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

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 the ambient environments of China. We here report size distributions of EC in the urban area of Shenzhen in South China. EC consistently exhibited two modes, a fine and a coarse mode. The majority of EC (~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 this region, the mode at 0.75 μm had to be a result of particle growth from smaller EC particles. We made a theoretical investigation of the particle growth processes that were responsible for 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 could not be produced through either coagulation or H2SO4 condensation; both were too slow to lead to significant EC growth. Hygroscopic growth was also calculated to be impossible. Instead, addition of sulfate through in-cloud processing was found to be able to significantly grow EC particles to explain the EC peak at 0.75 μm. We also estimated from the EC size distributions the mixing state of EC. In the droplet size, at least 45–60% of EC mass in the summer samples and 68% of EC mass in the winter samples was internally mixed with sulfate as a result of in-cloud processing. Such information on EC needs to be considered in modeling aerosol optical properties in this region. Our results also suggest that the in-cloud processing of primary EC particles could enhance light absorbing capacities through mixing EC and sulfate.

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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.

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Light absorption of black carbon aerosol and its enhancement by mixing state in an urban atmosphere in South China

Atmospheric Environment ◽

10.1016/j.atmosenv.2012.12.009 ◽

2013 ◽

Vol 69 ◽

pp. 118-123 ◽

Cited By ~ 57

Author(s):

Zi-Juan Lan ◽

Xiao-Feng Huang ◽

Kuang-You Yu ◽

Tian-Le Sun ◽

Li-Wu Zeng ◽

...

Keyword(s):

Black Carbon ◽

South China ◽

Light Absorption ◽

Urban Atmosphere ◽

Mixing State ◽

Black Carbon Aerosol

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Size-distributions of <i>n</i>-alkanes, PAHs and hopanes and their sources in the urban, mountain and marine atmospheres over East Asia

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-8869-2009 ◽

2009 ◽

Vol 9 (22) ◽

pp. 8869-8882 ◽

Cited By ~ 83

Author(s):

G. Wang ◽

K. Kawamura ◽

M. Xie ◽

S. Hu ◽

S. Gao ◽

...

Keyword(s):

East Asia ◽

Geometric Mean ◽

Bimodal Distribution ◽

Size Distributions ◽

Marine Aerosols ◽

Hygroscopic Growth ◽

Okinawa Island ◽

Marine Samples ◽

Fine Mode ◽

The Difference

Abstract. Size-segregated (9 stages) n-alkanes, polycyclic aromatic hydrocarbons (PAHs) and hopanes in the urban (Baoji city in inland China), mountain (Mt. Tai in east coastal China) and marine (Okinawa Island, Japan) atmospheres over East Asia were studied using a GC/MS technique. Ambient concentrations of n-alkanes (1698±568 ng m−3 in winter and 487±145 ng m−3 in spring), PAHs (536±80 and 161±39 ng m−3), and hopanes (65±24 and 20±2.4 ng m−3) in the urban air are 1–2 orders of magnitude higher than those in the mountain aerosols and 2–3 orders of magnitude higher than those in the marine samples. Mass ratios of n-alkanes, PAHs and hopanes clearly demonstrate coal-burning emissions as their major source. Size distributions of fossil fuel derived n-alkane, PAHs and hopanes were found to be unimodal in most cases, peaking at 0.7–1.1 μm size. In contrast, plant wax derived n-alkanes presented a bimodal distribution with two peaks at the sizes of 0.7–1.1 μm and >4.7 μm in the summer mountain and spring marine samples. Among the three types of samples, geometric mean diameter (GMD) of the organics in fine mode (<2.1 μm) was found to be smallest (av. 0.63 μm in spring) for the urban samples and largest (1.01 μm) for the marine samples, whereas the GMD in coarse mode (≥2.1 μm) was found to be smallest (3.48 μm) for the marine aerosols and largest (4.04 μm) for the urban aerosols. The fine mode GMDs of the urban and mountain samples were larger in winter than in spring and summer. Moreover, GMDs of 3- and 4-ring PAHs were larger than those of 5- and 6-ring PAHs in the three types of atmospheres. Such differences in GMDs can be interpreted by the repartitioning of organic compounds and the coagulation and hygroscopic growth of particles during a long-range transport from the inland continent to the marine area, as well as the difference in their sources among the three regions.

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Assessment of cloud-related fine-mode AOD enhancements based on AERONET SDA product

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-5991-2017 ◽

2017 ◽

Vol 17 (9) ◽

pp. 5991-6001 ◽

Cited By ~ 10

Author(s):

Antti Arola ◽

Thomas F. Eck ◽

Harri Kokkola ◽

Mikko R. A. Pitkänen ◽

Sami Romakkaniemi

Keyword(s):

Optical Depth ◽

Relative Role ◽

Hygroscopic Growth ◽

Cloud Optical Depth ◽

Cloud Processing ◽

Clear Sky ◽

Coarse Mode ◽

Fine Mode ◽

L1 And L2 ◽

Sky Conditions

Abstract. AERONET (AErosol RObotic NETwork), which is a network of ground-based sun photometers, produces a data product called the aerosol spectral deconvolution algorithm (SDA) that utilizes spectral total aerosol optical depth (AOD) data to infer the component fine- and coarse-mode optical depths at 500 nm. Based on its assumptions, SDA identifies cloud optical depth as the coarse-mode AOD component and therefore effectively computes the fine-mode AOD also in mixed cloud–aerosol observations. Therefore, it can be argued that the more representative AOD for fine-mode fraction should be based on all direct sun measurements and not only on those cloud screened for clear-sky conditions, i.e., on those from level 1 (L1) instead of level 2 (L2) in AERONET. The objective of our study was to assess, including all the available AERONET sites, how the fine-mode AOD is enhanced in cloudy conditions, contrasting SDA L1 and L2 in our analysis. Assuming that the cloud screening correctly separates the cloudy and clear-sky conditions, then the increases in fine-mode AOD can be due to various cloud-related processes, mainly by the strong hygroscopic growth of particles in the vicinity of clouds and in-cloud processing leading to growth of accumulation mode particles. We estimated these cloud-related enhancements in fine-mode AOD seasonally and found, for instance, that in June–August season the average over all the AERONET sites was 0.011, when total fine-mode AOD from L2 data was 0.154; therefore, the relative enhancement was 7 %. The enhancements were largest, both absolutely and relatively, in East Asia; for example, in June–August season the absolute and relative differences in fine-mode AOD, between L1 and L2 measurements, were 0.022 and 10 %, respectively. Corresponding values in North America and Europe were about 0.01 and 6–7 %. In some highly polluted areas, the enhancement is greater than these regional averages, e.g., in Beijing region and in June–July–August (JJA) season the corresponding absolute values were about 0.1. It is difficult to separate the fine-mode AOD enhancements due to in-cloud processing and hygroscopic growth, but we attempted to get some understanding by conducting a similar analysis for SDA-based fine-mode Ångström exponent (AE) patterns. Moreover, we exploited a cloud parcel model, in order to understand in detail the relative role of different processes. We found that in marine conditions, were aerosol concentration are low and cloud scavenging is efficient, the AE changes in opposite direction than in the more polluted conditions, were hygroscopic growth of particles leads to a negative AE change.

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Assessment of cloud related fine mode AOD enhancements based on AERONET SDA product

10.5194/acp-2016-600 ◽

2016 ◽

Author(s):

A. Arola ◽

T. F. Eck ◽

H. Kokkola ◽

M. R. A. Pitkänen ◽

S. Romakkaniemi

Keyword(s):

Relative Role ◽

Hygroscopic Growth ◽

Cloud Droplets ◽

Cloud Optical Depth ◽

Cloud Processing ◽

Clear Sky ◽

Coarse Mode ◽

Fine Mode ◽

L1 And L2 ◽

Sky Conditions

Abstract. AERONET (AErosol RObotic NETwork), which is a network of ground-based sun photometers, produces a data product called the Aerosol Spectral Deconvolution Algorithm (SDA) that utilizes spectral total extinction AOD data to infer the component fine and coarse mode optical depths at 500 nm. Based on its assumptions, SDA identifies cloud optical depth as the coarse mode AOD component and therefore effectively computes the fine mode AOD also in mixed cloud-aerosol ob- servations. Therefore, it can be argued that the more representative AOD for fine mode fraction should be based on all direct sun measurements and not only on those cloud-screened for clear-sky conditions, in other words on those from Level 1 (L1) instead of Level 2 (L2). The objective of our study was to assess, including all the available AERONET sites, the magnitude of this cloud enhancement in fine mode AOD, in other words contrasting SDA L1 and L2 in our analysis. Assuming that the cloud-screening correctly separates the cloudy and clear-sky conditions, then the increases in fine mode AOD in can be due to various cloud-related processes, mainly by in-cloud processing, hygroscopic growth and new particle formation from gas-to-particle conversion in aqueous phase in cloud droplets. We estimated these cloud-related enhancements in fine mode AOD seasonally and found, for instance, than in June-August season the average over all the AERONET sites was 0.011, when total fine mode AOD from L2 data was 0.154, therefore the relative enhancement was 7 %. The enhancements were largest, both absolutely and relatively, in East-Asia; for example in June–August season the absolute and relative differences in fine mode AOD, between L1 and L2 measurements, were 0.022 and 10 %, respectively. Corresponding values in North-America and Europe were about 0.01 and 6–7 %. In some some highly polluted cities the enhancement is greater than these regional averages, e.g. in Beijing and in JJA season the corresponding absolute values were about 0.1. It is difficult to separate the fine mode AOD enhancements due to in-cloud processing and hygroscopic growth, but we attempted to get some understanding by conducting a similar analysis for SDA-based fine mode Angstrom Exponent (AE) patterns. Moreover, we exploited a cloud parcel model, in order to understand in more depth the relative role of the processes inducing the changes in the effective fine mode particle size, and thus the changes in fine mode AE.

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The characteristics of atmospheric brown carbon in Xi'an, inland China: sources, size distributions and optical properties

10.5194/acp-2019-640 ◽

2019 ◽

Author(s):

Can Wu ◽

Gehui Wang ◽

Jin Li ◽

Jianjun Li ◽

Cong Cao ◽

...

Keyword(s):

Optical Properties ◽

Urban Atmosphere ◽

Chemical Compositions ◽

Size Distributions ◽

Brown Carbon ◽

Optical Wavelength ◽

Polycyclic Aromatic ◽

Fine Mode ◽

Semi Arid Region ◽

Oxygenated Pahs

Abstract. To investigate the characteristic of atmospheric brown carbon (BrC) in the semi-arid region of East Asia, PM2.5 and size-resolved particles in the urban atmosphere of Xi'an, inland China during the winter and summer of 2017 were collected and analyzed for optical properties and chemical compositions. Methanol extracts (MeOH-extracts) were more light-absorbing than water extracts (H2O- extracts) in the optical wavelength of 300–600 nm, and well correlated with nitrophenols, polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs (R2 > 0.6). The light absorptions (absλ=365nm) of H2O- extracts and MeOH-extracts in winter were 28 ± 16 M/m and 49 ± 32 M/m, respectively, which are about 10 times higher than those in summer, mainly due to the enhanced emissions from biomass burning for house heating. Water extracted BrC predominately occurred in the fine mode (

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A 3D study on the amplification of regional haze and particle growth by local emissions

npj Climate and Atmospheric Science ◽

10.1038/s41612-020-00156-5 ◽

2021 ◽

Vol 4 (1) ◽

Author(s):

Wei Du ◽

Lubna Dada ◽

Jian Zhao ◽

Xueshun Chen ◽

Kaspar R. Daellenbach ◽

...

Keyword(s):

Atmospheric Stability ◽

Ground Level ◽

Particle Growth ◽

Chemical Compositions ◽

Size Distributions ◽

Aerosol Composition ◽

Regional Haze ◽

Haze Formation ◽

Beijing China

AbstractThe role of new particle formation (NPF) events and their contribution to haze formation through subsequent growth in polluted megacities is still controversial. To improve the understanding of the sources, meteorological conditions, and chemistry behind air pollution, we performed simultaneous measurements of aerosol composition and particle number size distributions at ground level and at 260 m in central Beijing, China, during a total of 4 months in 2015–2017. Our measurements show a pronounced decoupling of gas-to-particle conversion between the two heights, leading to different haze processes in terms of particle size distributions and chemical compositions. The development of haze was initiated by the growth of freshly formed particles at both heights, whereas the more severe haze at ground level was connected directly to local primary particles and gaseous precursors leading to higher particle growth rates. The particle growth creates a feedback loop, in which a further development of haze increases the atmospheric stability, which in turn strengthens the persisting apparent decoupling between the two heights and increases the severity of haze at ground level. Moreover, we complemented our field observations with model analyses, which suggest that the growth of NPF-originated particles accounted up to ∼60% of the accumulation mode particles in the Beijing–Tianjin–Hebei area during haze conditions. The results suggest that a reduction in anthropogenic gaseous precursors, suppressing particle growth, is a critical step for alleviating haze although the number concentration of freshly formed particles (3–40 nm) via NPF does not reduce after emission controls.

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