Morphology and mixing of black carbon particles collected in central California during the CARES field study

Abstract. Aerosol absorption is strongly dependent on the internal heterogeneity (mixing state) and morphology of individual particles containing black carbon (BC) and other non-absorbing species. Here, we examine an extensive microscopic data set collected in the California Central Valley during the CARES 2010 field campaign. During a period of high photochemical activity and pollution buildup, the particle mixing state and morphology were characterized using scanning transmission X-ray microscopy (STXM) at the carbon K-edge. Observations of compacted BC core morphologies and thick organic coatings at both urban and rural sites provide evidence of the aged nature of particles, highlighting the importance of highly aged particles at urban sites during periods of high photochemical activity. Based on the observation of thick coatings and more convex BC inclusion morphology, either the aging was rapid or the contribution of fresh BC emissions at the urban site was relatively small compared to background concentrations. Most particles were observed to have the BC inclusion close to the center of the host. However, host particles containing inorganic rich inclusions had the BC inclusion closer to the edge of the particle. These measurements of BC morphology and mixing state provide important constraints for the morphological effects on BC optical properties expected in aged urban plumes.

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Morphology and Mixing of BC Particles Collected in Central California During the CARES Field Study

10.5194/acp-2016-634 ◽

2016 ◽

Author(s):

Ryan C. Moffet ◽

Rachel E. O'Brien ◽

Peter Alpert ◽

Stephen T. Kelly ◽

Don Q. Pham ◽

...

Keyword(s):

Central Valley ◽

Photochemical Activity ◽

Urban Site ◽

Mixing State ◽

Data Set ◽

Central California ◽

Aerosol Absorption ◽

Particle Mixing ◽

Scanning Transmission ◽

Rural Sites

Abstract. Aerosol absorption is strongly dependent on the internal heterogeneity (mixing state) and morphology of individual particles containing black carbon (BC) and other non-absorbing species. Here, we examine an extensive microscopic data set collected in the California central valley during the CARES 2010 field campaign. During a period of high photochemical activity and pollution buildup, the particle mixing state and morphology were characterized using Scanning Transmission X-ray Microscopy (STXM) at the carbon K-edge. Observations of compacted BC core morphologies and thick organic coatings at both urban and rural sites provide evidence of the aged nature of particles. Based on the observation of thick coatings and more convex BC inclusion morphology, the contribution of fresh BC emissions at the urban site was relatively small. These measurements of BC morphology and mixing state provide important constraints for the morphological effects on BC optical properties expected in aged urban plumes.

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Influences of Primary Emission and Secondary Coating Formation on the Particle Diversity and Mixing State of Black Carbon Particles

Environmental Science & Technology ◽

10.1021/acs.est.9b03064 ◽

2019 ◽

Vol 53 (16) ◽

pp. 9429-9438 ◽

Cited By ~ 2

Author(s):

Alex K.Y. Lee ◽

Laura-Hélèna Rivellini ◽

Chia-Li Chen ◽

Jun Liu ◽

Derek J. Price ◽

...

Keyword(s):

Black Carbon ◽

Mixing State ◽

Carbon Particles ◽

Coating Formation

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Characterising mass-resolved mixing state of black carbon in Beijing using a morphology-independent measurement method

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-3645-2020 ◽

2020 ◽

Vol 20 (6) ◽

pp. 3645-3661 ◽

Cited By ~ 3

Author(s):

Chenjie Yu ◽

Dantong Liu ◽

Kurtis Broda ◽

Rutambhara Joshi ◽

Jason Olfert ◽

...

Keyword(s):

Black Carbon ◽

Atmospheric Aerosols ◽

Particle Morphology ◽

Urban Site ◽

Inversion Method ◽

Mixing State ◽

State Index ◽

Cloud Scavenging ◽

Highly Correlated ◽

State Mixing

Abstract. Refractory black carbon (rBC) in the atmosphere is known for its significant impacts on climate. The relationship between the microphysical and optical properties of rBC remains poorly understood and is influenced by its size and mixing state. Mixing state also influences its cloud scavenging potential and thus atmospheric lifetime. This study presents a coupling of a centrifugal particle mass analyser (CPMA) and a single-particle soot photometer (SP2) for the morphology-independent quantification of the mixing state of rBC-containing particles, used in the urban site of Beijing as part of the Air Pollution and Human Health–Beijing (APHH-Beijing) project during winter (10 November–10 December 2016) and summer (18 May–25 June 2017). This represents a highly dynamic polluted environment with a wide variety of conditions that could be considered representative of megacity area sources in Asia. An inversion method (used for the first time on atmospheric aerosols) is applied to the measurements to present two-variable distributions of both rBC mass and total mass of rBC-containing particles and calculate the mass-resolved mixing state of rBC-containing particles, using previously published metrics. The mass ratio between non-rBC material and rBC material (MR) is calculated to determine the thickness of a hypothetical coating if the rBC and other material followed a concentric sphere model (the equivalent coating thickness). The bulk MR (MRbulk) was found to vary between 2 and 12 in winter and between 2 and 3 in summer. This mass-resolved mixing state is used to derive the mass-weighted mixing state index for the rBC-containing particles (χrBC). χrBC quantifies how uniformly the non-rBC material is distributed across the rBC-containing-particle population, with 100 % representing uniform mixing. The χrBC in Beijing varied between 55 % and 70 % in winter depending on the dominant air masses, and χrBC was highly correlated with increased MRbulk and PM1 mass concentration in winter, whereas χrBC in summer varied significantly (ranging 60 %–75 %) within the narrowly distributed MRbulk and was found to be independent of air mass sources. In some model treatments, it is assumed that more atmospheric ageing causes the BC to tend towards a more homogeneous mixture, but this leads to the conclusion that the MRbulk may only act as a predictor of χrBC in winter. The particle morphology-independent and mass-based information on BC mixing used in this and future studies can be applied to mixing-state-aware models investigating atmospheric rBC ageing.

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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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