Dense Plume Research Articles

Empirical Insights Into the Fate of Ammonia in Western U.S. Wildfire Smoke Plumes

AbstractWildfires are a major source of gas‐phase ammonia (NH3) to the atmosphere. Quantifying the evolution and fate of this NH3 is important to understanding the formation of secondary aerosol in smoke and its accompanying effects on radiative balance and nitrogen deposition. Here, we use data from the Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE‐CAN) to add new empirical constraints on the e‐folding loss timescale of NH3 and its relationship with particulate ammonium (pNH4) within wildfire smoke plumes in the western U.S. during summer 2018. We show that the e‐folding loss timescale of NH3 with respect to particle‐phase partitioning ranges from ∼24 to ∼4000 min (median of 55 min). Within these same plumes, oxidation of nitrogen oxides is observed concurrent with increases in the fraction of pNH4 in each plume sampled, suggesting that formation of ammonium nitrate (NH4NO3) is likely. We find wide variability in how close our in situ measurements of NH4NO3 are to those expected in a dry thermodynamic equilibrium, and find that NH4NO3 is most likely to form in fresh, dense smoke plumes injected at higher altitudes and colder temperatures. In chemically older smoke we observe correlations between both the fraction of pNH4 and the fraction of particulate nitrate (pNO3) in the aerosol with temperature, providing additional evidence of the presence of NH4NO3 and the influence of injection height on gas‐particle partitioning of NH3.

Characterization of forest fire and Saharan desert dust aerosols over south-western Europe using a multi-wavelength Raman lidar and Sun-photometer

In the morning of 21 July 2019, a dense forest fire smoke plume was detected over Évora (Portugal) in the lower troposphere. Around 13:00 UTC, a Sahara dust layer was detected by lidar between 3000 and 4000 m height above sea level. In this work results of these events using an EARLINET Raman lidar and AERONET Sun-photometer measurements are reported and discussed: the dense smoke layer, the mixing of smoke with dust and the lofted dust layer that crossed Évora. During the morning, in-situ hourly mean black carbon concentration reached a maximum of 6.28 ± 0.73 μgm−3. The AERONET fine mode aerosol optical depth at 500 nm reached 0.77 and the Ångström exponent at 440–870 nm varied between 1.45 and 1.82, indicating the presence of fine smoke particles in the atmospheric column. In the beginning of the afternoon, the lidar profiles indicated the presence of a smoke layer followed by two thin layers of pollution mixed with dust and a lofted dust layer. The smoke particles caused low particle linear depolarization ratios at 532 nm with mean value of 0.059 ± 0.002 in the smoke layer. In contrast, the lofted dust layer caused mean particle linear depolarization ratio at 532 nm of 0.26 ± 0.01. Mass concentrations were in the order of 22–29 μg m−3 in the smoke layer and 60–178 μg m−3 in the lofted dust layer. During the afternoon and at night, mixing dust layers were identified by using lidar data. In the afternoon, two aerosol layers exhibited mean particle linear depolarization ratios at 532 nm of 0.23 ± 0.01 and 0.25 ± 0.01 with the dust dominating the extinction and mass concentration in both aerosol layers. Mass concentrations of dust were in the order of 101–266 μg m−3 and 159–195 μg m−3. At night, the particle linear depolarization ratio presented low variability across the identified layer with mean value of 0.20 ± 0.01. The Ångström exponents were low, the mean lidar ratios were 50 ± 6 sr (355 nm) and 42 ± 4 sr (532 nm) and the aerosol optical depth was 0.32 (355 nm) and 0.30 (532 nm). Mass concentrations ranged in 10–28 μg m−3 for non-dust and in 77–186 μg m−3 for dust.

Sodium tracer measurements of an expanded dense aluminum plasma from e-beam isochoric heating

Spatially and temporally resolved visible absorption spectroscopy is performed on sodium D-lines present as surface contaminants on an expanded dense aluminum plasma plume. An 80-ns FWHM, intense, relativistic electron beam deposits 5.4 J into a 100-μm-thick Al foil, which isochorically heats and subsequently hydrodynamically expands the material through the warm dense matter state and into a classical-like plasma state, with a coupling parameter of approximately 0.2 and a degeneracy parameter of approximately 270. The Na contamination, carried along with the expanding plume, shows saturated absorption features in the dense Al continuum for λ> 450 nm. X-ray photoelectron spectroscopy and laser-induced breakdown spectroscopy confirm Na is a surface contaminant with an atomic concentration of ∼0.1% when interrogating identical foil samples. A spectroscopic-quality radiation transport model is used to post-process 2D hydrodynamic simulations to interpret the plasma conditions based on the measured Na 3p-3s doublet line profiles. A sodium number density of 3×1015 cm−3 best matches the experimental spectra, which originate from a dense surface plasma with ne=3.0±0.8×1018 cm−3.

The role of tides in bottom water export from the western Ross Sea

Approximately 25% of Antarctic Bottom Water has its origin as dense water exiting the western Ross Sea, but little is known about what controls the release of dense water plumes from the Drygalski Trough. We deployed two moorings on the slope to investigate the water properties of the bottom water exiting the region at Cape Adare. Salinity of the bottom water has increased in 2018 from the previous measurements in 2008–2010, consistent with the observed salinity increase in the Ross Sea. We find High Salinity Shelf Water from the Drygalski Trough contributes to two pulses of dense water at Cape Adare. The timing and magnitude of the pulses is largely explained by an inverse relationship with the tidal velocity in the Ross Sea. We suggest that the diurnal and low frequency tides in the western Ross Sea may control the magnitude and timing of the dense water outflow.

Superheated metastable water atomization: fine atomized water plumes diagnostics and disperse characteristics; summary of results, applications in power generation and new techniques.

Complex experimental investigation of superheated flow and dispersion characteristics of sprays in atomizing nozzles of various types is made. The comparative analysis of experimental and calculating investigations of thermo physic and hydro- gas-dynamic flow and disperse characteristics was carried out for various types of spray nozzles. It has shown that the main process, which determine peculiarities of superheated metastable water flow and phase transformation in spray nozzles, is quick (explosive) boiling up. And the optimal variant for superheated water atomization and achieving the most fine spray plumes, which contain mainly submicron droplet fraction, at initial temperature 240°C (and higher) is atomization by means of contracting-expanding nozzles. In such nozzles the explosive boiling is accomplished by quick transformation of foamed liquid into vapor-droplet flow. Diagnostic peculiarities are considered for these optically dense spray plumes; the auxiliary measurement methods were worked out for estimation superheated water high atomization level. The experimental and calculating data dimensionless treatment was made for achieving extremely fine (mainly submicron) superheated water spray. The dimensionless parameter, which determines necessary water (or some other liquids, for example – fuels) superheating level was derived. The possible technical applications of superheated water sprays are described, and up-to-date state of corresponding projects is given.

Superheated metastable atomized water plume diagnostics peculiarities in confusor-diffuser nozzles; atomizaton process: dimensionless treatment

Micron mode mass fraction ε determination method was tested for dense superheated water atomization plumes based on measurement attenuation coefficients of primary laser radiation. The initial water temperature in experiments was 200 and 240°C. The mass fraction of micron mode ε was determined using Bugger-Lambert equation and Mi theory. The comparison with previous data, which were obtained by scattering indicatrix analysis, was done. In terms of development of dimensionless treatment of experimental data on superheated water spray, the parameter expression for the transition to predominating role of nucleation in superheated water atomization in confusor-diffuser nozzles was revised the base of critical bubble formation.

Tropical Atlantic dust and the zonal circulation

This study examines the factors driving the variability of Saharan dust over the subtropical Atlantic during summer. Monthly tropospheric dust concentrations from satellite-based model assimilation averaged in the area 10–23 N, 30–65 W, are used to create an index over the period 1980–2017. The seasonal cycle peaks in summer and affects tropical cyclones from July to September. Point-to-field regression analysis is performed, and then composites of dusty and clean seasons are analyzed as maps and sections of meteorological fields. The regression reveals significant differences in oceanic trade winds, (detrended) sea surface temperature, and atmospheric convection. Dusty minus clean composites show a zonal overturning circulation with sinking/rising motions over Africa/western Caribbean and lower easterlies/upper westerlies over the subtropical Atlantic. This circulation spreads Saharan dust and warm dry air in the 1–4 km layer westward at ~ 10 m/s over cooler waters, inhibiting convection. Among the factors driving tropospheric dust variability is the Pacific El Nino Southern Oscillation. Composites of dusty and clean hurricane occurrence show a threefold difference in numbers and a tenfold difference in mean power dissipation index. Analysis of a dust event in August 2009 illustrates how wind shear and cool SST conspire to suppress tropical easterly waves. Supplementary work characterizes the dispersion of a dense Saharan dust plume in June 2020.

APIFLAME v2.0 biomass burning emissions model: impact of refined input parameters on atmospheric concentration in Portugal in summer 2016

Abstract. Biomass burning emissions are a major source of trace gases and aerosols. Wildfires being highly variable in time and space, calculating emissions requires a numerical tool able to estimate fluxes at the kilometer scale and with an hourly time step. Here, the APIFLAME model version 2.0 is presented. It is structured to be modular in terms of input databases and processing methods. The main evolution compared to version 1.0 is the possibility of merging burned area and fire radiative power (FRP) satellite observations to modulate the temporal variations of fire emissions and to integrate small fires that may not be detected in the burned area product. Accounting for possible missed detection due to small fire results in an increase in burned area ranging from ∼5 % in Africa and Australia to ∼30 % in North America on average over the 2013–2017 time period based on the Moderate-Resolution Imaging Spectroradiometer (MODIS) Collection 6 fire products. An illustration for the case of southwestern Europe during the summer of 2016, marked by large wildfires in Portugal, is presented. Emissions calculated using different possible configurations of APIFLAME show a dispersion of 80 % on average over the domain during the largest wildfires (8–14 August 2016), which can be considered as an estimate of uncertainty of emissions. The main sources of uncertainty studied, by order of importance, are the emission factors, the calculation of the burned area, and the vegetation attribution. The aerosol (PM10) and carbon monoxide (CO) concentrations simulated with the CHIMERE regional chemistry transport model (CTM) are consistent with observations (good timing for the beginning and end of the events, ±1 d for the timing of the peak values) but tend to be overestimated compared to observations at surface stations. On the contrary, vertically integrated concentrations tend to be underestimated compared to satellite observations of total column CO by the Infrared Atmospheric Sounding Interferometer (IASI) instrument and aerosol optical depth (AOD) by MODIS. This underestimate is lower close to the fire region (5 %–40 % for AOD depending on the configuration and 8 %–18 % for total CO) but rapidly increases downwind. For all comparisons, better agreement is achieved when emissions are injected higher into the free troposphere using a vertical profile as estimated from observations of aerosol plume height by the Multi-angle Imaging SpectroRadiometer (MISR) satellite instrument (injection up to 4 km). Comparisons of aerosol layer heights to observations by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) show that some parts of the plume may still be transported at too low an altitude. The comparisons of the different CTM simulations to observations point to uncertainties not only on emissions (total mass and daily variability) but also on the simulation of their transport with the CTM and mixing with other sources. Considering the uncertainty of the emission injection profile and of the modeling of the transport of these dense plumes, it is difficult to fully validate emissions through comparisons between model simulations and atmospheric observations.

Hydrogen infrastructure—Efficient risk assessment and design optimization approach to ensure safe and practical solutions

With the ambition to cut emissions from transport hydrogen fuelled vehicles and marine vessels are now being introduced several places in the society. To support this development there is a need for infrastructure to produce and transport gaseous and liquid hydrogen. The properties and safety challenges related to the use of hydrogen are very different from those of conventional fuels, thus safe design may require unconventional solutions. Hydrogen has extreme properties in many ways. It is buoyant when in gas phase while a liquid hydrogen spray will develop a dense plume. The reactivity is higher, flammable range wider and the ignition energy lower than for conventional fuels. Flames may be invisible, and radiation is low. When performing risk assessments for land planning purposes, bunkering assessments or passenger and crew safety these aspects must be reflected. Properties like the positive buoyancy, strong dilution for sonic releases into air, and a low reactivity and energy content for concentrations below 10% must be exploited during design to ensure acceptable risk levels. In this article a two-level risk assessment and design optimization approach is presented in which risk screening with rapid consequence calculations and frequency assessments for release, dispersion, fire and explosion can be performed during concept selection phase with indicative hazard distances estimated. Possible risks of concern are in this way identified, and design can be adjusted, or mitigation measures introduced. For final design risk assessment CFD calculations can be performed for more precise consequence estimates. The risk assessment approach is described with illustrating examples. The focus is not only to ensure safety, but to do so in a cost-efficient and practical way.

Unconfined Dense Plunging Jets Used for Brine Disposal from Desalination Plants

Laboratory experiments were conducted to measure entrained air bubble penetration depth and dilution of a dense vertical unconfined plunging jet to evaluate its performance as an outfall to dilute brine from desalination plants as well as a means to aerate water column. Experiments involved neutrally buoyant or dense plunging jets discharging in quiescent receiving water. The density difference between effluent and receiving water, the plunging jet length (height above water surface), and the receiving water salinity were varied in the experiments. Observed penetration depth for neutrally buoyant jets was somewhat greater than previously reported, and increased modestly with jet density. Increasing density also resulted in an increasing number of fine bubbles descending together with the dense plume. These observations can help guide the design of plunging jets to mitigate anoxic conditions in the water column when brine is introduced to a receiving water body, as with seawater desalination.

Characterizing ventilation events in an anoxic coastal basin: Observed dynamics and the role of climatic drivers

AbstractRestricted horizontal exchange and vertical stratification restrict ventilation of bottom waters in many coastal systems, leading to stagnant basin water conditions. Dense inflows from oceanic sources can lead to dramatic changes in basin‐scale properties over very short timescales. Here, we used a semi‐enclosed coastal basin with deep‐anoxia (Lough Furnace) as a test bed, in order to discern estuary‐ocean exchange dynamics that lead to irregular and ephemeral deep‐water ventilations. Measured densities and current profiler‐based estimates of volume fluxes were used to compute typical renewal times of individual water masses in the stratified inner basin. Renewal timescales were primarily determined by freshwater flux and the spring‐neap tidal cycle. The deployment period culminated with observations of a ventilation of the basin water which had been stagnant for over 2.5 yr. Entrainment of ambient resident water doubled the volume of the dense plume and diluted its oxygen content. Following ventilation, the volumetric extent of anoxia expanded by 20% within several months, owing to uplifting of old basin water and oxygen consumption in the new basin water. Founded on these observations, a predictive model was constructed relying only on freshwater, atmospheric pressure, and wind data and successfully recreated ventilation events over the past decade. Hindcasting the model back multiple decades implied contrasting periods of higher and lower frequency variability in ventilation occurrence. This model offers a diagnostic tool for assessing how climatic change may influence the oxygen climate in systems that experience contrasting regimes of suboxia and ventilation.

Comparison of the predictive results from the two dispersion models PUMA and LPELLO with the JR II field data

Abstract Events triggered by unfortunate accidents or malicious antagonistic attacks bear witness to the great health risks involved in sudden releases of poisonous liquefied gases. For the society to be better prepared for these types of crises, experimental data from controlled releases is essential. To address this, a set of large scale releases of chlorine gas was conducted in the Jack Rabbit II field trials. The resulting dense gas plumes were monitored at distances up to 11 km by means of a comprising network of sensors. A group of international researchers involved in atmospheric dispersion modelling was formed to reproduce the field trials with different models as a benchmarking process to collectively improve upon the model suite and, in the end, be able to provide enhanced support to the society. The Swedish Defence Research Agency has previously developed two custom-made models for atmospheric dispersion on the local scale: PUMA and LPELLO. They use different modelling schemes but are able to handle the same types of dispersion processes. The validation process presented in this study was based on three selected field trials from Jack Rabbit II. Necessary meteorology and source data was, with some simplifications, congregated and distributed by the organizers to obtain a high degree of uniformity in the input data for the different models. Simulations were conducted by replicating these prerequisites whereby the resulting concentration plumes were analysed and compared with the measured data. There are many different metrics, properties and phenomena to scrutinize in a model validation process. After a thorough analysis, it was found that the two models showed similar plume behaviours in some aspects but also possessed quite diverse characteristics in others. In particular, the simulated concentration maxima were in general higher than the measurements indicate, which is analysed and discussed in detail. Findings and analyses presented here will have bearing on other dispersion models using similar schemes.

Observation of Wildfire Smoke Transport and PBL Variation During Summer 2018 Listos Campaign in New York City

Air pollution associated with wildfire smoke transport and heat wave in summer pose serious public health concerns in the populated New York City (NYC) area. In this study, we present a synergistic lidar, ceilometer and in-situ observation for wildfire smoke transport and planetary-boundary-layer (PBL) variation in the NYC urban and coastal area during the summer 2018 Long Island Sound Tropospheric Ozone (O3) Study (LISTOS). A dense smoke plume and mixing into PBL on August 15-17, 2018 was analyzed while the coincident enhancement of PM2.5, CO and O3 exceedance of NAAQS was demonstrated from both the observation and model. In addition, we show the temporal-spatial variation and difference of the PBL-height (PBLH) in the NYC urban and its coastal vicinity. We further evaluate the NAM-CMAQ model forecast of O3, PM2.5 and PBLH with the ground observations.

Buoyancy-driven plumes in a layered porous medium

Thin, roughly horizontal low-permeability layers are a common form of large-scale heterogeneity in geological porous formations. In this paper, the dynamics of a buoyancydriven plume in a two-dimensional layered porous medium is studied theoretically, with the aid of high-resolution numerical simulations. The medium is uniform apart from a thin, horizontal layer of a much lower permeability, located a dimensionless distance L 1 below the dense plume source. If the dimensionless thickness 2eL and permeability Π of the low-permeability layer are small, the effect of the layer is found to be well parameterized by its impedance Ω = 2eL/Π. Five different regimes of flow are identified and characterized. For Ω L 1/3 , the layer has no effect on the plume, but as Ω is increased the plume widens and spreads over the layer as a gravity current. For still larger Ω, the flow becomes destabilized by convective instabilities both below and above the layer, until, for Ω L, the spread of the plume is dominated by convective mixing and buoyancy is transported across the layer by diffusion alone. Analytical models for the spread of the plume over the layer in the various different regimes are presented.

Mesoscale Eddies Observed at the Denmark Strait Sill

AbstractThe Denmark Strait overflow is the major export route of dense water from the Arctic Mediterranean into the North Atlantic. At the Strait's shallow sill, the overflow is a bottom‐intensified cold and dense plume, bound to the east by a thermal front formed with the warmer, northward flowing North Icelandic Irminger Current. More than two decades of observations at the sill show strong fluctuations of volume flux on daily time scales. To better understand the source of this variability, a five‐mooring array was installed at the sill, capturing nearly 1 year of velocity and bottom temperature measurements at a high temporal and spatial resolution. Bottom temperature fluctuations that exceed 4 °C indicate a meandering of the front between the plume and the North Icelandic Irminger Current. Current vector rotation shows trains of alternating cyclones and anticyclones at the sill. An eddy crosses the sill every 3 to 6 days with a mean velocity of 0.4 m/s and a typical diameter of 30 to 40 km. The results suggest that anticyclones, with centers passing through the deepest part of the sill, may be responsible for periods of increased volume flux—also referred to as boluses and pulses in previous studies. Although the relationship between eddies, pulses, and boluses is still unclear, the results show that eddies are directly linked to fluctuations in the strength, thickness, and position of the overflow plume.

Hydrogen infrastructure - efficient risk assessment and design optimization approach

With the ambition to cut emissions from transport hydrogen fuelled vehicles and marine vessels are now being introduced several places in the society. To support this development there is a need for infrastructure to produce and transport gaseous and liquid hydrogen. The properties and safety challenges related to the use of hydrogen are very different from those of conventional fuels, thus safe design solutions may require unconventional solutions. Hydrogen has extreme properties in many ways. It is buoyant when in gas phase while a liquid hydrogen spray will develop a dense plume. The reactivity is higher, flammable range wider and the ignition energy lower than for conventional fuels. Flames may be invisible and radiation is low. When performing risk assessments for land planning purposes, bunkering assessments or passenger and crew safety these aspects must be reflected. Properties like the positive buoyancy, strong dilution for sonic releases into air, and a low reactivity and energy content for concentrations below 10% must be exploited during design to ensure acceptable risk levels. In this article a two level risk assessment and design assistance approach is presented in which risk screening with rapid consequence calculations and frequency assessments for release, dispersion, fire and explosion are performed during design review with indicative hazard distances estimated. Possible risks of concern are in this way identified, and design can be adjusted or mitigation measures introduced. When required more accurate CFD calculations are thereafter performed for more precise consequence estimates. The risk assessment approach will be described with examples illustrating the approach.

A 3-D Reconstruction Method of Dense Bubbly Plume Based on Laser Scanning

Bubbly flow widely exists in many industrial applications of energy, metallurgy, and chemistry, etc. Due to the clusters and overlap of dense bubbles at a high void fraction, it is nearly impossible to obtain the information of flow structures and characteristics in the spatial field with traditional measurement methods. In this paper, a novel laser scanning based 3-D reconstruction method for dense bubbly plume is developed. The measurement area is scanned by a laser sheet through a rotating hexagonal optical prism, and a high-speed camera captures the sequentially sliced images in the flow field, which is parallel to the scanning direction. Meanwhile, a scanning mathematic model is established, and its linearization is analyzed in detail. An image preprocessing method is developed to extract the features of the bubbly plume. To be specific, a method involves adaptive wavelet threshold denoising is developed to remove the noise. Moreover, methods regarding sliced image-matching and interpolation based on Log-polar transformation are presented to improve the spatial resolution effectively, and a set of image evaluation standards are designed to investigate the interpolation efficiency and accuracy. The experimental results conclude that the reported 3-D reconstruction method for dense bubbly flow based on laser scanning is valid with high precision, which explores a new way for the visualization of the 3-D structures and measurement of the volumetric flow field and the complex flow characteristics.

Dynamics of Outgassing and Plume Transport Revealed by Proximal Unmanned Aerial System (UAS) Measurements at Volcán Villarrica, Chile

AbstractVolcanic gas emissions are intimately linked to the dynamics of magma ascent and outgassing and, on geological time scales, constitute an important source of volatiles to the Earth's atmosphere. Measurements of gas composition and flux are therefore critical to both volcano monitoring and to determining the contribution of volcanoes to global geochemical cycles. However, significant gaps remain in our global inventories of volcanic emissions, (particularly for CO2, which requires proximal sampling of a concentrated plume) for those volcanoes where the near‐vent region is hazardous or inaccessible. Unmanned Aerial Systems (UAS) provide a robust and effective solution to proximal sampling of dense volcanic plumes in extreme volcanic environments. Here we present gas compositional data acquired using a gas sensor payload aboard a UAS flown at Volcán Villarrica, Chile. We compare UAS‐derived gas time series to simultaneous crater rim multi‐GAS data and UV camera imagery to investigate early plume evolution. SO2 concentrations measured in the young proximal plume exhibit periodic variations that are well correlated with the concentrations of other species. By combining molar gas ratios (CO2/SO2 = 1.48–1.68, H2O/SO2 = 67–75, and H2O/CO2 = 45–51) with the SO2 flux (142 ± 17 t/day) from UV camera images, we derive CO2 and H2O fluxes of ~150 t/day and ~2,850 t/day, respectively. We observe good agreement between time‐averaged molar gas ratios obtained from simultaneous UAS‐ and ground‐based multi‐GAS acquisitions. However, the UAS measurements made in the young, less diluted plume reveal additional short‐term periodic structure that reflects active degassing through discrete, audible gas exhalations.

Impact Ejecta Plumes at the Moon

AbstractThe Lunar Dust Experiment, on‐board National Aeronautics and Space Administration's Lunar Atmosphere and Dust Environment Explorer, observed significant enhancements in impact rate measurements of lunar ejecta. These enhancements were attributed to the spacecraft crossing dense ejecta plumes generated by well‐timed and well‐placed interplanetary meteoroid impacts on the lunar surface. We have used a Monte Carlo approach to implement an initial speed distribution, derived from globally averaged Lunar Dust Experiment observations, in a 3‐D dynamical model describing the ballistic motion of ejecta particles. By matching this model to the observed enhancements, we constrained the initial ejecta angular distribution of these plumes. Our results indicate that lunar impact ejecta plumes reaching altitudes exceeding 24 km are far narrower than previously thought, with initial opening half angles of 8°±3°, suggesting that the high‐altitude lunar dust cloud may be dominated by reverse plumes.

Airborne measurements of volcanic gas composition during unrest at Kuchinoerabujima volcano, Japan

Airborne measurements of volcanic gas composition using an unmanned aerial vehicle (UAV) and Cessna aircraft were conducted at Kuchinoerabujima volcano, Japan, between 2014 and 2016. Because eruptions occurred in August 2014, May 2015, and June 2015, access to the summit crater was limited because of the risk of sudden eruption such that airborne measurements were the only viable method to measure the volcanic gas composition. Multi-GAS and alkali-filter pack measurements were made on the leeward side of the crater and around the crater, using the Cessna and UAV, respectively. Observations using the UAV could measure the dense plume and quantify the gas species of H2O, CO2, SO2, H2S, H2, HCl, and HF, while the observations using the Cessna could measure only the diluted plume and quantify CO2, SO2, H2S, and H2. The seven airborne observations enabled us to monitor variations in the volcanic gas composition. Over the observation period, the SO2/H2S ratio decreased from 10 to 1.9. The H2O/SO2 ratio, H2/SO2 ratio, and apparent equilibrium temperatures (AET) estimated using the volcanic gas composition increased after the 2014 eruption. The decrease in the SO2/H2S ratio might be attributed to changes in the pressure of degassing magma and interactions with the hydrothermal system. The airborne methods presented here highlight the utility of using light aircrafts to safely conduct volcanic gas measurements during periods of volcanic unrest when traditional ground-based methods are not possible.