Plume Emission Research Articles

Stark broadening measurements in plasmas produced by laser ablation of hydrogen containing compounds

We present a method for the measurement of Stark broadening parameters of atomic and ionic spectral lines based on laser ablation of hydrogen containing compounds. Therefore, plume emission spectra, recorded with an echelle spectrometer coupled to a gated detector, were compared to the spectral radiance of a plasma in local thermal equilibrium. Producing material ablation with ultraviolet nanosecond laser pulses in argon at near atmospheric pressure, the recordings take advantage of the spatially uniform distributions of electron density and temperature within the ablated vapor. By changing the delay between laser pulse and detector gate, the electron density could be varied by more than two orders of magnitude while the temperature was altered in the range from 6,000 to 14,000K. The Stark broadening parameters of transitions were derived from their simultaneous observation with the hydrogen Balmer alpha line. In addition, assuming a linear increase of Stark widths and shifts with electron density for non-hydrogenic lines, our measurements indicate a change of the Stark broadening-dependence of Hα over the considered electron density range. The presented results obtained for hydrated calcium sulfate (CaSO4⋅2H2O) can be extended to any kind of hydrogen containing compounds.

Impact of Siberian forest fires on the atmosphere over the Korean Peninsula during summer 2014

Abstract. Extensive forest fires occurred during late July 2014 across the forested region of Siberia, Russia. Smoke plumes emitted from Siberian forest fires underwent long-range transport over Mongolia and northeast China to the Korean Peninsula, which is located ∼ 3000 km south of the Siberian forest. A notably high aerosol optical depth of ∼ 4 was observed at a wavelength of 500 nm near the source of the Siberian forest fires. Smoke plumes reached 3–5 km in height near the source and fell below 2 km over the Korean Peninsula. Elevated concentrations of levoglucosan were observed (119.7 ± 6.0 ng m−3), which were ∼ 4.5 times higher than those observed during non-event periods in July 2014. During the middle of July 2014, a haze episode occurred that was primarily caused by the long-range transport of emission plumes originating from urban and industrial complexes in East China. Sharp increases in SO42− concentrations (23.1 ± 2.1 µg m−3) were observed during this episode. The haze caused by the long-range transport of Siberian forest fire emissions was clearly identified by relatively high organic carbon (OC) ∕ elemental carbon (EC) ratios (7.18 ± 0.2) and OC ∕ SO42− ratios (1.31 ± 0.07) compared with those of the Chinese haze episode (OC ∕ EC ratio: 2.4 ± 0.4; OC ∕ SO42− ratio: 0.21 ± 0.05). Remote measurement techniques and chemical analyses of the haze plumes clearly show that the haze episode that occurred during late July 2014 was caused mainly by the long-range transport of smoke plumes emitted from Siberian forest fires.

High spatial resolution imaging of methane and other trace gases with the airborne Hyperspectral Thermal Emission Spectrometer (HyTES)

Abstract. Currently large uncertainties exist associated with the attribution and quantification of fugitive emissions of criteria pollutants and greenhouse gases such as methane across large regions and key economic sectors. In this study, data from the airborne Hyperspectral Thermal Emission Spectrometer (HyTES) have been used to develop robust and reliable techniques for the detection and wide-area mapping of emission plumes of methane and other atmospheric trace gas species over challenging and diverse environmental conditions with high spatial resolution that permits direct attribution to sources. HyTES is a pushbroom imaging spectrometer with high spectral resolution (256 bands from 7.5 to 12 µm), wide swath (1–2 km), and high spatial resolution (∼ 2 m at 1 km altitude) that incorporates new thermal infrared (TIR) remote sensing technologies. In this study we introduce a hybrid clutter matched filter (CMF) and plume dilation algorithm applied to HyTES observations to efficiently detect and characterize the spatial structures of individual plumes of CH4, H2S, NH3, NO2, and SO2 emitters. The sensitivity and field of regard of HyTES allows rapid and frequent airborne surveys of large areas including facilities not readily accessible from the surface. The HyTES CMF algorithm produces plume intensity images of methane and other gases from strong emission sources. The combination of high spatial resolution and multi-species imaging capability provides source attribution in complex environments. The CMF-based detection of strong emission sources over large areas is a fast and powerful tool needed to focus on more computationally intensive retrieval algorithms to quantify emissions with error estimates, and is useful for expediting mitigation efforts and addressing critical science questions.

Simplified flare combustion model for flare plume rise calculations

AbstractThe dispersion of plumes released from stacks depends on wind speed, plume emission rate, stack height, and other meteorological and stack variables. Plume rise is an important aspect of plume dispersion because it increases the apparent release height, which leads to lower ground‐level concentrations. Plume rise linked with flare combustion has received only minimal attention in the literature to date, despite its importance. This study develops a numerical model of plume rise with flare combustion based on material, heat, mass, and momentum balances. The basis of the model is a numerical plume rise model used in CALPUFF to model plume rise of large buoyant area sources, and is also used in PRIME (plume rise model enhancements), which models building downwash. The proposed model considers the reaction kinetics. The competition between CH4 and CO combustion causes a modification of the temperature profile of up to 3 % in comparison with an instantaneous reaction model. Moreover, emissivity, which plays an important role in the heat conservation equations but which was only parameterized in an earlier work, is calculated more directly to increase the accuracy of the model. It was found that soot is the main contributor to flame emissivity. Finally, the air dispersion model CALPUFF was run according to the proposed flare model and an empirical flare model by Beychok to compare results of the models. This new flare method is sufficiently simple to be embedded into air dispersion modelling software such as CALPUFF.

A deepChandraobservation of the interacting star-forming galaxy Arp 299

We present results from a 90 ks Chandra ACIS-S observation of the X-ray luminous interacting galaxy system Arp 299 (NGC 3690/IC 694). We detect 25 discrete X-ray sources with luminosities above 4.0x10^38 erg s^-1 covering the entire Ultra Luminous X-ray source (ULX) regime. Based on the hard X-ray spectra of the non-nuclear discrete sources identified in Arp 299, and their association with young, actively star-forming region of Arp 299 we identify them as HMXBs. We find in total 20 off-nuclear sources with luminosities above the ULX limit, 14 of which are point-like sources. Furthermore we observe a marginally significant deficit in the number of ULXs, with respect to the number expected from scaling relations of X-ray binaries with the star formation rate (SFR). Although the high metalicity of the galaxy could result in lower ULX numbers, the good agreement between the observed total X-ray luminosity of ULXs, and that expected from the relevant scaling relation indicates that this deficit could be the result of confusion effects. The integrated spectrum of the galaxy shows the presence of a hot gaseous component with kT = 0.72+-0.03 keV, contributing 20% of the soft (0.1-2.0 keV) unabsorbed luminosity of the galaxy. A plume of soft X-ray emission in the west of the galaxy indicates a large scale outflow. We find that the AGN in NGC 3690 contributes only 22% of the observed broad-band X-ray luminosity of Arp 299.

Dynamics of colliding laser ablation plumes in background gas

We observed plume expansion dynamics during pulsed laser ablation in background gas when two plumes collided head-on. The Si target is irradiated followed by the Ge target with delay time t d. When t d is larger than a few μs, the Si plume emission quenches before the irradiation of the Ge target. Re-emission of quenched Si atomic species by the collision with counter Ge plume is observed. The intensity and lifetime of Si re-emission decrease with increasing t d, and rapid decrease at around t d = 60 μs is observed. These results indicate that non-luminescent Si atomic species exist between targets up to about t d = 60 μs and effects of the collision rapidly decrease at above about t d = 60 μs. Effects of the collision of Si and Ge plumes and the re-emission of quenched Si atomic species are discussed.

Investigation and in situ removal of spatter generated during laser ablation of aluminium composites

Spatter generated during laser irradiation of an aluminium alloy nanocomposite (AlMg5 reinforced with Al2O3 nanoparticles) was monitored by high speed imaging. Droplets trajectory and speed were assessed by computerized image analysis. The effects of laser peak power and laser focusing on the plume expansion and expulsed droplet speeds were studied in air or under argon flow. It was found that the velocity of visible droplets expulsed laterally or at the end of the plume emission from the metal surface was not dependent on the plasma plume speed. The neighbouring area of irradiation sites was studied by optical and scanning electron microscopy. Droplets deposited on the surface were classified according to their size and counted using a digital image processing software. It was observed that the number of droplets on surface was 1.5–3 times higher when the laser beam was focused in depth as compared to focused beams, even though the populations average diameter were comparable. Three methods were selected for removing droplets in situ, during plume expansion: an argon gas jet crossing the plasma plume, a fused silica plate collector transparent to the laser wavelength placed parallel to the irradiated surface and a mask placed onto the aluminium composite surface. The argon gas jet was efficient only for low power irradiation conditions, the fused silica plate failed in all tested conditions and the mask was successful for all irradiation regimes.

The effects of vegetation barriers on near-road ultrafine particle number and carbon monoxide concentrations

Numerous studies have shown that people living in near-roadway communities (within 100m of the road) are exposed to high ultrafine particle (UFP) number concentrations, which may be associated with adverse health effects. Vegetation barriers have been shown to affect pollutant transport via particle deposition to leaves and altering the dispersion of emission plumes, which in turn would modify the exposure of near-roadway communities to traffic-related UFPs. In this study, both stationary (equipped with a Scanning Mobility Particle Sizer, SMPS) and mobile (equipped with Fast Mobility Particle Sizer, FMPS) measurements were conducted to investigate the effects of vegetation barriers on downwind UFP (particle diameters ranging from 14 to 102nm) concentrations at two sites in North Carolina, USA. One site had mainly deciduous vegetation while the other was primarily coniferous; both sites have a nearby open field without the vegetation barriers along the same stretch of limited access road, which served as a reference. During downwind conditions (traffic emissions transported towards the vegetation barrier) and when the wind speed was above or equal to 0.5m/s, field measurements indicated that vegetation barriers with full foliage reduced UFP and CO concentrations by 37.7–63.6% and 23.6–56.1%, respectively. When the test was repeated at the same sites during winter periods when deciduous foliage was reduced, the deciduous barrier during winter showed no significant change in UFP concentration before and after the barrier. Results from the stationary (using SMPS) and mobile (using FMPS) measurements for UFP total number concentrations generally agreed to within 20%.

CONVERGING SUPERGRANULAR FLOWS AND THE FORMATION OF CORONAL PLUMES

ABSTRACT Earlier studies have suggested that coronal plumes are energized by magnetic reconnection between unipolar flux concentrations and nearby bipoles, even though magnetograms sometimes show very little minority-polarity flux near the footpoints of plumes. Here we use high-resolution extreme-ultraviolet (EUV) images and magnetograms from the Solar Dynamics Observatory (SDO) to clarify the relationship between plume emission and the underlying photospheric field. We find that plumes form where unipolar network elements inside coronal holes converge to form dense clumps, and fade as the clumps disperse again. The converging flows also carry internetwork fields of both polarities. Although the minority-polarity flux is sometimes barely visible in the magnetograms, the corresponding EUV images almost invariably show loop-like features in the core of the plumes, with the fine structure changing on timescales of minutes or less. We conclude that the SDO observations are consistent with a model in which plume emission originates from interchange reconnection in converging flows, with the plume lifetime being determined by the ∼1 day evolutionary timescale of the supergranular network. Furthermore, the presence of large EUV bright points and/or ephemeral regions is not a necessary precondition for the formation of plumes, which can be energized even by the weak, mixed-polarity internetwork fields swept up by converging flows.

Estimation of Volcanic Ash Emissions Using Trajectory-Based 4D-Var Data Assimilation

Abstract Volcanic ash forecasting is a crucial tool in hazard assessment and operational volcano monitoring. Emission parameters such as plume height, total emission mass, and vertical distribution of the emission plume rate are essential and important in the implementation of volcanic ash models. Therefore, estimation of emission parameters using available observations through data assimilation could help to increase the accuracy of forecasts and provide reliable advisory information. This paper focuses on the use of satellite total-ash-column data in 4D-Var based assimilations. Experiments show that it is very difficult to estimate the vertical distribution of effective volcanic ash injection rates from satellite-observed ash columns using a standard 4D-Var assimilation approach. This paper addresses the ill-posed nature of the assimilation problem from the perspective of a spurious relationship. To reduce the influence of a spurious relationship created by a radiate observation operator, an adjoint-free trajectory-based 4D-Var assimilation method is proposed, which is more accurate to estimate the vertical profile of volcanic ash from volcanic eruptions. The method seeks the optimal vertical distribution of emission rates of a reformulated cost function that computes the total difference between simulated and observed ash columns. A 3D simplified aerosol transport model and synthetic satellite observations are used to compare the results of both the standard method and the new method.

Black Carbon Emissions from Associated Natural Gas Flaring.

Approximately 150 billion cubic meters (BCM) of natural gas is flared and vented in the world annually, emitting greenhouse gases and other pollutants with no energy benefit. About 7 BCM per year is flared in the United States, and half is from North Dakota alone. There are few emission measurements from associated gas flares and limited black carbon (BC) emission factors have been previously reported from the field. Emission plumes from 26 individual flares in the Bakken formation in North Dakota were sampled. Methane, carbon dioxide, and BC were measured simultaneously, allowing the calculation of BC mass emission factors using the carbon balance method. Particle optical absorption was measured using a three-wavelength particle soot absorption photometer (PSAP) and BC particle number and mass concentrations were measured with a single particle soot photometer. The BC emission factors varied over 2 orders of magnitude, with an average and uncertainty range of 0.14 ± 0.12 g/kg hydrocarbons in associated gas and a median of 0.07 g/kg which represents a lower bound on these measurements. An estimation of the BC emission factor derived from PSAP absorption provides an upper bound at 3.1 g/kg. These results are lower than previous estimations and laboratory measurements. The BC mass absorption cross section was 16 ± 12 m(2)/g BC at 530 nm. The average absorption Ångström exponent was 1.2 ± 0.8, suggesting that most of the light absorbing aerosol measured was black carbon and the contribution of light absorbing organic carbon was small.

Atmospheric monitoring and detection of fugitive emissions for Enhanced Oil Recovery

In Weyburn, Saskatchewan, carbon dioxide (CO2) is injected into the Weyburn oilfield for Enhanced Oil Recovery (EOR). Cenovus Energy Inc. operates more than 1000 active wells, processing plants, and hundreds of kilometres of pipeline infrastructure over a >100km2 area. While vehicle-based atmospheric detection of gas leakage would be convenient for a distributed operation such as Weyburn, implementing atmospheric detection schemes, particularly those that target CO2, are challenging in that natural ecosystems and other human activities both emit CO2 and will contribute to regular false positives. Here we present field test results of a multi-gas atmospheric detection technique that uses observed trace gas ratios (CO2, CH4, and H2S) to discriminate plumes of gas originating from different sources. This work is part of a larger project focused on multi-scale fugitive emissions detection and plume discrimination. During 2013 and 2014, we undertook vehicle-based mobile surveys of CO2, CH4, H2S, and δ13CH4, in the Weyburn oilfield, using customized Cavity Ring Down Spectroscopy (CRDS) instruments that also alternated as stationary receptors. Mobile surveys provided georeferenced observations of atmospheric gas concentrations every 20–30m, along a route driven at roughly 70kmh−1. Data were uploaded to remote servers and processed using visualization tools that allowed us to constrain the location and timing of potential emission events. Results from one day of mobile surveying, September 24, 2013, are presented here to illustrate how industrial activities, combustion engine and flare stack source emissions can be discriminated on the basis of excess mixing gas ratios, at distances from a few hundreds metres, to kilometres, in the Weyburn oilfield.

A wide field-of-view imaging DOAS instrument for two-dimensional trace gas mapping from aircraft

Abstract. The Airborne imaging differential optical absorption spectroscopy (DOAS) instrument for Measurements of Atmospheric Pollution (AirMAP) has been developed for the purpose of trace gas measurements and pollution mapping. The instrument has been characterized and successfully operated from aircraft. Nitrogen dioxide (NO2) columns were retrieved from the AirMAP observations. A major benefit of the push-broom imaging instrument is the spatially continuous, gap-free measurement sequence independent of flight altitude, a valuable characteristic for mapping purposes. This is made possible by the use of a charge coupled device (CCD) frame-transfer detector. A broad field of view across track of around 48° is achieved with wide-angle entrance optics. This leads to a swath width of about the same size as the flight altitude. The use of fibre coupled light intake optics with sorted light fibres allows flexible instrument positioning within the aircraft and retains the very good imaging capabilities. The measurements yield ground spatial resolutions below 100 m depending on flight altitude. The number of viewing directions is chosen from a maximum of 35 individual viewing directions (lines of sight, LOS) represented by 35 individual fibres. The selection is adapted to each situation by averaging according to signal-to-noise or spatial resolution requirements. Observations at 30 m spatial resolution are obtained when flying at 1000 m altitude and making use of all 35 viewing directions. This makes the instrument a suitable tool for mapping trace gas point sources and small-scale variability. The position and aircraft attitude are taken into account for accurate spatial mapping using the Attitude and Heading Reference System of the aircraft. A first demonstration mission using AirMAP was undertaken in June 2011. AirMAP was operated on the AWI Polar-5 aircraft in the framework of the AIRMETH-2011 campaign. During a flight above a medium-sized coal-fired power plant in north-west Germany, AirMAP clearly detected the emission plume downwind from the exhaust stack, with NO2 vertical columns around 2 × 1016 molecules cm−2 in the plume centre. NOx emissions estimated from the AirMAP observations are consistent with reports in the European Pollutant Release and Transfer Register. Strong spatial gradients and variability in NO2 amounts across and along flight direction are observed, and small-scale enhancements of NO2 above a motorway are detected.

Combustion kinetics of laser irradiated porous graphite from imaging Fourier transform spectroscopy

The combustion plumes arising from laser-irradiated graphite targets were investigated experimentally using hyperspectral, imaging Fourier transform spectroscopy (IFTS). Porous graphite targets were irradiated with a 1.07 µm, 20-kW ytterbium fiber laser at irradiances of 0.25–4 kW/cm2. Emissive plumes from the oxidation of graphite in air were monitored using a mid-wave infrared imaging Fourier-transform spectrometer with spatial resolution of 0.52 mm per pixel. Strong spectral emission of CO and CO2 were observed in the infrared between 1900 and 2400 cm−1 with an instrument spectral resolution of 2 cm−1. A homogeneous single-layer plume, line-by-line radiative transfer model (LBLRTM) and two band models (EM2C and RADCAL) were applied to estimate spatial maps of temperature and column densities of CO and CO2 with a temporal resolution of 0.47 s per hyperspectral image. Steady surface temperatures of 1800–2900 K are achieved after ∼1 min for irradiances of 0.25–1.0 kW/cm2. A stable, gas phase combustion layer extends from 4 to 12 mm from the surface, with buoyancy driving a gas flow of ∼8 m/s. Plume extent and intensity is greater for the larger porosity (6 mm particle size) samples. Steady-state gas temperatures exceed surface temperature by up to 400 K. Column densities for CO and CO2 of up to 1018 molec/cm2 were observed. The CO/CO2 concentration ratio peaks at 2500 K. The initial rise with temperature is consistent with effective activation energies of 149–111 kJ/mol at distances between 0.72 mm and 3 mm, respectively.

Effects of polymer additives in the bulk of turbulent thermal convection

We present experimental evidence that a minute amount of polymer additives can significantly enhance heat transport in the bulk region of turbulent thermal convection. The effects of polymer additives are found to be the enhancement of coherent heat fluxes and suppression of incoherent heat fluxes. The enhanced heat transport is associated with the increased coherency of thermal plumes, as a result of the suppression of small-scale turbulent fluctuations by polymers. The incoherent heat flux, arising from turbulent background fluctuations, makes no net contribution to heat transport. The fact that polymer additives can increase the coherency of thermal plumes is supported by the measurements of a number of local quantities, such as the extracted plume amplitude and width, the velocity autocorrelation functions and the velocity–temperature cross-correlation coefficient. The results from local measurements also suggest the existence of a threshold value for the polymer concentration, only above which significant modification of the plume coherent properties and enhancement of the local heat flux can be observed. Estimation of the plume emission rate suggests a stabilization of the thermal boundary layer by polymer additives.

Prodigious emission rates and magma degassing budget of major, trace and radioactive volatile species from Ambrym basaltic volcano, Vanuatu island Arc

Ambrym volcano, in the Vanuatu arc, is one of the most active volcanoes of the Southwest Pacific region, where persistent lava lake and/or Strombolian activity sustains voluminous gas plume emissions. Here we report on the first comprehensive budget for the discharge of major, minor, trace and radioactive volatile species from Ambrym volcano, as well as the first data for volatiles dissolved in its basaltic magma (olivine-hosted melt inclusions). In situ MultiGAS analysis of H2O, CO2, SO2 and H2S in crater rim emissions, coupled with filter-pack determination of SO2, halogens, stable and radioactive metals demonstrates a common magmatic source for volcanic gases emitted by its two main active craters, Benbow and Marum. These share a high water content (~93mol%), similar S/Cl, Cl/F, Br/Cl molar ratios, similar (210Po/210Pb) and (210Bi/210Pb) activity ratios, as well as comparable proportions in most trace metals. Their difference in CO2/SO2 ratio (1.0 and 5.6–3.0, respectively) is attributed to deeper gas-melt separation at Marum (Strombolian explosions) than Benbow (lava lake degassing) during our measurements in 2007. Airborne UV sensing of the SO2 plume flux (90kgs−1 or 7800 tons d−1) demonstrates a prevalent degassing contribution (~65%) of Benbow crater in that period and allows us to quantify the total volatile fluxes during medium-level eruptive activity of the volcano. Results reveal that Ambrym ranks among the most powerful volcanic gas emitters on Earth, producing between 5% and 9% of current estimates for global subaerial volcanic emissions of H2O, CO2, HCl, Cu, Cr, Cd, Au, Cs and Tl, between 10% and 17% of SO2, HF, HBr, Hg, 210Po and 210Pb, and over 30% of Ag, Se and Sn. Global flux estimates thus need to integrate its contribution and be revised accordingly. Prodigious gas emission from Ambrym does not result from an anomalous volatile enrichment nor a differential excess degassing of its feeding basalt: this latter contains relatively modest dissolved amounts of H2O (≤1.3wt%), CO2 (~0.10wt%), S (0.075wt%) and Cl (0.05wt%), and its degassing under prevalent closed-system conditions well reproduces the composition of emitted volcanic gases. Instead, we show that the gas discharge is sustained by a very high basalt supply rate of 25m3s−1, from a large (~ 0.5km3) magma reservoir probably emplaced at ~3.8km depth below the summit caldera according to both the H2O-CO2 content of bubble-free melt inclusions and preliminary seismic data. Radioactive disequilibria in the volcanic gases constrain that this reservoir may be entirely renewed in about 240days. The comparatively low magma extrusion rate requires extensive convective overturn of the basaltic magma column and recycling of the unerupted (denser) degassed magma in the plumbing system, in agreement with textural features of erupted products. Finally, our results suggest that the Indian MORB-type mantle source of Ambrym basalts is modestly enriched in slab-derived water and other volatiles, in agreement with the prevalent volcanoclastic nature of subducted sediments and their lower subduction rate under the central Vanuatu arc due to its collision with the D'Entrecasteaux Ridge.

Physical and scale-by-scale analysis of Rayleigh–Bénard convection

A novel approach for the study of turbulent Rayleigh–Bénard convection (RBC) in the compound physical/scale space domain is presented. All data come from direct numerical simulations of turbulent RBC in a laterally unbounded domain confined between two horizontal walls, for Prandtl number $0.7$ and Rayleigh numbers $1.7\times 10^{5}$, $1.0\times 10^{6}$ and $1.0\times 10^{7}$. A preliminary analysis of the flow topology focuses on the events of impingement and emission of thermal plumes, which are identified here in terms of the horizontal divergence of the instantaneous velocity field. The flow dynamics is then described in more detail in terms of turbulent kinetic energy and temperature variance budgets. Three distinct regions where turbulent fluctuations are produced, transferred and finally dissipated are identified: a bulk region, a transitional layer and a boundary layer. A description of turbulent RBC dynamics in both physical and scale space is finally presented, completing the classic single-point balances. Detailed scale-by-scale budgets for the second-order velocity and temperature structure functions are shown for different geometrical locations. An unexpected behaviour is observed in both the viscous and thermal transitional layers consisting of a diffusive reverse transfer from small to large scales of velocity and temperature fluctuations. Through the analysis of the instantaneous field in terms of the horizontal divergence, it is found that the enlargement of thermal plumes following the impingement represents the triggering mechanism which entails the reverse transfer. The coupling of this reverse transfer with the spatial transport towards the wall is an interesting mechanism found at the basis of some peculiar aspects of the flow. As an example, it is found that, during the impingement, the presence of the wall is felt by the plumes through the pressure field mainly at large scales. These and other peculiar aspects shed light on the role of thermal plumes in the self-sustained cycle of turbulence in RBC, and may have strong repercussions on both theoretical and modelling approaches to convective turbulence.

Logarithmic Mean Temperature Profiles and Their Connection to Plume Emissions in Turbulent Rayleigh-Bénard Convection

Two-dimensional simulations of Rayleigh-Bénard convection at Ra=5×10^{10} show that vertical logarithmic mean temperature profiles can be observed in regions of the boundary layer where thermal plumes are emitted. The profile is logarithmic only in these regions and not in the rest of the boundary layer where it is sheared by the large-scale wind and impacted by plumes. In addition, the logarithmic behavior is not visible in the horizontal average. The findings reveal that the temperature profiles are strongly connected to thermal plume emission, and they support a perception that parts of the boundary layer can be turbulent while others are not. The transition to the ultimate regime, in which the boundary layers are considered to be fully turbulent, can therefore be understood as a gradual increase in the fraction of the plume-emitting ("turbulent") regions of the boundary layer.

Temporal and spatial profiles of emission intensities in atmospheric pressure helium plasma jet driven by microsecond pulse: Experiment and simulation

A needle-circular electrode structure helium plasma jet driven by microsecond pulsed power is studied. Spatially resolved emission results show that the emission intensity of He(33S1) line decreases monotonically along the axial direction, while those of N2(C3Πu), N2+(B2∑+u), and O(3p5P) reach their maxima at 3 cm, 2.6 cm, and 1.4 cm, respectively. The plasma plume of the four species shows different characteristics: The N2 emission plume travels at a fast speed along the entire plasma jet; the N2+ emission plume is composed of a bright head and relatively weak tail and travels a shorter distance than the N2 emission plume; the He emission plume travels at a slower speed for only a very short distance; propagation of the O emission plume is not observed. Results of calculation of radiation fluxes emitted by positive streamers propagating along helium plasma jets are presented. It is shown, in agreement with the results of the present experiment and with other available experimental data, that the intensities of radiation of N2(C3Πu) molecules and He(33S1) atoms vary with time (along the plasma jet) quite differently. The factors resulting in this difference are discussed.

Ammonia and methane dairy emission plumes in the San Joaquin Valley of California from individual feedlot to regional scales

AbstractAgricultural ammonia (NH3) emissions are highly uncertain, with high spatiotemporal variability and a lack of widespread in situ measurements. Regional NH3 emission estimates using mass balance or emission ratio approaches are uncertain due to variable NH3 sources and sinks as well as unknown plume correlations with other dairy source tracers. We characterize the spatial distributions of NH3 and methane (CH4) dairy plumes using in situ surface and airborne measurements in the Tulare dairy feedlot region of the San Joaquin Valley, California, during the NASA Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality 2013 field campaign. Surface NH3 and CH4 mixing ratios exhibit large variability with maxima localized downwind of individual dairy feedlots. The geometric mean NH3:CH4 enhancement ratio derived from surface measurements is 0.15 ± 0.03 ppmv ppmv−1. Individual dairy feedlots with spatially distinct NH3 and CH4 source pathways led to statistically significant correlations between NH3 and CH4 in 68% of the 69 downwind plumes sampled. At longer sampling distances, the NH3:CH4 enhancement ratio decreases 20–30%, suggesting the potential for NH3 deposition as a loss term for plumes within a few kilometers downwind of feedlots. Aircraft boundary layer transect measurements directly above surface mobile measurements in the dairy region show comparable gradients and geometric mean enhancement ratios within measurement uncertainties, even when including NH3 partitioning to submicron particles. Individual NH3 and CH4 plumes sampled at close proximity where losses are minimal are not necessarily correlated due to lack of mixing and distinct source pathways. Our analyses have important implications for constraining NH3 sink and plume variability influences on regional NH3 emission estimates and for improving NH3 emission inventory spatial allocations.