Bias in Filter-Based Aerosol Light Absorption Measurements Due to Organic Aerosol Loading: Evidence from Ambient Measurements

Lack, D. A.; Cappa, C. D.; Covert, David S.; Baynard, T.; Massoli, P.; Sierau, B.; Bates, T. S.; Quinn, Patricia K.; Lovejoy, Edward R.; Ravishankara, A. R.

doi:10.1080/02786820802389277

Cited by 272 publications

(272 citation statements)

References 31 publications

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“…In the case of absorption measurements, a positive bias is introduced when organic aerosol deposits on the filter, enhancing the scattering by the filter fibers and the absorption by previously deposited BC particles when coating them. This artifact can be between 12 and 70 % for particle soot absorption photometer (PSAP) measurements and will depend on the OA to BC ratio and the aging state of the organic aerosol particles (Lack et al, 2008). We expect a lower artifact for the MAAP since the scattering by filter fibers is accounted by the reflectance measurements, but using our instrumentation we are not able to estimate the artifact coming from embedded BC absorption being modified by organic aerosol deposition.…”

Section: Moranmentioning

confidence: 72%

Black and brown carbon over central Amazonia: Long-term aerosol measurements at the ATTO site

Saturno¹,

Holanda²,

Pöhlker³

et al. 2017

Preprint

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Abstract. The Amazon rain forest is considered a very sensitive ecosystem that could be significantly affected by a changing climate. It is still one of the few places on Earth where the atmosphere in the continent approaches near-pristine conditions for some periods of the year. The Amazon Tall Tower Observatory (ATTO) has been built in central Amazonia to monitor the atmospheric and forest ecosystem conditions. The atmospheric conditions at the ATTO site oscillate between biogenic and biomass burning (BB) dominated states. By using a comprehensive ground-based aerosol measurement setup, we studied the physical and chemical properties of aerosol particles at the ATTO site. This parameterization of å abs as a function of the BC to OA mass ratio was investigated and was found applicable to tropical forest emissions but further investigation is required, especially by segregating fuel types. Additionally, important enhancements of the BC mass absorption cross-section (α abs ) were found over the measurement period. This enhancement could be linked to heavy coating of the BC aerosol particles. In the future, the BC mixing state should be systematically investigated by using different instrumental approaches.

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Section: Moranmentioning

confidence: 72%

Black and brown carbon over central Amazonia: Long-term aerosol measurements at the ATTO site

Saturno¹,

Holanda²,

Pöhlker³

et al. 2017

Preprint

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“…The uncertainty in the measurements of these parameters has made it difficult to quantify the global impact of aerosols on Earth's climate (Hansen and Nazarenko 2004;Bond et al 2013). There has been an ongoing effort to develop a wide range of powerful aerosol measurement techniques, but there is still a need to develop instruments that can precisely and accurately measure the extensive and intensive optical properties of aerosols (Strawa et al 2003;Lack et al 2008;Moosmüller et al 2009;Radney et al 2009). …”

Section: Introductionmentioning

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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“…However, after coating, the AAE becomes less sensitive to RI real part, but more sensitive to RI imaginary part. Considering the significant uncertainty in estimated BC RI due to 10 differences on combustion fuels and conditions as well as whether BC is fresh or aged, it is highly questionable to use a fixed AAE value as in past studies (Lack and Langridge, 2013;Lack et al, 2008;Kirchstetter et al, 2004;Lewis et al, 2008).…”

Section: Bc Aae 15mentioning

confidence: 99%

“…Furthermore, it is not clear if the real 25 BC AAE is 1.0 on the average. Despite all these uncertainties, BC AAE has been assumed to be 1.0 in many studies (Lack and Langridge, 2013;Lack et al, 2008;Kirchstetter et al, 2004;Lewis et al, 2008). Meanwhile, numerical studies on BC AAE did not show systematic nor conclusive results to improve our understanding on them (Li et al, 2016;.…”

mentioning

confidence: 99%

The Absorption Ångström Exponent of black carbon: from numerical aspects

Liu¹,

Chung²,

Yin³

2017

Preprint

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Abstract. The Absorption Ångström Exponent (AAE) is an important aerosol optical parameter used for aerosol 10 characterization and apportionment studies. The AAE of black carbon (BC) is widely accepted to be 1.0, although observational estimates give a quite wide range of 0.6~1.1. With considerable uncertainties related to observations, a numerical study is a powerful method, if not the only one, to provide a better and more accurate understanding on BC AAE.This study calculates BC AAE using realistic particle geometries based on fractal aggregate and an accurate numerical optical model (namely the Multiple-Sphere T-Matrix method). At odds with the expectations, BC AAE is not 1.0, even when 15 BC is assumed to have small sizes and a wavelength independent refractive index. With a wavelength independent refractive index, the AAE of fresh BC is approximately 1.05, and is quite insensitive to particle size distribution. BC AAE goes lower when BC particles are aged (compact structures or coated by other scattering materials). For coated BC, we prescribed the coating thickness distribution based on a published experimental study, where smaller BC cores were shown to develop thicker coating than bigger BC cores. Both Compact and Coated BC the AAE ranges, at realistic particle sizes. For both 20Compact and Coated BC, the AAE is highly sensitive to particle size distribution, ranging from approximately 0.8 to 1.0 for relatively large BC with wavelength-independent refractive index. When the refractive index is allowed to vary with wavelength, a feature with observational backing, the BC AAE shows a much wider range. We propose that the presented results herein serve as a comprehensive guide for the response of BC AAE to BC size, refractive index, and geometry.

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Bias in Filter-Based Aerosol Light Absorption Measurements Due to Organic Aerosol Loading: Evidence from Ambient Measurements

Cited by 272 publications

References 31 publications

Black and brown carbon over central Amazonia: Long-term aerosol measurements at the ATTO site

Black and brown carbon over central Amazonia: Long-term aerosol measurements at the ATTO site

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

The Absorption Ångström Exponent of black carbon: from numerical aspects

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