Local Sinks Research Articles

Global-mean Vertical Tracer Mixing in Planetary Atmospheres. I. Theory and Fast-rotating Planets

Abstract Most chemistry and cloud formation models for planetary atmospheres adopt a one-dimensional (1D) diffusion approach to approximate the global-mean vertical tracer transport. The physical underpinning of the key parameter in this framework, eddy diffusivity K zz , is usually obscure. Here we analytically and numerically investigate vertical tracer transport in a 3D stratified atmosphere and predict K zz as a function of the large-scale circulation strength, horizontal mixing due to eddies and waves and local tracer sources and sinks. We find that K zz increases with tracer chemical lifetime and circulation strength but decreases with horizontal eddy mixing efficiency. We demarcated three K zz regimes in planetary atmospheres. In the first regime where the tracer lifetime is short compared with the transport timescale and horizontal tracer distribution under chemical equilibrium ( ) is uniformly distributed across the globe, global-mean vertical tracer mixing behaves diffusively. But the traditional assumption in current 1D models that all chemical species are transported via the same eddy diffusivity generally breaks down. We show that different chemical species in a single atmosphere should in principle have different eddy diffusion profiles. In the second regime where the tracer is short-lived but is non-uniformly distributed, a significant non-diffusive component might lead to a negative K zz under the diffusive assumption. In the third regime where the tracer is long-lived, global-mean vertical tracer transport is also largely influenced by non-diffusive effects. Numerical simulations of 2D tracer transport on fast-rotating zonally symmetric planets validate our analytical K zz theory over a wide parameter space.

Cooperative Data Collection Mechanism Using Multiple Mobile Sinks in Wireless Sensor Networks.

Data collection problems have received much attention in recent years. Many data collection algorithms that constructed a path and adopted one or more mobile sinks to collect data along the paths have been proposed in wireless sensor networks (WSNs). However, the efficiency of the established paths still can be improved. This paper proposes a cooperative data collection algorithm (CDCA), which aims to prolong the network lifetime of the given WSNs. The CDCA initially partitions the n sensor nodes into k groups and assigns each mobile sink acting as the local mobile sink to collect data generated by the sensors of each group. Then the CDCA selects an appropriate set of data collection points in each group and establishes a separate path passing through all the data collection points in each group. Finally, a global path is constructed and the rendezvous time points and the speed of each mobile sink are arranged for collecting data from k local mobile sinks to the global mobile sink. Performance evaluations reveal that the proposed CDCA outperforms the related works in terms of rendezvous time, network lifetime, fairness index as well as efficiency index.

Boundary Control of Embedded Heaters for Uniform Bondline Temperatures During Composite Joining

This paper investigates an out-of-autoclave (OoA), embedded-resistive heating method to precisely control the bondline temperature when curing high strength adhesives for joining composite adherends. A challenge with OoA methods is that nonuniform heat loss, e.g., due to substructures that act as local heat sinks, can lead to nonuniform temperatures in the bondline, which in turn, can result in uneven curing, residual stresses, and potentially weak joints. The main contribution of this work is to apply a voltage pattern at the boundary of the embedded heater to control the distribution of the electrical power at the interior bondline, and thereby reduce temperature variations. Additionally, this work devises an empirical model (that can be applied when material parameters and models are not readily available) to predict the desired power generation, and to design the embedded heater and voltage pattern that minimizes the bondline temperature variation. The technique is demonstrated experimentally for bonding a single-lap joint, and the maximum temperature variation in the bond area was reduced by five times from 31.6 °C to 6.0 °C.

Gyrokinetic theory of turbulent acceleration and momentum conservation in tokamak plasmas

Understanding the generation of intrinsic rotation in tokamak plasmas is crucial for future fusion reactors such as ITER. We proposed a new mechanism named turbulent acceleration for the origin of the intrinsic parallel rotation based on gyrokinetic theory. The turbulent acceleration acts as a local source or sink of parallel rotation, i.e., volume force, which is different from the divergence of residual stress, i.e., surface force. However, the order of magnitude of turbulent acceleration can be comparable to that of the divergence of residual stress for electrostatic ion temperature gradient (ITG) turbulence. A possible theoretical explanation for the experimental observation of electron cyclotron heating induced decrease of co-current rotation was also proposed via comparison between the turbulent acceleration driven by ITG turbulence and that driven by collisionless trapped electron mode turbulence. We also extended this theory to electromagnetic ITG turbulence and investigated the electromagnetic effects on intrinsic parallel rotation drive. Finally, we demonstrated that the presence of turbulent acceleration does not conflict with momentum conservation.

Arc-Malstrøm: A 1D hydrologic screening method for stormwater assessments based on geometric networks

A method is presented to perform a first screening of high-resolution digital terrain models to detect the extents and capacities of local landscape sinks. When identified their capacities and rain volumes provided from their local catchments during a rainstorm are saved as attributes for the pour points. Next, the downstream paths from the pour points are saved as junctions and edges in a geometric network leading to a final calculation of the accumulated spillover in the topologic data structure determined by a custom trace tool. Although the screening method is based on a representation of the overland surface in a 1D network not involving any hydrodynamic components, it is well suited to provide a quick first overview of a landscape's overall drainage basins, the location of sinks, their contributing watersheds and the accumulated downstream flow when the sinks spill over. The exemplified study assumes Hortonian flow and a uniform rain event, but if spatial variations in precipitation or infiltration capacities are available the local sinks' catchment level, they may easily be added to the workflow to produce first risk map approximations for residential areas threatened by future stormwater incidents.

Cyclic heliothermal behaviour of the shallow, hypersaline Lake Hayward, Western Australia

Lake Hayward is one of only about 30 hypersaline lakes worldwide that is meromictic and heliothermal and as such behaves as a natural salt gradient solar pond. Lake Hayward acts as a local groundwater sink, resulting in seasonally variable hypersaline lake water with total dissolved solids (TDS) in the upper layer (mixolimnion) ranging between 56 kg m−3 and 207 kg m−3 and the deeper layer (monimolimnion) from 153 kg m−3 to 211 kg m−3. This is up to six times the salinity of seawater and thus has the highest salinity of all eleven lakes in the Yalgorup National Park lake system. A program of continuously recorded water temperature profiles has shown that salinity stratification initiated by direct rainfall onto the lake’s surface and local runoff into the lake results in the onset of heliothermal conditions within hours of rainfall onset.The lake alternates between being fully mixed and becoming thermally and chemically stratified several times during the annual cycle, with the longest extended periods of heliothermal behaviour lasting 23 and 22 weeks in the winters of 1992 and 1993 respectively. The objective was to quantify the heat budgets of the cyclical heliothermal behaviour of Lake Hayward.During the period of temperature profile logging, the maximum recorded temperature of the monimolimnion was 42.6 °C at which time the temperature of the mixolimnion was 29.4 °C.The heat budget of two closed heliothermal cycles initiated by two rainfall events of 50 mm and 52 mm in 1993 were analysed. The cycles prevailed for 11 and 20 days respectively and the heat budget showed net heat accumulations of 34.2 MJ m−3 and 15.4 MJ m−3, respectively. The corresponding efficiencies of lake heat gain to incident solar energy were 0.17 and 0.18 respectively. Typically, artificial salinity gradient solar ponds (SGSP) have a solar radiation capture efficiencies ranging from 0.10 up to 0.30. Results from Lake Hayward have implications for comparative biogeochemistry and its characteristics should aid in identification of other hitherto unknown heliothermal lakes.

Long open-path measurements of greenhouse gases in air using near-infrared Fourier transform spectroscopy

Abstract. In complex and urban environments, atmospheric trace gas composition is highly variable in time and space. Point measurement techniques for trace gases with in situ instruments are well established and accurate, but do not provide spatial averaging to compare against developing high-resolution atmospheric models of composition and meteorology with resolutions of the order of a kilometre. Open-path measurement techniques provide path average concentrations and spatial averaging which, if sufficiently accurate, may be better suited to assessment and interpretation with such models. Open-path Fourier transform spectroscopy (FTS) in the mid-infrared region, and differential optical absorption spectroscopy (DOAS) in the UV and visible, have been used for many years for open-path spectroscopic measurements of selected species in both clean air and in polluted environments. Near infrared instrumentation allows measurements over longer paths than mid-infrared FTS for species such as greenhouse gases which are not easily accessible to DOAS.In this pilot study we present the first open-path near-infrared (4000–10 000 cm−1, 1.0–2.5 µm) FTS measurements of CO2, CH4, O2, H2O and HDO over a 1.5 km path in urban Heidelberg, Germany. We describe the construction of the open-path FTS system, the analysis of the collected spectra, several measures of precision and accuracy of the measurements, and the results a four-month trial measurement period in July–November 2014. The open-path measurements are compared to calibrated in situ measurements made at one end of the open path. We observe significant differences of the order of a few ppm for CO2 and a few tens of ppb for CH4 between the open-path and point measurements which are 2 to 4 times the measurement repeatability, but we cannot unequivocally assign the differences to specific local sources or sinks. We conclude that open-path FTS may provide a valuable new tool for investigations of atmospheric trace gas composition in complex, small-scale environments such as cities.

Soil organic carbon stock in Abune Yosef afroalpine and sub-afroalpine vegetation, northern Ethiopia

IntroductionSoil is the major reservoir of organic carbon. There is a paucity of soil organic carbon (SOC) stock data of afroalpine and sub-afroalpine vegetation in Ethiopia. Hence, this study was conducted to estimate the SOC stock and correlate it with soil physicochemical properties in Abune Yosef afroalpine and sub-afroalpine vegetation. Systematic sampling was employed to collect soil samples from upper 30 cm. Dry bulk density soil pH (1:2.5 water); organic carbon (Walkley and Black), and total nitrogen (Kjeldahl) were the methods used for soil analysis. Pearson correlation and linear regression analysis were performed in SPSS 24 statistical software.ResultsThe SOC stock of the study area was found to be 79.57 t C ha−1. Soil organic carbon stock showed statistically significant positive correlation with vegetation type (r = 0.522, p < 0.01), bulk density (r = 0.62, p < 0.01), total nitrogen (r = 0.41, p < 0.01), and altitude (r = 0.468, p < 0.01) and negative correlation with slope (r = − 0.298, p < 0.05). The present study revealed similar soil organic carbon stock (SOCS) with the Intergovernmental Panel on Climate Change (IPCC) default estimate for similar regions. Positive correlation of SOCS and altitude could be resulted from the variations in anthropogenic disturbances, temperature, and precipitation vegetation types. The negative correlation between SOCS and slope is the result from the predictably higher soil erosion at steeper slopes. Temporal livestock trampling increased the bulk density but never affected the SOCS to decline. Aspect did not show any significant relationship with SOCS due to either the under surveying of all aspects or similar solar radiation found in the study area. Moreover, gazing, aspect, and soil pH did not show statistically significant impact on SOCS.ConclusionThe SOCS of Abune Yosef afroalpine and sub-afroalpine vegetation is similar to the IPCC default estimate for similar regions. This is a great contribution both to the global and local terrestrial carbon sink.

Sympathetic neuron-associated macrophages contribute to obesity by importing and metabolizing norepinephrine.

The cellular mechanism(s) linking macrophages to norepinephrine (NE)-mediated regulation of thermogenesis have been a topic of debate. Here we identify sympathetic neuron-associated macrophages (SAMs) as a population of cells that mediate clearance of NE via expression of solute carrier family 6 member 2 (SLC6A2), an NE transporter, and monoamine oxidase A (MAOA), a degradation enzyme. Optogenetic activation of the sympathetic nervous system (SNS) upregulates NE uptake by SAMs and shifts the SAM profile to a more proinflammatory state. NE uptake by SAMs is prevented by genetic deletion of Slc6a2 or inhibition of the encoded transporter. We also observed an increased proportion of SAMs in the SNS of two mouse models of obesity. Genetic ablation of Slc6a2 in SAMs increases brown adipose tissue (BAT) content, causes browning of white fat, increases thermogenesis, and leads to substantial and sustained weight loss in obese mice. We further show that this pathway is conserved, as human sympathetic ganglia also contain SAMs expressing the analogous molecular machinery for NE clearance, which thus constitutes a potential target for obesity treatment.

Rutile geochemistry and thermometry of eclogites and associated garnet-mica schists in the Biga Peninsula, NW Turkey

In northwest Turkey, high-pressure metamorphic rocks occur as exotic blocks within the Çetmi mélange located on the south of the Biga Peninsula. Rutile chemistry and rutile thermometry obtained from the eclogite and associated garnet-mica schist in the Çetmi mélange indicate significant trace element behaviour of subducted oceanic crust and source-rock lithology of detrital rutiles. Cr and Nb contents in detrital rutile from garnet-mica schist vary from 355 to 1026μg/g and 323 and 3319μg/g, respectively. According to the Cr-Nb discrimination diagram, the results show that 85% of the detrital rutiles derived from metapelitic and 15% from metamafic rocks. Temperatures calculated for detrital rutiles and rutiles in eclogite range from 540°C to 624°C with an average of 586°C and 611°C to 659°C with an average of 630°C at P=2.3GPa, respectively. The calculated formation temperatures suggest that detrital rutiles are derived from amphibolite- and eclogite-facies metamorphic rocks. Amphibolite-facies rocks of the Kazdağ Massif could be the primary source rocks for the rutiles in the garnet-mica schist from the Çetmi mélange. Nb/Ta ratios of metapelitic and metamafic rutiles fall between 7–24 and 11–25, respectively. Nb/Ta characteristics in detrital rutiles may reflect a change in source-rock lithology. However, Nb/Ta ratios of rutiles in eclogite vary from 9 to 22. The rutile grains from eclogites are dominated by subchondritic Nb/Ta ratios. It can be noted that subchondritic Nb/Ta may record rutile growth from local sinks of aqueous fluids from metamorphic dehydration.

Impact of landslides on soil characteristics: Implications for estimating their age

The slopes of Mount Elgon, a complex volcano at the border between Uganda and Kenya, are frequently affected by landslides with disastrous effects on the livelihood of its population. Since local people greatly depend on the land for crop production, this paper examines if and how fast physico-chemical characteristics in landslide scars recover. A chronosequence of 18 landslides covering a period of 103years was sampled in order to explore differences between topsoil inside and outside landslide scars. For each landslide, two topsoil samples were taken within the landslide and two in nearby undisturbed soils to compare their physico-chemical characteristics. Samples inside the landslides were located at the transition zone between the depletion and accumulation zone, which is situated at the contact line between the plan concave and plan convex section of the landslide. No differences were found for available phosphorus, Ca2+, Mg2+ content or for the fine earth texture. Recent landslides had however lower content of soil organic carbon (OC) and K+, and higher content of rock fragments and Na+ than the adjacent soils. Soil OC content increased significantly with age and reached levels of the corresponding undisturbed soils after ca. 60years. Older landslides had even higher OC contents than soils adjacent to the landslide. Hence landslide scars act as local carbon sink. We suggest that the occurrence of rock fragments in the topsoil is a useful indicator for mapping past landslides. Moreover, the difference in soil OC content between landslide scars and adjacent soil could be used for estimating the age of landslides in data-poor regions.

Spatial Prediction of Soil Organic Matter Using a Hybrid Geostatistical Model of an Extreme Learning Machine and Ordinary Kriging

An accurate estimation of soil organic matter (SOM) content for spatial non-point prediction is an important driving force for the agricultural carbon cycle and sustainable productivity. This study proposed a hybrid geostatistical method of extreme learning machine-ordinary kriging (ELMOK), to predict the spatial variability of the SOM content. To assess the feasibility of ELMOK, a case study was conducted in a regional scale study area in Shaanxi Province, China. A total of 472 topsoil (0–20 cm) samples were collected. A total of 14 auxiliary variables (predictors) were obtained from remote sensing data and environmental factors. The proposed method was compared with the ability of traditional geostatistical methods such as simple kriging (SK) and ordinary kriging (OK), in addition to hybrid geostatistical methods such as regression-ordinary kriging (ROK) and artificial neural network-ordinary kriging (ANNOK). The results showed that the extreme learning machines (ELM) model used principal components (PCs) as input variables, and performed better than both multiple linear regression (MLR) and artificial neural network (ANN) models. Compared with geostatistical and hybrid geostatistical prediction methods of SOM spatial distribution, the ELMOK model had the highest coefficient of determination (R2 = 0.671) and ratio of performance to deviation (RPD = 2.05), as well as the lowest root mean square error (RMSE = 1.402 g kg−1). In conclusion, the application of remote sensing imagery and environmental factors has a deeper driven significance of a non-linear and multi-dimensional hierarchy relationship for explaining the spatial variability of SOM, tracing local carbon sink and high quality SOM maps. More importantly, it is possibly concluded that the sustainable monitoring of SOM is a significant process through the pixel-based revisit sampling, an analysis of the mapping results of SOM, and methodological integration, which is the primary step in spatial variations and time series. The proposed ELMOK methodology is a promising and effective approach which can play a vital role in predicting the spatial variability of SOM at a regional scale.

The fate of sediment, wood, and organic carbon eroded during an extreme flood, Colorado Front Range, USA

Identifying and quantifying the dominant processes of erosion and tracking the fate of sediment, wood, and carbon eroded during floods is important for understanding channel response to floods, downstream sediment and carbon loading, and the influence of extreme events on landscapes and the terrestrial carbon cycle. We quantify sediment, wood, and organic carbon (OC) from source to local sink following an extreme flood in the tectonically quiescent, semi-arid Colorado (USA) Front Range. Erosion of >500,000 m3 or as much as ~115 yr of weathering products occurred through landsliding and channel erosion during September 2013 flooding. More than half of the eroded sediment was deposited at the inlet and delta of a water supply reservoir, resulting in the equivalent of 100 yr of reservoir sedimentation and 2% loss in water storage capacity. The flood discharged 28 Mg C/km2, producing an event OC flux equivalent to humid, tectonically active areas. Post-flood remobilization resulted in a further ~100 yr of reservoir sedimentation plus export of an additional 1.3 Mg C/km2 of wood, demonstrating the ongoing impact of the flood on reservoir capacity and carbon cycling. Pronounced channel widening during the flood created accommodation space for 40% of flood sediment and storage of wood and eroded carbon. We conclude that confined channels, normally dismissed as transport reaches, can store and export substantial amounts of flood constituents.

Zr-in-rutile thermometry of eclogites from the Karakaya Complex in NW Turkey: Implications for rutile growth during subduction zone metamorphism

Eclogites occur as a tectonic slice within a metabasite-phyllite-marble unit of the Karakaya Complex in northwest Turkey. The high-pressure mineral assemblage in eclogite is mainly composed of garnet+omphacite+glaucophane+epidote+quartz. Trace element characteristics of rutile and Zr-in-rutile temperatures were determined for eclogites from the Karakaya Complex. Core-rim analyses of rutile grains yield remarkable trace element zoning with lower contents of Zr, Nb and Ta in the core than in the rim. The variations in Zr, Nb and Ta can be ascribed to growth zoning rather than diffusion effects. The Nb/Ta and Zr/Hf ratios increase with a decrease in Ta and Hf contents, which could be ascribed to the effect of metamorphic dehydration in subduction zones on rutile Nb/Ta differentiation. The rutile grains from eclogites in the Karakaya Complex are dominated by subchondritic Nb/Ta and Zr/Hf ratios. It can be noted that subchondritic Nb/Ta may record rutile growth from local sinks of aqueous fluids from metamorphic dehydration.The Zr contents of all rutile grains range between 81 and 160ppm with an average of 123ppm. The Zr-in-rutile thermometry yields temperatures of 559–604°C with an average temperature of 585°C for eclogites from the Karakaya Complex. This average temperature suggests growth temperature of rutile before peak pressure during the subduction. However, some rutile grains have higher Zr contents in the outermost rims compared to the core. Zr-in-rutile temperatures of the rims are about 20°C higher than those of the cores. This suggests that the outermost rims would have grown from a distinct fluid at higher temperatures than that of the cores. Moreover, Zr contents and calculated temperatures in both inclusion rutile and matrix rutile from eclogites are identical, which suggests that eclogites within the Karakaya Complex belong to the same tectonic slice and underwent similar metamorphic evolution.

Developing a canine vocal fold scar model by CO₂ laser and studying the LOX, HSP70 and HA expression in its extra celluar matrix

Objective:Building a canine vocal fold scar model and analyzing the changes in morphology, histopathology and related factors of extra cellular matrix (ECM) of vocal cord healing at different time periods.Method:Five experimental dogs were randomly divided into the control group(one dog) and the experimental group (four dogs). No special treatment was done on the control group, and the experimental group was given CO₂ laser through laryngoscope with minimally invasive surgery on bilateral vocal cords. Observation of the morphological changes of injured vocal cords was made at five different time, pre-operation and 6 h, 3 w, 8 w and 12 w post-operation. HE staining, immunofluorescence, were used respectively to observe the histopathological and ultrastructural changes of each layer of vocal cord. Observation were made on the changing pattern of lysyl oxidase (LOX), heat shock proteins70 (HSP70), and the integrated optical density index (IOD) of Hyaluronic acid (HA) in vocal cord tissues. Result:①Laryngoscope shows there were mild congestion and edema and inflammatory exudation on the wound surface of vocal cord 3w post-operation. On the wound surface of vocal cord 8 w post-operation, the congestion and edema disappear, the local contraction sink, and no adhesion and granulation form. 12 w post-operation, the surface of the vocal cord was smooth, there were local contractures, vocal fold scar form, and hoarseness in the bilateral vocal cords was obvious. ②HE staining shows 6 h post-operation there were a large number of inflammatory cell infiltration, red blood cell leakage, and cell congestion and edema on the wound surface of vocal cord. 3 w post-operation, there were fibroblast proliferation, angiogenesis, and a large number of fibrous tissues disorderly arranged on the wound surface of vocal cord. 8w post-operation, each layer of fibrous tissues were in hyperplasia and the blood vessels was thicken after on the wound surface of vocal cord, 12 w post-operation, a large number of collagens increases and were in group or fasciculation disorder. There were many irregular gaps in fibers, and blood vessels and glands become rare or disappear. ③The immunofluorescence showed LOX, HSP70 and HA were all localized in the cellular cytoplasm and nucleus. The expression levels were different at different postoperative time, and they were mainly relatively strong expressed in the inflammatory cells, vascular endothelial cells and the glands. ④The comparison of IOD values: The IOD values of LOX were different at different time periods (P< 0.05). There were no significant differences in IOD of HSP70 between pre-operation and 12 w post-operation, but there are significant differences among other groups (P< 0.05). There were no significant differences in IOD of HA between pre-operation and 12 w post-operation, but there were significant differences among other groups (P< 0.01). ⑤The expression of LOX decreased 6h post-operation and increased 3-12 w post-operation. The expression of HSP70 post-operation reached the peak 6 h post-operation and decreased 3-12 w post-operation. The expression of HA decreased 6 h post-operation, increased to the peak 8 w post-operation, and decreased 8-12 w post-operation.⑥The transmission electron microscope showed 3 w to 8 w post-operation, in the intrinsic layer of the vocal cord, the fibroblasts were extremely active, the cells swelled, and the organelles were abundant.12 w post-operation, there were a small number of fibroblasts in the active state, and larger gaps between the fibers and fewer and thinner elastic fibers. Conclusion:CO₂ laser ablation of vocal cords under the Micro Post-Laryngoscope could establish reliable animal model of vocal fold scar, and 12 w reticular the vocal fold scars basically form. LOX, HSP70, HA play different roles at early, middle, and late stages in the vocal fold scar formation, and they can be used as a more sensitive index for vocal fold scar formation.

Structure and density of Callisto’s atmosphere from a fluid-kinetic model of its ionosphere: Comparison with Hubble Space Telescope and Galileo observations

We develop a model of the ionospheric electron population of Jupiter’s moon Callisto using a prescribed neutral atmosphere composed of O2, CO2 and H2O. A kinetic description of ionospheric suprathermal electrons coupled with a fluid description of ionospheric thermal electrons is well suited to jointly analyze and interpret observations of electron density and atmospheric UV emission. Accordingly, we calculate the electron energy distribution function at each point in the ionosphere by solving a coupled set of equations consisting of the Boltzmann equation for suprathermal electrons and the continuity and energy equation for thermal electrons. We assume a stationary balance between local sources and sinks of electrons and electron energy. Electron transport within the ionosphere is neglected, since collision time scales are shorter than transport time scales in the region of Callisto’s ionosphere where the major concentrations of electrons is located and the major part of the atmospheric UV emission is generated. We consider photoionization, which is the dominant ionospheric electron source, and secondary ionization from collisions of photoelectrons with neutrals. Our calculations yield electron densities and electron impact generated UV emissions from Callisto’s atmosphere. Comparing our modeled UV emission intensities with the Hubble Space Telescope observation of Cunningham et al. (2015) , we find that Callisto’s atmosphere has a mean O2 column density of 2.1−1.1+1.1×1019 m−2. A joint comparison with this HST observation and radio occultation observations of Kliore et al. (2002) shows that Callisto’s atmosphere possesses a day night asymmetry. We derive terminator O2 column densities of ∼ 0.4 × 1019 m−2, for which we find subsolar O2 column densities in the range of 2.4−9.8×1019 m−2. Our calculations also show that the electron density is very sensitive to the relative abundance of H2O due to the thermal electron cooling by rotational state excitation of H2O. For the efficiency of Callisto’s atmospheric UV emission we find that on average one photon is emitted at OI λ135.6 nm per every 170 electron ion pairs generated and per every 60 electron ion pairs produced by secondary electron impact ionization.

Atmospheric molecular hydrogen (H2) at the Shangdianzi regional background station in China

Atmospheric molecular hydrogen (H2) mole fractions have been continuously measured at the Shangdianzi regional station in China. In this study, we present the atmospheric H2 time series from January 2015 to April 2016, and investigate the diurnal and seasonal cycles, and the impact of meteorological factors on the observed values. Atmospheric H2 mole fractions at Shangdianzi vary from a minimum of 381 ppb (parts per billion, 10−9 dry air mole fraction) to a maximum of 1535 ppb, with a median of 510 ppb and a mean (± standard deviation) of 555 ± 113 ppb during the observation period. The results indicate that H2 mole fractions at Shangdianzi are frequently influenced by local sources and sinks. Regionally representative conditions account for 44.7% of the total records with a mean mole fraction of 488 ± 20 ppb. The highest regionally representative H2 mole fraction is observed in July, while the lowest is observed in October. Peak-to-trough amplitude in the seasonal cycle is 63 ± 3 ppb. H2 mole fractions show nighttime depletion in all seasons, with the lowest values in the morning (7:00–10:00 local time). The H2 mole fractions are also influenced by local surface wind direction at Shangdianzi. Winds from NW-NNW-N-NNE-NE-ENE-E directions are always associated with negative contribution to atmospheric H2 loading, whereas winds from SSW-SW-WSW-W directions generally enhance the H2 values. The results of trajectory clustering analysis demonstrate that air masses from a southerly direction induce high H2 mole fractions. Conversely, mean H2 mole fractions are low when air masses are from the north, northwest, and east directions.

Cover crops have neutral effects on predator communities and biological control services in annual cellulosic bioenergy cropping systems

Maize stover is beginning to be used as a cellulosic biofuel feedstock in the Midwestern United States; however, there are concerns that stover removal could result in increased soil erosion and loss of soil organic matter. Use of a winter cover crop following maize harvest has the potential to mitigate these impacts and may have additional benefits by providing continuous living cover in annual crop habitats leading to changes in insect predator communities and increased biocontrol services. However, cover crops may also be harvested in cellulosic biofuel systems, adding a disturbance event that may negatively affect biocontrol. We contrasted insect predator communities and their impacts in four potential bioenergy cropping systems in Michigan and Wisconsin (USA) during the 2013 and 2014 growing seasons. Two annual maize systems were harvested for grain and stover; one maize system included a cereal rye/Austrian winter pea cover crop. Two perennial systems, switchgrass and a mixed prairie grasses and forbs, were harvested in the fall for biomass. Predatory insect abundance and diversity were lower in both annual cropping systems than in the perennial cropping systems and the inclusion of the cover crop did not significantly alter these responses. Similarly, removal of sentinel insect egg prey was also lower in the annual versus perennial cropping systems, with no significant influence of cover crop. We also explored the potential for cover crops to harbor prey populations in the spring that might encourage oviposition by mobile predators and potentially lead to local population sources or sinks of predators depending on the timing and effect of cover crop harvest. We found that existing predator communities in the cover crop treatments effectively suppressed aphid population growth, limiting their attractiveness to mobile predators. While we found no significant positive or negative impacts of this cover crop system on biocontrol services, bioenergy cover cropping systems could be managed to increase multiple ecosystem services by altering cover crop identity, or timing of planting and harvest.

Natural mitigation factor adjustment for re-suspended particulate matter emissions inventory for Bogotá, Colombia

This work improves atmospheric emissions of particulate matter in Bogotá Colombia, and provides a tool applying this technique around the world. Bogotá's air pollution is largely impacted by particulate matter, and specifically by re-suspended particulate matter (RPM). RPM sources include paved and unpaved roads, agricultural tilling, construction activities, mining and quarrying. RPM emissions are frequently estimated using annual emission factors, time-varying vehicle traffic activity, a time/space invariant meteorological scaling factor, and a time/space invariant correction factor. This work updates the meteorological factors to be hour-specific, and replacing the correction factor with land use-specific local deposition factors. These techniques are codified in a flexible Python tool based on EPA's AP42 methods and the broader emission literature.Meteorology inhibits RPM emission directly via precipitation scavenging and indirectly by accumulation of road surface moisture. The effects of precipitation and surface moisture are parameterized as mitigation factors differently for paved and unpaved roads due to their porosity and drainage characteristics.These estimates of hourly mitigation factors (on average for paved roads: 0.86 and for unpaved roads: 0.61) agree well with annual factors previously used (paved: 0.90; unpaved: 0.60), however hourly factors have clear diurnal patterns that reduce emissions more significantly latter in the day for paved roads (00–12: 0.95; 12–24: 0.78), and to a lesser extent for unpaved roads (00–12: 0.64; 12–24: 0.58).Emissions are also significantly reduced by vehicle induced turbulence and local deposition. The transportable fraction (0.59 ± 0.22), parameterized based on land use, significantly reduced emissions and correlates with unpaved roads (r = 0.30) more so than with paved roads (r = 0.02). These fractions were used to construct a new inventory, which might improve air pollution predictions compared to the raw inventory, as well as new efforts to simulate exposure fields in Bogotá and our understanding of local particulate sources and sinks.

Road transport emissions and capacity of forests in the region of Athens for sequestring these emissions: carbon flow before and after forest fires

One important component of the urban contribution to carbon dioxide atmospheric emissions is road transport. Carbon dioxide (CO2) emissions from urban road transport in the centre of Athens recorded over a period of five years (2000–2005) are compared with the carbon sequestration capacity of regional forests, prior to and after the devastating forest fires in Attica in 2007 and 2009, which is the administrative region of Athens. The comparison of carbon flow reveals two complementary aspects of the same socio-environmental issue: persistent sources versus weakening sinks for CO2 within a mixed (urban and rural) setting. Road transport emissions are calculated bottom-up using traffic data from in-situ measurements along segments of main roads. The sequestration capacity of forests is estimated by combining satellite images of changes in land cover with literature values of biomass growth rates. Over the study period, the per capita CO2 emissions averaged 0.72 t CO2/cap/year, which is four times higher than the sequestration capacity of forests before and six times higher after the fires. This imbalance highlights the inadequacy of the local carbon sink. Although there is no biogeochemical need to neutralise carbon budgets locally, defining the CO2 flows from urban activities and local ecosystems is likely to raise awareness and promote global environmental sustainability. The results are compared with top-down estimates of CO2 emissions at a regional scale, where suburban areas are dominant, and the differences are discussed in the light of local socioeconomic factors.