Source apportionment of fine particles in Tennessee using a source-oriented model

Source apportionment of fine particles (PM2.5, particulate matter < 2 microm in aerodynamic diameter) is important to identify the source categories that are responsible for the concentrations observed at a particular receptor. Although receptor models have been used to do source apportionment, they do not fully take into account the chemical reactions (including photochemical reactions) involved in the formation of secondary fine particles. Secondary fine particles are formed from photochemical and other reactions involving precursor gases, such as sulfur dioxide, oxides of nitrogen, ammonia, and volatile organic compounds. This paper presents the results of modeling work aimed at developing a source apportionment of primary and secondary PM2.5. On-road mobile source and point source inventories for the state of Tennessee were estimated and compiled. The national emissions inventory for the year 1999 was used for the other states. U.S. Environmental Protection Agency Models3/Community Multi-Scale Air Quality modeling system was used for the photochemical/secondary particulate matter modeling. The modeling domain consisted of a nested 36-12-4-km domain. The 4-km domain covered the entire state of Tennessee. The episode chosen for the modeling runs was August 29 to September 9, 1999. This paper presents the approach used and the results from the modeling and attempts to quantify the contribution of major source categories, such as the on-road mobile sources (including the fugitive dust component) and coal-fired power plants, to observed PM2.5 concentrations in Tennessee. The results of this work will be helpful in policy issues targeted at designing control strategies to meet the PM2.5 National Ambient Air Quality Standards in Tennessee.     

Darwin's Fox: A Distinct Endangered Species in a Vanishing Habitat

The temperate rain forest of Chiloé Island, Chile, is inhabited by an endemic fox ( Dusicyon fulvipes ) first described by Charles Darwin and now designated Darwin's fox. Despite morphological differences, Darwin's fox has been considered only an insular subspecies of the mainland chilla fox ( D. griseus ). This follows the assumption that the island population, with an estimated population of less than 500, has been separated from the mainland chilla fox for only about 15,000 years and may have received occasional immigrants from the mainland. Consequently, this island population has not been protected as endangered or bred in captivity. Recently, a population of Darwin's fox was discovered on the Chilean mainland 600 km north of Chiloé Island. This population exists in sympatry with chilla and possibly culpeo ( D. culpaeus ) foxes, which suggests that Darwin's fox may be reproductively isolated. To clarify the phylogenetic position of Darwin's fox, we analyzed 344 bp of mitochondrial DNA control-region sequence of the three species of Chilean foxes. Darwin's foxes from the island and mainland populations compose a monophyletic group distinct from the two other Chilean fox species. This indicates that Darwin's fox was probably an early inhabitant of central Chile, and that its present distribution on the mainland may be a relict of a once much wider distribution. Our results highlight the ability of molecular genetic techniques to uncover historical relationships masked by recent events, such as local extinctions. The "rediscovery" of Darwin's fox as a distinct species implies that greater significance should be given to the protection of this species and its unique habitat and to documenting the extent of its mainland distribution.     

Ion current densities produced by energetic electrons in electrostatic precipitator geometries

A new laboratory test system for electron beam ionization in electrostatic precipitator geometries has been constructed to measure ion current density as a function of voltage difference for clean plate (no dust contamination) conditions. The new system incorporates improved electrodes which withstand an applied voltage of ± 55 kV, a factor of 5 increase over the previous test system. A 3 MeV Van de Graaff accelerator produced ionizing electron beams of 1.2 and 2 MeV energy with beam currents of 10.5 and 21 μA in place of corona wire ionization. Ion current densities of up to 130 mA/m² were measured before breakdown between the plates, and no ion current saturation was observed. A comparison of I-V curves and sparkover voltages for various beam energies, currents, and types of collimation is discussed and the need for measurements with good beam geometry is addressed.     

Effects of elevated atmospheric carbon dioxide on biomass and carbon accumulation in a model regenerating longleaf pine community

Plant species vary in response to atmospheric CO2 concentration due to differences in physiology, morphology, phenology, and symbiotic relationships. These differences make it very difficult to predict how plant communities will respond to elevated CO2. Such information is critical to furthering our understanding of community and ecosystem responses to global climate change. To determine how a simple plant community might respond to elevated CO2, a model regenerating longleaf pine community composed of five species was exposed to two CO2 regimes (ambient, 365 micromol mol(-1) and elevated, 720 micromol mol(-1)) for 3 yr. Total above- and belowground biomass was 70 and 49% greater, respectively, in CO2-enriched plots. Carbon (C) content followed a response pattern similar to biomass, resulting in a significant increase of 13.8 Mg C ha(-1) under elevated CO2. Responses of individual species, however, varied. Longleaf pine (Pinus palustris Mill.) was primarily responsible for the positive response to CO2 enrichment. Wiregrass (Aristida stricta Michx.), rattlebox (Crotalaria rotundifolia Walt. Ex Gmel.), and butterfly weed (Asclepias tuberosa L.) exhibited negative above- and belowground biomass responses to elevated CO2, while sand post oak (Quercus margaretta Ashe) did not differ significantly between CO2 treatments. As with pine, C content followed patterns similar to biomass. Elevated CO2 resulted in alterations in community structure. Longleaf pine comprised 88% of total biomass in CO2-enriched plots, but only 76% in ambient plots. In contrast, wiregrass, rattlebox, and butterfly weed comprised 19% in ambient CO2 plots, but only 8% under high CO2. Therefore, while longleaf pine may perform well in a high CO2 world, other members of this community may not compete as well, which could alter community function. Effects of elevated CO2 on plant communities are complex, dynamic, and difficult to predict, clearly demonstrating the need for more research in this important area of global change science.     

Methods for evaluating investment strategies for environmental technologies

Environmental technology development, like other ventures, requires decisions regarding where to invest scarce capital. The investment option that offers the greatest benefit relative to the cost should be chosen. The problem is to determine a way to analyze the project and apply a useful measure for comparison to other investment opportunities. In this article, three methods of analysis are presented: return on investment, benefit-to-cost ratio, and payback period. Formulas are developed for each of the methods, and a case study illustrates their application.     

Man-made structures on marine sediments: Effects on adjacent benthic communities

This study (1975–1977) examines the effect of man-made structures on natural sand bottom communities in shallow water in San Diego County, southern California, USA. While there were shallow scour effects to 15 m around some artificial reefs, the reefs had no measurable effect on sand ripple patterns, grain size, organic carbon or infauna beyond the scoured areas. Foraging by reef-associated fishes produced profound alterations in the epifauna populations of the sea pen Stylatula elongata. The sea pen densities were 4 to 10 m^-2 before the reefs were established, but within 5 mo were eliminated from distances greater than 200 m around the reefs. On the other hand, densities of the tube-building polychaetes Diopatra spp. seemed to be enhanced in the immediate vicinity of the artificial reef. Oil platforms and bridge pilings seem to have much more profound effects on the nearby sand communities than do the relatively small artificial reefs. In addition to the elimination of sea pens, Diopatra spp. densities increased from <1.0 m^-2 in control areas to as many as 73 m^-2 in the vicinity of oil platforms. Grain size and infauna were strongly affected by the oil platform.     

Utilization of turkey manure as granular activated carbon: physical, chemical and adsorptive properties

The high availability of large quantities of turkey manure generated from turkey production makes it an attractive feedstock for carbon production. Pelletized samples of turkey litter and cake were converted to granular activated carbons (GACs) by steam activation. Water flow rate and activation time were changed to produce a range of activation conditions. The GACs were characterized for select physical (yield, surface area, bulk density, attrition), chemical (pH, surface charge) and adsorptive properties (copper ion uptake). Carbon physical and adsorptive properties were dependent on activation time and quantity of steam used as activant. Yields varied from 23% to 37%, surface area varied from 248 to 472 m(2)/g and copper ion adsorption varied from 0.72 to 1.86 mmol Cu(2+)/g carbon. Copper ion adsorption greatly exceeded the values for two commercial GACs. GACs from turkey litter and cake show considerable potential to remove metal ions from water.     

Potential nitrogen constraints on soil carbon sequestration under low and elevated atmospheric CO2

The interaction between nitrogen cycling and carbon sequestration is critical in predicting the consequences of anthropogenic increases in atmospheric CO2 (hereafter, Ca). The progressive N limitation (PNL) theory predicts that carbon sequestration in plants and soils with rising Ca may be constrained by the availability of nitrogen in many ecosystems. Here we report on the interaction between C and N dynamics during a four-year field experiment in which an intact C3/C4 grassland was exposed to a gradient in Ca from 200 to 560 micromol/mol. There were strong species effects on decomposition dynamics, with C loss positively correlated and N mineralization negatively correlated with Ca for litter of the C3 forb Solanum dimidiatum, whereas decomposition of litter from the C4 grass Bothriochloa ischaemum was unresponsive to Ca. Both soil microbial biomass and soil respiration rates exhibited a nonlinear response to Ca, reaching a maximum at approximately 440 micromol/mol Ca. We found a general movement of N out of soil organic matter and into aboveground plant biomass with increased Ca. Within soils we found evidence of C loss from recalcitrant soil C fractions with narrow C:N ratios to more labile soil fractions with broader C:N ratios, potentially due to decreases in N availability. The observed reallocation of N from soil to plants over the last three years of the experiment supports the PNL theory that reductions in N availability with rising Ca could initially be overcome by a transfer of N from low C:N ratio fractions to those with higher C:N ratios. Although the transfer of N allowed plant production to increase with increasing Ca, there was no net soil C sequestration at elevated Ca, presumably because relatively stable C is being decomposed to meet microbial and plant N requirements. Ultimately, if the C gained by increased plant production is rapidly lost through decomposition, the shift in N from older soil organic matter to rapidly decomposing plant tissue may limit net C sequestration with increased plant production.