Particle Mass Loading Research Articles

Particle dynamics investigation by means of shadow imaging inside an air separator

A multicamera shadow imaging (shadowgraphy) system is developed to simultaneously capture particle dynamics at multiple locations inside a so called zigzag air separator which is used for separating fine from coarse particle fractions. The adaption of the shadowgraphy system to the specific requirements of the separator apparatus to measure particle sizes and velocities including calibration and particle size correction strategies is described. Measurements reveal the behaviour of glass beads ranging from 1 to 4 mm in diameter with variable particle mass loadings and air flow rates inside the zigzag channel. From the processing of the shadow data, particle flow morphologies and characteristic particle trajectories inside the channel stages are obtained. Furthermore, it is shown that particle mean velocities and particle fluctuation energies depend on the particle mass loading, the air flow rate and the location inside the zigzag channel. The results reveal novel quantitative insights into particle velocities in such an air separator which can be used to better understand the underlying particle mechanisms and foster the development of refined process models.

Particle-to-fluid heat transfer in particle-laden turbulence

Preferential concentration of inertial particles by turbulence is a well recognized phenomenon. This study investigates how this phenomenon impacts the mean heat transfer between the fluid phase and the particle phase. Using direct numerical simulations of homogeneous and isotropic turbulent flows coupled with Lagrangian point particle tracking, we explore this phenomenon over wide range of input parameters. Among the nine independent dimensionless numbers defining this problem, we show that particle Stokes number, defined based on large eddy time, and a new identified number called heat mixing parameter have the most significant effect on particle to gas heat transfer, while variation in other non-dimensional numbers can be ignored. An investigation of regimes with significant particle mass loading, suggests that the mean heat transfer from particles to gas is hardly affected by momentum two-way coupling. Using our numerical results we propose an algebraic reduced order model for heat transfer in particle-laden turbulence.

Particle velocity and dispersion of high Stokes number particles by PTV measurements inside a transparent supersonic Cold Spray nozzle

The complexity of technical applications involving particle-laden gas flows often impedes a holistic understanding of the interplay of underlying physical aspects. The usual approach is to isolate phenomena and study them individually, forcing researchers to ignore realistic circumstances. An example is the coating formation process Cold Spray (CS), in which high Stokes number particles are accelerated in a supersonic nozzle and free jet. Along the flow, the particle laden gas undergoes extreme changes, e.g. in velocity, temperature and volume fraction, through a series of interconnected flow events for a poly-disperse distribution of particle sizes. A consequence of this complexity is an under-representation of research on the fluid-mechanics in this field. This manuscript aims to build a bridge between empirical testing in CS and more fundamental aspects of the relevant fluid mechanics: Parameters associated with the multi-phase character of the process are not yet well understood. In this sense, the particle mass loading is often ignored, so are particle-particle interactions and the strong variations of local conditions. Previous work has indicated that there is no conclusive understanding of the phase interaction mechanisms in CS beyond high-Mach number drag laws. In order to start filling this gap, the first experiment for the direct observation of the particle behaviour within a CS nozzle is designed. Rectangular de-Laval nozzles are manufactured from quartz glass and particle tracking velocimetry (PTV) is used to obtain particle velocities and positions at the injection zone, throughout the nozzle and in the supersonic jet under varying operating conditions. This study firstly reports the direct measurement of particle injection, acceleration, and dispersion in CS. It suggests physical explanations based on a statistical evaluation of the observed data and forms the basis for more fundamental understanding of CS fluid mechanics.

The Effect of Oxygen on Organic Haze Properties

Abstract Atmospheric organic hazes are present on many planetary bodies, possibly including the ancient Earth and exoplanets, and can greatly influence surface and atmospheric properties. Here we examine the physical and optical properties of organic hazes produced with molecular nitrogen, methane, carbon dioxide, and increasing amounts of molecular oxygen, and compare them to hazes produced without added oxygen. As molecular oxygen is included in increasing amounts from 0 to 200 ppmv, the mass loading of haze produced decreases nonlinearly. With 200 ppmv molecular oxygen, the mass loading of particles produced is on the order of the amount of organic aerosol in modern Earth’s atmosphere, suggesting that while not a thick organic haze, haze particles produced with 200 ppmv molecular oxygen could still influence planetary climates. Additionally, the hazes produced with increasing amounts of oxygen become increasingly oxidized and the densities increase. For hazes produced with 0, 2 and 20 ppmv oxygen, the densities were found to be 0.94, 1.03 and 1.12 g cm−3, respectively. Moreover, the hazes produced with 0, 2, and 20 ppmv oxygen are found to have real refractive indices of n = 1.58 ± 0.04, 1.53 ± 0.03 and 1.67 ± 0.03, respectively, and imaginary refractive indices of , 0.002 ± 0.002 and , respectively. These k values demonstrate that the particles formed with oxygen have no absorption within our experimental error, and could result in a light scattering layer in an oxygen-containing atmosphere.

Characterization of a catalyst-based conversion technique to measure total particulate nitrogen and organic carbon and comparison to a particle mass measurement instrument

Abstract. The chemical composition of aerosol particles is a key aspect in determining their impact on the environment. For example, nitrogen-containing particles impact atmospheric chemistry, air quality, and ecological N deposition. Instruments that measure total reactive nitrogen (Nr = all nitrogen compounds except for N2 and N2O) focus on gas-phase nitrogen and very few studies directly discuss the instrument capacity to measure the mass of Nr-containing particles. Here, we investigate the mass quantification of particle-bound nitrogen using a custom Nr system that involves total conversion to nitric oxide (NO) across platinum and molybdenum catalysts followed by NO−O3 chemiluminescence detection. We evaluate the particle conversion of the Nr instrument by comparing to mass-derived concentrations of size-selected and counted ammonium sulfate ((NH4)2SO4), ammonium nitrate (NH4NO3), ammonium chloride (NH4Cl), sodium nitrate (NaNO3), and ammonium oxalate ((NH4)2C2O4) particles determined using instruments that measure particle number and size. These measurements demonstrate Nr-particle conversion across the Nr catalysts that is independent of particle size with 98 ± 10 % efficiency for 100–600 nm particle diameters. We also show efficient conversion of particle-phase organic carbon species to CO2 across the instrument's platinum catalyst followed by a nondispersive infrared (NDIR) CO2 detector. However, the application of this method to the atmosphere presents a challenge due to the small signal above background at high ambient levels of common gas-phase carbon compounds (e.g., CO2). We show the Nr system is an accurate particle mass measurement method and demonstrate its ability to calibrate particle mass measurement instrumentation using single-component, laboratory-generated, Nr-containing particles below 2.5 µm in size. In addition we show agreement with mass measurements of an independently calibrated online particle-into-liquid sampler directly coupled to the electrospray ionization source of a quadrupole mass spectrometer (PILS–ESI/MS) sampling in the negative-ion mode. We obtain excellent correlations (R2 = 0.99) of particle mass measured as Nr with PILS–ESI/MS measurements converted to the corresponding particle anion mass (e.g., nitrate, sulfate, and chloride). The Nr and PILS–ESI/MS are shown to agree to within ∼ 6 % for particle mass loadings of up to 120 µg m−3. Consideration of all the sources of error in the PILS–ESI/MS technique yields an overall uncertainty of ±20 % for these single-component particle streams. These results demonstrate the Nr system is a reliable direct particle mass measurement technique that differs from other particle instrument calibration techniques that rely on knowledge of particle size, shape, density, and refractive index.

Theoretical analysis and simulation of methane/air flame inhibition by sodium bicarbonate particles

The capacity of sodium bicarbonate (NaHCO3)s powder to chemically reduce flame speeds and mitigate the effects of accidental explosions is well established. The inhibition of premixed hydrocarbon/air flames by monodisperse (NaHCO3)s solid particles is investigated, here, using theory and numerical simulations. First, an analytical solution for the temperature history of a solid (NaHCO3)s particle crossing a flame shows that the size of the largest (NaHCO3)s particle which can decompose inside the flame front, and act on chemical reactions efficiently, strongly depends on the flame speed. For various fuels and a wide range of equivalence ratios, particles with a strong potential for flame inhibition are identified: hence a criterion, on the maximum particle size, for efficient inhibition is proposed. Thereafter, a one-dimensional methane/air flame traveling in a premixed gas loaded with sodium bicarbonate is simulated using a chemical mechanism based on GRI-Mech, extended to include inhibition chemistry and reduced to 20 species with a DRGEP method (Pepiot-Desjardins and Pitsch, 2008). Inhibitor particle size and mass loading are varied to study the flame response to inhibition by (NaHCO3)s powders. Finally, two-dimensional simulations of a planar flame traveling in a flow with a non-uniform inhibitor mass loading distribution are analyzed. In the case of strong particle stratification, an acceleration of the flame is observed, instead of a mitigation. This fundamental mechanism may limit the actual potential of inhibition powders in real configurations.

Controlled deposition of size-selected MnO nanoparticle thin films for water splitting applications: reduction of onset potential with particle size

Emulating water oxidation catalyzed by the oxomanganese clusters in the photosynthetic apparatus of plants has been a long-standing scientific challenge. The use of manganese oxide films has been explored, but while they may be catalytically active on the surface, their poor conductivity hinders their overall performance. We have approached this problem by using manganese oxide nanoparticles with sizes of 4, 6 and 8 nm, produced in a sputter-gas-aggregation source and soft-landed onto conducting electrodes. The mass loading of these catalytic particles was kept constant and corresponded to 45%–80% of a monolayer coverage. Measurements of the water oxidation threshold revealed that the onset potential decreases significantly with decreasing particle size. The final stoichiometry of the catalytically active nanoparticles, after exposure to air, was identified as predominantly MnO. The ability of such a sub-monolayer film to lower the reaction threshold implies that the key role is played by intrinsic size effects, i.e., by changes in the electronic properties and surface fields of the nanoparticles with decreasing size. We anticipate that this work will serve to bridge the knowledge gap between bulk thick film electrocatalysts and natural photosynthetic molecular-cluster complexes.

Gas-particle turbulent flow of foursquare tangential jets in a simplified pulverized-coal firing boiler

An experimental cold-model of a simplified tangential firing boiler was established to investigate the mesoscale turbulent flow behaviors, including gas vortex structures, particle motions and interactions between two phases. A modified PIV technology, employing two pairs of lasers and cameras, was applied to measure the velocity and velocity gradient of turbulent flow in foursquare tangential jets alternatively. At a given initial gas velocity and particle mass loading, the interaction between gas and particles was studied at three different particle sizes. It was found that two main coherent vortex structures, circular eddy and hairpin eddy, distributed mainly in low speed area and heavy impingement area, respectively. The characteristics of particle motion in foursquare tangential jets correlated with gas turbulence dissipation, particle size, particle concentration and particle density. Small particles were easily entrained by gas vortex, so that they consumed more turbulence energy and attenuated the gas turbulence intensity. On the contrary, large particles had more inertia and led to heavier impingement in the chamber center, resulting in particle random distribution and complex momentum transfer between gas and particles. Moreover, large particles stretched the coherent vortex to be narrow and long, while small particles pulled down the vortices rotation intensity.

Characterization of Mega-Dalton-Sized Nanoparticles by Superconducting Tunnel Junction Cryodetection Mass Spectrometry.

The characterization of nanomaterials is critical to understand the size/structure-dependent properties of these particles. In this report, a form of heavy ion mass spectrometry, namely, superconducting tunnel junction (STJ) cryodetection mass spectrometry (MS) is used to characterize quantum dot semiconductor nanocrystals and gold nanoparticles. The nanoparticles studied ranged in mass from 200 kDa to >1.5 MDa and included lead sulfide quantum dots, various cadmium selenide and/or telluride-based core-shell quantum dots coated with different ligands, and gold nanoparticles. Nanoparticles were ionized by both matrix-assisted laser desorption ionization (MALDI) and laser desorption ionization (LDI), shot with an aimed ion gun into a flight tube, mass separated by time-of-flight (TOF), and detected by an energy-sensitive STJ cryodetector. STJ cryodetection MS can be used to analyze intact heterogeneous nanoparticles, allowing determination of average particle mass, dispersity, and ligand loading. Some nanoparticles, however, do undergo fragmentation during the MALDI or LDI-TOF mass analyses. The measurement of the energy deposited into the detector was found to be different for different types of particles. Metastable fragments from these nanoparticles were observed at lower energies. The lower energies deposited for metastable fragments can provide insight into the stability and surface compositions of these materials. Cadmium selenide core-shell quantum dots (655 nm emission) conjugated to biomacromolecules, such as cholera toxin B and human serum transferrin, were also analyzed. When compared to unconjugated particles by mass, it was determined that ∼96 cholera toxin B and ∼14 transferrin proteins were attached to the surface of these nanoparticles.

Numerical analysis of mitigating elbow erosion with a rib

Particle erosion is an ongoing problem in many engineering fields. In this work, a trapezoidal rib installed at different positions on the extrados of a 90° elbow is investigated numerically with the intent of mitigating the erosion. The CFD-DPM Eulerian-Lagrangian approach is employed to evaluate the anti-erosion effect. The computational model is validated by comparing the predicted CFD erosion magnitudes to the present and previous experimental data for a standard elbow. An ellipse erosion zone with a vee-shaped scar is formed on the extrados due to the first and second particle impacts. The rib placed in front of the first impingement can partly protect the elbow from the direct impacts. As a sacrificial element, the rib itself becomes more prone to erosion. A reduction of elbow erosion peak up to 31.4% can be achieved by placing the rib at θ=25°. However, the erosion resistance is reduced as the rib moves backward. As the flow velocity increases, the sacrificial speed of the rib is accelerated while the anti-erosion effect is weakened. The larger the particle mass loading, the severer the elbow erosion. Taking the sacrificial speed of the rib and the anti-erosion effect into account, placing the rib at θ=25° is a good choice for such measure.

Effect of relative humidity on the composition of secondary organic aerosol from the oxidation of toluene

Abstract. The effect of relative humidity (RH) on the chemical composition of secondary organic aerosol (SOA) formed from low-NOx toluene oxidation in the absence of seed particles was investigated. SOA samples were prepared in an aerosol smog chamber at < 2 % RH and 75 % RH, collected on Teflon filters, and analyzed with nanospray desorption electrospray ionization high-resolution mass spectrometry (nano-DESI–HRMS). Measurements revealed a significant reduction in the fraction of oligomers present in the SOA generated at 75 % RH compared to SOA generated under dry conditions. In a separate set of experiments, the particle mass concentrations were measured with a scanning mobility particle sizer (SMPS) at RHs ranging from < 2 to 90 %. It was found that the particle mass loading decreased by nearly an order of magnitude when RH increased from < 2 to 75–90 % for low-NOx toluene SOA. The volatility distributions of the SOA compounds, estimated from the distribution of molecular formulas using the “molecular corridor” approach, confirmed that low-NOx toluene SOA became more volatile on average under high-RH conditions. In contrast, the effect of RH on SOA mass loading was found to be much smaller for high-NOx toluene SOA. The observed increase in the oligomer fraction and particle mass loading under dry conditions were attributed to the enhancement of condensation reactions, which produce water and oligomers from smaller compounds in low-NOx toluene SOA. The reduction in the fraction of oligomeric compounds under humid conditions is predicted to partly counteract the previously observed enhancement in the toluene SOA yield driven by the aerosol liquid water chemistry in deliquesced inorganic seed particles.

Investigation of turbulence and skin friction modification in particle-laden channel flow using lattice Boltzmann method

Interaction between turbulence and particles is investigated in a channel flow. The fluid motion is calculated using direct numerical simulation (DNS) with a lattice Boltzmann (LB) method, and particles are tracked in a Lagrangian framework through the action of force imposed by the fluid. The particle diameter is smaller than the Kolmogorov length scale, and the point force is used to represent the feedback force of particles on the turbulence. The effects of particles on the turbulence and skin friction coefficient are examined with different particle inertias and mass loadings. Inertial particles suppress intensities of the spanwise and wall-normal components of velocity, and the Reynolds shear stress. It is also found that, relative to the reference particle-free flow, the overall mean skin-friction coefficient is reduced by particles. Changes of near wall turbulent structures such as longer and more regular streamwise low-speed streaks and less ejections and sweeps are the manifestation of drag reduction.

Effects of particle mass loading on the hydrodynamics and separation efficiency of a cyclone separator

Abstract The effect of the particle mass loading (1.6–115.3 g/m3) on the performances of a cyclone separator is studied by two-way coupling CFD simulation and experiments. The increasing of the particle mass loading enriches the particles at the wall region. At lower inlet air velocity, the separation efficiency increases with the increasing of the particle mass loading due to the larger particle sweeping effects and the aggregation of smaller particles. The full elastic particle–wall collision and the perfect dust box bottom collection assumptions cause CFD simulation overpredicting the separation efficiency of smaller particles. A partial elastic particle–wall collision assumption overcame the problem and reduced the calculated separation efficiency. Our CFD simulation can reasonably predict the separation efficiency at different particle mass loadings.

Non-intrusive temperature measurement of particles in a fluidised bed heated by well-characterised radiation

We report an important step towards the in-situ measurement of heat transfer in particle-laden flows via direct measurement of the temperatures of fluidised particles. Laser-induced phosphorescence (LIP) was employed to provide non-intrusive, temporally resolved and in-situ measurement of suspended particles as a function of heat flux and radiation attenuation. Excitation was performed at 355 nm with a repetition rate of 1.67 Hz. Particles were transported with dry air within an optically-accessible fluidised bed and heated with a well-defined source of high-flux radiation from a 3 kW solid-state solar thermal simulator radiation to achieve heating rates in order 23,000°/s. Particle and gas temperatures were measured simultaneously with the former determined from thermo-phosphorescent emissions following excitation at 355 nm. Irradiation flux and mass loading were found to play important roles in particle and gas temperature rise. Confidence in the method was obtained by verifying internal consistency between the energy absorbed by the particles and the temperature rise of the gas phase, taking into account the variability of particle mass loading.

Size-resolved particle measurements of polybrominated diphenyl ethers indoors: Implications for sources and human exposure.

Polybrominated diphenyl ethers (PBDEs) are flame retardant polymer additives that are widely detected in outdoor and indoor environments. Release of PBDEs from consumer products leads to high concentrations indoors, but mechanisms of release are poorly understood. Although ingestion of dust is a well-studied indoor PBDE exposure route, the importance of inhalation exposure is uncertain. To address these unknowns, dust was collected from household vacuum cleaners, and suspended particulate matter was collected from the same homes in St. John's, Newfoundland, Canada, using a cascade impactor. Size-fractionated particulate matter samples (0.01-18 μm diameter) were analyzed for PBDEs. The sum of PBDEs in all particulate matter ranged from 8.7 ± 0.5 to 15.7 ± 0.5 pg/m3 , with >50% of PBDE mass in respirable particulate matter (<1 μm). Mass loadings as a function of particle size suggested that both abrasion and off-gassing led to the presence of PBDEs in particulate matter. Variability in the particulate matter mass loadings indicated that emission mechanisms were both product- and location-dependent. Congener profiles in colocated vacuum dust and particulate matter samples were different, indicating that vacuum dust cannot accurately predict PBDE congeners in respirable particulate matter. A calculated lower limit inhalation exposure to PBDEs (0.19 ng/d) is lower than exposure via diet or ingestion of dust, although the different biochemical pathways for inhalation compared with ingestion may have different biological effects. The present study highlights the importance of contaminant analysis in size-fractionated particulate matter to assess human exposure via inhalation compared with traditional vacuum dust methods. Environ Toxicol Chem 2018;37:481-490. © 2017 SETAC.

Mass loading of particles in the supply ducts of mechanical ventilation systems in homes

The objective of this study was to measure the mass and number loading of particles in supply ducts of homes with different mechanical fan operation conditions. Fifteen occupied single-family homes were selected from three multi-family residential complexes located in suburban areas of Seoul. The sample homes have mechanical ventilation systems that operate independently of heating and cooling devices. Field measurements consisted of three parts: a questionnaire regarding the indoor environment and occupant behavior related to ventilation; measurements of size resolved particle concentrations before and after operating the mechanical fan; an inspection of the proper installation of a filter unit and airflow in the supply ducts. The PM10 mass loading in the supply ducts ranged from 13.0 to 450 mg/m2. The mass and number loading of particles in the supply ducts increased exponentially according to the built year of homes. The averaged PM10 loadings for two, five, and seven years after built were 11.6, 39.0, and 114.8 mg/m2, respectively. Most of the occupants, 10 of 15 (67%), did not use mechanical fans to ventilate their homes, and the operation time of the mechanical fan significantly influenced on the particle loading rate in the supply ducts.

Properties of particulate pollution in the port city of Valparaiso, Chile

The city of Valparaiso is home to one of the largest commercial ports on the west coast of South America. Port activities, that continue year-round, 24 h a day and seven days a week, produce emissions of pollutants, particularly aerosol particles composed of black and brown carbon (BC and BrC) that have serious impact on human population and the local environment. A measurement program was launched to document the magnitude of selected pollutants, to identify their sources and to evaluate the meteorological processes that enhance and transport these pollutants locally and regionally. In this study, we report the measurements made during four months: 25July - 25August 2014 (referred to as August 2014 throughout the manuscript), December 2014, January 2015 and March 2015. The daily mass concentrations of equivalent black carbon (eBC), derived from measurements of the light absorption coefficient, regularly exceed 5 μg m−3, a magnitude similar to values found in megacities such as Mexico City. The daily maximum number concentration of condensation nuclei (CN) is usually larger than 30000 cm−3. The Angstrom absorption exponent (AAE), derived from the absorption coefficients at 550 nm and 870 nm, is used to identify the primary sources of BC and BrC. In colder weather, emissions from the diesel fueled buses and trucks and the consumption of kerosene and wood for residential heating are the main sources of BC. In December, local wildfires contributed to the particle mass loading, but the day-to-day variability in boundary layer height and the presence of clouds and fog in occasions inhibited high concentrations. In March, the port activities reach a yearly peak during the seasonal export of agricultural products that translates into much more ship and truck traffic leading to very high eBC concentrations, comparable to values observed during August. The variability in weather patterns underscores the complexity of meteorological processes that drive the evolution and transport of pollution in Valparaiso.

Numerical modeling and simulation of particulate fouling of structured heat transfer surfaces using a multiphase Euler-Lagrange approach

A CFD-based multiphase method for the numerical modeling and simulation of particulate fouling of structured heat transfer surfaces is presented and validated using different benchmarks (turbulent particle-laden backward-facing step and channel flow) available in the literature. The proposed procedure is based on a coupling of the Lagrangian-Particle-Tracking (LPT) and Eulerian approach. Therefore, suspended particles are simulated according to their natural behavior by means of LPT as solid spherical particles, whereas the carrier phase is simulated using the Eulerian approach. Large eddy simulations (LES) are performed for fully developed turbulent channel flows at Reτ=395 with selected structured surfaces (single square cavity or spherical dimple) considering a depth/diameter ratio of t/D=0.26 and foulant particle mass loading ratios up to β=ṁp/ṁf=2×10-3 using a dynamic one equation eddy-viscosity turbulence model. These simulations demonstrate the great capabilities of the proposed method and reveal a slightly better fouling performance and thermo-hydraulic efficiency of the spherical dimple, due to the existence of asymmetric vortex structures compared to the square cavity.

Nitrate radical oxidation of &amp;lt;i&amp;gt;γ&amp;lt;/i&amp;gt;-terpinene: hydroxy nitrate, total organic nitrate, and secondary organic aerosol yields

Abstract. Polyolefinic monoterpenes represent a potentially important but understudied source of organic nitrates (ONs) and secondary organic aerosol (SOA) following oxidation due to their high reactivity and propensity for multi-stage chemistry. Recent modeling work suggests that the oxidation of polyolefinic γ-terpinene can be the dominant source of nighttime ON in a mixed forest environment. However, the ON yields, aerosol partitioning behavior, and SOA yields from γ-terpinene oxidation by the nitrate radical (NO3), an important nighttime oxidant, have not been determined experimentally. In this work, we present a comprehensive experimental investigation of the total (gas + particle) ON, hydroxy nitrate, and SOA yields following γ-terpinene oxidation by NO3. Under dry conditions, the hydroxy nitrate yield = 4(+1/−3) %, total ON yield = 14(+3/−2) %, and SOA yield ≤ 10 % under atmospherically relevant particle mass loadings, similar to those for α-pinene + NO3. Using a chemical box model, we show that the measured concentrations of NO2 and γ-terpinene hydroxy nitrates can be reliably simulated from α-pinene + NO3 chemistry. This suggests that NO3 addition to either of the two internal double bonds of γ-terpinene primarily decomposes forming a relatively volatile keto-aldehyde, reconciling the small SOA yield observed here and for other internal olefinic terpenes. Based on aerosol partitioning analysis and identification of speciated particle-phase ON applying high-resolution liquid chromatography–mass spectrometry, we estimate that a significant fraction of the particle-phase ON has the hydroxy nitrate moiety. This work greatly contributes to our understanding of ON and SOA formation from polyolefin monoterpene oxidation, which could be important in the northern continental US and the Midwest, where polyolefinic monoterpene emissions are greatest.

Quantifying the mass loading of particles in an ash cloud remobilized from tephra deposits on Iceland

Abstract. On 16–17 September 2013 strong surface winds over tephra deposits in southern Iceland led to the resuspension and subsequent advection of significant quantities of volcanic ash. The resulting resuspended ash cloud was transported to the south-east over the North Atlantic Ocean and, due to clear skies at the time, was exceptionally well observed in satellite imagery. We use satellite-based measurements in combination with radiative transfer and dispersion modelling to quantify the total mass of ash resuspended during this event. Typically ash clouds from explosive eruptions are identified in satellite measurements from a negative brightness temperature difference (BTD) signal; however this technique assumes that the ash resides at high levels in the atmosphere. Due to a temperature inversion in the troposphere over southern Iceland during 16 September 2013, the resuspended ash cloud was constrained to altitudes of &lt; 2 km a.s.l. We show that a positive BTD signal can instead be used to identify ash-containing pixels from satellite measurements. The timing and location of the ash cloud identified using this technique from measurements made by the Visible Infrared Imaging Radiometer Suite (VIIRS) on board the Suomi National Polar-orbiting Partnership (NPP) satellite agree well with model predictions using the dispersion model NAME (Numerical Atmospheric-dispersion Modelling Environment). Total column mass loadings are determined from the VIIRS data using an optimal estimation technique which accounts for the low altitude of the resuspended ash cloud and are used to calibrate the emission rate in the resuspended ash scheme in NAME. Considering the tephra deposits from the recent eruptions of Eyjafjallajökull and Grímsvötn as the potential source area for resuspension for this event, we estimate that ∼ 0.2 Tg of ash was remobilized during 16–17 September 2013.