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At least 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Effects of cloud condensation nuclei and ice nucleating particles on precipitation processes and supercooled liquid in mixed-phase orographic clouds

How orographic mixed-phase clouds respond to the change in cloud condensation nuclei (CCN) and ice nucleating particles (INPs) are highly uncertain. The main snow production mechanism in warm and cold mixed-phase orographic clouds (referred to as WMOCs and CMOCs, respectively, distinguished here as those having cloud tops warmer and colder than −20 °C) could be very different. We quantify the CCN and INP impacts on supercooled water content, cloud phases, and precipitation for a WMOC case and a CMOC case, with sensitivity tests using the same CCN and INP concentrations between the WMOC and CMOC cases. It was found that deposition plays a more important role than riming for forming snow in the CMOC case, while the role of riming is dominant in the WMOC case. As expected, adding CCN suppresses precipitation, especially in WMOCs and low INPs. However, this reverses strongly for CCN of 1000 cm −3 and larger. We found a new mechanism through which CCN can invigorate mixed-phase clouds over the Sierra Nevada and drastically intensify snow precipitation when CCN concentrations are high (1000 cm −3 or higher). In this situation, more widespread shallow clouds with a greater amount of cloud water form in the Central Valley and foothills west of the mountain range. The increased latent heat release associated with the formation of these clouds strengthens the local transport of moisture to the windward slope, invigorating mixed-phase clouds over the mountains, and thereby producing higher amounts of snow precipitation. Under all CCN conditions, increasing the INPs leads to decreased riming and mixed-phase fraction in the CMOC as a result of liquid-limited conditions, but has the opposite effects in the WMOC as a result of ice-limited conditions. However, precipitation in both cases is increased by increasing INPs due to an increase in deposition for the CMOC but enhanced riming and deposition in the WMOC. Increasing the INPs dramatically reduces supercooled water content and increases the cloud glaciation temperature, while increasing CCN has the opposite effect with much smaller significance.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

The relative impact of cloud condensation nuclei and ice nucleating particle concentrations on phase partitioning in Arctic mixed-phase stratocumulus clouds

This study investigates the interactions between cloud dynamics and aerosols in idealized large-eddy simulations (LES) of Arctic mixed-phase stratocumulus clouds (AMPS) observed at Oliktok Point, Alaska, in April 2015. This case was chosen because it allows the cloud to form in response to radiative cooling starting from a cloud-free state, rather than requiring the cloud ice an dliquid to adjust to an initial cloudy state. Sensitivity studies are used to identify whether there are buffering feedbacks that limit the impact of aerosol perturbations. The results of this study indicate that perturbations in ice nucleating particles (INPs) dominate over cloud condensation nuclei(CCN) perturbations; i.e., an equivalent fractional decrease in CCN and INPs results in an increase in the cloud-top long wave cooling rate, even though the droplet effective radius increases and the cloud emissivity decreases.The dominant effect of ice in the simulated mixed-phase cloud is a thinning rather than a glaciation, causing the mixed-phase clouds to radiate as a grey body and the radiative properties of the cloud to be more sensitive to aerosol perturbations. It is demonstrated that allowing prognostic CCN and INPs causes a layering of the aerosols, with increased concentrations of CCN above cloud top and increased concentrations of INPs at the base of the cloud-driven mixed layer. This layering contributes to the maintenance of the cloud liquid, which drives the dynamics of the cloud system.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

New particle formation in the sulfuric acid–dimethylamine–water system: reevaluation of CLOUD chamber measurements and comparison to an aerosol nucleation and growth model

Here, a recent CLOUD (Cosmics Leaving OUtdoor Droplets) chamber study showed that sulfuric acid and dimethylamine produce new aerosols very efficiently and yield particle formation rates that are compatible with boundary layer observations. These previously published new particle formation (NPF) rates are reanalyzed in the present study with an advanced method. The results show that the NPF rates at 1.7 nm are more than a factor of 10 faster than previously published due to earlier approximations in correcting particle measurements made at a larger detection threshold. The revised NPF rates agree almost perfectly with calculated rates from a kinetic aerosol model at different sizes (1.7 and 4.3 nm mobility diameter). In addition, modeled and measured size distributions show good agreement over a wide range of sizes (up toca. 30 nm). Furthermore, the aerosol model is modified such that evaporation rates for some clusters can be taken into account; these evaporation rates were previously published from a flow tube study. Using this model, the findings from the present study and the flow tube experiment can be brought into good agreement for the high base-to-acid ratios ( ~ 100)relevant for this study. This confirms that nucleation proceeds at rates that are compatible with collision-controlled (a.k.a.kinetically controlled) NPF for the conditions during the CLOUD7 experiment (278 K, 38 % relative humidity, sulfuric acid concentration between 1 × 10 6 and 3 × 10 7 cm -3 , and dimethylamine mixing ratio of ~ 40 pptv, i.e., 1 × 10 9 cm -3 ) .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Ice nucleating particles in the marine boundary layer in the Canadian Arctic during summer 2014

Ice nucleating particles (INPs) in the Arctic can influence climateand precipitation in the region; yet our understanding of the concentrations and sourcesof INPs in this region remain uncertain. In the following, we (1) measured concentrationsof INPs in the immersion mode in the Canadian Arctic marine boundary layer duringsummer 2014 on board the CCGS Amundsen , (2) determined ratios of surface areasof mineral dust aerosol to sea spray aerosol, and (3) investigated the source region ofthe INPs using particle dispersion modelling. Average concentrations of INPs at -15 , -20 , and -25 - C were 0.005, 0.044, and 0.154 L -1 ,respectively. These concentrations fall within the range of INP concentrations measuredin other marine environments. For the samples investigated the ratio of mineral dustsurface area to sea spray surface area ranged from 0.03 to 0.09. Based on these ratiosand the ice active surface site densities of mineral dust and sea spray aerosoldetermined in previous laboratory studies, our results suggest that mineral dust is amore important contributor to the INP population than sea spray aerosol for the samplesanalysed. Based on particle dispersion modelling, the highest concentrations of INPs wereoften associated with lower-latitude source regions such as the Hudson Bay area, easternGreenland, or north-western continental Canada. On the other hand, the lowestconcentrations were often associated with regions further north of the sampling sites andover Baffin Bay. A weak correlation was observed between INP concentrations and the timethe air mass spent over bare land, and a weak negative correlation was observed betweenINP concentrations and the time the air mass spent over ice and open water. Thesecombined results suggest that mineral dust from local sources is an important contributorto the INP population in the Canadian Arctic marine boundary layer during summer 2014.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Relative importance of high-latitude local and long-range-transported dust for Arctic ice-nucleating particles and impacts on Arctic mixed-phase clouds

Dust particles, serving as ice-nucleating particles (INPs), may impact the Arctic surface energy budget and regional climate by modulating the mixed-phase cloud properties and lifetime. In addition to long-range transport from low-latitude deserts, dust particles in the Arctic can originate from local sources. However, the importance of high-latitude dust (HLD) as a source of Arctic INPs (compared to low-latitude dust, LLD) and its effects on Arctic mixed-phase clouds are overlooked. In this study, we evaluate the contribution to Arctic dust loading and INP population from HLD and six LLD source regions by implementing a source-tagging technique for dust aerosols in version 1 of the US Department of Energy's Energy Exascale Earth System Model (E3SMv1). Our results show that HLD is responsible for 30.7 % of the total dust burden in the Arctic, whereas LLD from Asia and North Africa contributes 44.2 % and 24.2 %, respectively. Due to its limited vertical transport as a result of stable boundary layers, HLD contributes more in the lower troposphere, especially in boreal summer and autumn when the HLD emissions are stronger. LLD from North Africa and East Asia dominates the dust loading in the upper troposphere with peak contributions in boreal spring and winter. The modeled INP concentrations show better agreement with both ground and aircraft INP measurements in the Arctic when including HLD INPs. The HLD INPs are found to induce a net cooling effect (-0.24 W m -2 above 60 °N) on the Arctic surface downwelling radiative flux by changing the cloud phase of the Arctic mixed-phase clouds. The magnitude of this cooling is larger than that induced by North African and East Asian dust (0.08 and -0.06 W m -2 , respectively), mainly due to different seasonalities of HLD and LLD. Uncertainties of this study are discussed, which highlights the importance of further constraining the HLD emissions.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Measurement report: The Fifth International Workshop on Ice Nucleation phase 1 (FIN-01): intercomparison of single-particle mass spectrometers

Knowledge of the chemical composition and mixing state of aerosols at a single-particle level is critical for gaining insights into atmospheric processes. One common tool to make these measurements is single-particle mass spectrometry. There remains a need to compare the performance of different single-particle mass spectrometers (SPMSs). An intercomparison of SPMSs was conducted at the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) chamber at the Karlsruhe Institute of Technology (KIT) in November 2014, as part of the first phase of the Fifth International Workshop on Ice Nucleation (FIN-01). In this paper we compare size distributions and mass spectra of atmospherically relevant particle types measured by five SPMSs. These include different minerals, desert and soil dusts, soot, bioaerosol (Snomax; protein granule), secondary organic aerosol (SOA), and SOA-coated mineral particles. Most SPMSs reported similar vacuum aerodynamic diameter (d va ) within typical instrumental ranges from ~100–200 nm (lower limit) to ~2–3 µm (upper limit). In general, all SPMSs exhibited a wide dynamic range (up to ~10 3 ) and high signal-to-noise ratio (up to ~10 4 ) in mass spectra. Common spectral features with small diversities in mass spectra were found with high average Pearson's correlation coefficients, i.e., for average positive spectra r avg-pos =0.74 ± 0.12 and average negative spectra r avg-neg =0.67 ± 0.22. We found that instrument-specific detection efficiency (DE) was more dependent on particle size than particle type, and particle identification favored the use of bipolar, rather than monopolar, instruments. Particle classification from “blind experiments” showed that all instruments differentiated SOA, soot, and soil dust and detected subtle changes in the particle internal mixing but had difficulties differentiating among specific mineral types and dusts. This study helps to further understand the capabilities and limitations of the single-particle mass spectrometry technique in general and the specific performance of the instrument in characterizing atmospheric aerosol particles.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Bioaerosols as indicators of central Arctic ice nucleating particle sources

The Arctic is warming at a rapid rate, with implications for microbial communities as the ecosystems change. Some microbes and biogenic materials can affect the persistence of long-lived mixed-phase clouds by serving as ice nucleating particles (INPs). The presence of INPs modulates the cloud phase, and long-term measurements are important to elucidate their seasonal sources and to predict future change. The Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition in 2019–2020 provided the first year-long measurements of bioaerosols and INPs in the central Arctic, with 3 d filters for amplicon sequencing and cumulative INP concentrations from −5 to −30 °C. Here, we investigated the INP seasonal cycle and its relation to the seasonal cycle of bacteria and eukaryotes. INPs were greatly elevated and compositionally similar in summer, aligning with a greater prevalence of local bioaerosol sources, but, despite this, a diverse mixture of sources (marine and terrestrial) was present all times. A common broader Arctic INP population is hypothesized for much of the year by comparable coincident data collected in Svalbard and a sensitivity of both the INPs and bioaerosols to large-scale events.

Barry, Kevin R. [Colorado State Univ., Fort Collin↗
DOE OSTI2017

Using depolarization to quantify ice nucleating particle concentrations: a new method

We have developed a new method to determine ice nucleating particle (INP) concentrations observed by the Texas A&M University continuous flow diffusion chamber (CFDC) under a wide range of operating conditions. In this study, we evaluate differences in particle optical properties detected by the Cloud and Aerosol Spectrometer with POLarization (CASPOL) to differentiate between ice crystals, droplets, and aerosols. The depolarization signal from the CASPOL instrument is used to determine the occurrence of water droplet breakthrough (WDBT) conditions in the CFDC. The standard procedure for determining INP concentration is to count all particles that have grown beyond a nominal size cutoff as ice crystals. During WDBT this procedure overestimates INP concentration, because large droplets are miscounted as ice crystals. Here we design a new analysis method based on depolarization ratio that can extend the range of operating conditions of the CFDC. The method agrees reasonably well with the traditional method under non-WDBT conditions with a mean percent error of ±32.1 %. Additionally, a comparison with the Colorado State University CFDC shows that the new analysis method can be used reliably during WDBT conditions.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Ice nucleating particle concentrations measured by the PNNL-CFDC during the AGINSGP field experiment

Real-time, immersion mode ambient ice nucleating particle (INP) concentrations were measured at ARM’s Southern Great Plains (SGP) site during the AGINSGP field experiment using a continuous flow diffusion chamber (CFDC) from Pacific Northwest National Laboratory (PNNL). The PNNL-CFDC is an ice-thermal gradient diffusion chamber that optically detects the freezing of single aerosol particles (Kulkarni et al. 2020). The instrument was located in the guest instrument facility (GIF) and measured INP concentrations from April 8th to April 29th. Air was drawn into the GIF through custom aluminum stack inlets (6” inner diameter) attached vertically to the outer GIF wall and the GIF outside platform. A blower pulled air through the stacks at a velocity of 1 m/s. Aerosol instruments subsampled via wall ports, through either 3/8” or 1/4" copper lines, depending on sample flow of the instrument. Kulkarni, G., Hiranuma, N., Möhler, O., Höhler, K., China, S., Cziczo, D. J., & DeMott, P. J. (2020). A new method for operating a continuous-flow diffusion chamber to investigate immersion freezing: Assessment and performance study. Atmospheric Measurement Techniques, 13(12), 6631–6643. https://doi.org/10.5194/amt-13-6631-2020.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Ice nucleating particle concentrations in the Arctic during MOSAiC 2020

This data set contains ice nucleating particle (INP) measurements, using Colorado State University’s (CSU) Ice Spectrometer (IS) of samples collected during the Multidisciplinary Drifting Observatory for the Study of Arctic Climate (MOSAiC) field campaign. Samples were collected from five different media: aerosol filters, meltwater, ice cores, snow pits, and bulk sea water (BSW).

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Long-time variation in magnetic structure of CeIr 3 Si 2 : Observation of a nucleation-and-growth process of magnetic domains

CeIr 3 Si 2 is the first three-dimensional uniform magnet in which the long-time variation in magnetic structure was observed. To clarify the microscopic mechanism of this magnetic structural change, time-resolved neutron scattering measurements have been reinvestigated. Clear time variations in the line widths as well as the amplitudes of magnetic Bragg diffractions have been observed in this improved instrumentation. On the notion of this observation, a nucleation-and-growth model of magnetic structural change has been presented. The numerical calculation with this model reproduces well the observation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1968

Electron microscope study of film nucleation

Crystal structure and growth, and nucleation observed by electron diffraction and microscope in formation of thin metal films during vacuum deposition on carbon

Kronenberg, K. J.↗