The Experts below are selected from a list of 246 Experts worldwide ranked by ideXlab platform
Alfred Wiedensohler - One of the best experts on this subject based on the ideXlab platform.
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Design and performance of a three-wavelength LED-based total scatter and backscatter integrating nephelometer
Atmospheric Measurement Techniques, 2011Co-Authors: T. Müller, G. Kassell, Miguel Laborde, Alfred WiedensohlerAbstract:Integrating Nephelometers are instruments that directly measure a value close to the light scattering coefficient of airborne particles. Different models of Nephelometers have been used for decades for monitoring and research applications. Now, a series of Nephelometers (Ecotech models M9003, Aurora 1000 and Aurora 3000) with newly designed light sources based on light emitting diodes are available. This article reports on the design of these integrating Nephelometers and a comparison of the Aurora 3000 to another commercial instrument (TSI model 3563) that uses an incandescent lamp. Both instruments are three-wavelength, total and backscatter integrating Nephelometers. We present a characterization of the new light source design of the Aurora 3000 and provide parameterizations for its angular sensitivity functions. These parameterizations facilitate to correct for measurement artefacts using Mie-theory. Furthermore, correction factors are provided as a function of the Ångström exponent. Comparison measurements against the TSI 3563 with laboratory generated white particles and ambient air are also shown and discussed. Both instruments agree well within the calibration uncertainties and detection limit for total scattering with differences less than 5 %. Differences for backscattering are higher by up to 11 %. Highest differences were found for the longest wavelengths, where the signal to noise ratio is lowest. Differences at the blue and green wavelengths are less than 4 % and 3 %, respectively, for both total and backscattering.
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Design and performance of a three-wavelength LED-based total scatter and backscatter integrating nephelometer
2010Co-Authors: T. Müller, G. Kassell, M. Laborde, Alfred WiedensohlerAbstract:Abstract. Integrating Nephelometers are instruments that directly measure a value close to the light scattering coefficient of airborne particles. Different models of Nephelometers have been used for decades for monitoring and research applications. Now, a series of Nephelometers (Ecotech models M9003, Aurora 1000 and Aurora 3000) with newly designed light sources based on light emitting diodes are available. This article reports on the design of these integrating Nephelometers and a comparison of the Aurora 3000 to another commercial instrument (TSI model 3563) that uses an incandescent lamp. Both instruments are three-wavelength, total and backscatter integrating Nephelometers. We present a characterization of the new light source design of the Aurora 3000 and provide parameterizations for its angular sensitivity functions. These parameterizations facilitate to correct for measurement artefacts using Mie-theory. Comparison measurements against the TSI 3563 with laboratory generated white particles and ambient air are shown and discussed. Both instruments agree well within the calibration uncertainties and detection limit for total scattering with differences less than 5%. Differences for backscattering are higher by up to 11%. Highest differences were found for the longest wavelengths, where the signal to noise ratio is lowest. Differences at the blue and green wavelengths are less than 4% and 3%, respectively, for both total and backscattering.
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Angular Illumination and Truncation of Three Different Integrating Nephelometers: Implications for Empirical, Size-Based Corrections
Aerosol Science and Technology, 2009Co-Authors: Thomas Müller, Alfred Wiedensohler, A. Nowak, Patrick J. Sheridan, M. Laborde, David S. Covert, Angela Marinoni, Kornélia Imre, Bas Henzing, Jean-claude RogerAbstract:Integrating Nephelometers are widely used for monitoring and research applications related to air pollution and climate. Several commercial versions of the instrument are available and are in wide use in the community. This article reports on results from a calibration and intercomparison workshop where several units of the three most widely used nephelometer models were tested with respect to their CO2 calibration accuracy and stability and non-idealities of their angular illumination function. Correction factors that result from the non-ideal illumination due to truncation of the sensing volumes in the near-forward and near-backward angular ranges and for non-Lambertian illumination from the light sources are presented, in particular for two models that have not previously been tested in this respect. The correction factors ranged from 0.95 to 1.15 depending on the model of nephelometer and aerosol size distribution. Recommendations for operational data analysis in context of these and previous performance tests are presented.
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Intercomparisons and Aerosol Calibrations of 12 Commercial Integrating Nephelometers of Three Manufacturers
Journal of Atmospheric and Oceanic Technology, 2006Co-Authors: Jost Heintzenberg, Alfred Wiedensohler, Thomas Tuch, D. S. Covert, P. J. Sheridan, John A. Ogren, John L. Gras, R. Nessler, C. Kleefeld, Nikos KalivitisAbstract:Abstract This study determined measured and Mie-calculated angular signal truncations for total and backscatter TSI, Inc., Nephelometers, as a function of wavelength and for particles of known size and composition. Except for the total scattering channels, similar agreements as in a previous study of measured and calculated truncations were derived for submicrometer test aerosols. For the first time, instrument responses were also determined for supermicrometer test aerosols up to 1.9 μm in geometric mean diameter. These supermicrometer data confirm the theoretical predictions of strong angular truncations of the total scatter signals in integrating Nephelometers due to the limited range of measured forward scattering angles. Truncations up to 60% were determined for the largest measured particles. Rough empirical truncation corrections have been derived from the calibration data for Radiance Research and Ecotech Nephelometers for which no detailed response characteristics exist. Intercomparisons of the n...
Vanessa Selimovic - One of the best experts on this subject based on the ideXlab platform.
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Investigating biomass burning aerosol morphology using a laser imaging nephelometer
Atmospheric Chemistry and Physics, 2018Co-Authors: Katherine Manfred, Rebecca A. Washenfelder, Nicholas L. Wagner, Gabriela Adler, Frank Erdesz, Caroline C. Womack, Kara D. Lamb, Joshua P. Schwarz, Alessandro Franchin, Vanessa SelimovicAbstract:Abstract. Particle morphology is an important parameter affecting aerosol optical properties that are relevant to climate and air quality, yet it is poorly constrained due to sparse in situ measurements. Biomass burning is a large source of aerosol that generates particles with different morphologies. Quantifying the optical contributions of non-spherical aerosol populations is critical for accurate radiative transfer models, and for correctly interpreting remote sensing data. We deployed a laser imaging nephelometer at the Missoula Fire Sciences Laboratory to sample biomass burning aerosol from controlled fires during the FIREX intensive laboratory study. The laser imaging nephelometer measures the unpolarized scattering phase function of an aerosol ensemble using diode lasers at 375 and 405 nm. Scattered light from the bulk aerosol in the instrument is imaged onto a charge-coupled device (CCD) using a wide-angle field-of-view lens, which allows for measurements at 4–175 ∘ scattering angle with ∼ 0.5 ∘ angular resolution. Along with a suite of other instruments, the laser imaging nephelometer sampled fresh smoke emissions both directly and after removal of volatile components with a thermodenuder at 250 ∘ C. The total integrated aerosol scattering signal agreed with both a cavity ring-down photoacoustic spectrometer system and a traditional integrating nephelometer within instrumental uncertainties. We compare the measured scattering phase functions at 405 nm to theoretical models for spherical (Mie) and fractal (Rayleigh–Debye–Gans) particle morphologies based on the size distribution reported by an optical particle counter. Results from representative fires demonstrate that particle morphology can vary dramatically for different fuel types. In some cases, the measured phase function cannot be described using Mie theory. This study demonstrates the capabilities of the laser imaging nephelometer instrument to provide realtime, in situ information about dominant particle morphology, which is vital for understanding remote sensing data and accurately describing the aerosol population in radiative transfer calculations.
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Investigating biomass burning aerosol morphology using a laser imaging nephelometer
2017Co-Authors: Katherine M. Manfred, Rebecca A. Washenfelder, Nicholas L. Wagner, Gabriela Adler, Frank Erdesz, Caroline C. Womack, Kara D. Lamb, Joshua P. Schwarz, Alessandro Franchin, Vanessa SelimovicAbstract:Abstract. Particle morphology is an important parameter affecting aerosol optical properties that are relevant to climate and air quality, yet it is poorly constrained due to sparse in situ measurements. Biomass burning is a large source of aerosol that generates particles with different morphologies. Quantifying the optical contributions of non-spherical aerosol populations is critical for accurate radiative transfer models, and for correctly interpreting remote sensing data. We deployed a laser imaging nephelometer at the Missoula Fire Sciences Laboratory to sample biomass burning aerosol from controlled fires during the FIREX intensive laboratory study. The laser imaging nephelometer measures the unpolarized scattering phase function of an aerosol ensemble using diode lasers at 375 nm and 405 nm. Scattered light from the bulk aerosol in the instrument is imaged onto a CCD using a wide-angle field-of-view lens, which allows for measurements at 4–175° scattering angle with ~ 0.5° angular resolution. Along with a suite of other instruments, the laser imaging nephelometer sampled fresh smoke emissions both directly and after removal of volatile components with a thermodenuder at 250 °C. The total integrated aerosol scattering signal agreed with both a cavity ring-down photoacoustic spectrometer system and a traditional integrating nephelometer within instrumental uncertainties. We compare the measured scattering phase functions at 405 nm to theoretical models for spherical (Mie) and fractal (Rayleigh-Debye-Gans) particle morphologies based on the size distribution reported by an optical particle counter. Results from representative fires demonstrate that particle morphology can vary dramatically for different fuel types. In some cases, the measured phase function cannot be described using Mie theory. This study demonstrates the capabilities of the laser imaging nephelometer instrument to provide real-time, in situ information about dominant particle morphology, which is vital for understanding remote sensing data and accurately describing the aerosol population in radiative transfer calculations.
Catherine P Koshland - One of the best experts on this subject based on the ideXlab platform.
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field performance of a nephelometer in rural kitchens effects of high humidity excursions and correlations to gravimetric analyses
Journal of Exposure Science and Environmental Epidemiology, 2007Co-Authors: Susan L Fischer, Catherine P KoshlandAbstract:Rural kitchens of solid-fuel burning households constitute the microenvironment responsible for the majority of human exposures to health-damaging air pollutants, particularly respirable particles and carbon monoxide. Portable Nephelometers facilitate cheaper, more precise, time-resolved characterization of particles in rural homes than are attainable by gravitational methods alone. However, field performance of Nephelometers must contend with aerosols that are highly variable in terms of chemical content, size, and relative humidity. Previous field validations of nephelometer performance in residential settings explore relatively low particle concentrations, with the vast majority of 24-h average gravitational PM2.5 concentrations falling below 40 microg/m3. We investigate relationships between 24-h gravitational particle measurements and nephelometric data logged by the personal DataRAM (pDR) in highly polluted rural Chinese kitchens, where gravitationally determined 24-h average respirable particle concentrations were as high as 700 microg/m3. We find that where relative humidity remained below 95%, nephelometric response was strongly linear despite complex mixtures of aerosols and variable ambient conditions. Where 95% relative humidity was exceeded for even a brief duration, nephelometrically determined 24-h mean particle concentrations were nonsystematically distorted relative to gravitational data, and neither concurrent relative humidity measurements nor use of robust statistical measures of central tendency offered means of correction. This nonsystematic distortion is particularly problematic for rural exposure assessment studies, which emphasize upper quantiles of time-resolved particle measurements within 24-h samples. Precise, accurate interpretation of nephelometrically resolved short-term particle concentrations requires calibration based on short-term gravitational sampling.
Valery Shcherbakov - One of the best experts on this subject based on the ideXlab platform.
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cloud chamber experiments on the origin of ice crystal complexity in cirrus clouds
Atmospheric Chemistry and Physics, 2015Co-Authors: Martin Schnaiter, Emma Jarvinen, Olivier Jourdan, Carl G Schmitt, Paul Vochezer, Ahmed Abdelmonem, G Mioche, R Wagner, Valery Shcherbakov, Ugo TricoliAbstract:Abstract. This study reports on the origin of small-scale ice crystal complexity and its influence on the angular light scattering properties of cirrus clouds. Cloud simulation experiments were conducted at the AIDA (Aerosol Interactions and Dynamics in the Atmosphere) cloud chamber of the Karlsruhe Institute of Technology (KIT). A new experimental procedure was applied to grow and sublimate ice particles at defined super- and subsaturated ice conditions and for temperatures in the −40 to −60 °C range. The experiments were performed for ice clouds generated via homogeneous and heterogeneous initial nucleation. Small-scale ice crystal complexity was deduced from measurements of spatially resolved single particle light scattering patterns by the latest version of the Small Ice Detector (SID-3). It was found that a high crystal complexity dominates the microphysics of the simulated clouds and the degree of this complexity is dependent on the available water vapor during the crystal growth. Indications were found that the small-scale crystal complexity is influenced by unfrozen H2SO4 / H2O residuals in the case of homogeneous initial ice nucleation. Angular light scattering functions of the simulated ice clouds were measured by the two currently available airborne polar Nephelometers: the polar nephelometer (PN) probe of Laboratoire de Meterologie et Physique (LaMP) and the Particle Habit Imaging and Polar Scattering (PHIPS-HALO) probe of KIT. The measured scattering functions are featureless and flat in the side and backward scattering directions. It was found that these functions have a rather low sensitivity to the small-scale crystal complexity for ice clouds that were grown under typical atmospheric conditions. These results have implications for the microphysical properties of cirrus clouds and for the radiative transfer through these clouds.
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On the scattering phase‐function of non‐symmetric ice‐crystals
Quarterly Journal of the Royal Meteorological Society, 2005Co-Authors: Anthony J. Baran, Valery Shcherbakov, Brad Baker, Jean-françois Gayet, R. P. LawsonAbstract:SUMMARY Theoretical phase-functions representing randomly oriented fractal ice-crystals, bullet-rosettes, ice aggregates, and an ensemble of ice crystals are compared to measured phase-functions using a Polar Nephelometer located in the Antarctic. The Polar Nephelometer operated at a wavelength of 0.80 μm and measured the scattering phase-functions of individual ice-crystals between the scattering angles of 5.86 ◦ and 167 ◦ .T he Polar Nephelometer was operated in tandem with a Cloud Particle Imager (supplied by SPEC Inc.) both were situated at the South Pole Amundsen–Scott base station during January 2002. In this paper we report on a sample of Polar Nephelometer data obtained over a time interval of 2000 seconds consisting of 3256 phase-functions measured from individual ice-crystals. The 3256 measured phase-functions were averaged to produce an ensemble-averaged phase-function. The theoretical phase-functions have been compared to the measured ensemble-averaged phasefunction. The paper demonstrates that phase functions representing single ice-crystal geometries do not reproduce the measured data well. However, the theoretical phase-function representing scattering from an ensemble of ice crystals is found to be the best description of the measured phase-function over all scattering angles.
Ugo Tricoli - One of the best experts on this subject based on the ideXlab platform.
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cloud chamber experiments on the origin of ice crystal complexity in cirrus clouds
Atmospheric Chemistry and Physics, 2015Co-Authors: Martin Schnaiter, Emma Jarvinen, Olivier Jourdan, Carl G Schmitt, Paul Vochezer, Ahmed Abdelmonem, G Mioche, R Wagner, Valery Shcherbakov, Ugo TricoliAbstract:Abstract. This study reports on the origin of small-scale ice crystal complexity and its influence on the angular light scattering properties of cirrus clouds. Cloud simulation experiments were conducted at the AIDA (Aerosol Interactions and Dynamics in the Atmosphere) cloud chamber of the Karlsruhe Institute of Technology (KIT). A new experimental procedure was applied to grow and sublimate ice particles at defined super- and subsaturated ice conditions and for temperatures in the −40 to −60 °C range. The experiments were performed for ice clouds generated via homogeneous and heterogeneous initial nucleation. Small-scale ice crystal complexity was deduced from measurements of spatially resolved single particle light scattering patterns by the latest version of the Small Ice Detector (SID-3). It was found that a high crystal complexity dominates the microphysics of the simulated clouds and the degree of this complexity is dependent on the available water vapor during the crystal growth. Indications were found that the small-scale crystal complexity is influenced by unfrozen H2SO4 / H2O residuals in the case of homogeneous initial ice nucleation. Angular light scattering functions of the simulated ice clouds were measured by the two currently available airborne polar Nephelometers: the polar nephelometer (PN) probe of Laboratoire de Meterologie et Physique (LaMP) and the Particle Habit Imaging and Polar Scattering (PHIPS-HALO) probe of KIT. The measured scattering functions are featureless and flat in the side and backward scattering directions. It was found that these functions have a rather low sensitivity to the small-scale crystal complexity for ice clouds that were grown under typical atmospheric conditions. These results have implications for the microphysical properties of cirrus clouds and for the radiative transfer through these clouds.