Detection of iodine monoxide radicals in the marine boundary layer using laser induced fluorescence spectroscopy

A Laser Induced Fluorescence (LIF) instrument has been developed to detect iodine monoxide (IO) radicals in the atmosphere. An all solid-state Nd:YAG pumped Ti:Sapphire laser operating at approximately 445 nm was used to excite the (2,0) band of the IO A²Π_3/2 ← X²Π_3/2 electronic transition, with off-resonance fluorescence in the (2,5) band detected at 521 nm. The sensitivity of the instrument was determined by calibration. IO (between 10 and 150 pptV) was generated following the 184.9 nm photolysis of N₂O/CF₃I/N₂ mixtures with O₃ actinometry used to determine the photolysis flux. The detection limit was determined to be 0.3 pptV for a 300 s integration period, with an uncertainty of 23% (1σ). The instrument was deployed in August/September 2006 during the RHaMBLe (Reactive Halogens in the Marine Boundary Layer) campaign in Roscoff, France. Located on a small jetty, a few metres from the water’s edge at high tide, the instrument measured significant levels of IO on 11 days, with a maximum of 27.6 ± 3.2 pptV observed on one day (averaged over 10 s) representing the highest IO mixing ratio recorded in the marine boundary layer to date. IO displayed a clear diurnal profile with a maximum at low tide during the daytime. These results represent the first point measurements of IO in the atmosphere by LIF.     

The effects of several common anthropogenic contaminants on proliferation of the parasitic oyster pathogen Perkinsus marinus

Estuarine contaminants have varying effects on estuarine inhabitants and host-parasite interactions. Some field collected contaminant mixtures have been shown to increase oyster susceptibility to parasitism by Perkinsus marinus, but little is known about contaminant effects on the parasite itself. This study examined the effects of ammonium, nitrate, phosphate, fluoranthene, phenanthrene and a common herbicide mixture (Weed-B-Gone) on in vitro proliferation of P. marinus. Only the herbicide had a significant effect, but not at or below the manufacture's recommended application rate (7.81 microl ml(-1)). The herbicide's active ingredients (3.1% 2,4-dichlorophenoxyacetic acid, 10.6% mecoprop and 1.3% dicamba) mimic growth hormones of broadleaf plants; over stimulation of growth results in death. The mode of action of these compounds on P. marinus warrants further investigation which may provide insight towards the identification of biocides to control P. marinus.     

Novel measurements of atmospheric iodine species by resonance fluorescence

A field instrument has been developed for the purpose of measuring gas-phase atmospheric iodine species in the marine boundary layer. Vacuum UV resonance-fluorescence (RF), generated using a microwave discharge lamp, is employed to detect atomic iodine via the (5p⁴6s)–(5p⁵) transitions around 178–184 nm. The system can be operated in two modes; either to directly measure ambient iodine atoms, or to measure the total photolabile iodine loading of ambient air, through broadband visible photolysis of photolabile iodine-containing species, with subsequent RF detection of the iodine atoms released. In both cases the instrument allows for the in situ measurement of the species detected, which is advantageous for gathering information concerning their local sources and distribution. The instrument is calibrated through generation of a known concentration of iodine atoms from the photolysis of I₂ using a mercury pen-ray lamp. The instrument was deployed for the first time in August 2007 at Mace Head on the west coast of Ireland; initial results from this field trial are presented. Ambient iodine atoms were measured at levels up to 22 ± 4.8 ppt during the day, coinciding with the lowest tides, when Laminaria seaweed beds were exposed. The total photolabile iodine loading was also measured during several night-time and day-time periods and was found to correlate inversely with tidal height. Inferred I₂ concentrations based on these measurements indicate levels of several hundred ppt at the Mace Head site. These measurements represent the first direct observations of ambient iodine atoms and measurement of total photolabile iodine in the atmosphere.     

Improved discrete element modeling for proppant embedment into rock surfaces

Brinell indentation tests were performed on Montney siltstone, and the results were compared with discrete element indentation simulations that use the micro-parameters calibrated using compression test data from the same siltstone samples. The simulated proppant indentation into the rock surface can be 15% less than the laboratory measurements. A lower effective particle–particle modulus and thus a lower Young’s modulus are needed in discrete element models for proper simulation of indentation. An equation to find the appropriate value of Young’s modulus for indentation simulation is proposed using Brinell indentation tests including 198 laboratory tests and 32 discrete element simulations. This equation can improve the prediction of Young’s modulus and thus the particle–particle effective modulus for indentation simulations to match the measured force–indentation depth curve in the laboratory. Using the improved micro-parameters, a parametric analysis of the influence of rock Young’s modulus and proppant particle size on proppant embedment was performed. An equation to estimate Brinell hardness as a function of Young’s modulus and closure stress was derived. A practical procedure was developed to predict proppant embedment from the estimated hardness. The predictions agree with the laboratory measurements in a case study on the Montney Formation.

     

Assessment of failure mechanisms in deep longwall faces based on mining-induced seismicity

Failure mechanisms of the rock mass in the regions of maximum stress concentrations around a longwall face were assessed. In this respect, seismic events that result from changes in the stress field were analyzed to gain more knowledge about rock failure mechanisms in the proximity of the face area. A deep longwall mine developed at depths of about 3–3.5 km in South Africa was selected as a case study. Seismic moment tensor solutions were obtained for 32 seismic events with moment magnitudes in the range of 0.49 and 2.10. Through moment tensor decomposition, the dominant failure mechanisms were investigated by drawing focal mechanism plots. Further analysis was implemented by depicting the corresponding 3D radiation patterns of P-wave particle motions. Although the results cover various failure mechanisms, the dominant mechanisms are shear, implosional, and compressional failures. According to the results, most of the maximum principal stresses in the mine are compressive and oriented nearly vertical, which are in accordance with the gravitational collapses of the mined out areas. The results obtained from this research show that measuring and analyzing mining-induced seismicity can be a reliable measure to characterize the dominant failure mechanisms in a nondestructive manner and to provide a useful assessment of the stability of the longwall face in advance of extraction.     

Improvements to Shellfish Harvest Area Closure Decision Making Using GIS,Remote Sensing,and Predictive Models

Currently, many states use precipitation information to regulate periodic closures of shellfish harvest areas based on a presumptive relationship between rainfall and bacteria concentration. We evaluate this relationship in four South Carolina estuaries and suggest new predictive models that integrate remote sensing precipitation data with additional environmental and climatic data. Model comparisons using Akaike’s information criterion, tenfold cross-validation, and model r ² values show substantial and consistent improvements using integrated precipitation, salinity, and water temperature data as predictors. These models may be useful for shellfish area closure regulation support. The model development approaches used here may also be useful in estimating bacteria concentration at beaches and can serve as the basis for developing near-real-time estimates and forecast predictions of bacteria levels for closure decision-making tools.     

DOAS observations of formaldehyde and its impact on the HO<Subscript>x</Subscript> balance in the tropical Atlantic marine boundary layer

Measurements of formaldehyde (HCHO) were made at the Cape Verde Atmospheric Observatory between November 2006 and June 2007 using the Long-Path Differential Optical Absorption Spectroscopy (LP-DOAS) technique. Observations show that typical HCHO mixing ratios ranged between 350 and 550 pptv (with typical 2-σ uncertainties of ~110 pptv), with several events of high HCHO, the maximum being 1,885?±?149 pptv. The observations indicate a lack of strong seasonal or diurnal variations, within the uncertainty of the measurements. A box model is employed to test whether the observations can be explained using known hydrocarbon photochemistry; the model replicates well the typical diurnal profile and monthly mean values. The model results indicate that on average 20% of HO₂ production and 10% of OH destruction can be attributed to the mean HCHO levels, suggesting that even at these low average mixing ratios HCHO plays an important role in determining the HO_x (HO₂+OH) balance of the remote marine boundary layer.     

Field monitoring and deformation characteristics of a landslide with piles in the Three Gorges Reservoir area

Landslides often occur within the reservoir area behind dams. In China, a common strategy for stabilizing these landslides is to install large piles through the landslide and into the stable ground below. The piles interact with the landslide and constitute a landslide-stabilizing pile system. The deformation of this system under the reservoir operation is more complicated than the deformation of the landslide itself. Understanding the behaviour of this system is very important to the long-term safety of landslides stabilized with piles in reservoirs. The Majiagou landslide, which was selected as a case study, was triggered by the first impoundment of the reservoir behind the Three Gorges dam. A row of anti-slide piles was installed in the landslide in 2007, but monitoring results found these were ineffective at stabilizing the landslide. Subsequently, in 2011, two longer test piles and an integrated monitoring system were installed in the landslide to better understand the failure mode of the landslide and to measure the deformation characteristics of the landslide-stabilizing pile system. Monitoring results show that the Majiagou landslide is a translational landslide with three slip surfaces. The test piles provided local resistance and partially slowed down the sliding mass behind the piles, and the landslide deformation response to external factors decreased for a time. However, after 2 years, the deformation of the landslide-stabilizing pile system reverted to seasonal stepwise cumulative displacements influenced by cycles of reservoir drawdown and rainfall. The monitoring results provide fundamental data for evaluating the long-term performance of anti-slide piles and for assessing long-term stability of the stabilized landslide under the reservoir operation.     

The Creston,California, meteorite fall and the origin of L chondrites

It has been proposed that all L chondrites resulted from an ongoing collisional cascade of fragments that originated from the formation of the ~500 Ma old asteroid family Gefion, located near the 5:2 mean‐motion resonance with Jupiter in the middle Main Belt. If so, L chondrite pre‐atmospheric orbits should be distributed as expected for that source region. Here, we present contradictory results from the orbit and collisional history of the October 24, 2015, L6 ordinary chondrite fall at Creston, CA (here reclassified to L5/6). Creston's short 1.30 ± 0.02 AU semimajor axis orbit would imply a long dynamical evolution if it originated from the middle Main Belt. Indeed, Creston has a high cosmic ray exposure age of 40–50 Ma. However, Creston's small meteoroid size and low 4.23 ± 0.07° inclination indicate a short dynamical lifetime against collisions. This suggests, instead, that Creston originated most likely in the inner asteroid belt and was delivered via the ν₆ resonance. The U‐Pb systematics of Creston apatite reveals a Pb‐Pb age of 4,497.1 ± 3.7 Ma, and an upper intercept U‐Pb age of 4,496.7 ± 5.8 Ma (2σ), circa 70 Ma after formation of CAI, as found for other L chondrites. The K‐Ar (age ~4.3 Ga) and U,Th‐He (age ~1 Ga) chronometers were not reset at ~500 Ma, while the lower intercept U‐Pb age is poorly defined as 770 ± 320 Ma. So far, the three known L chondrites that impacted on orbits with semimajor axes a <2.0 AU all have high (>3 Ga) K‐Ar ages. This argues for a source of some of our L chondrites in the inner Main Belt. Not all L chondrites originate in a continuous population of Gefion family debris stretching across the 3:1 mean‐motion resonance.