Low Number Concentrations Research Articles

First Insights for the Investigation of the Electrical Contact Among the Particles of Lithium Ion Battery Cathode Materials

Mechanical degradation phenomena arising from the volume change during charging and discharging can severely affect the electrical contact among the particles within the composite cathode material. Furthermore, electrochemically induced particle disintegration at high currents (e.g. for LiNi1/3Mn1/3Co1/3O2 (NMC111)) is conceivable to have a major influence on the loss of electrochemical performance. There is a variety of electrochemical monitoring and investigation techniques for the analysis of electrode materials (e.g. impedance spectroscopy, X-Ray Diffraction, Raman spectroscopy). However, there is no sensitive analytical method in the field of battery research for the investigation of particles and the integrity of the conductive network among them within the composite electrode material. Therefore, the development of novel analytical approaches for the investigation of particle contact and the resulting contribution on the capacity fading is mandatory. The focus of this work is the development of a method for particle analysis of lithium ion battery (LIB) cathode materials by means of inductively coupled plasma based techniques with optical emission spectroscopy (ICP-OES) and mass spectrometry (ICP-MS). Presuming an intact conductive network among the particles of the active material, the state-of-charge (SOC) should be equal throughout the electrode. Because the SOC correlates to the degree of lithiation (DOL) of the particles, the assessment of electrical contact is accessible by determining the ratio of lithium and host element (e.g. nickel, cobalt, manganese). For ICP-based techniques, the particle size distribution requires to be narrow and small-sized for the accurate element determination. Furthermore, due to potentially occurring Li+-H+ exchange reactions, the sample introduction of NMC cathode materials in aqueous media is not feasible[1]. Therefore, the size dependent separation is performed by the principle of air classification and the particulate sample is introduced by means of an argon flow to the plasma. The utilization of particle classification indicates the applicability for ICP-based particle analysis due to the facilitation of low particle number concentrations and narrow size distributions and the results for ICP-MS and -OES exhibit the fundamental functioning for the application in particle analysis. [1] J. Li, R. Klöpsch, S. Nowak, M. Kunze, M. Winter, S. Passerini, J. Power Sources. 2011, 196 , 7687-7691.

Development and Validation of a Novel Particle Source for Nano-sized Test Aerosols

ABSTRACT In the EU, there is an increasing need for regulatory agencies to establish health-based threshold limits for airborne particles. A prerequisite for such projects is the validation and comparison of existing and newly developed particle analyzers. Corresponding proficiency tests have often been conducted with the help of inter-laboratory tests using test aerosols. Although test aerosols in the micro- and the nanoscale range were produced with different generator systems at the technical center of the Institute for the Research on Hazardous Substances (IGF) in Dortmund, a stable and reproducible method of producing a low number concentration for nano-sized particles was not achieved. Inspired by a method of monodisperse droplet generation, we coupled a flame generator with a droplet generator and examined the concentration and the diameter of the formed particles as a consequence of the precursor concentration and the droplet frequency. In addition, the reproducibility of the method was tested daily, and the nanoparticles were collected and characterized microscopically. Finally, the measurements of the particle size distribution were mathematically examined. The resulting fits enable the prediction of the median particle diameter as a function of the precursor concentration and the frequency of the droplets. Overall, the performed experiments confirm that this system meets all the requirements with regard to a low number concentration and long-term stability and reproducibility and should therefore be suitable for further inter-laboratory round robin tests.

Aerial Observation of Atmospheric Nanoparticles on Fukue Island, Japan

ABSTRACT New particle formation (NPF) in the East Asian region is strongly influenced by photochemical processes during the long-range transport of air pollutants. Our previous measurements (Seto et al., 2013; Chandra et al., 2016) relating to the incomplete and weak NPF (onset diameter > 10 nm) on Fukue Island in Japan (downstream from the Asian continent) suggested nucleation in the upstream region. The vertical structure of atmospheric nanoparticle concentrations (particle size > 6 nm and altitude 35,000 particles cm–3) than in our previous measurements (from 2012 to 2016, ~20,000 particles cm–3) with a particle size as small as 5 nm, affected by the long-range transport of air pollutants under a high-pressure system, was detected. A sudden increase in particle number and SO2 concentrations with weak NPF caused by a change in the air mass origin (Event II: < 10,000 particles cm–3) as well as no NPF with aged sulfate particles during conditions with low particle number and SO2 concentrations (< 0.15 ppb) (Event III: < 2,000 particles cm–3) were also observed.

Turbulence Effects on Precipitation and Cloud Radiative Properties in Shallow Cumulus: an Investigation Using the WRF-LES Model Coupled with Bin Microphysics

Using the large-eddy simulation version of the Weather Research and Forecasting (WRF) model coupled with a detailed bin microphysics scheme, the effects of turbulence-induced collision enhancement (TICE) on precipitation and cloud radiative properties in shallow cumulus are investigated. Similar to previous studies, the enhanced droplet collision results in an increase in rainwater content and surface precipitation amount. However, under low aerosol number concentration, the relative frequency of large surface precipitation amount is decreased mainly due to the decreased condensation amount. Due to TICE, the mean drop size increases and the drop number concentration decreases, which results in a decrease in evaporation and hence increasing cloud fraction. However, these changes induce a decrease in cloud optical thickness which largely offsets the increased cloud fraction when the domain-averaged albedo is calculated. Similarly, a decrease in cloud top height caused by the decreased in-cloud vertical velocity largely offsets the increased cloud fraction when the domain-averaged outgoing longwave radiation is calculated. Therefore, the effects of TICE on cloud radiative properties in shallow cumulus do not appear prominently. In addition, TICE results in a decrease in the shear production of turbulent kinetic energy, which indicates that TICE acts to produce a negative feedback.

Low number concentration of ice nucleating particles in an aged smoke plume

Smoke from forest fires in the western part of North America reached the High Altitude Research Station Jungfraujoch, Switzerland, at the beginning of September 2017. Number concentration of ice nucleating particles (INPs) active at −15 °C or warmer decreased by about half during its passage. This is different to observations of enhanced INP concentrations in fresh plumes from forest fires. We hypothesise that INPs initially present in a smoke plume are lost or deactivated during long‐range transport, while components of smoke capable of deactivating INPs originally present or mixed later into the plume continue to remain active across a longer distance.

Characterization of aerosol emissions from CO2 capture plants treating various power plant and industrial flue gases

Undesired aerosol formation in gas–liquid contact devices has been a well-known phenomenon in the chemical industry for several decades and can cause severe problems in industrial gas cleaning processes. Several studies indicate that aerosols can govern the total amine emissions from amine based CO2 capture (PCCC) plants. Despite the importance of aerosol formation and mitigation for the design of a PCCC plant, very little knowledge is available on the characterization and growth of these aerosols.Four different atmospheric flue gases were modelled in this work, ranging from 4 to 20% in CO2 content and representing natural gas, oil and coal fired power plants, and gas from the cement industry. Inlet droplets of size 0.15 μ were tested in number concentrations from 1 to 107 droplets/cm3. For 20% CO2, the effect of intercooling was studied.The findings are: Aerosol droplets grow from their initial size regardless of their initial composition and type of flue gas processed. The initial composition of the droplets has a significant effect on emissions.With increasing CO2 concentration, more carbamate is formed relative to free MEA. This leads to less effective water wash and significantly higher final emissions.With low droplet number concentration no visible depletion of MEA in the absorber and water wash sections was found for any of the CO2 concentrations. At 107 droplets/cm3, gas phase MEA partial pressure changes are clearly seen, first in the water wash, and then, at higher contents, the effect starts lower and lower down in the absorber.The carry-over of amine into the water wash increases with increasing gas phase CO2 content. However, the effect on the gas phase MEA content in the water wash goes through a maximum caused by strong carbamate formation at high CO2 concentrations.The droplet temperature profiles are unaffected by number concentration and initial composition of aerosol droplets.It is found that the water wash section reduces significantly the aerosol-based, and thereby the total, amine emissions. The effect of the water wash is reduced when the flue gas CO2 content increases.Intercooling lowers the partial pressure of MEA in both absorber and water wash significantly. This reduces the droplet growth and MEA content. The combined effect is a strong reduction in MEA emissions; in the case of 20% CO2 in the flue gas, by a factor of 5–10.

Foams stabilization by silica nanoparticle with cationic and anionic surfactants in column flotation: Effects of particle size

Abstract Foams have been widely used in flotation, but they stabilized solely by surfactants was unstable. Nanoparticles (NPs) can improve the performance of aqueous foams. It is interesting to evaluate and understand the effect of NPs on foam property in column flotation. In this paper, silica nanoparticles (SNPs) with three different sizes (20, 100 and 500 nm) were chosen as model NPs; the performance of foams stabilized by SNPs and two surfactant, cetyltrimethylammonium bromide (CTAB) and anionic sodium dodecylsulfate (SDS), were investigated experimentally. For CTAB/SNPs dispersion, although the foamability was lower, SNPs obviously improved static foam stability. Moreover, smaller SNP exhibited a more effective improvement for foam stability because of its low adhesion energy and high number concentration. For SDS/SNPs dispersion, even if SNPs were hydrophilic, the foam stability was still enhanced since these particles induced congestion in the node and slowed down drainage. Larger SNP had a greater ability to delay the liquid drainage and enhance the foam stability. Besides, CTAB/SNPs and SDS/SNPs foams also maintained their dynamic stability through weakening the foam drainage. These results provided theoretical supports for the usage of NPs in practical application such as flotation.

Feedback effect of electric field force on electrification and charge structure in thunderstorm

The electrification within the thunderstorm, caused mainly by inductive and noninductive charging mechanism, can produce strong local electric field inside the thundercloud. Due to the resulting electric field force, the vertical velocity of the graupel and hail particles which are the main in-cloud charge carriers, would change. As a feedback, this variation could affect the original electrification and charge structure of the thunderstorm. In order to investigate such a feedback effect, a weather research forecasting (WRF) model coupled with explicit lightning physics including charging and discharge lightning scheme (hereafter WRF-Elec) is employed and modified in this study. We derive the formulas for calculating the mass-weighted mean terminal velocities of graupel and hail under the balance among gravity, resistance and electric field force. Then, the National Sever Storm Laboratory (NSSL) two-moment bulk microphysics scheme is modified by adding the calculating code with consideration of electric field force (EFF) acting on the fall speed of graupel and hail particles. Eventually, the two-coupled WRF-Elec is developed successfully.#br#Based on this modified WRF-Elec, sensitivity tests are conducted to quantitatively investigate the influences of EFF on the thunderstorm electrification and the corresponding charge structure in an idealized supercell case. The results show that during the rapid enhancement of the thunderstorm, the grid-scale mass-weighted mean fall speed of graupel and hail vary significantly in consideration of EFF, with the maximum values both exceeding 4 m/s, although this situation occurs within a local area and lasts a short time. The action of EFF tends to enhance the falling of graupel and weaken the falling of hail. The influences of EFF on those graupel and hail particles with smaller-size and lower number concentration are stronger, as determined by composite factors of the strength and polarity of electric field, the diameter and number concentration of graupel and hail, and their charge density and polarity as well. The adjustment of the terminal velocity of the graupel and hail in consideration of EFF, eventually results in increasing the rate of both inductive and noninductive charge separation, where the inductive charging is the much more significant one. This leads to a grid-scale total charge density variation of -0.6-1.2 nC/m3 and a redistribution of the charge structure in the thunderstorm, and correspondingly, an increase of the local vertical electric field by 5 kV/m, thus producing stronger lightning eventually. In addition, due to the effect of electric field force, the mass mixing ratio of four precipitation particles including graupel, hail, ice crystal and snow is changed in the ranges of -0.09-0.24, -0.16-0.04, -0.04-0.05, and -0.01-0.006 g/kg, respectively. Therefore, the electric field force in thunderstorm affects not only the electrification and charge structure, but also the microphysical process. Generally, the overall influence of EFF on electrification tends to be positive, and the feedback effect of EFF on the charge structure should not be neglected.

A Case Study in Low Aerosol Number Concentrations Over the Eastern North Atlantic: Implications for Pristine Conditions in the Remote Marine Boundary Layer

AbstractWe present a case study (20 September to 13 October 2015) of synergistic, multi‐instrument observations of aerosols, clouds, and the marine boundary layer (MBL) at the Eastern North Atlantic (ENA) Atmospheric Radiation Measurement site centered on a period of exceptionally low (20–50 cm−3) surface accumulation mode (0.1–1 μm) aerosol particle number concentrations. We divide the case study into three regimes (high, clean, and ultraclean) based on daily median number concentrations and compare finer resolution (hourly or less) observations between these regimes. The analysis focuses on the possibility of using these ultraclean events to study pristine conditions in the remote MBL, as well as examining evidence for a recently proposed conceptual model for the large‐scale depletion of cloud condensation nuclei‐sized particles in postfrontal air masses. Relative to the high and clean regimes, the ultraclean regime tends to exhibit significantly fewer particles between 0.1 and 0.4 μm in diameter and a relatively increased prevalence of larger accumulation mode particles. In addition, supermicron particles tend to dominate total scattering in the ultraclean regime, and there is little evidence for absorbing aerosol. These observations are more in‐line with a heavily scavenged but natural marine aerosol population and minimal contribution from continental sources such as anthropogenic pollution, biomass burning, or dust. The air masses with the consistently lowest accumulation mode aerosol number concentrations are largely dominated by heavily drizzling clouds with high liquid water path cores, deep decoupled boundary layers, open cellular organization, and notable surface forcing of subcloud turbulence, even at night.

Impact of biofuels on contrail warming

Contrails and contrail-cirrus may be the largest source of radiative forcing (RF) attributable to aviation. Biomass-derived alternative jet fuels are a potentially major way to mitigate the climate impacts of aviation by reducing lifecycle CO2 emissions. Given the up to 90% reduction in soot emissions from paraffinic biofuels, the potential for a significant impact on contrail RF due to the reduction in contrail-forming ice nuclei (IN) remains an open question. We simulate contrail formation and evolution to quantify RF over the United States under different emissions scenarios. Replacing conventional jet fuels with paraffinic biofuels generates two competing effects. First, the higher water emissions index results in an increase in contrail occurrence (~ +8%). On the other hand, these contrails are composed of larger diameter crystals (~ +58%) at lower number concentrations (~ −75%), reducing both contrail optical depth (~ −29%) and albedo (~ −32%). The net changes in contrail RF induced by switching to biofuels range from −4% to +18% among a range of assumed ice crystal habits (shapes). In comparison, cleaner burning engines (with no increase in water emissions index) result in changes to net contrail RF ranging between −13% and +5% depending on habit. Thus, we find that even 67% to 75% reductions in aircraft soot emissions are insufficient to substantially reduce warming from contrails, and that the use of biofuels may either increase or decrease contrail warming—contrary to previous expectations of a significant decrease in warming.

Refractive index matching of large polydisperse silica spheres in aqueous suspensions

Standard synthesis protocols produce silicon dioxide (SiO2) particles with an inhomogeneous material distribution, which defines their optical properties. The inner structure and effective refractive index of the particles can be investigated by light scattering and optical contrast variation techniques. The standard analysis relies on scattering models for particles smaller than the wavelength of the scattering probe, thus restricting its use for a large variety of particle systems of academic and industrial interest. However, to overcome this difficulty should be possible by using the appropriate scattering model in the analysis. Here, SiO2 particles of size comparable to the wavelength of the illuminating source are dispersed at low particle number concentration in different mixtures of polar solvents to study the optical contrast. The angle-dependent scattered intensity from SiO2 particles suspended in different mixtures of water and DMSO are obtained by static light scattering (SLS) and the effective refractive index of the particles is estimated from refractometry experiments. The measured angle-dependent scattered intensity is well described by the Aden-Kerker theory for coated polydisperse spherical particles. Fitting of experimental data is performed by using a non-linear least squares routine assuming that the core-to-shell ratio remains constant from where the refractive index and radius of the particles shell are obtained. Additionally, we use the structural characterization to estimate the effective refractive index of SiO2 particles, which allows identification of the solvent composition that produces the minimal optical contrast between colloids and suspending medium. This is, to our knowledge, the first report describing the interplay between internal structure and optical properties of core-shell spherical colloids of size comparable to the wavelength of the scattering probe. Consequently, our study provides an experimental scheme that could be useful in the structural and optical characterization of large complex colloids.

Simulation of fine polydisperse particle condensational growth under an octadecane–nitrogen atmosphere

The evolution of particle size distribution (PSD) of fine polydisperse particles at high number concentrations (>105cm−3) was simulated through a combined model employing direct quadrature method of moments (DQMOM) with heat and mass transfer equations. The PSD was assumed to retain log-normal distribution during the heterogeneous condensation process. The model was first verified by exact solution and experimental data prior to investigating the influence of initial conditions on final PSD under an octadecane–nitrogen atmosphere. Low particle number concentrations and high vapor concentrations were beneficial to shift the PSD to larger particles having a narrower distribution. Additionally, vapor depletion has more influence on the final PSD than the heat release parameter for a number concentration of 106cm−3. This study may assist the design process of a gas–solid separating cyclone, to eliminate dust from high-temperature volatiles by pyrolysis of solid fuels.

Investigation of Combustion and Emission Performance of Hydrogenated Vegetable Oil (HVO) Diesel

Hydrogenated Vegetable Oil (HVO) diesel fuels have the potential to provide a reduced carbon footprint for diesel engines and reduce exhaust emissions. Therefore, it is a strong candidate for transport and diesel powered machines including electricity generators and other off-road machines. In this research, a waste cooking oil derived HVO diesel was investigated for its combustion and emission performance including ignition delays, size segregated particulate number emissions and gaseous emissions. The results were compared to the standard petroleum diesel. A EURO5 emission compliant three litre, direct injection, intercooled IVECO diesel engine equipped with EGR was used which has a maximum power output of 96kW. The engine was equipped with an integrated DOC and DPF aftertreatment system. Both the upstream and downstream of the aftertreatment emissions were measured. The tests were conducted at different RPM and loads at steady state conditions. A DMS500 particle size measurement instrument was used for measuring particles between 5 nm and 1000nm. The engine was instrumented with a number of thermocouples so that the engine conditions were closely monitored. Gaseous emissions were measured using a HORIBA 7100 series gas analyzer. The results showed that HVO reduced particulate numbers significantly at the upstream of the aftertreatment system. The particle number emissions were not much different between HVO and standard diesel at the downstream of the aftertreatment system due to the low particle number concentrations.

Intercomparison study and optical asphericity measurements of small ice particles in the CERN CLOUD experiment

Abstract. Optical probes are frequently used for the detection of microphysical cloud particle properties such as liquid and ice phase, size and morphology. These properties can eventually influence the angular light scattering properties of cirrus clouds as well as the growth and accretion mechanisms of single cloud particles. In this study we compare four commonly used optical probes to examine their response to small cloud particles of different phase and asphericity. Cloud simulation experiments were conducted at the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber at European Organisation for Nuclear Research (CERN). The chamber was operated in a series of multi-step adiabatic expansions to produce growth and sublimation of ice particles at super- and subsaturated ice conditions and for initial temperatures of −30, −40 and −50 °C. The experiments were performed for ice cloud formation via homogeneous ice nucleation. We report the optical observations of small ice particles in deep convection and in situ cirrus simulations. Ice crystal asphericity deduced from measurements of spatially resolved single particle light scattering patterns by the Particle Phase Discriminator mark 2 (PPD-2K, Karlsruhe edition) were compared with Cloud and Aerosol Spectrometer with Polarisation (CASPOL) measurements and image roundness captured by the 3View Cloud Particle Imager (3V-CPI). Averaged path light scattering properties of the simulated ice clouds were measured using the Scattering Intensity Measurements for the Optical detectioN of icE (SIMONE) and single particle scattering properties were measured by the CASPOL. We show the ambiguity of several optical measurements in ice fraction determination of homogeneously frozen ice in the case where sublimating quasi-spherical ice particles are present. Moreover, most of the instruments have difficulties of producing reliable ice fraction if small aspherical ice particles are present, and all of the instruments cannot separate perfectly spherical ice particles from supercooled droplets. Correlation analysis of bulk averaged path depolarisation measurements and single particle measurements of these clouds showed higher R2 values at high concentrations and small diameters, but these results require further confirmation. We find that none of these instruments were able to determine unambiguously the phase of the small particles. These results have implications for the interpretation of atmospheric measurements and parametrisations for modelling, particularly for low particle number concentration clouds.

Subvisible cirrus clouds – a dynamical system approach

Abstract. Ice clouds, so-called cirrus clouds, occur very frequently in the tropopause region. A special class are subvisible cirrus clouds with an optical depth lower than 0.03, associated with very low ice crystal number concentrations. The dominant pathway for the formation of these clouds is not known well. It is often assumed that heterogeneous nucleation on solid aerosol particles is the preferred mechanism although homogeneous freezing of aqueous solution droplets might be possible, since these clouds occur in the low-temperature regime T &lt; 235 K. For investigating subvisible cirrus clouds as formed by homogeneous freezing we develop a reduced cloud model from first principles, which is close enough to complex models but is also simple enough for mathematical analysis. The model consists of a three-dimensional set of ordinary differential equations, and includes the relevant processes as ice nucleation, diffusional growth and sedimentation. We study the formation and evolution of subvisible cirrus clouds in the low-temperature regime as driven by slow vertical updraughts (0 &lt; w ≤ 0. 05 m s−1). The model is integrated numerically and also investigated by means of theory of dynamical systems. We found two qualitatively different states for the long-term behaviour of subvisible cirrus clouds. The first state is a stable focus; i.e. the solution of the differential equations performs damped oscillations and asymptotically reaches a constant value as an equilibrium state. The second state is a limit cycle in phase space; i.e. the solution asymptotically approaches a one-dimensional attractor with purely oscillatory behaviour. The transition between the states is characterised by a Hopf bifurcation and is determined by two parameters – vertical updraught velocity and temperature. In both cases, the properties of the simulated clouds agree reasonably well with simulations from a more detailed model, with former analytical studies, and with observations of subvisible cirrus, respectively. The reduced model can also provide qualitative interpretations of simulations with a complex and more detailed model at states close to bifurcation qualitatively. The results indicate that homogeneous nucleation is a possible formation pathway for subvisible cirrus clouds. The results motivate a minimal model for subvisible cirrus clouds (SVCs), which might be used in future work for the development of parameterisations for coarse large-scale models, representing structures of clouds.

Modelling micro- and macrophysical contributors to the dissipation of an Arctic mixed-phase cloud during the Arctic Summer Cloud Ocean Study (ASCOS)

Abstract. The Arctic climate is changing; temperature changes in the Arctic are greater than at midlatitudes, and changing atmospheric conditions influence Arctic mixed-phase clouds, which are important for the Arctic surface energy budget. These low-level clouds are frequently observed across the Arctic. They impact the turbulent and radiative heating of the open water, snow, and sea-ice-covered surfaces and influence the boundary layer structure. Therefore the processes that affect mixed-phase cloud life cycles are extremely important, yet relatively poorly understood. In this study, we present sensitivity studies using semi-idealized large eddy simulations (LESs) to identify processes contributing to the dissipation of Arctic mixed-phase clouds. We found that one potential main contributor to the dissipation of an observed Arctic mixed-phase cloud, during the Arctic Summer Cloud Ocean Study (ASCOS) field campaign, was a low cloud droplet number concentration (CDNC) of about 2 cm−3. Introducing a high ice crystal concentration of 10 L−1 also resulted in cloud dissipation, but such high ice crystal concentrations were deemed unlikely for the present case. Sensitivity studies simulating the advection of dry air above the boundary layer inversion, as well as a modest increase in ice crystal concentration of 1 L−1, did not lead to cloud dissipation. As a requirement for small droplet numbers, pristine aerosol conditions in the Arctic environment are therefore considered an important factor determining the lifetime of Arctic mixed-phase clouds.

Air‐Sea exchange of biogenic volatile organic compounds and the impact on aerosol particle size distributions

AbstractWe report simultaneous, underway eddy covariance measurements of the vertical flux of isoprene, total monoterpenes, and dimethyl sulfide (DMS) over the Northern Atlantic Ocean during fall. Mean isoprene and monoterpene sea‐to‐air vertical fluxes were significantly lower than mean DMS fluxes. While rare, intense monoterpene sea‐to‐air fluxes were observed, coincident with elevated monoterpene mixing ratios. A statistically significant correlation between isoprene vertical flux and short wave radiation was not observed, suggesting that photochemical processes in the surface microlayer did not enhance isoprene emissions in this study region. Calculations of secondary organic aerosol production rates (PSOA) for mean isoprene and monoterpene emission rates sampled here indicate that PSOA is on average &lt;0.1 μg m−3 d−1. Despite modest PSOA, low particle number concentrations permit a sizable role for condensational growth of monoterpene oxidation products in altering particle size distributions and the concentration of cloud condensation nuclei during episodic monoterpene emission events from the ocean.

Microphysical sensitivity of coupled springtime Arctic stratocumulus to modelled primary ice over the ice pack, marginal ice, and ocean

Abstract. This study uses large eddy simulations to test the sensitivity of single-layer mixed-phase stratocumulus to primary ice number concentrations in the European Arctic. Observations from the Aerosol-Cloud Coupling and Climate Interactions in the Arctic (ACCACIA) campaign are considered for comparison with cloud microphysics modelled using the Large Eddy Model (LEM, UK Met. Office). We find that cloud structure is very sensitive to ice number concentrations, Nice, and small increases can cause persisting mixed-phase clouds to glaciate and break up.Three key dependencies on Nice are identified from sensitivity simulations and comparisons with observations made over the sea ice pack, marginal ice zone (MIZ), and ocean. Over sea ice, we find deposition–condensation ice formation rates are overestimated, leading to cloud glaciation. When ice formation is limited to water-saturated conditions, we find microphysics comparable to aircraft observations over all surfaces considered. We show that warm supercooled (−13 °C) mixed-phase clouds over the MIZ are simulated to reasonable accuracy when using both the DeMott et al.(2010) and Cooper(1986) primary ice nucleation parameterisations. Over the ocean, we find a strong sensitivity of Arctic stratus to Nice. The Cooper(1986) parameterisation performs poorly at the lower ambient temperatures, leading to a comparatively higher Nice (2.43 L−1 at the cloud-top temperature, approximately −20 °C) and cloud glaciation. A small decrease in the predicted Nice (2.07 L−1 at −20 °C), using the DeMott et al.(2010) parameterisation, causes mixed-phase conditions to persist for 24 h over the ocean. However, this representation leads to the formation of convective structures which reduce the cloud liquid water through snow precipitation, promoting cloud break-up through a depleted liquid phase. Decreasing the Nice further (0.54 L−1, using a relationship derived from ACCACIA observations) allows mixed-phase conditions to be maintained for at least 24 h with more stability in the liquid and ice water paths. Sensitivity to Nice is also evident at low number concentrations, where 0.1 × Nice predicted by the DeMott et al.(2010) parameterisation results in the formation of rainbands within the model; rainbands which also act to deplete the liquid water in the cloud and promote break-up.

Health effects of laser printer emissions: a controlled exposure study.

Ultrafine particles emitted from laser printers are suspected to elicit adverse health effects. We performed 75-minute exposures to emissions of laser printing devices (LPDs) in a standardized, randomized, cross-over manner in 23 healthy subjects, 14 mild, stable asthmatics, and 15 persons reporting symptoms associated with LPD emissions. Low-level exposures (LLE) ranged at the particle background (3000cm-3 ) and high-level exposures (HLE) at 100000cm-3 . Examinations before and after exposures included spirometry, body plethysmography, transfer factors for CO and NO (TLCO, TLNO), bronchial and alveolar NO, cytokines in serum and nasal secretions (IL-1β, IL-5, IL-6, IL-8, GM-CSF, IFNγ, TNFα), serum ECP, and IgE. Across all participants, no statistically significant changes occurred for lung mechanics and NO. There was a decrease in volume-related TLNO that was more pronounced in HLE, but the difference to LLE was not significant. ECP and IgE increased in the same way after exposures. Nasal IL-6 showed a higher increase after LLE. There was no coherent pattern regarding the responses in the participant subgroups or single sets of variables. In conclusion, the experimental acute responses to short but very high-level LPD exposures were small and did not indicate clinically relevant effects compared to low particle number concentrations.

Comparison of nanoparticle generation by two plasma techniques: Dielectric barrier discharge and spark discharge

ABSTRACTDielectric barrier discharge (DBD) and spark discharge, two versatile atmospheric pressure plasma-based techniques, have been employed to generate nanoparticles. This study compares the characteristics of metal nanoparticles generated by a DBD reactor and a spark discharge generator with argon as the working gas. The gas temperature in the discharge region of the DBD reactor remained near room temperature, while that of the spark reactor varied from 470 to 1120 K and generally increased with increasing applied voltage amplitude in the range of 2–10 kV and driving frequency in the range of 1–10 kHz. Comparing to spark-generated nanoparticles under the same voltage, frequency, and flow rate, DBD-generated nanoparticles have smaller sizes, better monodispersity, and lower number concentrations. The number concentration of DBD-generated particles decreases significantly under high working voltage and frequency, while the number concentration of spark-generated particles increases with increasing worki...