Atmospheric Entrainment Research Articles

Identification of the atmospheric boundary layer structure through vertical distribution of PM2.5 obtained by unmanned aerial vehicle measurements

Variations in the atmospheric boundary layer (ABL) structure present a close relationship with the vertical diffusion of air pollutants. However, the effect of the ABL structure on the vertical distribution of air pollutants is rarely investigated in detail, especially through in-situ measurement. In this study, from November 26th to December 20th, 2017, an unmanned aerial vehicle (UAV) outfitted with sensors was used to monitor meteorological factors and pollutants concentrations (including PM2.5, O3, and BC) in the suburbs of Shanghai. According to the vertical profiles of PM2.5 concentrations, the gradient and the lidar backscatter methods were used to determine the parameters of the ABL structure. Results indicate that the maximum height of the atmospheric boundary layer occurred at noon exceeding 1000 m, and the maximum thickness of the atmospheric entrainment layer occurred at twilight exceeding 360 m during the field campaign. Additionally, the relationships between the structure of ABL and pollutant concentrations were analyzed and quantified. In contrast to the height of the ABL, the concentrations of ground-level aerosol pollutants show a stronger correlation with the thickness of the atmospheric entrainment layer. It also confirms that the entrainment flux ratio was an important factor affecting ground-level ozone concentrations. In summary, the in-situ measurements can provide experimental support for modeling the ABL structure and provide insights for the control of aerosol pollution.

Insight Into Formation Processes of Layered Ejecta Craters on Mars From Thermophysical Observations

AbstractUnderstanding the morphological characteristics of craters that are indicative of their formation environment can provide insight into surface geology. Layered ejecta (LE) craters, found on Mars and some other planetary bodies, have been hypothesized to have formed as a result of either interaction with subsurface volatiles (volatile fluidization model) and/or with the atmosphere (atmospheric entrainment model). Formation of LE craters by either model should result in different grain size distributions throughout the ejecta deposit. Using thermal inertia to infer surface properties, we investigated LE craters and their ejecta deposits in an effort to distinguish between possible LE formation processes on Mars. We used thermophysical properties of crater ejecta to determine grain size distribution, to model horizontal mixtures and vertical layering, and to identify materials present within the ejecta. We assessed the thermal properties of 50 uniformly sampled LE craters using Mars Odyssey Thermal Emission Imaging System (THEMIS) and Mars Global Surveyor Thermal Emission Spectrometer (TES) data. Our THEMIS analysis identifies 12 craters with grain size distributions consistent with the volatile fluidization model, 3 craters that have characteristics potentially associated with either model, and 22 craters that do not exhibit characteristics matching either model. Our TES analysis identifies 11 craters with characteristics consistent with the volatile fluidization model and 8 craters that are consistent with the atmospheric entrainment model. While some observations of grain size distributions provide evidence for either or both models, there is not overwhelming support for either model, potentially due to uncertainties of derived thermal inertia data.

A comparison of two cold atmospheric helium plasma devices which utilise the same RF power generator

PurposeThis research was conducted to analyse and compare a Renuvion hand piece and TheraDep's deposition device at various gas flow rates and power settings. Both devices were powered by an Apyx Ultimate Electrosurgical generator. MethodsCurrent, voltage, optical emission spectroscopy (OES) and thermal imaging were used to investigate the resulting plasma intensities and species being ionised. It was found that the Renuvion device could deliver 5.6 to 8.2 W of power whereas the Deposition Accessory was significantly less at between 1.9 and 4.2 W depending on the power setting selected. Differences in the OES results were also observed which are thought to have resulted from variations in the atmospheric entrainment between the two devices. ResultsTaken in combination, the electrical, optical emission and thermal data analysis has demonstrated that the addition of the Deposition Accessory transforms the Renuvion electrosurgical tool from a device that operates in the coagulation and cutting arena into a device with a dramatic reduction in the energy delivered to the target tissue. Consequently, this limits the localised heating of adjacent tissue and results in a device that has controlled coagulation capability and one which is not capable of cutting tissue. ConclusionsThis offers significant potential to allow clinicians to evaluate applications in plasma medicine using an FDA cleared electrosurgical power source.

Precipitation chemistry and deposition at a high-elevation site in the Pacific Northwest United States (1989–2015)

Emissions from fuel combustion and agricultural activities contribute significantly to the continuous atmospheric entrainment of pollutants into protected and vulnerable ecosystems where long-term monitoring is often a challenge. Here, results are presented from a 26-year study (1989–2015) of wet precipitation collected at Paradise Station (1654 m above sea level), Mount Rainier National Park, Washington, USA. Weekly samples were analyzed for pH, conductivity and major anions and cations. While precipitation concentrations for sulfate, nitrate, protons and conductivity peaked in the early 2000s, overall trends decreased by 54%, 46%, 41%, and 37%, respectively. Associated pH values increased from 5.2 to 5.6, and were largely controlled by non-sea-salt contributions of sulfate and neutralizing calcium, potassium and magnesium. Between 1999 and 2015, nitrogen (N) deposition rates from ammonium increased by a factor of 3.6, from 0.27 to 0.96 kg N ha−1 yr−1 (p = 0.02), while nitrate deposition did not change statistically (0.91–0.74 kg N ha−1 yr−1, p = 0.30). Combined, these N sources are reaching reported critical loads of 2.0 kg N ha−1 yr−1. Results indicate that emission regulations focused on stationary sources have effectively decreased apparent acid precipitation, however, increased nitrogen deposition from ammonium may lead to further fertilization and acidification of delicate soils and waters. Continued long-term monitoring is thus imperative to track continued anthropogenic inputs to vulnerable ecosystems.

New insights on entrainment and condensation in volcanic plumes: Constraints from independent observations of explosive eruptions and implications for assessing their impacts

The turbulent entrainment of atmosphere and the condensation of water vapor govern the heights of explosive volcanic plumes. These processes thus determine the delivery and the lifetime of volcanic ash and aerosols into the atmosphere. Predictions of plume heights using one-dimensional “integral” models of volcanic plumes, however, suffer from very large uncertainties, related to parameterizations for entrainment and condensation. In particular, the wind entrainment coefficient β, which governs the contribution of crosswinds to turbulent entrainment, is subject to uncertainties of one order of magnitude, leading to relative uncertainties of the order of 50% on plume height. In this study, we use a database of 94 eruptive phases with independent estimates of mass eruption rate and plume height to constrain and evaluate four popular 1D models. We employ re-sampling methods to account for observational uncertainties. We show that plume height predictions are significantly improved when: i) the contribution of water vapor condensation to the plume buoyancy flux is excluded; and ii) the wind entrainment coefficient β is held constant between 0.1 and 0.4. We explore implications of these results for predicting the climate impacts of explosive eruptions and the likelihood that eruptions will form stable umbrella clouds or devastating pyroclastic flows. Last, we discuss the sensitivity of our results to the definition of plume height in the model in light of a recent set of laboratory experiments and draw conclusions for improving future databases of eruption parameters.

A combined field and numerical approach to understanding dilute pyroclastic density current dynamics and hazard potential: Auckland Volcanic Field, New Zealand

The most dangerous and deadly hazards associated with phreatomagmatic eruptions in the Auckland Volcanic Field (AVF; Auckland, New Zealand) are those related to volcanic base surges — dilute, ground-hugging, particle laden currents with dynamic pressures capable of severe to complete structural damage. We use the well-exposed base surge deposits of the Maungataketake tuff ring (Manukau coast, Auckland), to reconstruct flow dynamics and destructive potential of base surges produced during the eruption. The initial base surge(s) snapped trees up to 0.5m in diameter near their base as far as 0.7–0.9km from the vent. Beyond this distance the trees were encapsulated and buried by the surge in growth position. Using the tree diameter and yield strength of the wood we calculate that dynamic pressures (Pdyn) in excess of 12–35kPa are necessary to cause the observed damage. Next we develop a quantitative model for flow of and sedimentation from a radially-spreading, dilute pyroclastic density currents (PDCs) to determine the damage potential of the base surges produced during the early phases of the eruption and explore the implications of this potential on future eruptions in the region. We find that initial conditions with velocities on the order of 65ms−1, bulk density of 38kgm−3 and initial, near-vent current thicknesses of 60m reproduce the field-based Pdyn estimates and runout distances. A sensitivity analysis revealed that lower initial bulk densities result in shorter run-out distances, more rapid deceleration of the current and lower dynamic pressures. Initial velocity does not have a strong influence on run-out distance, although higher initial velocity and slope slightly decrease runout distance due to higher rates of atmospheric entrainment. Using this model we determine that for base surges with runout distances of up to 4km, complete destruction can be expected within 0.5km from the vent, moderate destruction can be expected up to 2km, but much less damage is expected up to the final runout distance of 4km. For larger eruptions (base surge runout distance 4–6km), Pdyn of >35kPa can be expected up to 2.5km from source, ensuring complete destruction within this area. Moderate damage to reinforced structures and damage to weaker structures can be expected up to 6km from source. In both cases hot ash may still cause damage due to igniting flammable materials in the distal-most regions of a base surge. This work illustrates our ability to combine field observations and numerical models to explore the depositional mechanisms, macroscale current dynamics, and potential impact of dilute PDCs. Thus, this approach may serve as a tool to understand the damage potential and extent of previous and potential future eruptions in the AVF.

Deuterium excess reveals diurnal sources of water vapor in forest air

An understanding of atmospheric water vapor content and its isotopic composition is important if we are to be able to model future water vapor dynamics and their potential feedback on future climate change. Here we present diurnal and vertical patterns of water isotope ratios in forest air (δ(2)H(v) and δ(18)O(v)) not observed previously. Water vapor observed at three heights over 3 consecutive days in a coniferous forest in the Pacific Northwest of the United States, shows a stratified nocturnal structure of δ(2)H(v) and δ(18)O(v), with the most positive values consistently observed above the canopy (60 m). Differences between 0.5 m and 60 m range between 2-6‰ for δ(18)O and 20-40‰ for δ(2)H at night. Using a box model, we simulated H(2)O isotope fluxes and showed that the low to high δ(2)H(v) and δ(18)O(v) profiles can be explained by the vapor flux associated with evaporation from the forest floor and canopy transpiration. We used d-excess as a diagnostic tracer to identify processes that contribute to the diurnal variation in atmospheric moisture. Values of d-excess derived from water vapor measurements showed a repeated diel pattern, with the lowest values occurring in the early morning and the highest values occurring at midday. The isotopic composition of rain water, collected during a light rain event in the first morning of our experiment, suggested that considerable below-cloud secondary evaporation occurred during the descent of raindrops. We conclude that atmospheric entrainment appears to drive the isotopic variation of water vapor in the early morning when the convective boundary layer rapidly develops, while evapotranspiration becomes more important in the mid-afternoon as a primary moisture source of water vapor in this forest. Our results demonstrate the interplay between the effects of vegetation and boundary layer mixing under the influence of rain evaporation, which has implications for larger-scale predictions of precipitation across the terrestrial landscape.

Saccharide composition in atmospheric particulate matter in the southwest US and estimates of source contributions

Saccharide compositions were measured in ambient particulate matter (PM) samples collected at four sites in Eastern Texas and Central Arizona in an effort to assess the contribution from biomass burning, atmospheric entrainment of soil, and primary biological aerosol particles (PBAPs) in regions with different climate patterns and ecosystems. In spite of the concentration difference, samples from the four study sites showed similar saccharide composition and seasonal variation, with the only exception being trehalose, likely resulting from the influence of local climatic conditions. Comparison of samples at the Arizona site showed different saccharide enrichment patterns between PM2.5 and PM10, which is consistent with their proposed sources as determined by a correlation analysis between observations. A positive matrix factorization (PMF) model was used to resolve three saccharide-related source factors and their relative source contributions to ambient PM using saccharides as tracers. Both the correlation and PMF model results indicate a stronger influence from local biogenic sources on aerosol saccharides at the rural sites than the urban site in Texas, and a greater impact from the PBAP and other biologically derived sources for PM collected in the Arizona location. This paper will provide the first analysis of saccharides in both fine and coarse PM in two US regions with dramatically different climates and ecosystem and provide a characterization of the ambient aerosol sources.

The Tsenkher structure in the Gobi-Altai, Mongolia: Geomorphological hints of an impact origin

The Tsenkher structure, in the Gobi-Altai region of Mongolia, was studied using a wide array of remote sensing data and field observations. The structure has a shallow, 3.6 km wide, central depression bordered by a near-circular ridge (putative crater rim) with breaches to the northwest. The central depression is obliterated partially by fluvial infill through these breaches. Outside the ridge, the western side is a rugged terrain, but the eastern half is characterized by a concentric outer ridge that occurs at about one radius distance from the inner ridge. Although intrusion, salt tectonics and maar crater hypotheses cannot be completely ruled out, its morphology strongly implies an impact origin for the Tsenkher structure. If of impact origin, it has a well-preserved morphology and its position in the basin fills indicates that the formation may have occurred relatively recently, sometime during the late Tertiary or Quaternary. The outer ridge morphology is similar to rampart craters on Mars, whose formation has been attributed to fluidization of a water-rich target layer and ejecta materials, or to atmospheric entrainment and deposition of ejected materials. However, other hypotheses including erosional remnant of ejecta blanket, erosional scarp of structural rim uplift, multi-ring or deeply eroded crater rim of a peak-ring crater are also possible at this stage. A complex fluvial and probable lacustrine history is envisaged within the Tsenkher structure. The structure is also associated with archaeology, including Paleolithic and Bronze Age remains.

Field Measurements of the Amount of Surface Layer Air versus Height in the Entrainment Zone

Abstract The structure of the atmospheric entrainment zone, an interfacial layer between the convective boundary layer and the stable air aloft, is studied using coincident high resolution aircraft and lidar observations obtained during Boundary Layer Experiment–1983 in Oklahoma. Humidity as measured by a fast-response Lyman alpha humidiometer is used as a tracer to estimate the amount of surface-layer origin air reaching various heights in the entrainment zone. Two approaches are taken to describe the humidity structure of the entrainment zone. The first approach models the frequency distributions of the three types of air in the entrainment zone: unmixed free atmosphere (dry); unmixed surface layer air (moist); and a mixture of these two. The resultant modeled frequency distributions of specific humidity capture the following observed features: Low in the convective boundary layer, surface layer air is frequently observed with little mixture air and no free atmosphere air. Higher in the convective bound...

Lidar measurements of the atmospheric entrainment zone and the potential temperature jump across the top of the mixed layer

Lidar measurements of the thickness of the atmospheric entrainment zone are presented. The measurements were obtained in central Illinois during 6 days of clear-air convection.

Influence of burner rim aerodynamics on polyhedral flames and flame stabilization

The influence of burner rim aerodynamics on the behavior of polyhedral flames of butane/air mixtures is investigated for burner rims of different geometries. By systematically varying the mixture concentration and velocity, regimes corresponding to stationary, rotating, and unstable polyhedral flames with various numbers of sides are identified. The rotational velocity and the temperature in the crest and trough regions of polyhedral flames as well as the periodic temperature fluctuation of the gases through which flames rotate are measured. The effects associated with the outer diffusion flame mantle are assessed and the influence of the conductive heat loss to the burner rim is determined. Stabilization of the Bunsen flames is also studied; for the various burner rims the critical flow velocity and concentration corresponding to flame flashback and blow-off are determined. The observations can be successfully interpreted on the bases of flame stretch, preferential diffusion, heat loss, and atmospheric entrainment.

Effects of gas composition and flame sheathing on the spatial velocity profiles of laminar analytical acetylene flames

A recently developed technique has been employed to spatially map the rise velocity pronies (horizontal and vertical) of commonly used laminar analytical flames and to determine the influence on the profiles of fuel-to-oxidant ratio and the presence of a flame sheath. The rise velocities for fuel-rich, lean, and stoichiometric flames were found to differ substantially, the entire profile being greatest for the fuel-rich condition and lowest for the fuel-lean flame. In addition, the change in rise velocity with the addition of a solid (quartz tube) or gas (N 2) sheath was studied. The flowing sheath, at several different flow rates, affected each rise velocity profile principally by altering atmospheric entrainment and thereby changing secondary combustion in the flame. In contrast, a solid quartz tube used as a sheath produces an additional increase in the entire velocity profile of each flame, since it constrains gas expansion to the direction of flame propagation. The degree to which the velocity of each flame is affected by either a flowing N 2 and quartz sheath is strongly influenced by fuel-to-oxidant ratio.