Black carbon linked aerosol hygroscopic growth: Size and mixing state are crucial

Abstract. Measurements of ageing and hygroscopicity variation of black carbon (BC) particles in Beijing were conducted using a 1.2 m3 quasi-atmospheric aerosol evolution study (QUALITY) chamber, which consisted of a bottom flow chamber through which ambient air was pulled continuously and an upper reaction chamber where ageing of BC particles occurred. Within the reaction chamber, transmission of the solar ultraviolet irradiation was approximately 50–60 %, wall loss of primary gaseous pollutants was negligible, and BC exhibited a half-lifetime of about 3–7 h. Typically, equilibrium for the primary gases, temperature and relative humidity between the reaction chamber and ambient air was established within 1 h. Rapid growth of BC particles occurred, with an average total growth of 77 ± 33 nm and average growth rate of 26 ± 11 nm h−1. Secondary organic aerosols (SOA) accounted for more than 90 % of the coating mass. The O ∕ C ratio of SOA was 0.5, lower than the ambient level. The hygroscopic growth factor of BC particles decreased slightly with an initial thin coating layer because of BC reconstruction, but subsequently increased to 1.06–1.08 upon further ageing. The κ (kappa) values for BC particles and coating materials were calculated as 0.035 and 0.040 at the subsaturation and supersaturation conditions, respectively, indicating low hygroscopicity of coated SOA on BC particles. Hence, our results indicate that initial photochemical ageing of BC particles leads to considerable modifications to morphology and optical properties but does not appreciably alter the particle hygroscopicity in Beijing.

Download Full-text

Size distributions of elemental carbon in the atmosphere of a coastal urban area in South China: characteristics, evolution processes, and implications for the mixing state

Atmospheric Chemistry and Physics ◽

10.5194/acp-8-5843-2008 ◽

2008 ◽

Vol 8 (19) ◽

pp. 5843-5853 ◽

Cited By ~ 53

Author(s):

X.-F. Huang ◽

J. Z. Yu

Keyword(s):

Urban Area ◽

Elemental Carbon ◽

Southern China ◽

Global Climate ◽

Particle Growth ◽

Size Distributions ◽

Hygroscopic Growth ◽

Mixing State ◽

Cloud Processing ◽

Fine Mode

Abstract. Elemental carbon (EC), as one of the primary light-absorbing components in the atmosphere, has a significant impact on both regional and global climate. The environmental impacts of EC are strongly dependent on its particle size. Little is known about the size distribution characteristics of EC particles in China's ambient environments. We report size distributions of EC particles in the urban area of Shenzhen in Southern China. In our samples, EC was consistently found in two modes, a fine mode and a coarse mode. The majority of EC mass (~80%) in this coastal metropolitan city resided in particles smaller than 3.2 μm in diameter. The fine mode peaked at around either 0.42 μm or 0.75 μm. While the mode at 0.42 μm could be ascribed to fresh vehicular emissions in the region, the mode at 0.75 μm was likely a result of particle growth from smaller EC particles. We theoretically investigated the particle growth processes that caused the EC particles to grow from 0.42 μm to 0.75 µm in the atmosphere. Our calculations indicate that the EC peak at 0.75 μm was not produced through either coagulation or H2SO4 condensation; both processes are too slow to lead to significant EC growth. Hygroscopic growth was also determined to be insignificant. Instead, addition of sulfate through in-cloud processing was found to cause significant growth of the EC particles and to explain the EC peak at 0.75 μm. We also estimated the mixing state of EC from the EC size distributions. In the droplet size, at least 45–60% of the EC mass in the summer samples and 68% of the EC mass in the winter samples was internally mixed with sulfate as a result of in-cloud processing. This information on EC should be considered in models of the optical properties of aerosols in this region. Our results also suggest that the in-cloud processing of primary EC particles could increase the light absorbing capacities through mixing EC with sulfate.

Download Full-text

The single-particle mixing state and cloud scavenging of black carbon at a high-altitude mountain site in southern China

10.5194/acp-2017-785 ◽

2017 ◽

Author(s):

Guohua Zhang ◽

Qinhao Lin ◽

Long Peng ◽

Xinhui Bi ◽

Duohong Chen ◽

...

Keyword(s):

Black Carbon ◽

Single Particle ◽

Southern China ◽

Climate Impacts ◽

Limited Information ◽

Mixing State ◽

Cloud Droplets ◽

Mountain Site ◽

Cloud Scavenging ◽

Scavenging Efficiency

Abstract. In the present study, a ground-based counterflow virtual impactor (GCVI) was used to sample cloud droplet residual (cloud RES) particles, while a parallel PM2.5 inlet was used to sample cloud-free or cloud interstitial (cloud INT) particles. The mixing state of black carbon (BC)-containing particles in a size range of 0.1–1.6 µm and the mass concentrations of BC in the cloud-free, RES and INT particles were investigated using a single particle aerosol mass spectrometer (SPAMS) and two aethalometers, respectively, at a mountain site (1690 m a.s.l.) in southern China. The measured BC-containing particles were internally mixed extensively with sulfate, and were activated into cloud droplets to the same extent as all the measured particles. The results indicate the preferential activation of larger particles and/or that the production of secondary compositions shifts the BC-containing particles towards larger sizes. BC-containing particles with an abundance of both sulfate and organics were activated less than those with sulfate but limited organics, implying the importance of the mixing state on the incorporation of BC-containing particles into cloud droplets. The mass scavenging efficiency of BC with an average of 33 % was similar for different cloud events independent of the air mass. This is the first time that both the mixing state and cloud scavenging of BC in China have been reported. Since limited information on BC-containing particles in the free troposphere is available, the results also provide an important reference for the representation of BC concentrations, properties, and climate impacts in modeling studies.

Download Full-text

Seasonal size distribution and mixing state of black carbon aerosols in a polluted urban environment of the Yangtze River Delta region, China

The Science of The Total Environment ◽

10.1016/j.scitotenv.2018.11.087 ◽

2019 ◽

Vol 654 ◽

pp. 300-310 ◽

Cited By ~ 6

Author(s):

Yifan Yang ◽

Xiaofeng Xu ◽

Yunjiang Zhang ◽

Shanshan Zheng ◽

Lingrui Wang ◽

...

Keyword(s):

Urban Environment ◽

Size Distribution ◽

Black Carbon ◽

Yangtze River ◽

Yangtze River Delta ◽

The Yangtze River ◽

Mixing State ◽

Yangtze River Delta Region ◽

Carbon Aerosols ◽

The Yangtze River Delta

Download Full-text

Size distribution and coating thickness of black carbon from the Canadian oil sands operations

10.5194/acp-2017-1015 ◽

2017 ◽

Author(s):

Yuan Cheng ◽

Shao-Meng Li ◽

Mark Gordon ◽

Peter Liu

Keyword(s):

Size Distribution ◽

Black Carbon ◽

Coating Thickness ◽

Oil Sands ◽

Radiative Forcing ◽

Climate Models ◽

Source Area ◽

Size Distributions ◽

Mixing State ◽

Earth’S Climate

Abstract. Black carbon (BC) plays an important role in the Earth’s climate system. However, parameterization of BC size and mixing state have not been well addressed in aerosol-climate models, introducing substantial uncertainties into the estimation of radiative forcing by BC. In this study, we focused on BC emissions from the massive oil sands (OS) industry in northern Alberta, based on an aircraft campaign conducted over the Athabasca OS region in 2013. A total of 14 flights were made over the OS source area, in which the aircraft was typically flown in a 4- or 5-sided polygon pattern along flight tracks encircling an OS facility. Another 3 flights were performed downwind of the OS source area, each of which involved at least three intercepting locations where the well-mixed OS plume was measured along flight tracks perpendicular to the wind direction. Comparable size distributions were observed for refractory black carbon (rBC) over and downwind of the OS facilities, with rBC mass median diameters (MMD) between ~ 135 and 145 nm that were characteristic of fresh urban emissions. This MMD range corresponded to rBC number median diameters (NMD) of ~ 60–70 nm, approximately 100 % higher than the NMD settings in some aerosol-climate models. The typical in- and out-of-plume segments of a flight, which had different rBC concentrations and photochemical ages, showed consistent rBC size distributions. Moreover, rBC size distributions remained unchanged at different downwind distances from the source area, suggesting that atmospheric aging would not necessarily change rBC size distribution. However, aging indeed influenced rBC mixing state. Coating thickness for rBC cores in the diameter range of 130–160 nm was nearly doubled within three hours when the OS plume was transported over a distance of 90 km from the source area.

Download Full-text

Mixing state of refractory black carbon aerosol in the South Asian outflow over the northern Indian Ocean during winter

10.5194/acp-2020-836 ◽

2020 ◽

Author(s):

Sobhan Kumar Kompalli ◽

Surendran Nair Suresh Babu ◽

Krishnaswamy Krishnamoorthy ◽

Sreedharan Krishnakumari Satheesh ◽

Mukunda M. Gogoi ◽

...

Keyword(s):

Indian Ocean ◽

Black Carbon ◽

South Asian ◽

Arabian Sea ◽

Equatorial Indian Ocean ◽

Mixing State ◽

Air Masses ◽

Continental Outflow ◽

Mass Concentrations

Abstract. Regional climatic implications of aerosol black carbon (BC) are well recognized over South Asia, which has a wide variety of anthropogenic sources in a large abundance. Significant uncertainties remain in its quantification due to lack of sufficient information on the microphysical properties (its concentration, size, and mixing state with other aerosol components), which determine the absorption potential of BC. Especially the information on mixing state of BC is extremely sparse over this region. In this study, first-ever observations of the size distribution and mixing state of individual refractory black carbon (rBC) particles in the south Asian outflow to Southeastern Arabian Sea, northern and equatorial Indian Ocean regions are presented based on measurements using a single particle soot photometer (SP2) aboard the ship cruise of the Integrated Campaign for Aerosols, gases, and Radiation Budget (ICARB-2018) during winter-2018 (16 January to 13 February). The results revealed significant spatial heterogeneity of BC characteristics. Highest rBC mass concentrations (~ 938 ± 293 ng m−3) with the highest relative coating thickness (RCT; the ratio of BC core to its coating diameters) of ~ 2.16 ± 0.19 are found over the Southeast Arabian Sea (SEAS) region, which is in the proximity of the continental outflow. As we move to farther oceanic regions, though the mass concentrations decreased by nearly half (~ 546 ± 80 ng m−3), BC still remained thickly coated (RCT ~ 2.05 ± 0.07). The air over the remote equatorial Indian Ocean, which received considerable marine air masses compared to the other regions, showed the lowest rBC mass concentrations (~ 206 ± 114 ng m−3), with a moderately thick coating (RCT ~ 1.73 ± 0.16). Even over oceanic regions far from the landmass, regions which received the outflow from more industrialized east coast/the Bay of Bengal had thicker coating (~ 104 nm) compared to regions that received outflow from the west coast/peninsular India (~ 86 nm). Although different regions of the ocean depicted contrasting concentrations and mixing state parameters due to varying extent and nature of the continental outflow as well as the atmospheric lifetime of air masses, the modal parameters of rBC mass-size distributions were similar over all the regions. The observed mono-modal distribution with mean mass median diameters (MMD) in the range of 0.19–0.20 μm suggested mixed sources of BC. The mean fraction of BC containing particles (FBC) varied in the range 0.20–0.28 (suggesting significant amounts of non-BC particles), whereas the bulk mixing ratio of coating mass to rBC mass was highest (8.77 ± 2.77) over the outflow regions compared to the remote ocean (4.29 ± 1.54) highlighting the role of outflow in providing condensable material for coating on rBC. These parameters, along with the information on size-resolved mixing state of BC cores, throw light on the role of sources and secondary processing of their complex mixtures for coating on BC under highly polluted conditions. Examination of the non-refractory sub-micrometre aerosol chemical composition obtained using the aerosol chemical speciation monitor (ACSM) suggested that the overall aerosol system was sulfate dominated over the far-oceanic regions. In contrast, organics were equally prominent adjacent to the coastal landmass. Association between the BC mixing state and aerosol chemical composition suggested that sulfate was the probable dominant coating material on rBC cores.

Download Full-text

Variation of the radiative properties during black carbon aging: theoretical and experimental intercomparison

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-19835-2015 ◽

2015 ◽

Vol 15 (14) ◽

pp. 19835-19872 ◽

Cited By ~ 1

Author(s):

C. He ◽

K.-N. Liou ◽

Y. Takano ◽

R. Zhang ◽

M. L. Zamora ◽

...

Keyword(s):

Black Carbon ◽

Cross Sections ◽

Theoretical Calculations ◽

Absorption Enhancement ◽

Core Shell ◽

Hygroscopic Growth ◽

Aging Model ◽

Scattering Cross ◽

Coating Morphology ◽

Scattering Cross Sections

Abstract. A theoretical black carbon (BC) aging model is developed to account for three typical evolution stages, namely, freshly emitted aggregates, coated BC by soluble material, and BC particles undergoing further hygroscopic growth. The geometric-optics surface-wave (GOS) approach is employed to compute the BC single-scattering properties at each aging stage, which are subsequently compared with laboratory measurements. Theoretical calculations are consistent with measurements in extinction and absorption cross sections for fresh BC aggregates, but overestimate the scattering cross sections for BC mobility diameters of 155, 245, and 320 nm, because of uncertainties associated with theoretical calculations for small particles as well as laboratory scattering measurements. The measured optical cross sections for coated BC by sulfuric acid and for those undergoing further hygroscopic growth are captured by theoretical calculations using a concentric core-shell structure, with differences of less than 20 %. This suggests that the core-shell shape represents the realistic BC coating morphology reasonably well in this case, which is consistent with the observed strong structure compaction during aging. We find that the absorption and scattering properties of fresh BC aggregates vary by up to 60 % due to uncertainty in the BC refractive index, which, however, is a factor of two smaller in the case of coated BC particles. Sensitivity analyses on the BC morphology show that the optical properties of fresh BC aggregates are more sensitive to fractal dimension than primary spherule size. The absorption and scattering cross sections of coated BC particles vary by more than a factor of two due to different coating structures. We find an increase of 20–250 % in absorption and a factor of 3–15 in scattering during aging, significantly depending on coating morphology and aging stages. Applying the aging model to CalNex 2010 field measurements, we show that the resulting BC direct radiative forcing (DRF) first increases from 1.5 to 1.7 W m-2 and subsequently decreases to 1.0 W m-2 during the transport from the Los Angeles Basin to downwind regions, as a result of the competition between absorption enhancement due to coating and dilution of BC concentration. The BC DRF can vary by up to a factor of two due to differences in BC coating morphology. Thus, an accurate estimate of BC DRF requires the incorporation of a dynamic BC aging process that accounts for realistic morphology in climate models, particularly for the regional analysis with high atmospheric heterogeneity.

Download Full-text