Aerosol Absorption Measurement using Photoacoustic Spectroscopy: Sensitivity, Calibration, and Uncertainty Developments

Lack, D. A.; Lovejoy, Edward R.; Baynard, T.; Pettersson, Anders; Ravishankara, A. R.

doi:10.1080/02786820600803917

Cited by 251 publications

(282 citation statements)

References 33 publications

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“…Photoacoustic spectroscopy (PAS) has become a popular technique for measuring absorption of light by atmospheric aerosols for PAS (Lack et al, 2006(Lack et al, , 2012, recent works exploring its validity have come to contradictory conclusions: Bluvshtein et al (2017) saw a discrepancy between ozone calibrations and particle-based calibrations, while Davies et al (2018) found this not to be the case. Concurrent to these publications, we have been exploring the use of ozone as a PAS calibrant for multipass, multi-wavelength, aerosol photoacoustic spectrometers; our observations are presented here to add to the discussion on the topic.…”

Section: Introductionmentioning

confidence: 94%

“…The PAS cell itself sits within the multipass cell and follows the design of Lack et al (2006). A calibrated photodiode behind the rear multipass mirror is used to monitor the power of each laser simultaneously.…”

Section: Photoacoustic Spectrometermentioning

confidence: 99%

“…By using multiple concentrations (or sizes, in the case of aerosols), a linear regression of s vs. b abs can be performed from which the slope, m, can be determined. Examples of calibrants include aerosol particles such as flame-generated soot (Arnott et al, 2000) and gas-phase absorbers such as ozone (Lack et al, 2006(Lack et al, , 2012 or nitrogen 20 dioxide (Arnott et al, 2000;Lewis et al, 2008;Cross et al, 2010). Although ozone absorbs weakly in the UV-A and violet regions of the spectrum and is difficult to measure at those wavelengths, it has been employed for field calibrations because it can be easily generated using a UV lamp or corona discharge.…”

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confidence: 99%

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Technical Note: Can ozone be used to calibrate aerosol photoacoustic spectrometers?

Fischer

Smith

2018

Preprint

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Abstract. Photoacoustic spectroscopy (PAS) has become a popular technique for measuring absorption of light by atmospheric aerosols in both the laboratory and in field campaigns. It has low detection limits, measures suspended aerosols, and is insensitive to scattering. But PAS requires rigorous calibration to be applied quantitatively. Often, a PAS instrument is either filled with a gas of known concentration and absorption cross section, such that the absorption in the cell can be calculated from the product of the two, or the absorption is measured independently with a technique such as cavity ringdown spectroscopy. Then, 5 the PAS signal can be regressed upon the known absorption to determine a calibration slope that reflects the sensitivity constant of the cell and microphone. Ozone has been used for calibrating PAS instruments due to its well-known UV-visible absorption spectrum and the ease with which it can be generated. However, it is known to photodissociate up to approximately 1120 nmpathway, which is likely to lead to inaccuracies in aerosol measurements. Two recent studies have investigated the use of O 3 for PAS calibration but have reached seemingly contradictory conclusions 10 with one finding that it results in a sensitivity that is a factor of two low and the other concluding that it is accurate. The present work is meant to add to this discussion by exploring the extent to which O 3 photodissociates in the PAS cell and the role that the identity of the bath gas plays in determining the PAS sensitivity. We find a 5% loss in PAS signal attributable to photodissociation at 532 nm in N 2 but no loss in a 5% mixture of O 2 in N 2 . Furthermore, we discovered a dramatic increase of more than a factor of two in the PAS sensitivity as we increased the O 2 fraction in the bath gas, which reached an asymptote near 15 100% O 2 that nearly matched the sensitivity measured with both NO 2 and nigrosin particles. We interpret this dependence with a kinetic model that suggests the reason for the observed results is a more efficient transfer of energy from excited O 3 to O 2 than to N 2 by a factor of 22-55 depending on excitation wavelength.

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Section: Introductionmentioning

confidence: 94%

Section: Photoacoustic Spectrometermentioning

confidence: 99%

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confidence: 99%

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Technical Note: Can ozone be used to calibrate aerosol photoacoustic spectrometers?

Fischer

Smith

2018

Preprint

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“…While PSL falls in the ≤1% category for C(λ) A&O error, APSL error is likely >2% due to its SSA of 0.71-0.89 (Lack et al 2006;Flores 2011) and strong wavelength dependence. Since there is no error in the extrapolated cross-sections (due to extrapolating between two data points with two variables), error only stems from the variability of the nephelometer (1%), the uncertainty of the correction factor (1%, see Bond et al 2009), and the CPC error (10%).…”

Section: The Nephelometermentioning

confidence: 99%

“…3. The SSA of absorbing PSL with a comparison with measurements, by Lack et al (2006) and Flores (2011). Dotted lines or bars are the error (1s).…”

Section: Ssa Ab and Absorbing Pslmentioning

confidence: 99%

Error Analysis and Uncertainty in the Determination of Aerosol Optical Properties Using Cavity Ring-Down Spectroscopy, Integrating Nephelometry, and the Extinction-Minus-Scattering Method

Singh

Fiddler

Smith

et al. 2014

Aerosol Science and Technology

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Despite the substantial improvements in the measurements of aerosol physical and chemical properties and in the direct and indirect radiative effects of aerosols, there is still a need for studying the properties of aerosols under controlled laboratory conditions to develop a mechanistic and quantitative understanding of aerosol formation, chemistry, and dynamics. In this work, we present the factors that affect measurement accuracy and the resulting uncertainties of the extinction-minus-scattering method using a combination of cavity ring-down spectroscopy (CRDS) and integrating nephelometry at a wider range of optical wavelengths than previously attempted. Purely scattering polystyrene latex (PSL) spheres with diameters from 107-303 nm and absorbing polystyrene spheres (APSL) with 390 nm diameter were used to determine the consistency and agreement, within experimental uncertainties, of CRDS and nephelometer values with theoretical calculations derived from Mie theory for non-absorbing spheres. Overall uncertainties for extinction cross-section were largely 10%-11% and dominated by condensation particle counter (CPC) measurement error. Two methods for determining σ ext error are described, and they were found to produce equivalent results. Systematic uncertainties due to particle losses, RD cell geometry (R L ), CPC counting efficiency, ring-down regression fitting, blank drift, optical tweezing, and recapturing of forward scattered light are also investigated. The random error observed in this work for absorbing spheres is comparable to previous reported measurements. For both absorbing and non-absorbing spheres, a statistical framework is developed for including the contributions to random error due to CPC measurement uncertainty, R L , statistical fluctuations in

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Impacts of nonrefractory material on light absorption by aerosols emitted from biomass burning

et al. 2014

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We present laboratory measurements of biomass-burning aerosol light-scattering and light absorption coefficients at 405, 532, and 781 nm and investigate their relationship with aerosol composition and fuel type. Aerosol composition measurements included nonrefractory components measured by a high-resolution aerosol mass spectrometer (AMS), composition of refractory black carbon-containing particles by a soot particle aerosol mass spectrometer (SP-AMS), and refractory black carbon measured by a single-particle soot photometer (SP2). All measurements were performed downstream of a thermal denuder system to probe the effects of nonrefractory material on observed optical properties. The fires studied emitted aerosol with a wide range of optical properties with some producing more strongly light-absorbing particles (single-scattering albedo or SSA at 781 nm = 0.4) with a weak wavelength dependence of absorption (absorption Ångström exponent or AAE = 1-2) and others producing weakly light-absorbing particles (SSA at 781 nm~1) with strong wavelength dependence of absorption (AAE~7). Removal of nonrefractory material from the particles by the thermal denuder system led to substantial (20-80%) decreases in light absorption coefficients, particularly at shorter wavelengths, reflecting the removal of light-absorbing material that had enhanced black carbon absorption in internally mixed untreated samples. Observed enhancements of absorption by all mechanisms were at least factors of 1.2-1.5 at 532 nm and 781 nm as determined from the heated samples. A mass absorption cross-section-based approach indicated larger enhancements, particularly at shorter wavelengths.

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Aerosol Absorption Measurement using Photoacoustic Spectroscopy: Sensitivity, Calibration, and Uncertainty Developments

Cited by 251 publications

References 33 publications

Technical Note: Can ozone be used to calibrate aerosol photoacoustic spectrometers?

Technical Note: Can ozone be used to calibrate aerosol photoacoustic spectrometers?

Error Analysis and Uncertainty in the Determination of Aerosol Optical Properties Using Cavity Ring-Down Spectroscopy, Integrating Nephelometry, and the Extinction-Minus-Scattering Method

Impacts of nonrefractory material on light absorption by aerosols emitted from biomass burning

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