroinvertebrate community-tolerance scores increased rapidly as fipronil concentrations approached about 1 microg/L. Pesticide toxicity index determinations indicated that aquatic macroinvertebrates respond to a gradient of fipronil compounds in water although stream size and habitat cannot be ruled out as contributing influences.     

Soil suspension/dispersion modeling methods for estimating health-based soil cleanup levels of hexavalent chromium at chromite ore processing residue sites

The primary health concern associated with exposures to chromite ore processing residue (COPR)-affected soils is inhalation of hexavalent chromium [Cr(VI)] particulates. Site-specific soil alternative remediation standards (ARSs) are set using soil suspension and dispersion models to be protective of the theoretical excess cancer risk associated with inhalation of soil suspended by vehicle traffic and wind. The purpose of this study was to update a previous model comparison study that identified the 1995 AP-42 particulate emission model for vehicle traffic over unpaved roads and the Fugitive Dust Model (FDM) as the most appropriate model combination for estimating site-specific ARSs. Because the AP-42 model has been revised, we have updated our past evaluation. Specifically, the 2006 AP-42 particulate emissions model; the Industrial Source Complex-Short Term model, version 3 (ISCST3); and the American Meteorological Society/Environmental Protection Agency Regulatory Model (AERMOD) air dispersion models were evaluated, and the results were compared with those from the previously used modeling approaches. Two sites with and two sites without vehicle traffic were evaluated to determine if wind erosion is a significant source of emissions. For the two sites with vehicle traffic, both FDM and ISCST3 produced total suspended particulate (TSP) estimates that were, on average, within a factor of 2 of measured; whereas AERMOD produced estimates that were as much as 5-fold higher than measured. In general, the estimated TSP concentrations for FDM were higher than those for ISCST3. For airborne Cr(VI), the ISCST3 model produced estimates that were only 2- to 8-fold of the measured concentrations, and both FDM and AERMOD estimated airborne Cr(VI) concentrations that were approximately 4- to 14-fold higher than measured. Results using the 1995 AP-42 model were closer to measured than those from the 2006 AP-42 model. Wind erosion was an insignificant contributor to particulate emissions at COPR sites.     

Evidence of enhanced atmospheric ammoniacal nitrogen in Hells Canyon national recreation area: implications for natural and cultural resources

Agriculture releases copious fertilizing pollutants to air sheds and waterways of the northwestern United States. To evaluate threats to natural resources and historic rock paintings in remote Hells Canyon, Oregon and Idaho, deposition of ammonia (NH3), nitrogen oxides (NOx), sulfur dioxide (SO2), and hydrogen sulfide (H2S) at five stations along 60 km of the Snake River valley floor were passively sampled from July 2002 through June 2003, and ozone data and particulate chemistry were obtained from the Interagency Monitoring of Protected Visual Environments (IMPROVE) station at Hells Canyon. NH3 concentrations were high; biweekly averages peaked at 5-19 ppb in spring and summer and the nutrient-laden Snake River is a likely source. Fine particulate ammonium nitrate (NH4NO3) averaged 2.6 microg/m3 during the 20% of worst visibility days with winter drainage of air masses from the Snake River Basin and possibly long distance transport from southern California. Other pollutants were within background ranges. NH3 is corrosive to clay-based pictographs; nitrogen deposition can alter natural biotic communities and terrestrial ecosystem processes at levels reported here.     

Influence of soil type and extraction conditions on perchlorate analysis by ion chromatography

Perchlorate is a stable anion that has been introduced into the environment through activities related to its production and use as a solid rocket propellant. Perchlorate is thought to transport through soils without being adsorbed; thus, for determination of perchlorate in soil, samples are typically extracted with water prior to analysis. The completeness of extraction depends on perchlorate existing as a free ion within the soil matrix. In this study, perchlorate extraction efficiency was evaluated with five soil types under two different oxygen states. For each soil, 30% (w/w) slurries were prepared and equilibrated under either oxic or anoxic conditions prior to spiking with a stock solution of sodium perchlorate, and the slurries were then maintained for 1-week or 1-month. At the end of the exposure, slurries were centrifuged and separated into aqueous and soil phases. After phase separation, the soil was washed first with deionized water and then with 50mM NaOH, producing second and third aqueous phases, respectively. Perchlorate concentrations in the three aqueous phases were determined using ion chromatography. The results obtained from this study suggest that matrix interference and signal suppression due to high conductivity have greater effects upon observed perchlorate concentrations by ion chromatography than does perchlorate interaction with soil. Thus, a single water extraction is sufficient for quantitative determination of perchlorate in soil.     

Solubilization of nitrotoluenes in micellar nonionic surfactant solutions

A key factor in selecting surfactants to enhance chemical or biological transformation or physical removal of an organic pollutant from contaminated soil is knowledge of the pollutant's solubility behavior in the surfactant solution. This study investigated the influence of nonionic surfactant structure on the solubility of 4-nitrotoluene (NT), 2,3-dinitrotoluene, 2,4-dinitrotoluene, 2,6-dinitrotoluene, and 2,4,6-trinitrotoluene (TNT) at room temperature. For a series of alkyl phenol ethoxylates (Tergitol NP-8 to NP-40), decreasing the ethoxylate chain length increased the solubility of these nitrotoluenes by a factor of two or less in 10 g l(-1) surfactant solutions, but did not significantly change their molar solubilization ratios (MSR, e.g. 0.02 for TNT) or their micelle-water partition coefficients (K(m), e.g. 3.4 for TNT). For Tergitol NP-8 solutions ranging from 1.0 to 12.4 g l(-1), no enhancement in NT solubility was found, suggesting that the cloud point was reached. The MSRs for Tween 80 were higher than those of Tween 20 and the MSRs of Brij-58 were higher than those for Brij-35. When comparing solutes, NT had the highest solubility and MSR (0.28-0.41), while TNT had the lowest solubility and MSR (0.02-0.03). A linear relationship between K(m) values and octanol-water partition coefficients based on Triton X-100 predicted the logK(m) values within 0.5 of their measured values. A linear solvation free energy correlation for K(m) suggested the importance of solute volume and effective hydrogen bond basicity in the partitioning process while implying that the nitrotoluenes are solubilized in a polar portion of the micelle.