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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Pinatubo Global- to Micro-Scale Evolution: A Unified Picture from Space, Air, and Ground Measurements

We combine space, air, and ground measurements to develop a composite picture of the post-Pinatubo aerosol, and assess the consistency and uncertainties of various measurement and retrieval techniques. impactor and optical counter measurements, as well as retrievals from optical depth spectra, paint a generally consistent picture of the evolution of particle effective radii, R(sub eff). In the first month after the eruption, although particle numbers increased by orders of magnitude, R(sub eff) was similar to the preeruption value of 4.2 micrometers, because both small (r less than 0.25 micrometers) and large (r greater than 0.6 micrometers) particles increased in number, Over the next 3-6 months, R(sub eff) increased rapidly to about 0.5 micrometers. In general, R(sub eff) continued to increase for about a year after the eruption. The peak wavelength of optical depth spectra increased from initial values of less than 0.42 micrometers to values between 0.78 and 1 micrometer. This coupled evolution in particle size distribution and optical depth spectra helps explain the relationship between the global maps of 0.5 and 1.0-micrometer optical depth derived from the AVHRR and SAGE satellite measurements. It also sets a context for evaluating remaining uncertainties in each of these satellite data products. We also make consensus recommendations for particle composition, shape, and temperature- and wavelength-dependent refractive index, and show how the latter effect on backscatter spectra can influence particle sizes retrieved from multiwavelength lidar measurements.

Russell, Philip B.↗
NASA NTRS1979

Simulated lidar return from a one-dimensional stratospheric aerosol model

Results are presented for theoretical calculations of lidar backscatter at wavelengths of 0.6943 and 1.06 microns from the stratospheric aerosol. The computations are based on the size distribution, particle number density, and particle composition predicted by a one-dimensional model of the stratospheric aerosol layer that assumes that the primary source of sulfur to the stratosphere is biogenic OCS released at ground level. The aerosol particles are taken to be spherical liquid H2SO4-H2O solution droplets with solid cores, which undergo condensation, evaporation, coagulation, sedimentation, and vertical eddy mixing. The theoretical backscatter profiles are compared with experimental results obtained from actual lidar observations of the stratospheric aerosol layer before and after the eruption of Volcan de Fuego in October 1974. The model predictions are shown to be in good agreement with the average of a number of observations.

Hamill, P.↗
NASA NTRS1996

Are Planetary Regolith Particles Back Scattering? Response to a Paper by M. Mishchenko

In a recent paper Mishchenko asserts that soil particles are strongly forward scattering, whereas particles on the surfaces of objects in the solar system have been inferred to be back scattering. Mishchenko suggests that this apparent discrepancy is an artifact caused by using an approximate light scattering model to analyse the data, and that planetary regolith particles are actually strong forward scatterers. The purpose of the present paper is to point out the errors in Mishchenko's paper and to show from both theoretical arguments and experimental data that inhomogencous composite particles which are large compared to the wavelength of visible light, such as rock fragments and agglutinates, can be strongly back scattering and are the fundamental scatterers in media composed of them. Such particles appear to be abundant in planetary regoliths and can account for the back scattering character of the surfaces of many bodies in the solar system. If the range of phase angles covered by a data set is insufficient, serious errors in retrieving the particle scattering properties can result whether an exact or approximate scattering model is used. However, if the data set includes both large and small phase angles, approximate regolith scattering models can correctly retrieve the sign of the particle scattering asymmetry.

Hapke, Bruce↗
NASA NTRS1977

The clouds of Venus

The current state of knowledge of the Venusian clouds is reviewed. The visible clouds of Venus are shown to be quite similar to low level terrestrial hazes of strong anthropogenic influence. Possible nucleation and particle growth mechanisms are presented. The Pioneer Venus experiments that emphasize cloud measurements are described and their expected findings are discussed in detail. The results of these experiments should define the cloud particle composition, microphysics, thermal and radiative heat budget, rough dynamical features and horizontal and vertical variations in these and other parameters. This information should be sufficient to initialize cloud models which can be used to explain the cloud formation, decay, and particle life cycle.

Knollenberg, R. G.↗
NASA NTRS1999

Automated Propellant Blending

An automated propellant blending apparatus and method uses closely metered addition of countersolvent to a binder solution with propellant particles dispersed therein to precisely control binder precipitation and particle aggregation. A profile of binder precipitation versus countersolvent-solvent ratio is established empirically and used in a computer algorithm to establish countersolvent addition parameters near the cloud point for controlling the transition of properties of the binder during agglomeration and finishing of the propellant composition particles. The system is remotely operated by computer for safety, reliability and improved product properties, and also increases product output.

Hohmann, Carl W.↗
NASA NTRS2000

Automated Propellant Blending

An automated propellant blending apparatus and method that uses closely metered addition of countersolvent to a binder solution with propellant particles dispersed therein to precisely control binder precipitation and particle aggregation is discussed. A profile of binder precipitation versus countersolvent-solvent ratio is established empirically and used in a computer algorithm to establish countersolvent addition parameters near the cloud point for controlling the transition of properties of the binder during agglomeration and finishing of the propellant composition particles. The system is remotely operated by computer for safety, reliability and improved product properties, and also increases product output.

Hohmann, Carl W.↗
NASA NTRS2012

Characterizing the Vertical Profile of Aerosol Particle Extinction and Linear Depolarization over Southeast Asia and the Maritime Continent: The 2007-2009 View from CALIOP

Vertical profiles of 0.532 μm aerosol particle extinction coefficient and linear volume depolarization ratio are described for Southeast Asia and the Maritime Continent. Quality-screened and cloud-cleared Version 3.01 Level 2 NASA Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) 5-km Aerosol Profile datasets are analyzed from 2007 to 2009. Numerical simulations from the U.S. Naval Aerosol Analysis and Predictive System (NAAPS), featuring two-dimensional variational assimilation of NASA Moderate Resolution Imaging Spectroradiometer and Multi-angle Imaging Spectro- Radiometer quality-assured datasets, combined with regional ground-based lidar measurements, are considered for assessing CALIOP retrieval performance, identifying bias, and evaluating regional representativeness. CALIOP retrievals of aerosol particle extinction coefficient and aerosol optical depth (AOD) are high over land and low over open waters relative to NAAPS (0.412/0.312 over land for all data points inclusive, 0.310/0.235 when the per bin average is used and each is treated as single data points; 0.102/0.151 and 0.086/0.124, respectively, over ocean). Regional means, however, are very similar (0.180/0.193 for all data points and 0.155/0.159 when averaged per normalized bin), as the two factors offset one another. The land/ocean offset is investigated, and discrepancies attributed to interpretation of particle composition and a-priori assignment of the extinction-to-backscatter ratio ("lidar ratio") necessary for retrieving the extinction coefficient from CALIOP signals. Over land, NAAPS indicates more dust present than CALIOP algorithms are identifying, indicating a likely assignment of a higher lidar ratio representative of more absorptive particles. NAAPS resolvesmore smoke overwater than identified with CALIOP, indicating likely usage of a lidar ratio characteristic of less absorptive particles to be applied that biases low AOD there. Over open waters except within the Bay of Bengal, aerosol particle scattering is largely capped below 1.5 km MSL, though ground-based lidar measurements at Singapore differ slightly from this finding. Significant aerosol particle presence over land is similarly capped near 3.0 km MSL over most regions. Particle presence at low levels regionally, except over India, is dominated by relatively non-depolarizing particles. Industrial haze, sea salt droplets and fresh smoke are thus most likely present.

linear volume depolarization ratio↗
NASA NTRS2016

Satellite Maps and Relevant Compositional Properties of PM2.5 in Difficult Winter Situations and Comparisons to DISCOVER-AQ Airborne Sampling

Mediterranean-climate regions like California's San Joaquin Valley are subject to severe wintertime particulate pollution affecting public health. We present maps of episodes and particulate diagnostics to aid diagnosis and amelioration. For abatement at sources, we require an understanding of sources and transport. Remote sensing should be of aid, but radiance-to-particle relationships are far different from methods which have been of use in the Eastern USA, Northern and Central Europe. Here are the problems: (a) Thin if very polluted mixed layers (MLs) yield optical depths, AOD, near the detection level, (b) bright and quite variegated surfaces (c) Unusual particle composition (e.g., predominance of NH4NO3 and fireplace buning aerosol), which complicate the relationship of AOD to PM2.5. Specialized analysis of MODIS-Aqua data to obtain AOD using the multi-angle (MAIAC) technique employed by Lyapustin and Wang. Meteorological analyses like NOAA's Rapid Analysis Product (RAP, or newer products like HRRR), which are formulated to remain close to observations (e.g. of water), provide useful ML information corroborated by DISCOVER-AQ in-situ and lidar observations. The many PM2.5 measurements allow a calibration of these products and thus maps of aerosol on many successive aerosol buildups. These calibrations also allow insight into compositional information relevant to MODIS retrievals, the product of aerosol density and specific scattering. We have found that the rich in-situ, lidar, and sun-photometer data sets of NASA'S DISCOVER-AQ data set (2013) of great aid. We will highlight the most interesting of many intercomparisons possible with this rich data set. We conclude with a description of new work to extend these insights to similar regions, e.g. the Imperial Valley of California, the Po Valley and maritime Southern Europe, and the litoral regions of Israel.

aerosols↗
NASA NTRS2023

Automated Machine Learning to Evaluate the Information Content of Tropospheric Trace Gas Columns for Fine Particle Estimates Over India: A Modeling Testbed

India is largely devoid of high-quality and reliable on-the-ground measurements of fine particulate matter (PM 2.5 ). Ground-level PM 2.5 concentrations are estimated from publicly available satellite Aerosol Optical Depth (AOD) products combined with other information. Prior research has largely overlooked the possibility of gaining additional accuracy and insights into the sources of PM using satellite retrievals of tropospheric trace gas columns. We evaluate the information content of tropospheric trace gas columns for PM 2.5 estimates over India within a modeling testbed using an Automated Machine Learning (AutoML) approach, which selects from a menu of different machine learning tools based on the data set. We then quantify the relative information content of tropospheric trace gas columns, AOD, meteorological fields, and emissions for estimating PM 2.5 over four Indian sub-regions on daily and monthly time scales. Our findings suggest that, regardless of the specific machine learning model assumptions, incorporating trace gas modeled columns improves PM 2.5 estimates. We use the ranking scores produced from the AutoML algorithm and Spearman’s rank correlation to infer or link the possible relative importance of primary versus secondary sources of PM 2.5 as a first step toward estimating particle composition. Our comparison of AutoML-derived models to selected baseline machine learning models demonstrates that AutoML is at least as good as user-chosen models. The idealized pseudo-observations (chemical-transport model simulations) used in this work lay the groundwork for applying satellite retrievals of tropospheric trace gases to estimate fine particle concentrations in India and serve to illustrate the promise of AutoML applications in atmospheric and environmental research.

Machine learning↗
NASA NTRS1973

A cosmochemical view of cosmic rays and solar particles

The composition of cosmic rays and solar particles is reviewed with emphasis on the question of whether they are representative samples of Galactic and solar matter. The composition of solar particles changes with energy and from flare to flare. A strong excess of heavy elements at energies below a few MeV/nuc decreases with energy, and at energies above 15 MeV/nuc the composition of solar particles resembles that of galactic cosmic rays somewhat better than that of the solar atmosphere. The elements Ne through Pb have remarkably similar abundances in cosmic ray sources and in the matter of the solar system. The lighter elements are depleted in cosmic rays, whereas U and Th may be enriched or not, depending on whether the meteoritic or solar abundance of Th is used.

Price, P. B.↗
NASA NTRS2000

North Atlantic Aerosol Radiative Impacts Based on Satellite Measurements and Aerosol Intensive Properties from TARFOX and ACE-2

We estimate the impact of North Atlantic aerosols on the net short-wave flux at the tropopause by combining satellite-derived aerosol optical depth (AOD) maps with model aerosol properties determined via closure analyses in TARFOX and ACE 2. We exclude African dust, primarily by restricting latitudes to 25-60 N. The analyses use in situ aerosol composition measurements and air- and ship-borne sun-photometer measurements of AOD spectra. The aerosol model yields computed flux sensitivities (dFlux/dAOD) that agree with measurements by airborne flux radiometers in TARFOX. Its midvisible single-scattering albedo is 0.9. which is in the range obtained from in situ measurements of scattering and absorption in both TARFOX and ACE 2. Combining satellite-derived AOD maps with the aerosol model yields maps of 24-hour average net radiative flux changes. For simultaneous AVHRR, radiance measurements exceeded the sunphotometer AODs by about 0.04. However. shipboard sunphotometer and AVHRR AODs agreed Within 0.02 for data acquired during satellite overflights on two other days. We discuss attempts to demonstrate column closure within the MBL by comparing shipboard sunphotometer AODs and values calculated from simultaneous shipboard in-situ aerosol size distribution measurements. These comparisons were mostly unsuccessful, but they illustrate the difficulties inherent in this type of closure analysis. Specifically, AODs derived from near-surface in-situ size distribution measurements are extremely sensitive to the assumed hygroscopic growth model that itself requires an assumption of particle composition as a function of height and size, to the radiosonde-measured relative humidity, and to the vertical profile of particle number. We investigate further the effects of hygroscopic particle growth within the MBL by using shipboard lidar aerosol backscatter profiles together with the sunphotometer AOD.

Russell, P. B.↗
NASA NTRS1985

Particle size, number, composition and velocity from solid rocket motors

The damage potentials to the space shuttle orbiter caused by the high velocity particles contained in the exhaust plume of an upper stage is discussed. In particular, the particle size distribution and composition, the velocity of the particles and the expected contribution from shuttle launched upper stages are addressed. Particle size estimates based on historical data are compapred with those derived from upper stage motor performance testing. The particle velocities as determined by the best available plume computational technique are presented. The shuttle is scheduled to launch approximately 135 upper-stages over its lifetime looking at the currently scheduled flights and averaging over a yearly basis yields the contribution of particulates from the uper-stages. On the average, 91,645 llbs of Al2O3 will be ejected on each launch. The analysis to determine how much of this 91,645 lbs will remain in orbit or the decay rate is yet to be accomplished.

Roberts, B. B.↗
NASA NTRS2019

Evaluation of Global Simulations of Aerosol Particle and Cloud Condensation Nuclei Number, with Implications for Cloud Droplet Formation

A total of 16 global chemistry transport models and general circulation models have participated in this study; 14 models have been evaluated with regard to their ability to reproduce the near-surface observed number concentration of aerosol particles and cloud condensation nuclei (CCN), as well as derived cloud droplet number concentration (CDNC). Model results for the period 2011-2015 are compared with aerosol measurements (aerosol particle number, CCN and aerosol particle composition in the submicron fraction) from nine surface stations located in Europe and Japan. The evaluation focuses on the ability of models to simulate the average across time state in diverse environments and on the seasonal and short-term variability in the aerosol properties. There is no single model that systematically performs best across all environments represented by the observations. Models tend to underestimate the observed aerosol particle and CCN number concentrations, with average normalized mean bias (NMB) of all models and for all stations, where data are available, of -24% and -35% for particles with dry diameters > 50 and > 120nm, as well as -36% and -34% for CCN at supersaturations of 0.2% and 1.0%, respectively. However, they seem to behave differently for particles activating at very low supersaturations (< 0.1%) than at higher ones. A total of 15 models have been used to produce ensemble annual median distributions of relevant parameters. The model diversity (defined as the ratio of standard deviation to mean) is up to about 3 for simulated N3 (number concentration of particles with dry diameters larger than 3 nm) and up to about 1 for simulated CCN in the extra-polar regions. A global mean reduction of a factor of about 2 is found in the model diversity for CCN at a supersaturation of 0.2% (CCN(0.2)) compared to that for N3, maximizing over regions where new particle formation is important. An additional model has been used to investigate potential causes of model diversity in CCN and bias compared to the observations by performing a perturbed parameter ensemble (PPE) accounting for uncertainties in 26 aerosol-related model input parameters. This PPE suggests that biogenic secondary organic aerosol formation and the hygroscopic properties of the organic material are likely to be the major sources of CCN uncertainty in summer, with dry deposition and cloud processing being dominant in winter. Models capture the relative amplitude of the seasonal variability of the aerosol particle number concentration for all studied particle sizes with available observations (dry diameters larger than 50, 80 and 120nm). The short-term persistence time (on the order of a few days) of CCN concentrations, which is a measure of aerosol dynamic behavior in the models, is underestimated on average by the models by 40% during winter and 20% in summer.

cloud droplets↗
NASA NTRS1984

Solar wind ionization temperatures inferred from the charge state composition of diffuse particle events

Detailed measurements of the charge state composition of energetic heavy ions in the diffuse component are presented for the first time. Spectral characteristics and charge state measurements for 12 diffuse ion events observed upstream of the earth's bow shock are reported. One event is analyzed in order to illustrate the basic assumptions and general techniques involved in the determination of charge state composition from the data. The probable solar wind origin of the seed population of the diffuse component is used together with the charge state composition of these heavy ions to estimate the charge state composition in the concurrent solar wind, and hence to infer the equilibrium coronal temperatures associated with a variety of solar wind flows. The results are compared with predicted solar wind values.

Galvin, A. B.↗
NASA NTRSDate not supplied

Inefficient Growth of Refractory Grains: Implications for Grains in the Solar Nebula

Introduction: We report the results of a sounding rocket experiment in which SiO nucleation and growth in an argon atmosphere was observed in microgravity starting from a vapor generated by evaporation of waterglass deposited on a heated Ta wire. The temperature and pressure at the point of nucleation was determined using a double wavelength Mach–Zehnder-type interferometer. The particle composition and grain size distribution were measured after payload recovery using a Transmission Electron Microscope (TEM; JEM-2100F. JEOL Ltd., Tokyo). The results were analyzed using Modified Classical Nucleation Theory (MCNT)[1]. We report a measurement of the SiO-silicate grain sticking coefficient of 0.016, indicating very inefficient grain growth from the vapor. In other words, for every 100 SiO molecules that collide with a growing grain only one to two are captured. In the only two previous studies of the growth of solid particles from the gas phase the calculated sticking coefficients were much lower. For zinc atoms colliding with zinc crystals only three out of 100,000 collisions resulted in grain growth [2]. Iron atoms colliding with growing iron particles similarly showed an efficiency of ~0.00002 [3]. For zinc, we can explain inefficient growth due to the difficulty of the colliding atom coming upon a vacancy in the growing crystal lattice before it evaporates from the grain surface. The much higher sticking coefficient of SiO molecules on silica grains is reasonable because the silica grains are highly amorphous or glassy and therefore provide a much higher defect density where SiO molecules can be captured into the grains. In the case of similar Fe experiment, the critical cluster was the dimer. In this case the forming dimer returns to the vapor phase by dissociation due to the excess energy from the formation of the Fe-Fe bond.

Joseph A Nuth↗
NASA NTRS2002

Studies of Transient Meteor Activity

Meteoroids bombard Earth's atmosphere daily, but occasionally meteor rates increase to unusual high levels when Earth crosses the relatively fresh ejecta of comets. These transient events in meteor activity provide clues about the whereabouts of Earth-threatening long-period comets, the mechanisms of large-grain dust ejection from comets, and the particle composition and size distribution of the cometary ejecta. Observations of these transient events provide important insight in natural processes that determine the large grain dust environment of comets, in natural phenomena that were prevalent during the time of the origin of life, and in processes that determine the hazard of civilizations to large impacts and of man-made satellites to the periodic blizzard of small meteoroids. In this proposal, three tasks form a coherent program aimed at elucidating various aspects of meteor outbursts, with special reference to planetary astronomy and astrobiology. Task 1 was a ground-based effort to observe periods of transient meteor activity. This includes: (1) stereoscopic imaging of meteors during transient meteor events for measurements of particle size distribution, meteoroid orbital dispersions and fluxes; and (2) technical support for Global-MS-Net, a network of amateur-operated automatic counting stations for meteor reflections from commercial VHF radio and TV broadcasting stations, keeping a 24h vigil on the level of meteor activity for the detection of new meteor streams. Task 2 consisted of ground-based and satellite born spectroscopic observations of meteors and meteor trains during transient meteor events for measurements of elemental composition, the presence of organic matter in the meteoroids, and products generated by the interaction of the meteoroid with the atmosphere. Task 3 was an airborne effort to explore the 2000 Leonid meteor outbursts, which are anticipated to be the most significant of transient meteor activity events in the remainder of the agreement period. This includes technical support for a multi-instrument aircraft campaign, Leonid MAC.

Jenniskens, Peter M. M.↗
NASA NTRS2021

Airborne and Ground-Based Measurements of Aerosol Optical Depth of Freshly Emitted Anthropogenic Plumes in the Athabasca Oil Sands Region

In this work we report the airborne aerosol optical depth (AOD) from measurements within freshly emitted anthropogenic plumes arising from mining and processing operations in the Athabasca Oil Sands Region (AOSR) in the context of ground-based AERONET climatological daily averaged AODs at Fort McMurray (Alberta, Canada). During two flights on 9 and 18 June 2018, the NASA airborne 4STAR (Spectrometers for Sky-Scanning, Sun-Tracking Atmospheric Research) Sun photometer registered high fine-mode (FM, <1 µm) in-plume AODs of up to 0.4 and 0.9, respectively, in the vicinity of the plume source (<20 km). Particle composition shows that the plumes were associated with elevated concentrations of sulfates and ammonium. These high AODs significantly exceed climatological averages for June and were not captured by the nearby AERONET instrument (mean daily AODs of 0.10±0.01 and 0.07±0.02, maximum AOD of 0.12) due possibly to horizontal inhomogeneity of the plumes, plume dilution and winds which in certain cases were carrying the plume away from the ground-based instrument. The average 4STAR out-of-plume (background) AODs deviated only marginally from AERONET daily averaged values. While 4STAR AOD peaks were generally well correlated in time with peaks in the in situ-measured particle concentrations, we show that differences in particle size are the dominant factor in determining the 4STAR-derived AOD. During the two flights of 24 June and 5 July 2018 when plumes likely travelled distances of 60 km or more, the average 4STAR FM AOD increased by 0.01–0.02 over ∼50 km of downwind particle evolution, which was supported by the increases in layer AODs calculated from the in situ extinction measurements. Based on these observations as well as the increases in organic mass, we attribute the observed AOD increase, at least in part, to secondary organic aerosol formation. The in-plume and out-of-plume AODs for this second pair of flights, in contrast to clear differences in in situ optical and other measurements, were practically indistinguishable and compared favourably to AERONET within 0.01–0.02 AOD. This means that AERONET was generally successful in capturing the background AODs, but missed some of the spatially constrained high-AOD plumes with sources as close as 30–50 km, which is important to note since the AERONET measurements are generally thought to be representative of the regional AOD loading. The fact that industrial plumes can be associated with significantly higher AODs in the vicinity of the emission sources than previously reported from AERONET can potentially have an effect on estimating the AOSR radiative impact.

AERONET↗
NASA NTRS1973

Unusual chemical compositions of noctilucent-cloud particle nuclei

Two sounding rocket payloads were launched from the ESRO range in Sweden during a noctilucent cloud display. Large numbers of submicron particles were collected, most of which appear to be made up of a high density material coated with a low density material. Typical electron micrographs are shown. Particle chemical compositions have been measured by use of dispersive X-ray analysis equipment attached to an electron microscope and have revealed that most of the high density particle nuclei have atomic weights greater than iron.

Hemenway, C. L.↗