Virtual Impactor Research Articles

Overview of the Cumulus Humilis Aerosol Processing Study

The primary goal of the Cumulus Humilis Aerosol Processing Study (CHAPS) was to characterize and contrast freshly emitted aerosols below, within, and above fields of cumuli, and to study changes to the cloud microphysical structure within these same cloud fields in the vicinity of Oklahoma City during June 2007. CHAPS is one of few studies that have had an aerosol mass spectrometer (AMS) sampling downstream of a counterflow virtual impactor (CVI) inlet on an aircraft, allowing the examination of the chemical composition of activated aerosols within the cumuli. The results from CHAPS provide insights into changes in the aerosol chemical and optical properties as aerosols move through shallow cumuli downwind of a moderately sized city. Three instrument platforms were employed during CHAPS, including the U.S. Department of Energy Gulfstream-1 aircraft, which was equipped for in situ sampling of aerosol optical and chemical properties; the NASA Langley King Air B200, which carried the downward-looking NASA Langley High Spectral Resolution Lidar (HSRL) to measure profiles of aerosol backscatter, extinction, and depolarization between the King Air and the surface; and a surface site equipped for continuous in situ measurements of aerosol optical properties, profiles of aerosol backscatter, and meteorological conditions, including total sky cover and thermodynamic profiles of the atmosphere. In spite of record precipitation over central Oklahoma, a total of 8 research flights were made by the G-l and 18 by the B200, including special satellite verification flights timed to coincide with NASA satellite A-Train overpasses.

EURONEAR: Data mining of asteroids and Near Earth Asteroids

AbstractBesides new observations, mining old photographic plates and CCD image archives represents an opportunity to recover and secure newly discovered asteroids, also to improve the orbits of Near Earth Asteroids (NEAs), Potentially Hazardous Asteroids (PHAs) and Virtual Impactors (VIs). These are the main research aims of the EURONEAR network. As stated by the IAU, the vast collection of image archives stored worldwide is still insufficiently explored, and could be mined for known NEAs and other asteroids appearing occasionally in their fields. This data mining could be eased using a server to search and classify findings based on the asteroid class and the discovery date as “precoveries” or “recoveries”. We built PRECOVERY, a public facility which uses the Virtual Observatory SkyBoT webservice of IMCCE to search for all known Solar System objects in a given observation. To datamine an entire archive, PRECOVERY requires the observing log in a standard format and outputs a database listing the sorted encounters of NEAs, PHAs, numbered and un‐numbered asteroids classified as precoveries or recoveries based on the daily updated IAU MPC database. As a first application, we considered an archive including about 13 000 photographic plates exposed between 1930 and 2005 at the Astronomical Observatory in Bucharest, Romania. Firstly, we updated the database, homogenizing dates and pointings to a common format using the JD dating system and J2000 epoch. All the asteroids observed in planned mode were recovered, proving the accuracy of PRECOVERY. Despite the large field of the plates imaging mostly 2.27° × 2.27° fields, no NEA or PHA could be encountered occasionally in the archive due to the small aperture of the 0.38m refractor insufficiently to detect objects fainter than V ∼ 15. PRECOVERY can be applied to other archives, being intended as a public facility offered to the community by the EURONEAR project. This is the first of a series of papers aimed to improve orbits of PHAs and NEAs using precovered data derived from archives of images to be data mined in collaboration with students and amateurs. In the next paper we will search the CFHT Legacy Survey, while data mining of other archives is planned for the near future (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Determination of elemental composition of air particulates and soils in Khartoum area

Investigations were carried out for elemental composition of air particulates in the background air and near roadsides in Khartoum area. Investigations were also performed for the elemental composition of soils at the same locations. A cyclone and a dichotomous virtual impactor were used to measure the air particulates. The cyclone was adjusted to collect particles having an aerodynamic diameter of 2.5!m. The virtual impactor, through its fine channel, was capable of collecting airborne particles with an aerodynamic diameter of 2.5 μm. Energy Dispersive X-Ray Fluorescence (EDXRF) analysis was used to study the elemental concentrations of the air and soil samples. The analysis of the results indicated that all elements in the proximity of roadsides have elevated concentrations compared to the background air levels. Enrichment factors were calculated relative to crust rock and Khartoum soil. The results showed that the elements K, Ca, Ti, Fe, and Sr in the aerosols have their origin from the soil, while the elements Zn, Ni and Pb have their source from automobile emissions. The results also indicated a correlation between lead and bromine. The lead to bromine ratio was found to be within the range of those derived from vehicular exhaust, and in good agreement with the ratios obtained from some other countries.

Elemental content of aerosol particles in an underground tram station

AbstractParticulate matter is an important air pollutant, especially in closed environments like a tunnel. The aim of this study was to determine the mass, black carbon, and elemental concentrations of particulate matter of two size fractions at an underground tram station in Hammarkullen, Gothenburg, Sweden. Samples were collected during June 2007 using a dichotomous virtual impactor separating the sampled aerosol particles into coarse (PM(2.5–10)) and fine (PM2.5) fractions. To minimize the possible influence of waiting passengers, the platform for trams going towards the suburb Angered was chosen. The elemental analysis of the samples, collected on Teflon filters, was carried out using energy dispersive x‐ray fluorescence (EDXRF) spectrometry, resulting in concentrations of 14 elements in most of the samples. Principal component analysis (PCA) was applied to identify possible sources for the elements in the particles. Owing to the tunnel environment, the elemental difference between the fine and coarse particle fractions was not as large as that in similar particles collected under normal outdoor ambient conditions. Likewise, the influence of the local weather situation was not significant. Particle content from the tram traffic was identified by PCA, with Fe being the major element in both coarse and fine particles. The particle mass concentration was higher in the tunnel compared to the ambient concentration at the monitoring station Femman in downtown Gothenburg. In some days, the mass concentration exceeded the Swedish daily ambient air quality standard of 50 µg m−3, but it was lower than the limits in the environmental work act, 5 mg m−3. Copyright © 2009 John Wiley & Sons, Ltd.

Stagnation Point Displacement: Control of Losses on a Conically Shaped Aerosol Distributor

A cone was placed just upstream of the second stage of a Two-Stage Circumferential Slot Virtual Impactor in an attempt to uniformly distribute 10 μm aerodynamic diameter (AD) aerosol particles so a circumferential inlet of the second stage, which was located below the cone, could uniformly aspirate aerosol. Large losses were observed near the apex of the cone; however, the losses can be significantly reduced by injecting a small counter-flow jet of sheath flow through the apex of the cone. The jet displaces the stagnation point of the main flow and thereby alters the particle trajectories. Computational Fluid Dynamics (CFD) was the primarily tool used to investigate the concept through simulating the effects of different operational conditions such as the ratio of counterflow jet velocity to main flow velocity and the Stokes number. The velocity of the counterflow jet should be approximately 1–2 times the main airflow velocity to achieve low particle losses. The jet becomes asymmetric when the ratio of it...

A New Semivolatile Aerosol Dichotomous Sampler

This study reports the results of a numerical investigation and an experimental study on a round nozzle virtual impactor (VI) operated in two different modes. The newly proposed sampler, the semivolatile aerosol dichotomous sampler (SADS), was studied to overcome some of the problems of existing personal sampling methods such as evaporative loss during filter sampling. The main difference between VIs and the SADS was the inverted flow ratio between the major flow and the minor flow. Sampling in the SADS settings gives a lower cutsize in both numerical simulations and experimental results. Whereas the 50% separation efficiency for a VI occurred in numerical simulations when the square root of Stokes number equaled 0.97, the 50% efficiency for the same sampler run in the SADS settings occurred when the square root of the Stokes number was 0.27. The back pressure on each flow direction was studied and greater pressure drop was observed through the vapor flow in SADS settings. Sampling using a SADS was more effective than traditional filter methods because of its smaller cutsize, instant separation of vapor from particles and reduced particle losses.

New bio-aerosol collector using a micromachined virtual impactor

For collection and concentration of bioaerosols, we designed and evaluated a single stage virtual impactor, which was fabricated by micro-electro-mechanical systems (MEMS) process. The cut-off diameter of 1 μm was selected, since 1 μm is the lowest size as used in the US Government Joint Biological Point Detection System [Haglund, J. S., & McFarland, A. R. (2004). A circumferential slot virtual impactor. Aerosol Science and Technology, 38, 664–674; Moshier, T., & Buonaugurio, T. (2000). Joint Biological Point Detection System (JBPDS) requirements and design interplay. Proceedings of the First Joint Conference on Point Detection for Chemical and Biological Defense, October 23–27, 2000, Williamsburg, VA.] The design value of a 1 μm cut-off diameter required a nozzle width and thickness of 880 and 200 μm, respectively. The virtual impactor was evaluated for physical and biological collection efficiencies. For the performance evaluation of physical collection efficiency and wall loss, polystyrene latex (PSL) particles were generated from an atomizer and their size distribution was measured using an aerodynamic particle sizer (APS, TSI model 3321) and a scanning mobility particle sizer (SMPS, TSI model 3936). The measured cut-off diameter was 0.95 μm, which agreed with the calculated results (=0.94 μm) determined with a commercial computational fluid dynamics (CFD) package, FLUENT, and the measured wall loss was below 33.5%. For the performance evaluation of biological collection efficiency, Staphylococcus epidermidis bioaerosols were dispersed into air by a nebulizer. The bioaerosols were measured using APS and sampled with a bioaerosol sampler. The overall physical collection efficiency based on the number concentration was 73.8±3%, which was similar to the one based on the number of colonies (=76.7±7%). We found that most of the bioaerosols collected and concentrated by our virtual impactor were viable.

A hybrid chip based on aerodynamics and electrostatics for the size-dependent classification of ultrafine and nano particles

Conventional virtual impactors experience a large pressure drop when they classify particles according to size, in particular ultrafine particles smaller than 100 nm in diameter. Therefore, most virtual impactors have been used to classify particles larger than 100 nm. Their cut-off diameters are also fixed by the geometry of their flow channels. In the proposed virtual impactor, particles smaller than 100 nm are accelerated by applying DC potentials to an integrated electrode pair. By the electrical acceleration, the large pressure drop could be significantly decreased and new cut-off diameters smaller than 100 nm could be successfully added. The geometric cut-off diameter (GCD) of the proposed virtual impactor was designed to be 1.0 microm. Performances including the GCD and wall loss were examined by classifying dioctyl sebacate of 100 to 600 nm in size and carbon particles of 0.6 to 10 microm in size. The GCD was measured to be 0.95 microm, and the wall loss was highest at 1.1 microm. To add new cut-off diameters, monodisperse NaCl particles ranging from 15 to 70 nm were classified using the proposed virtual impactor with applying a DC potential of 0.25 to 3.0 kV. In this range of the potential, the new cut-off diameters ranging from 15 to 35 nm was added.

Iodine speciation in rain, snow and aerosols

Abstract. Iodine oxides, such as iodate, should be the only thermodynamically stable sink species for iodine in the troposphere. However, field observations have increasingly found very little iodate and significant amounts of iodide and soluble organically bound iodine (SOI) in precipitation and aerosols. The aim of this study was to investigate iodine speciation, including the organic fraction, in rain, snow, and aerosols in an attempt to further clarify aqueous phase iodine chemistry. Diurnal aerosol samples were taken with a 5 stage cascade impactor and a virtual impactor (PM2.5) from the Mace Head research station, Ireland, during summer 2006. Rain was collected from Australia, New Zealand, Patagonia, Germany, Ireland, and Switzerland and snow was obtained from Greenland, Germany, Switzerland, and New Zealand. Aerosols were extracted from the filters with water and all samples were analysed for total soluble iodine (TSI) by inductively coupled plasma mass spectrometry (ICP-MS) and iodine speciation was determined by coupling an ion chromatography unit to the ICP-MS. The median concentration of TSI in aerosols from Mace Head was 222 pmol m−3 (summed over all impactor stages) of which the majority was associated with the SOI fraction (median day: 90±4%, night: 94±2% of total iodine). Iodide exhibited higher concentrations than iodate (median 6% vs. 1.2% of total iodine), and displayed significant enrichment during the day compared to the night. Interestingly, up to 5 additional, presumably anionic iodo-organic peaks were observed in all IC-ICP-MS chromatograms, composing up to 15% of the TSI. Soluble organically bound iodine was also the dominant fraction in all rain and snow samples, with lesser amounts of iodide and iodate (iodate was particularly low in snow). Two of the same unidentified peaks found in aerosols were also observed in precipitation from both Southern and Northern Hemispheres. This suggests that these species are transferred from the aerosols into precipitation and that they have either a relatively long lifetime or are rapidly recycled. It is thought that SOI is formed by reactions between HOI or I2 and organic matter derived from the ocean surface layer. SOI may then photolytically decompose to yield iodide and the unidentified species. The data in this study show that iodine oxides are the least abundant species in rain, snow, and aerosols and therefore considerably more effort is required on aqueous phase iodine chemistry for a holistic understanding of the iodine cycle.

Inorganic and black carbon aerosol concentrations at a high altitude on Mt Kenya

AbstractAerosol samples were collected at an altitude of 3678 m on Mt Kenya in August 2001. A virtual impactor was used to collect particles in fine (aerodynamic diameter, da < 2.5 µm) and coarse (2.5 µm < da < 10 µm) size fractions. The samples were analyzed for particulate mass (PM), black carbon (BC) and 15 elements. The PM concentrations varied in the ranges 3.3 ± 1.1–7.8 ± 2.5 µg m−3 (in fine fraction) and 3.7 ± 1.2–9.6 ± 3.0 µg m−3 (in coarse fraction). The fine fraction was dominated by high concentrations of BC, S and K due to particles formed during biomass burning and sulfate particles from secondary processes in the atmosphere. The coarse fraction was dominated by high concentrations of Si, S, Cl, K, Ca and Fe indicative of the presence of soil dust particles. This was further verified by enrichment factors (EFs) calculated using the elemental content of the average crustal rock. Chemical mass balance (CMB) calculations indicated that the PM was largely attributable to biomass burning, mineral dust and sulfate, while contributions from anthropogenic sources were small. Source apportionment of elemental concentrations compared well with that of an earlier study on the southwestern slope of Mt Kenya, while PM and sulfate concentrations were comparable with those observed at high‐altitude sites in North America and Europe. The observed concentrations were 5–50 times lower than those of urban Kenya. Copyright © 2008 John Wiley & Sons, Ltd.

Circumferential-Slot Virtual Impactors with Stable Flow

Flow instabilities in a virtual impactor designed for bioaerosol concentration (size range about 2 to 10 μ m AD) can seriously degrade performance. When the flow in a 100 L/min circumferential slot virtual impactor (CSVI) was unstable, the transmission efficiency was 30% for 7.2 μ m AD aerosol particles, but when the instability problems were corrected, the transmission efficiency was increased to above 90%. Three-dimensional CFD simulations have been used to examine flows in two CSVIs, a nominal 10 L/min device in which the flow was stable, and the 100 L/min device in which the flow was initially unstable. From the CFD flow patterns in the 100 L/min device, the principal instability was in the minor flow region and was caused by overly rapid flow deceleration, too large of a volume, and too low of a jet velocity in that region. Changes were made to the geometry of the CSVI, and CFD was used as the diagnostic tool to determine when stable flow was achieved. Also, for the 100 L/min unit, wake effects from ...

Single Particle Laser Mass Spectrometry Applied to Differential Ice Nucleation Experiments at the AIDA Chamber

Experiments conducted at the Aerosol Interactions and Dynamics in the Atmosphere (AIDA) chamber located in Karlsruhe, Germany permit investigation of particle properties that affect the nucleation of ice at temperature and water vapor conditions relevant to cloud microphysics and climate issues. Ice clouds were generated by heterogeneous nucleation of Arizona test dust (ATD), illite, and hematite and homogeneous nucleation of sulfuric acid. Ice crystals formed in the chamber were inertially separated from unactivated, or “interstitial” aerosol particles with a pumped counterflow virtual impactor (PCVI), then evaporated. The ice residue (i.e., the aerosol which initiated ice nucleation plus any material which was scavenged from the gas- and/or particle-phase), was chemically characterized at the single particle level using a laser ionization mass spectrometer. In this manner the species that first nucleated ice could be identified out of a mixed aerosol population in the chamber. Bare mineral dust particle...

Computational fluid dynamics simulation of virtual impactor performance: Comparison to experiment

Computational fluid dynamics (CFD) simulations were performed on a slit virtual impactor (SVI). A full-section planar model of the critical zone (nozzle) was constructed based on the measured values of geometrical dimensions of the SVI. Simulation was performed for a flow rate of 20.33 SCFH (standard cubic feet per hour) that corresponded to a Reynolds number value of 448 in the experiment. Impactor efficiency curve was computed and compared to experimental data. Details of internal wall losses were characterized and the wall loss curve was generated. Performance characteristics obtained from simulation results are in good agreement to the observed experimental trend over the complete range of Stokes numbers and the exact value of the cut-point Stokes number. Tracks for lower Stokes number particles faithfully reproduce the trend observed in the experiment, namely the regional demarcation of particle origin in the inlet nozzle, based on their final destination. Further, the effect of crossing trajectories that was visualized in the experiment for higher Stokes number particles of value of ~ 50 was captured. Additional details from the simulation results indicated that the onset of effect of crossing trajectories occurred for particles larger than a Stokes number of 6 and the collection efficiency for the above device was nearly unity over a wide range of Stokes number (Stk ~ 2 to 125) values.

Impact of Biomass Combustion on Urban Fine Particulate Matter in Central and Northern Europe

The impact of biomass combustion on atmospheric particulate matter was investigated at Central and Northern European urban background sites (Duisburg, Prague, Amsterdam, Helsinki) in 2002–2003. In Helsinki, additional 4-week sampling campaigns were carried out during the four seasons in 2003–2004. During campaigns fine particles (PM2.5) and size-segregated samples were collected with a virtual impactor and a ten-stage Berner low-pressure impactor, respectively. From the aerosol samples monosaccharide anhydrides (MA) were determined as source specific tracers for biomass combustion. MA comprised 0.29–6.3% of the PM2.5 mass and 0.45–7.3% of its organic carbon content. According to size-segregated samples, the mean diameter of a prominent MA mode coincided with the accumulation mode of particulate mass, except for Prague where the MA mode appeared in a slightly smaller particle size range than the mass. The estimated contribution of biomass combustion to the OC and PM2.5 mass concentration was the highest in wintertime Prague, 79% and 37%, respectively. It seems that, in addition to traffic in densely populated areas, incomplete biomass combustion with current heating appliances can be a major source of particulate pollution both at local and regional scales.

Integrated particle detection chip for environmental monitoring

This paper reports an integrated particle detection chip for low-cost and point-of-interest environmental monitoring; it consists of a micro virtual impactor and a micro corona discharger. With this system, airborne particles are introduced into the micro virtual impactor of the chip where they are classified according to their aerodynamic diameters. The particles are then charged and their number-concentration is detected in the micro corona discharger from the electrical current carried by the charged particles. The characteristics of each component were first analyzed, and the components were then integrated into a single chip. The micro virtual impactor was designed to have a cut-off diameter of 600 nm or 1.0 microm. Its classification characteristics were examined by classifying polydisperse particles-dioctyl sebacate particles ranging in diameter from 100 to 600 nm and carbon particles ranging in diameter from 0.6 to 10 microm. From the classification results, the cut-off diameter of the micro virtual impactor was measured to be either 550 nm or 1.1 microm. The micro corona discharger was fabricated based on a sharp silicon tip and a planar electrode and charged particles at 1.3 kV. Using the integrated particle detection chip comprising the micro virtual impactor and the micro corona discharger, the sensitivity for monodisperse particles-500 nm dioctyl sebacate in diameter-was measured to be 8 x 10(-7) pA/(particle cm(-3)).

A Circumferential Slot In-Line Virtual Impactor

An In-line Virtual Impactor is presented, which has an application as a pre-separator for sampling inlets, where the device scalps large particles from the aerosol size distribution. Numerical simulation was the principal tool employed in the design process, with physical experiments used to verify computational predictions. Performance investigations were primarily carried out for a configuration that provides a nominal cutpoint particle size of 10 μ m aerodynamic diameter at an inlet flow of 111 L/min and a major flow exhaust of 100 L/min; however, the concept is scalable in terms of both flow rates and cutpoint sizes. An inverted dual cone configuration contained within a tube provides a characteristic circumferential slot of width 2.54 mm (0.100 inches) and a slot length of 239 mm (9.42 inches) at the critical zone. The upper cone causes the flow to accelerate to an average throat velocity of 3.15 m/s, while the lower cone directs the major flow toward the exit port and minimizes recirculation zones t...

Ice properties of single‐layer stratocumulus during the Mixed‐Phase Arctic Cloud Experiment: 1. Observations

During the Department of Energy's Atmospheric Radiation Measurement Program's Mixed‐Phase Arctic Cloud Experiment (M‐PACE) in fall 2004, the University of North Dakota Citation measured 53 profiles within single‐layer stratus clouds by executing spiral ascents and descents over Barrow and Oliktok Point, Alaska, and by flying ramped ascents and descents between. Cloud phase was identified from an algorithm that uses voltage change from the Rosemount ice detector, the size distribution (SD) shape measured by the Forward Scattering Spectrometer Probe (FSSP), and manual identification of particles imaged by the Cloud Particle Imager, the two‐dimensional cloud probe (2DC) and the high‐volume precipitation sampler (HVPS). Size and mass distribution functions were derived using data from the FSSP, one‐dimensional cloud probe, 2DC and HVPS in conjunction with total water content (TWC) measured by the Counterflow Virtual Impactor. With clouds defined as locations where TWC > 0.001 g m−3, there were a total of 513 30‐s averaged SDs in single‐layer clouds, of which 71% were in mixed‐phase parcels, 23% in ice‐phase and 6% in liquid‐phase. The mixed‐phase parcels were dominated by contributions from liquid drops, with the liquid mass fraction fl having averages and standard deviations of 0.89 ± 0.18 with 75% of cases having fl > 0.9. For these single‐layer clouds, fl increased with normalized cloud altitude zn, defined as linearly increasing from 0 at cloud base to 1 at cloud top with fl averaging 0.96 ± 0.13 near zn = 1 and 0.70 ± 0.30 near zn = 0. The effective radius of water droplets rew increased with zn, from an average of 6.9 ± 1.8 μm near zn = 0 to 11.4 ± 2.4 μm near zn = 1, whereas the effective radius of ice crystals rei (25.2 ± 3.9 μm) was nearly independent of zn. The averaged cloud droplet number concentration and concentrations of ice crystals with maximum dimensions greater than 53 μm were 43.6 ± 30.5 × 103 L−1 and 2.8 ± 6.9 L−1, respectively, and nearly independent of zn. In contrast to past measurements in mixed‐phase clouds combined from many geographical locations where fl increased with temperature, fl decreased from −12° to −3°C as clouds typically consisted of a liquid topped layer with precipitating ice below.

Apophis: the Story Behind the Scenes

On December 20, 2004 the Minor Planet Center issued the Minor Planet Electronic Circular (MPEC) 2004-Y25 announcing the discovery of a new Near Earth Asteroid (NEA) with designation 2004 MN4. Only two days later, when the Christmas holidays were about to begin, it was already apparent that this asteroid, currently known as Apophis, would be notorious: our close-approach monitoring system, CLOMON2, was already showing a Virtual Impactor (VI) in 2029 reaching the level 2 in the Torino Scale, the first asteroid to reach that level since our monitoring system had been operational. However, this was just the beginning of what it was to come in the subsequent days. In this paper we will give an overview of the NEODyS-CLOMON2 system and provide the details on how Apophis’ collision scenario evolved, the way NEODyS’ team handled it and the crazy 2004’ Christmas holidays we had due to this unexpected guest.

CFD Study on the Effects of the Large Particle Crossing Trajectory Phenomenon on Virtual Impactor Performance

Two-dimensional CFD simulations were performed on a full-section numerical model of an as-built slot virtual impactor prototype and its completely symmetric ideal counterpart. The simulations reproduce the trends of the experimentally observed performance including verification of a third region in the transmission efficiency curve, which is a drop-in transmission efficiency for large particle sizes. Visualization of simulated particle tracks show this decrease is attributed to a crossing trajectory phenomenon, whereby larger particles that acquire enough inertia in a chamfered acceleration nozzle, crossover the vertical mid-plane and impact on the opposite-side wall, particularly on the wall of the receiver section. Some experimental data presented in the literature for rectangular slot and round-nozzle virtual impactors with chamfered 45° half-angle acceleration nozzles (similar to the geometry tested herein), show a similar drop-in transmission efficiency that commences at a particle Stokes numbers of ...

Counterflow Virtual Impactor Based Collection of Small Ice Particles in Mixed-Phase Clouds for the Physico-Chemical Characterization of Tropospheric Ice Nuclei: Sampler Description and First Case Study

A ground-based sampling system named Ice-CVI is introduced that is able to extract small ice particles with sizes between 5 and 20 μ m out of mixed-phase clouds. The instrument is based on a counterflow virtual impactor (CVI) removing interstitial particles and is supplemented by additional modules that pre-segregate other constituents of mixed-phase clouds. Ice particles of 20 μ m and smaller are expected to grow only by water vapor diffusion and there is a negligible probability that they scavenge aerosol particles by impaction and riming. Thus, their residuals which are released by the Ice-CVI can be interpreted as the original ice nuclei (IN). In a first field test within the Cloud and Aerosol Characterization Experiment (CLACE-3) at the high alpine research station Jungfraujoch, the collection behavior of the single components and the complete system was evaluated under atmospheric sampling conditions. By comparing parameters measured by the Ice-CVI with corresponding results obtained from other inlets or with in-situ instrumentation it is verified that the small ice particles are representatively collected whereas all other mixed phase cloud constituents are effectively suppressed. In a case study it is observed that super-micrometer particles preferentially serve as IN although in absolute terms the IN concentration is dominated by sub-micrometer particles. Mineral dust (Si), non-volatile organic matter and black carbon could be identified as IN components by means of different chemical analyses. The latter suggests an anthropogenic influence on the heterogeneous ice nucleation in supercooled, tropospheric clouds.