Soot Aerosol Research Articles

A Radiative Transfer Simulator for PACE: Theory and Applications

A radiative transfer simulator was developed to compute the synthetic data of all three instruments onboard NASA’s Plankton Aerosol, Cloud, ocean Ecosystem (PACE) observatory, and at the top of the atmosphere (TOA). The instrument suite includes the ocean color instrument (OCI), the Hyper-Angular Rainbow Polarimeter 2 (HARP2), and the Spectro-Polarimeter for Planetary Exploration 1 (SPEXone). The PACE simulator is wrapped around a monochromatic radiative transfer model based on the successive order of scattering (RTSOS), which accounts for atmosphere and ocean coupling, polarization, and gas absorption. Inelastic scattering, including Raman scattering from pure ocean water, fluorescence due to chlorophyll, and colored dissolved organic matter (CDOM), is also simulated. This PACE simulator can be used to explore the sensitivity of the hyperspectral and polarized reflectance of the Earth system with tunable atmosphere and ocean parameters, which include aerosol and cloud number concentration, refractive indices, and size distribution, ocean particle microphysical parameters, and solar and sensor-viewing geometry. The PACE simulator is used to study two important case studies. One is the impact of the significant uncertainty in pure ocean water absorption coefficient to the radiance field in the ultraviolet (UV) spectral region, which can be as much as 6%. The other is the influence of different amounts of brown carbon aerosols and CDOM on the polarized radiance field at TOA. The percentage variation of the radiance field due to CDOM is mostly for wavelengths smaller than 600 nm, while brown aerosols affect the whole spectrum from 350 to 890 nm, primarily due to covaried soot aerosols. Both case studies are important for aerosol and ocean color remote sensing and have not been previously reported in the literature.

Bi-modal moment model for predicting the formation and growth of soot aggregate particles

Numerical simulations of the formation and growth of soot particles in combustion processes are important for estimating the emission rate of particulate air pollutants and predicting the accurate size and morphology of industrial commodity particles. A new bi-modal soot aerosol model called the Soot Aerosol Moment Model (SAMM) was developed. The SAMM can predict the changes in the soot particle size distribution and morphology simultaneously by monitoring only five variables evolving due to nucleation, surface reaction, PAH condensation, coagulation, sintering, and condensational obliteration. The performance of the SAMM was evaluated by comparing its predictions with those of a sectional soot model and available measurements. The SAMM provided comparable information on the soot particle size distribution and morphology with a more than 100-fold shorter computation time than the sectional model, suggesting that it can be used effectively to develop and test sophisticated chemical mechanisms for soot formation.

Experimental and numerical analysis of fine particle and soot formation in a modern 100 MW pulverized biomass heating plant

The formation of soot, organic, and inorganic aerosols has a profound effect on the environmental and technological feasibility of biomass combustion. In this work, the soot and aerosol processes are examined for a modern pulverized wood-burning 100 MWth district heating plant. Experimental data was collected from two locations inside the furnace (30% and 100% thermal loads), including measurements for fine particle (PM1) number size distribution, number concentration, and chemical composition. The experiments were complemented with Computational Fluid Dynamics (CFD) simulations and Plug-Flow Reactor (PFR) modeling. The measurements and modeling are combined in a comprehensive analysis, providing fundamental understanding on the aerosol processes inside the furnace. The wood-powder combustion is efficient under both thermal loads, indicated by the low unburned carbon content in fly-ash, and the low CO, NO and soot emissions (<0.3 mg/Nm3). The fine particles consist mainly of K2SO4, and of lesser amounts of alkali salts (NaCl, KCl), and Ca and Mg compounds (oxides or sulfates). A large concentration of KOH/K2CO3 vapor may exist in the flue gas and play a significant role in the heat exchanger fouling. The applied modeling tools are shown to provide accurate estimations for the composition and formation regions of fine particles inside the industrial biomass furnaces.

Filtration of Submicron Soot Particles, Oil Droplets, and their Mixtures on Single- and Multi-layer Fibrous Filters

The dynamics of filtration efficiency and pressure drop during the simultaneous filtration of soot and oil aerosols on single- and multi-layer filters were investigated, and the determined filtration efficiency was compared with the theoretical efficiency obtained via the classical filtration theory. Additionally, the influence of liquid-phase aerosols on the morphology of the formed deposits was investigated. It was concluded that the addition of oil aerosols decreased the filtration efficiency and lowered the pressure drop increase rate for multi-layer filters. Additionally, for the filtration of aerosols containing soot and high oil concentrations, once maximum filtration efficiency was reached, an efficiency decrease occurred. The system imperfection factor was proposed as a mean to predict the efficiency of multi-layer filters. The modified version of the single fibre efficiency method was used to calculate filter mass change with reasonable accuracy.

Number concentration and size distribution of soot aerosols of heptane fire at low pressures

SummaryThe number concentration and size distribution of soot aerosols are imperative parameters in fire detection which is closely related to safety management, risk assessment, and fire analysis. The experiment of n‐heptane pool fire is conducted in a pressure chamber which simulates the 101, 90.9, 80.8, 70.7, 60.6, and 50.5 kPa environments. The influence of air pressure on the number concentration and size distribution of soot aerosols is investigated. The DMS500 fast particulate analyzer is used to analyze the number concentration and size distribution of gas samples. Both the geometric mean diameter and count median diameter of smoke particles increases with pressure. A second‐order polynomial equation with correlation coefficient of 0.99 is fitted to the geometric mean diameter of particles against pressure. The particle number concentration is significantly decreased when pressure is reduced according to a linear relationship with correlation coefficient of 0.92. The environmental pressure puts influence on the soot optical properties that affect fire smoke detection technologies used in the regions of different altitudes or air pressures.

Modeling microplastics’ climate impact

Microplastics are abundant in the world’s waterways and even in the air. In fact, researchers estimate there are hundreds to thousands of microplastic particles in each cubic meter of air in urban environments. University of Canterbury environmental physicist Laura Revell wondered how atmospheric microplastics might impact the climate. After all, she says, “other types of particulates in the atmosphere, such as dust, soot, and sulfate aerosols, influence the climate by absorbing and scattering sunlight.” To determine whether atmospheric microplastics are warming or cooling the planet, Revell’s group analyzed their optical properties, finding that the types of particles assumed to be abundant scatter ultraviolet and visible light but absorb infrared radiation. The researchers plugged those data, along with estimates of these particles’ abundance, into a global climate simulation ( Nature 2021, DOI: 10.1038/s41586-021-03864-x ). The climate impact of microplastics depends on what altitudes they reach—something researchers don’t yet know, Revell says.

Mass-Independent Fractionation of Mercury Isotopes during Photoreduction of Soot Particle Bound Hg(II).

Soot and mercury (Hg) are two notorious air pollutants, and the fate and transport of Hg may be affected by soot at various scales in the environment as soot may be both a carrier and a reactant for active Hg species. This study was designed to quantify photoreduction of Hg(II) in the presence of soot and the associated Hg isotope fractionation under both atmospheric aerosol and aqueous conditions (water-saturated). Photoreduction experiments were conducted with diesel soot particulate matter under controlled temperature and relative humidity (RH) conditions using a flow-through semibatch reactor system. Mass-dependent fractionation resulted in the enrichment of heavier Hg isotopes in the remaining Hg(II) with enrichment factors (ε202Hg) of 1.48 ± 0.02‰ (±2 standard deviation) to 1.75 ± 0.05‰ for aerosol-phase reactions (RH 28-68%) and from 1.26 ± 0.11 to 1.50 ± 0.04‰ for aqueous-phase reactions. Positive odd mass-independent fractionation (MIF) was observed in aqueous-phase reactions, resulting in Δ199Hg values for reactant Hg(II) as high as 5.29‰, but negative odd-MIF occurred in aerosol-phase reactions, in which Δ199Hg values of reactant Hg(II) varied from -1.02 to 0‰. The average ratio of Δ199Hg/Δ201Hg (1.1) indicated that under all conditions, MIF was dominated by magnetic isotope effects during photoreduction of Hg(II). Increasing RH resulted in higher reduction rates but lower extents of negative MIF in the aerosol-phase experiments, suggesting that the reduction of soot particle-bound Hg(II) was responsible for the observed negative odd-MIF. Our results suggest that mass-independent Hg isotope fractionation during Hg(II) photoreduction varies with soot aerosol water content and that Hg-stable isotope ratios may be used to understand the transformational histories of aerosol-bound Hg(II) in the environment.

Crumpled few-layer graphene: Connection between morphology and optical properties

Comprehensive characterization of crumpled graphene materials is required to understand their morphologically dependent properties. This study connects the optical properties of crumpled few-layer graphene (FLG) aerosols and colloidal suspensions with particle morphology. The mass absorption cross-section (MAC) of crumpled FLG was measured in the aerosol phase and it is shown that such aerosols absorb visible light more efficiently than soot aerosols. The UV–Vis spectra of FLG suspensions in ethanol were correlated with the mean nanoparticle layer number and the lateral size. The measured optical properties were also simulated using discrete dipole approximation (DDA) applied to volume-reconstructed particles with refractive indices of graphene and graphite from literature. The measurements were more closely reproduced using the refractive index of graphite pellets rather than flat graphene on a substrate. Moreover, we show that a simpler Rayleigh–Debye–Gans (RDG) model can predict the wavelength dependence of the crumpled FLG absorption cross-section.

Coated soot particles with tunable, well-controlled properties generated in the laboratory with a miniCAST BC and a micro smog chamber

A Micro Smog Chamber (MSC) was coupled for the first time with a miniCAST 5201 Type BC combustion generator with the aim to produce a series of stable and reproducible model aerosols simulating the physical properties of combustion particles present in ambient air. With this setup it was possible to generate particles ranging from “fresh” soot (single scattering albedo SSA≤0.05, absorption Ångström exponent AAE close to 1, high EC/TC mass fraction (approximately 90%) and mobility diameter typically <100 nm) to “aged” soot with different amounts of organic coating. The “aged” soot particles could grow up to 200 nm and exhibited high SSA (up to 0.7 at λ = 870 nm), an increased AAE (up to 1.7) and low EC/TC mass fraction (down to <10%). The ageing was achieved by coating the soot particles with increasing amounts of secondary organic matter (SOM) formed by the photo-oxidation of α-pinene or mesitylene in the MSC. Thereby, the SSA and AAE increased with coating thickness, while the EC/TC mass fraction decreased. Over the experimental period of 2 h, the generation of the “aged” soot aerosols was stable with a standard deviation in particle size and number concentration of <1% and <6%, respectively. The day-to-day reproducibility was also satisfactory: with α-pinene as SOM precursor the variability (standard deviation) in particle size was <2% and in the AAE and SSA < 6%. Particle number concentrations up to 106 cm−3 and mass concentrations up to 15 mg/m3 (depending on particle size and SOM amount) could be generated, much higher than what has been reported with other oxidation flow reactors. The generated carbonaceous aerosols could find useful applications in the field of aerosol instrument calibration, particularly in the standardization of filter-based absorption photometers under controlled conditions.

Calibration Uncertainty of 23nm Engine Exhaust Condensation Particle Counters with Soot Generators: a European Automotive Laboratory Comparison

Calibration of condensation particle counters (CPC) to measure non-volatile particle number (PN) from vehicle emissions is a significant source of uncertainty of the regulated particle number measurements. In this work, the calibration uncertainty of automotive and calibration laboratories was determined in a first-of-its-kind comparison. For this purpose, the counting efficiency of a reference CPC for automotive exhaust emission measurements was determined at seven participants across Europe with ten soot aerosol generators. Calibration uncertainty was found to be very different in the CPC’s cut-off regime (around the D50 of 23nm) with a coefficient of variation (CoV) of 11% and the plateau regime (from the D90 of 41nm upwards) with a CoV of 4.5%. The uncertainty was higher for a group of soot generators with poorly optimized operating points with a CoV of 31% at 23nm and 5.8% at ≥41nm. Specific influence factors on the calibration uncertainty (measured as the inter-lab variability) could be identified. The calibration of the laboratories’ reference counters accounted for most of the variability in the plateau regime, while 20% of the variability was attributed to the sample flow measurement. Differences between soot generators were the main cause of variability in the cut-off regime due to the increased material sensitivity of the CPC at this particle size but had only secondary relevance in the plateau regime. The calibration uncertainty found in this inter-laboratory exercise should be a guideline for users and legislators, as it provides a typical value for the expected measurement uncertainty of a CPC for automotive exhaust PN.

Numerical investigation of pressure effects on soot formation in laminar coflow ethylene/air diffusion flames

This study aims to provide fundamental understandings of the pressure effects on the soot formation and compare the performances of different soot aerosol models. Numerical simulations are performed in laminar coflow diffusion flames at pressures ranging from 1 to 16 bar. Two soot aerosol models are considered: the acetylene-based semi-empirical (SE) model and polycyclic aromatic hydrocarbons (PAH) based hybrid method of moment (HMOM). To study the effect of large-sized PAH species, a detailed reaction mechanism is used with PAH pathways up to coronene. Results show that the SE model provides good predictions of pressure scaling of peak soot mass with a deviation of 7%, while HMOM obtains better soot predictions on the flame centerline. Due to the shifting of PAH position towards the burner with increasing pressure, the nascent soot is formed earlier. The increase in the particle residence time is found to be an additional factor that further promotes the increased soot formation with pressure, apart from the increase in density, temperature, and PAH concentration. The residence time at 8 bar case is 2.5 times and 3.0 times longer than those at 1 bar case on the flame centerline and flame wings, respectively. Moreover, the pressure effects on the PAH contribution to the nucleation process are studied. Although small-sized PAH species (A2 and A2R5) dominate the nucleation process, the contribution of large-sized PAH species (larger than A4) increases from 5% to 20% of the total on the flame wings, when the pressure increases from 1 bar to 8 bar.

Comparison of equations used to estimate soot agglomerate absorption efficiency with the Rayleigh-Debye-Gans approximation

The contribution of soot aerosols to radiative forcing and climate change depends on their optical properties. Since these aerosols are agglomerates composed of quasi-spherical primary particles (usually small with respect to the radiation wavelength), their properties can be calculated following the Rayleigh-Debye-Gans approximation, which considers primary particles as independent absorbers and scatterers, with corrections made to account for multiple scattering and absorption within the agglomerate. A variety of equations can be used for particles small compared to the wavelength. In this study, results of the Rayleigh, Bohren and Huffman, simplified Bohren and Huffman, and Dobbins and Megaridis equations have been compared to the results from the exact Mie equations for the absorption efficiency. This comparison has been made for individual particles with different diameters and for an ensemble of primary particles composing an agglomerate. It has been shown that some of the largest primary particles of a typical agglomerate may not behave as Rayleigh absorbers at short wavelengths, contributing to errors in the estimation of the absorption efficiency. Both Bohren and Huffman and Dobbins and Megaridis equations are useful to extend the application range of the Rayleigh equation, thus reducing the accumulated error in the estimation of the agglomerate absorption efficiency. This analysis has been performed for several complex refractive index spectra. To choose the best equation for a particular application, the wavelength spectrum of the radiation and the range of primary particle sizes should be considered, aiming for a compromise between simplicity and accuracy.

Interaction between strong sound waves and cloud droplets: Cloud chamber experiment

Acoustic agglomeration refers to the group effect of micro-particle groups in a strong sound field, which promotes relative motion among the particles, leading to the rapid agglomeration of the particle groups. The existing theoretical and experimental research on acoustic agglomeration is focused on solid particles such as soot particles and aerosols, and the acoustic agglomeration of micron-scale cloud droplets has not been intensively investigated. In this study, a cloud with an average particle size of ~10 μm is generated in a cloud chamber at room temperature, and a series of acoustic agglomeration experiments of cloud droplets under the action of sound waves with a frequency and sound pressure level (SPL) of 35–100 Hz and 112–122 dB, respectively, are conducted to examine the impact law of the sound waves with different frequencies and SPLs on the cloud droplet size spectrum. At a constant sound frequency, the agglomeration effect of the cloud droplets is more pronounced under the action of sound waves with a higher SPL. Under a constant SPL, the agglomeration effect is the most notable when the sound frequency ranges from 50 to 65 Hz. The threshold SPL for the effective agglomeration ranges from 114 to 121 dB when the sound frequency is 35–100 Hz, and the threshold SPL gradually increases with the sound frequency. The findings can clarify the effect of the sound waves in promoting cloud condensation and provide guidance to develop atmospheric intervention technologies based on strong sound waves.

Laser Irradiation of Super-Nonwettable Carbon Soot Coatings–Physicochemical Implications

Accounting the increasing commercial need of rational strategies for passive icing and anti-microbial protection, the development of simple, time-efficient and scalable laboratory micropatterning techniques is highly desirable. Whilst the laser irradiation is an acknowledged technology for rapidly tuning the properties of any carbon allotropes, including soot aerosols, very barely is known about the impact of the laser beam on the physicochemical profile of the soot if it appears as a functional coating. In this pioneering research, the prolonged laser treatment of a super-nonwettable soot coating actuates morpho-chemical transformations in the material, depending on the laser power and irradiation time, without interfering its anti-wetting capability and optical transmittance. Our observations could be used as a foundation for facilitating the launch of soot coatings with customized anti-icing and anti-microbial performance.

Seed traits linked to differential survival of plants during the Cretaceous/Paleogene impact winter

In past investigations the pattern of differential survival of plants across the K/Pg boundary has been viewed as incompatible with severe asteroid impact winter scenarios (i.e., an impact winter lasting more than a few months), particularly the enigmatic survival of coryphoid palms and Pandanus (screw pine). Stateof- the-art climate models based on soot, sulfate and nano-sized dust aerosols predict a global impact winter that drastically reduced precipitation and resulted in a transient period of total darkness and permafrost conditions. This suggests that the plants most likely to have been affected by the global mass-extinction event were tropical phanerophytes that produce recalcitrant seeds, which by definition are desiccation-intolerant, survive less than a year, and cannot survive freezing. However, this hypothesis has never been tested. In this study I sampled over 100 plant species from the global fossil record that have a high probability of having produced either recalcitrant seeds/disseminules (n1 = 58) or orthodox seeds (n2 = 59), based on their phylogenetic relationships with extant taxa that either are monomorphic for these traits or specifically exhibit a genetic marker for abscisic acid inhibition associated with seed dormancy and recalcitrance. A one-tailed z-test for the difference between two proportions revealed that plant taxa with a high probability of having produced recalcitrant seeds had significantly lower survivorship than plant taxa with a high probability of having produced orthodox seeds (p &lt; 0.0001). Based on these data, it can be concluded that plants which formed a frost-tolerant seed bank during the latest Maastrichtian were significantly more likely to survive the K/Pg impact winter than plants which did not (including palms). These data clearly indicate that the K/Pg impact winter probably lasted longer than a year and that it selected for seed-based traits that effectively sorted correlated functional traits of mature plants (i.e., leaf physiognomic features). This novel hypothesis stands as an alternative to J.A. Wolfe’s classic hypothesis that a mild K/Pg impact winter selected for fast-growing angiosperms with deciduous leaves and did not affect the plant communities of the Southern Hemisphere. Potential mechanisms for the rare survival of tropical, recalcitrant-seeded plants are discussed.

Sooting characteristics of ethanol-ethylene blends in laminar coflow diffusion flames up to 10 bar

Ethanol, being a renewable product, has been perceived for a long time as a fuel that burns clean and more complete than conventional hydrocarbons as well as being thought as a soot suppressant in blends with gasoline and diesel fuel. Some of the results from a wide-range of studies investigating soot-suppression potential of ethanol at atmospheric pressure, including Smoke Point measurements, have yielded occasionally contradictory conclusions. Further, scaling of soot studies conducted under atmospheric conditions to engine-relevant pressures has always been problematic because of the non-monotonic response of combustion events to pressure. Ethanol’s soot inhibiting characteristics at elevated pressures under tractable conditions have not been previously documented and may not be inferred easily from atmospheric pressure measurements. Information from benchmark investigations with ethanol-hydrocarbon blends at elevated pressures could help in understanding the soot aerosol emissions from practical engines fueled with ethanol blends. Soot production in ethanol/ethylene laminar diffusion flames at elevated pressures was investigated on a 3 mm diameter coflow burner mounted in a high-pressure combustion vessel. Ethanol was added to ethylene, which is diluted with nitrogen, in various quantities from 0% to 40% in terms of total carbon of the fuel stream keeping the carbon flow rate constant at 0.41 mg/s. Experiments were conducted at pressures from 3 to 10 bar, and in addition to keeping the mass flow of carbon constant, the ratio of mass flow of nitrogen to mass flow of carbon was also kept fixed at 6 at the fuel nozzle. The soot spectral emission spectroscopy technique was used to obtain line-of-sight intensities of soot radiation which were then converted to radial soot temperature and volume fraction distributions at a given axial height within the flame. Soot production increased by a small but measurable amount with the fuel mixture containing 10% carbon from ethanol at 5 and 8 bar pressure flames indicating synergistic interactions; while at 3 and 10 bar, no measurable change was observed. When the ethanol’s carbon contribution was increased to 30% and 40%, soot formation was suppressed and the soot yields decreased below the soot level of neat nitrogen-diluted ethylene at 3 to 10 bar pressures. Sensitivity of soot production to pressure in ethylene/ethanol flames is found to be similar to that of ethylene up to 8 bar.

On the growth of Polycyclic Aromatic Hydrocarbons (PAHs) in a coflow diffusion flame of ethylene

In the last two decades several mechanisms have been proposed for the growth of PAHs during combustion. Studies have suggested that the growth of PAHs of different structures should be analyzed carefully to improve our understanding of PAH formation during combustion. In this study, a wide of range of PAHs of different structures have been measured along the centreline of a coflow diffusion flame of ethylene using GC/MS, allowing for a previously not possible detailed analysis of potential formation routes. The discussed potential global empirical pathways can help in the development of accurate and detailed chemical mechanisms in the future. The experimental results show that the difference in reactivity of the sites of a PAH where growth takes place limits the formation of benzenoid PAHs at high temperatures. This difference in reactivity also leads to the formation of PAHs with a five-membered ring at high temperatures. The recombination of PAH radicals may not be favoured in this flame which explains the small amounts of alkyl-bridged PAHs at high temperatures. PAHs with an alkyl sidechain are favoured only along the free edge. Alkyl substituted PAHs are formed in low amounts and decrease with an increase in temperature. Methylene-bridged PAHs can lead to faster growth of large PAHs and become significant at intermediate temperatures. The target flame has also been simulated using state-of-the-art models. The simultaneous measurements of both PAHs and soot allowed for a comprehensive assessment of the chemical mechanisms and soot aerosol dynamics. The assessment suggests that both the chemical mechanisms and the soot aerosol dynamics need further improvements. The results confirm the importance of accounting for PAH structure when developing kinetic mechanisms and their coupled soot formation models. A complete database comprising of PAHs, soot and temperature is generated for future model validations.

The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018

Global aviation operations contribute to anthropogenic climate change via a complex set of processes that lead to a net surface warming. Of importance are aviation emissions of carbon dioxide (CO2), nitrogen oxides (NOx), water vapor, soot and sulfate aerosols, and increased cloudiness due to contrail formation. Aviation grew strongly over the past decades (1960–2018) in terms of activity, with revenue passenger kilometers increasing from 109 to 8269 billion km yr−1, and in terms of climate change impacts, with CO2 emissions increasing by a factor of 6.8 to 1034 Tg CO2 yr−1. Over the period 2013–2018, the growth rates in both terms show a marked increase. Here, we present a new comprehensive and quantitative approach for evaluating aviation climate forcing terms. Both radiative forcing (RF) and effective radiative forcing (ERF) terms and their sums are calculated for the years 2000–2018. Contrail cirrus, consisting of linear contrails and the cirrus cloudiness arising from them, yields the largest positive net (warming) ERF term followed by CO2 and NOx emissions. The formation and emission of sulfate aerosol yields a negative (cooling) term. The mean contrail cirrus ERF/RF ratio of 0.42 indicates that contrail cirrus is less effective in surface warming than other terms. For 2018 the net aviation ERF is +100.9 milliwatts (mW) m−2 (5–95% likelihood range of (55, 145)) with major contributions from contrail cirrus (57.4 mW m−2), CO2 (34.3 mW m−2), and NOx (17.5 mW m−2). Non-CO2 terms sum to yield a net positive (warming) ERF that accounts for more than half (66%) of the aviation net ERF in 2018. Using normalization to aviation fuel use, the contribution of global aviation in 2011 was calculated to be 3.5 (4.0, 3.4) % of the net anthropogenic ERF of 2290 (1130, 3330) mW m−2. Uncertainty distributions (5%, 95%) show that non-CO2 forcing terms contribute about 8 times more than CO2 to the uncertainty in the aviation net ERF in 2018. The best estimates of the ERFs from aviation aerosol-cloud interactions for soot and sulfate remain undetermined. CO2-warming-equivalent emissions based on global warming potentials (GWP* method) indicate that aviation emissions are currently warming the climate at approximately three times the rate of that associated with aviation CO2 emissions alone. CO2 and NOx aviation emissions and cloud effects remain a continued focus of anthropogenic climate change research and policy discussions.

Concentration and Isotopic Composition of Methane, Associated Gases, and Black Carbon over Russian Arctic Seas (Shipborne Measurements)

In Russian Arctic seas, observations of surface methane concentrations (CH4), ozone, nitrogen and carbon oxides, as well as the content of $${{\delta }^{{13}}}{{{\text{C}}}_{{{\text{C}}{{{\text{H}}}_{4}}}}}$$ isotope and black carbon (BC, soot aerosol), were carried out from onboard of the R/V Academician Mstislav Keldysh. The areas of local methane releasing from bottom sediments were investigated. It was shown that the studied methane releasing on the Arctic shelf are of a local nature and, on the whole, insignificantly affect the composition of the atmosphere in the region. The average concentration of methane in the surface air in the Arctic seas is mainly determined by large-scale processes of air mass transfer. An analysis of the distribution of black carbon along the route of the vessel was carried out. It was found that the excess in the concentration of black carbon over the background values is observed occasionally during advection of air masses from the mainland and from the areas of associated gases burning and forest fires. The effect of emissions from a ship’s chimney on the data obtained was analyzed.

Airborne Release Fractions from Surrogate Nuclear Waste Fires Containing Lanthanide Nitrates and Depleted Uranium Nitrate in 30% Tributyl Phosphate in Kerosene

Airborne contaminants from fires containing nuclear waste represent significant health hazards and shape the design and operation of nuclear facilities. Much of the data used to formulate DOE-HDBK-3010-94, “Airborne Release Fractions/Rates and Respirable Fractions for Nonreactor Nuclear Facilities,” from the U.S. Department of Energy, were taken over 40 years ago. The objectives of this study were to reproduce experiments from Pacific Northwest Laboratories conducted in June 1973 employing current aerosol measurement methods and instrumentation, develop an enhanced understanding of particulate formation and transport from fires containing nuclear waste, and provide modeling and experimental capabilities for updating current standards and practices in nuclear facilities. A special chamber was designed to conduct small fires containing 25 mL of flammable waste containing lutetium nitrate, ytterbium nitrate, or depleted uranium nitrate. Carbon soot aerosols showed aggregates of primary particles ranging from 20 to 60 nm in diameter. In scanning electron microscopy, ~200-nm spheroidal particles were also observed dispersed among the fractal aggregates. The 200-nm spherical particles were composed of metal phosphates. Airborne release fractions (ARFs) were characterized by leaching filter deposits and quantifying metal concentrations with mass spectrometry. The average mass-based ARF for 238U experiments was 1.0 × 10−3 with a standard deviation of 7.5 × 10−4. For the original experiments, DOE-HDBK-3010-94 states, “Uranium ARFs range from 2 × 10−4 to 3 × 10−3, an uncertainty of approximately an order of magnitude.” Thus, current measurements were consistent with DOE-HDBK-3010-94 values. ARF values for lutetium and ytterbium were approximately one to two orders of magnitude lower than 238U. Metal nitrate solubility may have varied with elemental composition and temperature, thereby affecting ARF values for uranium surrogates (Yb and Lu). In addition to ARF data, solution boiling temperatures and evaporation rates can also be deduced from experimental data.