Size- and Composition-Dependent Response of the DAWN-A Multiangle Single-Particle Optical Detector

Dick, William D.; McMurry, Peter H.; Bottiger, Jerold R.

doi:10.1080/02786829408959690

Cited by 33 publications

(19 citation statements)

References 27 publications

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“…This procedure essentially consisted of selecting responses that were likely to correspond to particles that exited the inlet without recirculation and traversed the laser beam through its center. Selection in the current study was more liberal than that of Dick et al (1994), typically yielding selected counts greater than 400 for calibration measurements consisting of 512 particle records. Responses from multiply-charged particles, which are larger than the primary singly-charged particles of interest, were also deselected with this procedure but not entirely.…”

Section: Discussionmentioning

confidence: 99%

“…• , as originally described by Dick et al (1994). This procedure essentially consisted of selecting responses that were likely to correspond to particles that exited the inlet without recirculation and traversed the laser beam through its center.…”

Section: Discussionmentioning

confidence: 99%

“…We refer the reader to previous works (Wyatt et al 1988;Dick et al 1994;Sachweh et al 1995;Dick et al 1996; for supplemental descriptions.…”

Section: Refractive Index Measurement Approachmentioning

confidence: 99%

“…The capabilities of the MLS technique include characterization of particle shape (Hirst et al 1994;Kaye et al 1996;Sachweh et al 1995;Dick et al 1996;, determination of particle refractive index (Dick et al 1994;Baumgardner et al 1996), and measurement of particle size (Baumgardner et al 1996;Szymanski et al 2002). Optical measurements of particle sphericity offer a direct validation or invalidation of the use of Mie theory in visibility modeling, and may reveal unexpected microphysical properties .…”

Section: Introductionmentioning

confidence: 99%

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Multiangle Light-Scattering Measurements of Refractive Index of Submicron Atmospheric Particles

Dick

Ziemann

McMurry

2007

Aerosol Science and Technology

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Multiangle light scattering (MLS) measurements of monodisperse atmospheric particles ranging in diameter from 0.2 to 0.8 µm were made with the DAWN-A optical detector during the Southeastern Aerosol and Visibility Study (SEAVS). The study was conducted on the southwestern edge of the Great Smoky Mountains National Park from July 15 to August 25, 1995. Individual particles were separated into spherical and nonspherical classes on the basis of the variability in elastic light scattering measured at eight azimuthal angles. Values of the real part of the refractive index, n, were then inferred for spherical particles by comparing LorenzMie theory calculations to calibrated light scattering responses from narrow-aperture detectors positioned at seven polar angles ranging from 40-140 degrees. The instrument was calibrated with submicron laboratory particles with n ranging from 1.38 to 1.61 for an illumination wavelength of 488 nm. The overall uncertainty in measured n was estimated to be ±0.02. For hygroscopic particles, refractive index was found to decrease as relative humidities increased due to the addition of water; the study-average value at low humidities (dry particles) was 1.49, while the average value at high humidities (wet particles) was 1.42. The lowest and highest values measured during the study were 1.34 and 1.54. Daily size-and RH-dependent measurements are compared to indices modeled for mixtures of ammoniated sulfate, organic carbon (OC), elemental carbon (EC), and water. Size-dependent mass concentrations of these species, with the exception of water, were measured with MOUDI cascade impactors.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

“…We refer the reader to previous works (Wyatt et al 1988;Dick et al 1994;Sachweh et al 1995;Dick et al 1996; for supplemental descriptions.…”

Section: Refractive Index Measurement Approachmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Multiangle Light-Scattering Measurements of Refractive Index of Submicron Atmospheric Particles

Dick

Ziemann

McMurry

2007

Aerosol Science and Technology

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“…The information on the scattered light intensity can be used to derive information on the size of the individual particles under certain assumptions regarding their refractive index and shape (Dick et al, 1994). For a well-defined observation volume, the frequency of encountered light pulses is used to derive the particle concentration, and with the measured size the aerosol number size distribution can be inferred.…”

Section: Z Jurányi Et Al: Dual-wavelength Volcanic Ash Detectormentioning

confidence: 99%

Dual-wavelength light-scattering technique for selective detection of volcanic ash particles in the presence of water droplets

et al. 2015

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Abstract.A new method is presented in this paper which analyses the scattered light of individual aerosol particles simultaneously at two different wavelengths in order to retrieve information on the particle type. We show that dust-like particles, such as volcanic ash, can be unambiguously discriminated from water droplets on a single-particle level. As a future application of this method, the detection of volcanic ash particles should be possible in a humid atmosphere in the presence of cloud droplets. The characteristic behaviour of pure water's refractive index can be used to separate water droplets and dust-like particles which are commonly found in the micrometre size range in the ambient air. The low real part of the water's refractive index around 2700-2800 nm results in low scattered light intensities compared to e.g. the visible wavelength range, and this feature can be used for the desired particle identification.The two-wavelength measurement set-up was theoretically and experimentally tested and studied. Theoretical calculations were done using Mie theory. Comparing the ratio of the scattered light at the two wavelengths (visible-to-IR (infrared), R value) for water droplets and different dust types (basalt, andesite, African mineral dust, sand, volcanic ash, pumice) showed at least 9-times-higher values (on average 70 times) for water droplets than for the dust types at any diameter within the particle size range of 2-20 µm. The envisaged measurement set-up was built up into a laboratory prototype and was tested with different types of aerosols. We generated aerosols from the following powders, simulating dust-like particles: cement dust, ISO 12103-1 A1 Ultrafine Test Dust and ash from the 2012 eruption of the Etna volcano. Our measurements verified the theoretical considerations; the median experimental R value is 8-21 times higher for water than for the "dust" particles.

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Direct Reading Instruments for the Determination of Aerosols and Particulates

Pui

Chen

2000

Encyclopedia of Analytical Chemistry

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Solid and liquid particles suspended in a gas are referred to as aerosols. The suspending medium can be air, or some other gases, such as argon, nitrogen, helium, etc. Aerosols have found numerous scientific and technical applications. Beneficial applications include pharmaceutical aerosols for medical inhalation therapy or diagnosis, industrial aerosols for coating wave guides, refractories, gas sensors and semiconductors, as well as particles ofmodern materials for forming advanced ceramics, optical and optoelectronic devices, cosmetic products, paint pigments, and catalysts. Harmful effects of aerosols include atmospheric aerosols that contribute to urban air pollution and global radiation balance, dust particles ingested by engines causing premature failure of the equipment, and particles deposited on semiconductor wafers causing device failure and product yield loss. Aerosols and particles can be analyzed by collecting them on a filter or a sampling surface for subsequent microscopic, gravimetric, or chemical analyses. The collection by the samplers gives an integrated sample and a time averaged concentration over a period of hours or days. Direct reading instruments carry out the sampling and analysis within the instrument and the property of interest can be obtained in near real‐time. Direct reading instruments are available to cover particles in the size range of 0.002 to 100 µm. These instruments have fast time response and can follow rapid changes in both particle size and concentration. Good counting statistics can also be obtained because repeated measurements can be performed in a short time. However, these instruments usually rely on indirect sensing techniques and more calibration efforts are usually required.

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Size- and Composition-Dependent Response of the DAWN-A Multiangle Single-Particle Optical Detector

Cited by 33 publications

References 27 publications

Multiangle Light-Scattering Measurements of Refractive Index of Submicron Atmospheric Particles

Multiangle Light-Scattering Measurements of Refractive Index of Submicron Atmospheric Particles

Dual-wavelength light-scattering technique for selective detection of volcanic ash particles in the presence of water droplets

Direct Reading Instruments for the Determination of Aerosols and Particulates

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