Implication of Light Absorption Enhancement and Mixing State of Black Carbon (BC) by Coatings in Hong Kong

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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Dynamic shape factor and mixing state of refractory black carbon particles in winter in Beijing using an AAC-DMA-SP2 tandem system

10.5194/acp-2019-433 ◽

2019 ◽

Author(s):

Xiaole Pan ◽

Hang Liu ◽

Yu Wu ◽

Yu Tian ◽

Yele Sun ◽

...

Keyword(s):

Black Carbon ◽

Light Absorption ◽

Shape Factor ◽

Absorption Enhancement ◽

Urban Site ◽

Optical Simulation ◽

Mixing State ◽

Dynamic Shape Factor ◽

Dynamic Shape ◽

Pollution Episodes

Abstract. Refractory black carbon (rBC) is one of the most important short-lived climate forcers in the atmosphere. Light absorption enhancement capacity largely depends on the morphology of rBC-containing particles and their mixing state. In this study, a tandem measuring system, consisting of an aerodynamic aerosol classifier (AAC), a differential mobility analyzer (DMA) and a single particle soot photometer (SP2), was adopted to investigate dynamic shape factor (𝜒) and its relationship with the mixing state of rBC-containing particles at an urban site of Beijing megacity in winter. The results demonstrated that the aerosol particles with an aerodynamic diameter of 400 ± 1.2 nm normally had a mobility diameter (Dmob) ranging from 250 nm to 320 nm, reflecting a large variation in shape under different pollution conditions. Multiple Gaussian fitting on the number mass-equivalent diameter (Dmev) distribution of the rBC core determined by SP2 had two peaks at Dmev = 106.5 nm and Dmev = 146.3 nm. During pollution episodes, rBC-containing particles tended to have a smaller rBC core than those during clean episodes due to rapid coagulation and condensation processes. The 𝜒 values of the particles were found to be ~ 1.2 during moderate pollution conditions, although the shell-core ratio (S/C) of rBC-containing particles was as high as 2.7 ± 0.3, suggesting that the particles had an irregular structure as a result of the high fraction of nascent rBC aggregates. During heavy pollution episodes, the 𝜒 value of the particles was approximately 1.0, indicating that the majority of particles tended to be spherical, and a shell-core model could be reasonable to estimate the light enhancement effect. Considering the variation in shape of the particles, the light absorption enhancement of the particles differed significantly according to the T-matrix model simulation. This study suggested that accurate description of the morphology of rBC-containing particles was crucially important for optical simulation and better evaluation of their climate effect.

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Measurement report: Strong light absorption induced by aged biomass burning black carbon over the southeastern Tibetan Plateau in pre-monsoon season

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-8499-2021 ◽

2021 ◽

Vol 21 (11) ◽

pp. 8499-8510

Author(s):

Tianyi Tan ◽

Min Hu ◽

Zhuofei Du ◽

Gang Zhao ◽

Dongjie Shang ◽

...

Keyword(s):

Tibetan Plateau ◽

Black Carbon ◽

Biomass Burning ◽

Climate Warming ◽

Light Absorption ◽

Monsoon Season ◽

Absorption Enhancement ◽

The Tibetan Plateau ◽

Mixing State ◽

Strong Light

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 a factor of 13 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 in 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. Resulting from both increase in BC loading and aging degree, the transported BB plumes eventually enhanced the total light absorption by a factor of 15, of which 21 % was contributed by the BC aging, and 79 % was contributed from the increase in 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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Method to quantify black carbon aerosol light absorption enhancement with a mixing state index

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-18055-2021 ◽

2021 ◽

Vol 21 (23) ◽

pp. 18055-18063

Author(s):

Gang Zhao ◽

Tianyi Tan ◽

Yishu Zhu ◽

Min Hu ◽

Chunsheng Zhao

Keyword(s):

Black Carbon ◽

Light Absorption ◽

Binary Systems ◽

Absorption Enhancement ◽

Mixing State ◽

Radiative Effects ◽

State Index ◽

Black Carbon Aerosol ◽

Mixing States ◽

Radiative Absorption

Abstract. Large uncertainties remain when estimating the warming effects of ambient black carbon (BC) aerosols on climate. One of the key challenges in modeling the radiative effects is predicting the BC light absorption enhancement, which is mainly determined by the mass ratio (MR) of non-BC coating material to BC in the population of BC-containing aerosols. For the same MR, recent research has found that the radiative absorption enhancements by BC are also controlled by its particle-to-particle heterogeneity. In this study, the BC mixing state index (χ) is developed to quantify the dispersion of ambient black carbon aerosol mixing states based on binary systems of BC and other non-black carbon components. We demonstrate that the BC light absorption enhancement increases with χ for the same MR, which indicates that χ can be employed as a factor to constrain the light absorption enhancement of ambient BC. Our framework can be further used in the model to study the radiative effects of black carbon on climate change.

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Bias in quantification of light absorption enhancement of black carbon aerosol coated with low-volatility brown carbon

Aerosol Science and Technology ◽

10.1080/02786826.2021.1873909 ◽

2021 ◽

pp. 1-18

Author(s):

Nishit Shetty ◽

Payton Beeler ◽

Theodore Paik ◽

Fred J. Brechtel ◽

Rajan K. Chakrabarty

Keyword(s):

Black Carbon ◽

Light Absorption ◽

Absorption Enhancement ◽

Brown Carbon ◽

Black Carbon Aerosol

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Effects of primary particle size on light absorption enhancement of black carbon aerosols using the superposition T-matrix method

Journal of Quantitative Spectroscopy and Radiative Transfer ◽

10.1016/j.jqsrt.2020.107388 ◽

2021 ◽

Vol 258 ◽

pp. 107388

Author(s):

Lijuan Zheng ◽

Yu Wu

Keyword(s):

Particle Size ◽

Black Carbon ◽

Light Absorption ◽

Matrix Method ◽

Primary Particle ◽

Primary Particle Size ◽

Absorption Enhancement ◽

T Matrix ◽

Carbon Aerosols ◽

Black Carbon Aerosols

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Light absorption enhancement of black carbon in urban Beijing in summer

Atmospheric Environment ◽

10.1016/j.atmosenv.2019.06.041 ◽

2019 ◽

Vol 213 ◽

pp. 499-504 ◽

Cited By ~ 13

Author(s):

Conghui Xie ◽

Weiqi Xu ◽

Junfeng Wang ◽

Dantong Liu ◽

Xinlei Ge ◽

...

Keyword(s):

Black Carbon ◽

Light Absorption ◽

Absorption Enhancement

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Mixing characteristics of refractory black carbon aerosols determined by a tandem CPMA-SP2 system at an urban site in Beijing

10.5194/acp-2019-244 ◽

2019 ◽

Cited By ~ 2

Author(s):

Hang Liu ◽

Xiaole Pan ◽

Dantong Liu ◽

Xiaoyong Liu ◽

Xueshun Chen ◽

...

Keyword(s):

Black Carbon ◽

Fractal Structure ◽

Particle Mass ◽

Shell Structures ◽

Absorption Enhancement ◽

Urban Site ◽

Core Shell ◽

Mixing State ◽

Carbon Aerosols ◽

Black Carbon Aerosols

Abstract. Black carbon aerosols play an important role in climate change by absorbing solar radiation and degrading visibility. In this study, the mixing state of refractory black carbon (rBC) at an urban site in Beijing was studied with a single particle soot photometer (SP2), as well as a tandem observation system with a centrifugal particle mass analyzer (CPMA) and a differential mobility analyzer (DMA), in early summer of 2018. The results demonstrated that the mass-equivalent size distribution of rBC exhibited an approximately lognormal distribution with a mass median diameter (MMD) of 171.2 nm. When the site experienced prevailing southerly winds, the MMD of rBC increased notably by 19 %. During the observational period, the ratio of the diameter of rBC-containing particles (Dp) to the rBC core (Dc) was 1.20 on average for Dc = 180 nm, indicating that the majority of rBC particles were thinly coated. The Dp / Dc value exhibited a clear diurnal pattern, with a maximum at 1400 LST and an enhancing rate of 0.013/h; higher Ox conditions increased the coating enhancing rate. Bare rBC particles were primarily in a fractal structure with a mass fractal dimension (Dfm) of 2.35, with limited variation during both clean and pollution periods, indicating significant impacts from on-road vehicle emissions. The morphology of rBC-containing particles vairied with aging processes. The mixing state of rBC particles could be indicated by the mass ratio of non-refractory matter to rBC (MR). In the present study, rBC-containing particles were primarily found in an external fractal structure when MR 6, at which the measured scattering cross section of rBC-containing particles was consistent with that based on the Mie-scattering simulation. We found only 9 % of the rBC-containing particles were in core-shell structures on clean days with a particle mass of 10 fg, and the number fraction of core-shell structures increased considerably to 32 % on pollution days. Considering the morphology change, the absorption enhancement (Eabs) was 11.7 % higher based on core-shell structures. This study highlights the combined effects of morphology and coating thickness on the Eabs of rBC-containing particles, which will be helpful for determining the climatic effects of BC.

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