Correlations between absorption Angström exponent (AAE) of wintertime ambient urban aerosol and its physical and chemical properties

Utry, Noémi; Ajtai, Tibor; Filep, Ágnes; Pintér, Máté; Török, Zsófia; Bozóki, Zoltán; Szabó, Gábor

doi:10.1016/j.atmosenv.2014.03.047

Cited by 68 publications

(53 citation statements)

References 34 publications

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“…Utry et al (2014) also revealed a strong correlation between AAE and aerosol OC/EC at an urban site in Hungary, where OC was mainly emitted from wood burning and contained a large amount of BrC. The intercepts of the fitting curves in Fig.…”

Section: Determination Of the Aae For "Pure" Bc Aerosolmentioning

confidence: 96%

“…Some previous studies showed that ambient AAE was significantly affected by aerosol OC / EC (organic carbon / elemental carbon) ratio, suggesting a potentially important role of organic matter in aerosol light absorption (Utry et al, 2014). In this study, we tried to apply the AAE method to both urban and rural areas in the Pearl River Delta (PRD) region of China to attribute light absorption of BrC, with an emphasis of exploring realistic AAE BC based on on-line measurements in field campaigns.…”

Section: Introductionmentioning

confidence: 99%

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Light absorption of brown carbon aerosol in the PRD region of China

et al. 2016

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Abstract. The strong spectral dependence of light absorption of brown carbon (BrC) aerosol is regarded to influence aerosol's radiative forcing significantly. The Absorption Angstrom Exponent (AAE) method has been widely used in previous studies to attribute light absorption of BrC at shorter wavelengths for ambient aerosols, with a theoretical assumption that the AAE of "pure" black carbon (BC) aerosol equals to 1.0. In this study, the AAE method was applied to both urban and rural environments in the Pearl River Delta (PRD) region of China, with an improvement of constraining the realistic AAE of "pure" BC through statistical analysis of on-line measurement data. A threewavelength photo-acoustic soot spectrometer (PASS-3) and aerosol mass spectrometers (AMS) were used to explore the relationship between the measured AAE and the relative abundance of organic aerosol to BC. The regression and extrapolation analysis revealed that more realistic AAE values for "pure" BC aerosol (AAE BC ) were 0.86, 0.82, and 1.02 between 405 and 781 nm, and 0.70, 0.71, and 0.86 between 532 and 781 nm, in the campaigns of urban winter , urban fall , and rural fall , respectively. Roadway tunnel experiments were conducted and the results further confirmed the representativeness of the obtained AAE BC values for the urban environment. Finally, the average light absorption contributions of BrC (± relative uncertainties) at 405 nm were quantified to be 11.7 % (±5 %), 6.3 % (±4 %), and 12.1 % (±7 %) in the campaigns of urban winter , urban fall , and rural fall , respectively, and those at 532 nm were 10.0 % (±2 %), 4.1 % (±3 %), and 5.5 % (±5 %), respectively. The relatively higher BrC absorption contribution at 405 nm in the rural fall campaign could be reasonably attributed to the biomass burning events nearby, which was then directly supported by the biomass burning simulation experiments performed in this study. This paper indicates that the BrC contribution to total aerosol light absorption at shorter wavelengths is not negligible in the highly urbanized and industrialized PRD region.

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Section: Determination Of the Aae For "Pure" Bc Aerosolmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Light absorption of brown carbon aerosol in the PRD region of China

et al. 2016

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“…Because the AAE is widely approximated with the absorptions at two wavelengths using Eq. (2) (Utry et al, 2014;Li et al, 25 2016), BC also shows noticeable different AAE values over different ranges of spectrum. To obtain the most representative AAE value, we use BC absorptions at multiple wavelengths between 0.3 and 1.0 µm in steps of 0.05 µm, and the best AAE value to fit the absorptions over the spectrum is obtained by linear regression.…”

Section: Bc Aae 15mentioning

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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“…The spectral dependence of absorption (i.e., AAE) depends upon particle size and the imaginary refractive index, and excellent overviews of the relationship between AAE and aerosol microphysics are provided by Moosmüller et al (2009Moosmüller et al ( , 2011. Generally, AAE is obtained from photoacoustic measurements (Lewis et al, 2008;Chow et al, 2009;Gyawali et al, 2009;Flowers et al, 2010;Lack et al, 2012b;Chakrabarty et al, 2013;Utry et al, 2014), particle soot absorption photometer measurements (Roden et al, 2006), aethalometer measurements (Ganguly et al, 2005), the solar-flux-AOD technique (Russell et al, 2010), integrating plate methods (Schnaiter et al, 2003), differencing extinction and scattering coefficients , or aerosol robotic network (AERONET) retrievals (Bahadur et al, 2012;Chung et al, 2012b;Giles et al, 2012;Cazorla et al, 2013;Xu et al, 2013;Russell et al, 2014).…”

Section: G L Schuster Et Al: Understanding the Aae For Remote Sensmentioning

confidence: 99%

Remote sensing of soot carbon – Part 2: Understanding the absorption Ångström exponent

et al. 2016

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Abstract. Recently, some authors have suggested that the absorption Ångström exponent (AAE) can be used to deduce the component aerosol absorption optical depths (AAODs) of carbonaceous aerosols in the AERONET database. This AAE approach presumes that AAE 1 for soot carbon, which contrasts the traditional small particle limit of AAE = 1 for soot carbon. Thus, we provide an overview of the AERONET retrieval, and we investigate how the microphysics of carbonaceous aerosols can be interpreted in the AERONET AAE product. We find that AAE 1 in the AERONET database requires large coarse mode fractions and/or imaginary refractive indices that increase with wavelength. Neither of these characteristics are consistent with the current definition of soot carbon, so we explore other possibilities for the cause of AAE 1. AAE is related to particle size, and coarse mode particles have a smaller AAE than fine mode particles for a given aerosol mixture of species. We also note that the mineral goethite has an imaginary refractive index that increases with wavelength, is very common in dust regions, and can easily contribute to AAE 1. We find that AAE 1 can not be caused by soot carbon, unless soot carbon has an imaginary refractive index that increases with wavelength throughout the visible and near-infrared spectrums. Finally, AAE is not a robust parameter for separating carbonaceous absorption from dust aerosol absorption in the AERONET database.

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Correlations between absorption Angström exponent (AAE) of wintertime ambient urban aerosol and its physical and chemical properties

Cited by 68 publications

References 34 publications

Light absorption of brown carbon aerosol in the PRD region of China

Light absorption of brown carbon aerosol in the PRD region of China

The Absorption Ångström Exponent of black carbon: from numerical aspects

Remote sensing of soot carbon – Part 2: Understanding the absorption Ångström exponent

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