NIST interlaboratory study of aerosol absorption measurements using photoacoustic spectroscopy

Zangmeister, Christopher D.; Radney, James G.

doi:10.6028/nist.tn.1989

Cited by 8 publications

(5 citation statements)

References 10 publications

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“…The resulting correlations at λ = 532 nm were C abs = (5.28 ± 0.41) × 10 −14 m 2 · ( D m /250 nm) 2.51 ± 0.14 = (1.14 ± 0.13) × 10 −14 · ( m m (fg)) 0.816 ± 0.034 for (150 ≤ D m ≤ 500) nm, where D m is the particle mobility diameter (i.e., particle diameter from a differential mobility analyzer with a bipolar charger, which size-selects aerosol of known electrical mobility) and m m is the corresponding particle mass (based on D m ). Using these correlations and the calculated value for trueC¯abs of 1.485 × 10 −14 m 2 (as based on the measured particle size distribution for this study and given refractive index, see Table 3), D m = 150.8 nm (within the range of the aerosol geometric mean mobility diameter reported in Zangmeister and Radney (2018) and similar to the surface-area mean diameter, D 20 = 156.0 nm) and m m = 1.38 fg. Note that the average geometric mean mobility diameter among the 11 reported values was 134.0 nm, compared to 136.7 nm for this investigation.…”

Section: Resultssupporting

confidence: 55%

“…This may be an artifact of the larger uncertainty associated with estimating the particle mass on the lighter coated filters. However, this observed change in c abs with mass loading may be evidence that the underlying particle size distribution is also a function of loading (assumed to be untrue) since at λ = 532 nm, c abs for the carbon-black particles measured presently is size dependent (Zangmeister and Radney 2018). The table also provides an estimate of the corresponding decrease in particle number concentration (as determined from the above-mentioned definition for α p ) for each filter.…”

Section: Resultsmentioning

confidence: 93%

“…The particle mass absorption coefficient was recently reported (Zangmeister and Radney 2018) for the same water-soluble carbon black, but as measured by photoacoustic spectroscopy from 11 different laboratories that participated in an interlaboratory round-robin. The resulting correlations at λ = 532 nm were C abs = (5.28 ± 0.41) × 10 −14 m 2 · ( D m /250 nm) 2.51 ± 0.14 = (1.14 ± 0.13) × 10 −14 · ( m m (fg)) 0.816 ± 0.034 for (150 ≤ D m ≤ 500) nm, where D m is the particle mobility diameter (i.e., particle diameter from a differential mobility analyzer with a bipolar charger, which size-selects aerosol of known electrical mobility) and m m is the corresponding particle mass (based on D m ).…”

Section: Resultsmentioning

confidence: 98%

“…Simultaneous transmissivity and absorptivity measurements were carried out at a laser wavelength of 532 nm on drop-cast, carbon-black-laden filters under ambient (laboratory) conditions. The focus of this investigation was to establish the feasibility of this approach to estimate the absorption coefficient of the particles and particle mass absorption coefficient, while comparing results to earlier investigations by You et al (2016) and Zangmeister and Radney (2018) that used the same carbon source. Transmissivity measurements were carried out with a laser probe beam positioned normal to the particle-laden filter surface.…”

Section: Discussionmentioning

confidence: 99%

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Simultaneous transmission and absorption photometry of carbon-black absorption from drop-cast particle-laden filters

Presser

Radney

Jordan

et al. 2019

Aerosol Science and Technology

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Simultaneous transmissivity and absorptivity measurements were carried out in the visible at a laser wavelength of 532 nm on drop-cast, carbon-black-laden filters under ambient (laboratory) conditions. The focus of this investigation was to establish the feasibility of this approach to estimate the mass absorption coefficient of the isolated particles and compare results to earlier work with the same carbon-black source. Transmissivity measurements were carried out with a laser probe beam positioned normal to the particle-laden filter surface. Absorptivity measurements were carried out using a laser-heating approach to record in time the sample temperature rise to steady-state and decay back to the ambient temperature. The sample temperature was recorded using a fine-wire thermocouple that was integrated into the transmission arrangement by placing the thermocouple flush with the filter back surface. The advantage of this approach is that the sample absorptivity can be determined directly (using laser heating) instead of resolving the difference between reflectivity (filter surface scattering) and transmissivity. The current approach also provides the filter optical characteristics, as well as an estimate of filter effects on the absorption coefficient due to particle absorption enhancement or shadowing. The approach may also be incorporated into other filter-based techniques, like the particle/soot absorption photometer, with the simple addition of a thermocouple to the commercial instrument. For this investigation, measurements were carried out with several blank uncoated quartz filters. A range of solution concentrations was prepared with a well-characterized carbon black in deionized water (i.e., a water-soluble carbonaceous material referred to as a surrogate black carbon or ‘carbon black’). The solution was then drop cast using a calibrated syringe onto blank filters to vary particle loading. After evaporation of the water, the measurements were repeated with the coated filters. The measurement repeatability (95% confidence level) was better than 0.3 K for temperature and 3 × 10−5 mW for laser power. From the measurements with both the blank and coated filters, the absorption coefficient was determined for the isolated particles. The results were then compared with an earlier investigation by You et al. and Zangmeister and Radney, who used the same carbon-black material. The measurements were also compared with Lorenz-Mie computations for a polydispersion of spherical particles dispersed throughout a volume representative of the actual particles. The mass absorption coefficient for the polydispersion of carbon-black particles was estimated to be about 7.7 ± 1.4m2 g−1, which was consistent with the results expected for these carbon black particles.

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Section: Resultssupporting

confidence: 55%

Section: Resultsmentioning

confidence: 93%

Section: Resultsmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

See 2 more Smart Citations

Simultaneous transmission and absorption photometry of carbon-black absorption from drop-cast particle-laden filters

Presser

Radney

Jordan

et al. 2019

Aerosol Science and Technology

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“…and that has a known constant refractive index for several years. Zangmeister and Radney (2018) are currently developing a substance that can be atomized from aqueous solution that would have a constant known refractive index and could eventually be a NIST aerosol absorption standard, but at this point that approach still requires selection of a monodisperse distribution. This paper presents a novel calibration technique that utilizes polydisperse absorbing aerosol and does not require a substance with a known refractive index.…”

mentioning

confidence: 99%

A novel approach to calibrating a photo-acoustic absorption spectrometer using polydisperse absorbing aerosol

Foster¹,

Pokhrel²,

Burkhart³

et al. 2018

Preprint

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Abstract. A new technique for calibrating photo-acoustic aerosol absorption spectrometers with multiple laser passes in the acoustic cavity (multi-pass PAS) has been developed utilizing polydisperse, highly-absorbing, aerosol. This is the first calibration technique for multi-pass PAS instruments that utilizes particles instead of reactive gases and does not require knowledge of the exact size or refractive index of the absorbing aerosol. In this new method, highly-absorbing materials are aerosolized into a polydisperse distribution and measured simultaneously with a multi-pass PAS and a cavity attenuated phase shift particulate matter single scattering albedo (CAPS PMSSA, Aerodyne Inc.) instrument. The CAPS PMSSA measures the bulk absorption coefficient through the subtraction of the scattering coefficient from the extinction coefficient. While this approach can have significant errors in ambient aerosol, the accuracy and precision of the CAPS PMSSA are high when the measured aerosol has a low SSA and particles are less than 300 nm in size where truncation errors are small. To confirm the precision and accuracy of this approach, a range of aerosol concentrations were sent to the multi-pass PAS and CAPS PMSSA instruments using three different absorbing substances: Aquadag, Regal Black, and Nigrosin. Six repetitions with each of the three substances produced stable calibrations, with the standard deviation of the measurements being less than 2 % at 660 nm and less than 5 % at 405 nm for all substances. Calibrations were also consistent across the different calibration substances (standard deviation of 2 % at 660 nm and 10 % at 405 nm) except for Nigrosin at 405 nm. The accuracy of the calibration approach is dependent on the single scattering albedo (SSA) of the calibration substance, but is roughly 6 % for the calibration substances used here, which all have an SSA near 0.4. This calibration technique is easily deployed to the field as it involves no toxic or reactive gases and it does not require generation of a monodisperse aerosol. Advantages to this particle-based calibration technique versus techniques based on ozone or nitrogen dioxide absorption include no reactive losses or impact from carrier gases, and the broad absorption characteristics of the particles which eliminate potentially significant errors in calibration with small errors in the peak wavelength of the laser light.

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Air-Coupled Photoacoustic Detection of Airborne Particulates

et al. 2023

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In this study, we present a novel method to detect airborne particulates using aircoupled photoacoustics, with a goal toward detecting viral content in respiratory droplets. The peak photoacoustic frequency emitted from micrometer-sized particulates is over 1000 MHz, but at this frequency, the signals are highly attenuated in air. Measurements were taken using a thin planar absorber and ultrasound transducers with peak sensitivity between 50 kHz and 2000 kHz and a 532 nm pulsed laser to determine the optimum detection frequency. 350 kHz to 500 kHz provided the highest amplitude signal while minimizing attenuation in air. To simulate the expulsion of respiratory droplets, an atomizer device was used to spray droplets into open air through a pulsed laser. Droplets were composed of water, water with acridine orange dye, and water with gold nanoparticles. The dye and nanoparticles were chosen due to their similarity in the UV absorption peaks when compared to RNA. Using a 260 nm laser, the average photoacoustic signal from water was the highest, and then the signal decreased with dye or nanoparticles. Increasing absorber concentrations within their respective solutions resulted in a decreasing photoacoustic signal, which is opposite to our expectations. Monte Carlo simulations demonstrated that depending on the droplet dimensions, water droplets focus photons to create a localized fluence elevation. Absorbers within the droplet can inhibit photon travel through the droplet, decreasing the fluence. Photoacoustic signals are created through optical absorption within the droplet, potentially amplified with the localized fluence increase through the droplet focusing effect, with a trade-off in signal amplitude depending on the absorber concentration.

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NIST interlaboratory study of aerosol absorption measurements using photoacoustic spectroscopy

Cited by 8 publications

References 10 publications

Simultaneous transmission and absorption photometry of carbon-black absorption from drop-cast particle-laden filters

Simultaneous transmission and absorption photometry of carbon-black absorption from drop-cast particle-laden filters

A novel approach to calibrating a photo-acoustic absorption spectrometer using polydisperse absorbing aerosol

Air-Coupled Photoacoustic Detection of Airborne Particulates

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