Hygroscopic behavior of aerosol particles from biomass fires using environmental transmission electron microscopy

We used both a conventional transmission electron microscope and an environmental transmission electron microscope (ETEM) to determine morphology, composition, and water uptake of 80 individual aerosol particles collected from the young smoke of flaming and smoldering fires during SAFARI-2000, a comprehensive air quality campaign in southern Africa. Six representative carbonaceous particle types are described, including soot, tar balls, and heterogeneously internally mixed particles containing C with S-, K-, Mg- or Na-rich inorganic phases. The hygroscopic behavior of these particles over the range 0–100% relative humidity (RH) was studied in detail. Soot and tar balls did not take up water, whereas the mixed organic–inorganic particles took up water between 55 and 100% RH, the exact value depending on the composition of their water-soluble phases. The inorganic phase appeared to determine the hygroscopic properties of all mixed organic–inorganic particles. Thus, incorporation of inorganic plant material or reactions with inorganic atmospheric components can dramatically alter the hygroscopic properties of carbonaceous particles in smoke plumes. The fraction of these mixed organic–inorganic particles plausibly increases with time, which will modulate the effects of smoke on radiative budgets.     

Ion microprobe measurement of strontium isotopes in calcium carbonate with application to salmon otoliths

The ion microprobe has the capability to generate high resolution, high precision isotopic measurements, but analysis of the isotopic composition of strontium, as measured by the ⁸⁷Sr/⁸⁶Sr ratio, has been hindered by isobaric interferences. Here we report the first high precision measurements of ⁸⁷Sr/⁸⁶Sr by ion microprobe in calcium carbonate samples with moderate Sr concentrations. We use the high mass resolving power (7000 to 9000 M.R.P.) of the SHRIMP-RG ion microprobe in combination with its high transmission to reduce the number of interfering species while maintaining sufficiently high count rates for precise isotopic measurements. The isobaric interferences are characterized by peak modeling and repeated analyses of standards. We demonstrate that by sample-standard bracketing, ⁸⁷Sr/⁸⁶Sr ratios can be measured in inorganic and biogenic carbonates with Sr concentrations between 400 and 1500 ppm with ∼2‰ external precision (2σ) for a single analysis, and subpermil external precision with repeated analyses. Explicit correction for isobaric interferences (peak-stripping) is found to be less accurate and precise than sample-standard bracketing. Spatial resolution is ∼25 μm laterally and 2 μm deep for a single analysis, consuming on the order of 2 ng of material. The method is tested on otoliths from salmon to demonstrate its accuracy and utility. In these growth-banded aragonitic structures, one-week temporal resolution can be achieved. The analytical method should be applicable to other calcium carbonate samples with similar Sr concentrations.     

Pulsed Air Sparging in Aquifers Contaminated with Dense Nonaqueous Phase Liquids

Air sparging was evaluated for remediation of tetrachloroethylene (PCE) present as dense nonaqueous phase liquid (DNAPL) in aquifers. A two-dimensional laboratory tank with a transparent front wall allowed for visual observation of DNAPL mobilization. A DNAPL zone 50 cm high was created, with a PCE pool accumulating on an aquitard. Detailed process control and analysis yielded accurate mass balances and insight into the mass-transfer limitations during air sparging. Initial PCE recovery rates were high, corresponding to fast removal of residual DNAPL within the zone influenced directly by air channels. The vadose zone DNAPL was removed within a few days, and the recovery in the extracted soil vapors decreased to low values. Increasing the sparge rate and pulsing the air injection led to improved mass recovery, as the pulsing induced water circulation and increased the DNAPL dissolution rate. Dissolved PCE concentrations both within and outside the zone of air channels were affected by the pulsing. Inside the sparge zone, aqueous concentrations decreased rapidly, matching the declining effluent PCE flux. Outside the sparge zone, PCE concentrations increased because highly contaminated water was pushed away from the air injection point. This overall circulation of water may lead to limited spreading of the contaminant, but accelerated the time-weighted average mass removal by 40% to 600%, depending on the aggressiveness of the pulsing. For field applications, pulsing with a daily or diurnal cycling time may increase the average mass removal rate, thus reducing the treatment time and saving in the order of 40% to 80% of the energy cost used to run the blowers. However, air sparging will always fail to remove DNAPL pools located below the sparge point because the air will rise upward from the top of a screen, unless very localized geological layers force the air to migrate horizontally. Unrecognized presence of DNAPL at chlorinated solvent sites residual and pools could potentially hamper success of air sparging cleanups, since the presence of small DNAPL pools, ganglia or droplets can greatly extend the treatment time.     

Lithologic, structural, and geomorphic controls on ribbon forest patterns in a glaciated mountain environment

So-called “ribbon forests” have been attributed to snowdrift patterns and fire history without reference to geomorphology [Vegetatio 19 (1969) 192.]. This paper illustrates how site conditions of geomorphology and geology explain the origin of ribbon forests. In Glacier National Park, MT (USA), regional tectonic uplift associated with the Laramide Orogeny produced structural features that amplify lithologic differences. Pleistocene glaciation scoured deeply along the strike of bedding planes, highlighting this pattern and in some cases producing fine-scale parallel finger lakes between forested ribbon strips.Twelve ribbon forest sites on both sides of the Continental Divide were closely studied on stereoscopic aerial photographs, and several of these sites were examined in the field or from helicopter overflights. In all cases, geologic and geomorphic conditions explain the location and distribution of the ribbon forests. Change-detection of the distribution of trees versus nontree-covered surfaces in an area of ribbon forest on Flattop Mountain, a complex uplifted synclinal structure, was undertaken using panchromatic, low-altitude aerial photographs from 1966 to 1991. Areas changed from forest to meadow and from meadow to forest in roughly equal amounts in a generally random spatial pattern. No evidence was seen to suggest that the creation of one ribbon eventually created another downwind, as suggested by Billings. Aerial photograph interpretation, field examination and soils analyses of forest ribbons and adjacent unforested meadows clearly illustrated that trees occupy higher, parallel to subparallel, well-drained sites where the spatial pattern is in turn a distinct reflection of the spatial pattern of structure and stratigraphy. Meadows occupy topographically lower positions between ridges where erosion along bedding plane strike was concentrated. Topography sets conditions that allow tree growth in certain locations while precluding it in immediately adjacent areas. Ribbon forests there are thus a spatial manifestation of the interaction between structure, lithology, and topography.     

Citizenship,Community, and Struggles for Public Space

On April 16, 1993, a group of male students at the University of Colorado got into a fight with another group of males not associated with the university; this fight unleashed a broader debate over who should have access to the public spaces surrounding the university. We examine this debate in terms of its implications for citizenship, public space, and community. We discuss conflicts over public space and the role these conflicts have played in defining a citizenship that rejects notions of equal membership in a larger polity. This strategy is examined using newspaper accounts, interviews, and participant observation techniques to understand the conflict over access to “the Hill” in Boulder, Colorado. Central to these conflicts is the issue of how “the public” is constituted. As we detail the actions of agents involved in the Hill, it will become clear that this fight is about competing definitions of who belongs to the public, who is a citizen, and what should be the criteria for membership in the public or community.     

Volcanic and Seismic Swarm Events on the Reykjanes Ridge and Their Similarities to Events on Iceland: Results of a Rapid Response Mission

On 21 May 1989, a major earthquake swarm on the Reykjanes Ridge at59°44 N, 29°32 W at a water depth of about 1000 m andabout 500 km southwest of Iceland was detected on both the WorldwideStandard Seismic Network (WWSSN) and Icelandic seismic networks. As part ofa multi-institutional response to this swarm, the Naval ResearchLaboratory arranged for a P3 Orion Aircraft to deploy sonobuoys and AXBTs inthe immediate vicinity of the swarm activity. The detection of the swarmmotivated a survey of the region in 1990, using the towed SeaMARC IIside-looking sonar system. In 1990–1991 the Russian ShirshovInstitute of Oceanology offered the use of its MIR deep-divingsubmersibles to investigate the rise axis for recent volcanism. During 1992,a scientific team comprised of five US and ten Russian scientists mobilizedthe twin, deep diving Russian submersibles to study the spreading axis ofthe Reykjanes Ridge. The resulting data analyses allows us to conclude thatthe 1989 seismic swarm event occurred adjacent to and east of the largeaxial high in the center of our survey area. The length, width and depthrange of the earthquakes were very similar to major seismic swarm eventsconfined to fissure systems in the Krafla region of Iceland. It is likelythat the earthquake swarm was located on a fresh, well-defined systemof fissures and faults extending south of the northernmost axial highstudied. The earthquake swarm was probably associated with an emanation oflava creating a region of high backscatter, located just to the east of thecentral axial high. In addition, the region of high-backscatterremains unsampled because it lay underneath the nadir of the processedSeaMARC tracks used to plan the submersible survey. However many sampleswere taken and structural studies of the evolving Reykjanes Ridge werecarried out.     

Interannual modulation of subtropical Atlantic boreal summer dust variability by ENSO

Dust variability in the climate system has been studied for several decades, yet there remains an incomplete understanding of the dynamical mechanisms controlling interannual and decadal variations in dust transport. The sparseness of multi-year observational datasets has limited our understanding of the relationship between climate variations and atmospheric dust. We use available in situ and satellite observations of dust and a century-length fully coupled Community Earth System Model (CESM) simulation to show that the El Niño-Southern Oscillation (ENSO) exerts a control on North African dust transport during boreal summer. In CESM, this relationship is stronger over the dusty tropical North Atlantic than near Barbados, one of the few sites having a multi-decadal observed record. During strong La Niña summers in CESM, a statistically significant increase in lower tropospheric easterly wind is associated with an increase in North African dust transport over the Atlantic. Barbados dust and Pacific SST variability are only weakly correlated in both observations and CESM, suggesting that other processes are controlling the cross-basin variability of dust. We also use our CESM simulation to show that the relationship between downstream North African dust transport and ENSO fluctuates on multidecadal timescales and is associated with a phase shift in the North Atlantic Oscillation. Our findings indicate that existing observations of dust over the tropical North Atlantic are not extensive enough to completely describe the variability of dust and dust transport, and demonstrate the importance of global models to supplement and interpret observational records.     

Ages of regional metamorphism and ductile deformation in the central and southern Appalachians

A summary of available geochronology of deformational fabrics formed at greenschist and higher grades in the central and southern Appalachians is presented as a map showing the ages of regional metamorphism and ductile deformation. The ca. 480-435 Ma Taconic event affected most of the Piedmont and Blue Ridge provinces. The ca. 380-340 Ma Acadian event was milder and was centered in the west central Piedmont and eastern Blue Ridge. The 330-230 Ma Alleghanian event exhibits an abrupt ductile deformation front in the eastern Piedmont and extends an unknown distance eastward below the Atlantic Coastal Plain.