Radiative absorption enhancements by black carbon controlled by particle-to-particle heterogeneity in composition

Fierce, Laura; Onasch, T. B.; Cappa, C. D.; Mazzoleni, Cláudio; China, Swarup; Bhandari, Janarjan; Davidovits, P.; Fischer, D. Al; Helgestad, Taylor M.; Lambe, Andrew T.; Sedlacek, Arthur J.; Smith, Geoffrey D.; Wolff, Lindsay

doi:10.1073/pnas.1919723117

Cited by 109 publications

(80 citation statements)

References 50 publications

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“…Liu et al (2015) reported lower enhancement factors (up to 1.5) consistent with Cappa et al (2012). Discrepancies among laboratory and field observations are also due to the heterogeneity of particle ensemble composition (particle-to-particle differences) and the inaccurate assumption of spherical concentric core-shell structure (Fierce et al, 2020). Limited comparability among measurement techniques contributes to the variability of observed BC optical properties as well (Lack et al 2008, Moosmuller et al 2009, Subramanian et al 2007.…”

Section: Accepted Manuscriptmentioning

confidence: 97%

Spatial and Temporal Variability of Carbonaceous Aerosol Absorption in the Po Valley

Gilardoni¹,

Massoli

Marinoni

et al. 2020

Aerosol Air Qual. Res.

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Knowledge gaps in the optical properties of carbonaceous aerosols account for a significant fraction of the uncertainty of aerosol-light interactions in climate models. Both black carbon (BC) and brown carbon (BrC) can display a range of optical properties in ambient aerosol due to different sources and chemical transformation pathways. This study investigates the optical absorption properties of BC and BrC at an urban and a rural site in the Po Valley (Italy), a known European pollution hot spot. We observed spatial and seasonal variability of aerosol absorption coefficients, with the highest values measured in winter at the urban site of Milan (12 Mm-1 on average) and the lowest values in summer at the rural site of Motta Visconti (3 Mm-1 on average). The average aerosol Absorption Å ngström Exponent (AAE) measured during the two experiments across the 370-880 nm wavelength range was 1.1 and 1.2 at the urban and the rural site, respectively. The observed AAE values in winter (the average AAE during the two winter campaigns was 1.2) are consistent with the contribution of wood burning BrC, as confirmed by macro-tracer analysis. The BC mass absorption cross section (MACBC) did not show a specific seasonal or spatial variability across the two sites and maintained an average value of 10  5 m 2 g-1 at 880 nm. The optical properties of BrC, investigated off-line after extraction of organic aerosol (OA) indicate that wood burning was the dominant BrC source in winter, while secondary organic aerosol (SOA) from other anthropogenic emissions was the main source of BrC in summer.

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Section: Accepted Manuscriptmentioning

confidence: 97%

Spatial and Temporal Variability of Carbonaceous Aerosol Absorption in the Po Valley

Gilardoni¹,

Massoli

Marinoni

et al. 2020

Aerosol Air Qual. Res.

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“…One of the key questions in the field of aerosol absorption is the relative importance of black and brown carbon. This is particularly important in biomass burning plumes, where BrC is thought to have a strong effect near the source that diminishes with age (Forrister et al, 2015). Our measurements have shown that the AAE 405−655 values in smoke plumes over the southeast Atlantic were always close to 1 (with a mean AAE 405−655 of 1.13), which was consistent between our airborne measurements in 2017 and ground-based measurements taken on Ascension Island the previous year over a similar wavelength range (Zuidema et al, 2018).…”

Section: Physical and Optical Properties Of Highly Aged Biomass Burnimentioning

confidence: 99%

“…Liu et al, 2017), as well as absorption by brown carbon (BrC; e.g. Forrister et al, 2015;Healy et al, 2015). Where BC is encapsulated by non-BC material, the MAC of the soot may increase due to a lensing effect, which is often quantified using the absorption enhancement (E Abs , which refers to the ratio of the absorption of coated BC to that of uncoated BC).…”

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“…Primary BrC becomes less absorbing with time due to photochemical bleaching. The majority of BrC absorption decays with a half-life in the region of 9-15 h (Lee et al, 2014;Forrister et al, 2015), but laboratory studies have shown that some BrC species are particularly resistant to some bleaching pathways, such as reactions with ozone (Browne et al, 2019). Moreover, aged biomass burning aerosol may also have a sig-nificant BrC component arising from consistent mechanisms acting towards secondary BrC formation over the aerosol atmospheric lifetime.…”

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confidence: 99%

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Absorption closure in highly aged biomass burning smoke

Taylor

Szpek

et al. 2020

Atmos. Chem. Phys.

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Abstract. The optical properties of black carbon (BC) are a major source of uncertainty in regional and global climate studies. In the past, detailed investigation of BC absorption has been hampered by systematic biases in the measurement instrumentation. We present airborne measurements of aerosol absorption and black carbon microphysical properties in highly aged biomass burning plumes measured 4–8 d from their source over the southeast Atlantic Ocean during CLARIFY-2017, using a suite of novel photoacoustic spectrometers to measure aerosol absorption at 405, 514, and 655 nm and a single-particle soot photometer to measure the BC mass concentration, size, and mixing state. These measurements are of sufficient quality and detail to provide constraint on optical schemes used in climate models for the first time in biomass burning plumes far from their source – an aerosol environment that is one of the most important climatically. The average absorption Ångström exponents (AAE) were 1.38 over the wavelength range from 405 to 514 nm and 0.88 over the range from 514 to 655 nm, suggesting that brown carbon (BrC) contributed to 11±2 % of absorption at 405 nm. The effective organic aerosol (OA) mass absorption coefficient (MAC) was 0.31±0.09 m2 g−1 at 405 nm. The BC particles were universally thickly coated, and almost no externally mixed BC particles were detected. The average MAC of BC was 20±4, 15±3, and 12±2 m2g−1 at wavelengths of 405, 514, and 655 nm respectively, with equivalent absorption enhancements of around 1.85±0.45 at all three wavelengths, suggesting that the thick coatings acted as a lens that enhanced light absorption by the BC. We compared the measured MAC and AAE values with those calculated using several optical models and absorption parameterisations that took the measured BC mass and mixing state as inputs. Homogeneous grey-sphere Mie models were only able to replicate MAC for some low (real and imaginary) values of the complex BC refractive index (mBC) at the shortest wavelength, but they would have to use unrealistically low values of mBC to accurately replicate the AAE. A core–shell Mie model was able to generate good agreement for MAC in the green–red end of the visible spectrum for most values of mBC. However, there are no possible values of mBC that produce MAC values that agree with our observations at all three wavelengths, due to a wavelength-dependent underestimation of the MAC of the underlying BC core. Four semiempirical parameterisations from the literature were also tested, linking the BC mixing state to either the MAC or absorption enhancement. Two of these schemes produced results that agreed within a few percent with the measured MAC at all three wavelengths, and the AAE agreed well when discounting the effects of BrC. Our results uniquely demonstrate the validity of absorption parameterisations, as well as the failings of Mie calculations, in this highly aged environment. We recommend that future work should conduct similar analyses in environments where BC has different properties; future studies should also investigate the impact of implementing these types of schemes within climate models as well as the impact of developing equivalent schemes for light scattering by soot particles at visible wavelengths.

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“…Those coatings on BC will enhance the light absorption of BC through the so-called lensing effect (Lack and Cappa, 2010), which will further enhance the refractive heating of BC (Jacobson, 2001; Peng et al, 2016). Quantifying the light absorption enhancement of BC requires the information of size distribution, mixing state, morphology and chemical compositions (Fierce et al, 2016;Fierce et al, 2020).…”

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confidence: 99%

Strong Light Absorption Induced by Aged Biomass Burning Black Carbon over the Southeastern Tibetan Plateau in Pre-monsoon Season

Tan

et al. 2020

Preprint

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Abstract. During the pre-monsoon season, biomass burning (BB) activities are intensive in southern Asia. Facilitated by westerly circulation, those BB plumes can be transported to the Tibetan Plateau (TP). Black carbon (BC), the main aerosol species in BB emissions, is an important climate warming agent, and its absorbing property strongly depends on its size distribution and mixing state. To elucidate the influence of those transported BB plumes on the TP, a field campaign was conducted on the southeast edge of the TP during the pre-monsoon season. It was found that the transported BB plumes substantially increased the number concentration of the atmospheric BC particles by 13 times, and greatly elevated the number fraction of thickly-coated BC from 52 % up to 91 %. Those transported BC particles had slightly larger core size and much thicker coatings than the background BC particles. However, the coating mass was not evenly distributed on BC particles with different sizes. The smaller BC cores were found to have larger shell/core ratios than the larger cores. Besides, the transported BB plumes strongly affected the vertical variation of the BC's abundance and mixing state, resulting in a higher concentration, larger number fraction and higher aging degree of BC particles in the upper atmosphere. Resulted from both increase of BC loading and aging degree, the transported BB plumes eventually enhanced the total light absorption by 15 times, in which 21 % was contributed by the BC aging and 79 % was contributed from the increase of BC mass. Particularly, the light absorption enhancement induced by the aging process during long-range transport has far exceeded the background aerosol light absorption, which implicates a significant influence of BC aging on climate warming over the TP region.

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Radiative absorption enhancements by black carbon controlled by particle-to-particle heterogeneity in composition

Cited by 109 publications

References 50 publications

Spatial and Temporal Variability of Carbonaceous Aerosol Absorption in the Po Valley

Spatial and Temporal Variability of Carbonaceous Aerosol Absorption in the Po Valley

Absorption closure in highly aged biomass burning smoke

Strong Light Absorption Induced by Aged Biomass Burning Black Carbon over the Southeastern Tibetan Plateau in Pre-monsoon Season

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