Brown Carbon Spheres in East Asian Outflow and Their Optical Properties

Abstract. Black carbon, brown carbon, and mineral dust are three of the most important light absorbing aerosols. Their optical properties differ greatly and are distinctive functions of the wavelength of light. Most optical instruments that quantify light absorption, however, are unable to distinguish one type of absorbing aerosol from another. It is thus instructive to separate total absorption from these different light absorbers to gain a better understanding of the optical characteristics of each aerosol type. During the EAST-AIRE (East Asian Study of Tropospheric Aerosols: an International Regional Experiment) campaign near Beijing, we measured light scattering using a nephelometer, and light absorption using an aethalometer and a particulate soot absorption photometer. We also measured the total mass concentrations of carbonaceous (elemental and organic carbon) and inorganic particulates, as well as aerosol number and mass distributions. We were able to identify periods during the campaign that were dominated by dust, biomass burning, fresh (industrial) chimney plumes, other coal burning pollution, and relatively clean (background) air for Northern China. Each of these air masses possessed distinct intensive optical properties, including the single scatter albedo and Ångstrom exponents. Based on the wavelength-dependence and particle size distribution, we apportioned total light absorption to black carbon, brown carbon, and dust; their mass absorption efficiencies at 550 nm were estimated to be 9.5, 0.5 (a lower limit value), and 0.03 m2/g, respectively. While agreeing with the common consensus that black carbon is the most important light absorber in the mid-visible, we demonstrated that brown carbon and dust could also cause significant absorption, especially at shorter wavelengths.

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Deposition of brown carbon onto snow: changes in snow optical and radiative properties

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-6095-2020 ◽

2020 ◽

Vol 20 (10) ◽

pp. 6095-6114 ◽

Cited By ~ 2

Author(s):

Nicholas D. Beres ◽

Deep Sengupta ◽

Vera Samburova ◽

Andrey Y. Khlystov ◽

Hans Moosmüller

Keyword(s):

Optical Properties ◽

Organic Carbon ◽

Total Organic Carbon ◽

Radiative Forcing ◽

Radiative Properties ◽

Unit Mass ◽

Small Scale ◽

Snow Surface ◽

Brown Carbon ◽

Snow Albedo

Abstract. Light-absorbing organic carbon aerosol – colloquially known as brown carbon (BrC) – is emitted from combustion processes and has a brownish or yellowish visual appearance, caused by enhanced light absorption at shorter visible and ultraviolet wavelengths (0.3 µm≲λ≲0.5 µm). Recently, optical properties of atmospheric BrC aerosols have become the topic of intense research, but little is known about how BrC deposition onto snow surfaces affects the spectral snow albedo, which can alter the resulting radiative forcing and in-snow photochemistry. Wildland fires in close proximity to the cryosphere, such as peatland fires that emit large quantities of BrC, are becoming more common at high latitudes, potentially affecting nearby snow and ice surfaces. In this study, we describe the artificial deposition of BrC aerosol with known optical, chemical, and physical properties onto the snow surface, and we monitor its spectral radiative impact and compare it directly to modeled values. First, using small-scale combustion of Alaskan peat, BrC aerosols were artificially deposited onto the snow surface. UV–Vis absorbance and total organic carbon (TOC) concentration of snow samples were measured for samples with and without artificial BrC deposition. These measurements were used to first derive a BrC (mass) specific absorption (m2 g−1) across the UV–Vis spectral range. We then estimate the imaginary part of the refractive index of deposited BrC aerosol using a volume mixing rule. Single-particle optical properties were calculated using Mie theory, and these values were used to show that the measured spectral snow albedo of snow with deposited BrC was in general agreement with modeled spectral snow albedo using calculated BrC optical properties. The instantaneous radiative forcing per unit mass of total organic carbon deposited to the ambient snowpack was found to be 1.23 (+0.14/-0.11) W m−2 per part per million (ppm). We estimate the same deposition onto a pure snowpack without light-absorbing impurities would have resulted in an instantaneous radiative forcing per unit mass of 2.68 (+0.27/-0.22) W m−2 per ppm of BrC deposited.

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Chemical and optical properties of carbonaceous aerosols in Nanjing, eastern China: regionally transported biomass burning contribution

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-11213-2019 ◽

2019 ◽

Vol 19 (17) ◽

pp. 11213-11233 ◽

Cited By ~ 8

Author(s):

Xiaoyan Liu ◽

Yan-Lin Zhang ◽

Yiran Peng ◽

Lulu Xu ◽

Chunmao Zhu ◽

...

Keyword(s):

Optical Properties ◽

Organic Carbon ◽

Solar Energy ◽

Energy Absorption ◽

Biomass Burning ◽

Eastern China ◽

Water Soluble ◽

Carbonaceous Aerosols ◽

Southeastern China ◽

Brown Carbon

Abstract. Biomass burning can significantly impact the chemical and optical properties of carbonaceous aerosols. Here, the biomass burning impacts were studied during wintertime in a megacity of Nanjing, eastern China. The high abundance of biomass burning tracers such as levoglucosan (lev), mannosan (man), galactosan (gal) and non-sea-salt potassium (nss-K+) was found during the studied period with the concentration ranges of 22.4–1476 ng m−3, 2.1–56.2 ng m−3, 1.4–32.2 ng m−3 and 0.2–3.8 µg m−3, respectively. The significant contribution of biomass burning to water-soluble organic carbon (WSOC; 22.3±9.9 %) and organic carbon (OC; 20.9±9.3 %) was observed in this study. Backward air mass origin analysis, potential emission sensitivity of elemental carbon (EC) and MODIS fire spot information indicated that the elevations of the carbonaceous aerosols were due to the transported biomass-burning aerosols from southeastern China. The characteristic mass ratio maps of lev∕man and lev∕nss-K+ suggested that the biomass fuels were mainly crop residuals. Furthermore, the strong correlation (p < 0.01) between biomass burning tracers (such as lev) and light absorption coefficient (babs) for water-soluble brown carbon (BrC) revealed that biomass burning emissions played a significant role in the light-absorption properties of carbonaceous aerosols. The solar energy absorption due to water-soluble brown carbon and EC was estimated by a calculation based on measured light-absorbing parameters and a simulation based on a radiative transfer model (RRTMG_SW). The solar energy absorption of water-soluble BrC in short wavelengths (300–400 nm) was 0.8±0.4 (0.2–2.3) W m−2 (figures in parentheses represent the variation range of each parameter) from the calculation and 1.2±0.5 (0.3–1.9) W m−2 from the RRTMG_SW model. The absorption capacity of water-soluble BrC accounted for about 20 %–30 % of the total absorption of EC aerosols. The solar energy absorption of water-soluble BrC due to biomass burning was estimated as 0.2±0.1 (0.0–0.9) W m−2, considering the biomass burning contribution to carbonaceous aerosols. Potential source contribution function model simulations showed that the solar energy absorption induced by water-soluble BrC and EC aerosols was mostly due to the regionally transported carbonaceous aerosols from source regions such as southeastern China. Our results illustrate the importance of the absorbing water-soluble brown carbon aerosols in trapping additional solar energy in the low-level atmosphere, heating the surface and inhibiting the energy from escaping the atmosphere.

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

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-2017-2020 ◽

2020 ◽

Vol 20 (4) ◽

pp. 2017-2030 ◽

Cited By ~ 3

Author(s):

Can Wu ◽

Gehui Wang ◽

Jin Li ◽

Jianjun Li ◽

Cong Cao ◽

...

Keyword(s):

Optical Properties ◽

Biomass Burning ◽

Isotope Composition ◽

Stable Carbon Isotope ◽

Urban Atmosphere ◽

Semiarid Region ◽

Chemical Compositions ◽

Brown Carbon ◽

Polycyclic Aromatic ◽

Fine Mode

Abstract. To investigate the characteristics of atmospheric brown carbon (BrC) in the semiarid 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 (r > 0.78). The light absorptions (absλ=365 nm) of H2O extracts and MeOH extracts in winter were 28±16 and 49±32 M m−1, 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 (< 2.1 µm) during winter and summer, accounting for 81 % and 65 % of the total absorption of BrC, respectively. The light absorption and stable carbon isotope composition measurements showed an increasing ratio of absλ=365 nm-MeOH to absλ=550 nm-EC along with an enrichment of 13C in PM2.5 during the haze development, indicating an accumulation of secondarily formed BrC (e.g., nitrophenols) in the aerosol aging process. Positive matrix factorization (PMF) analysis showed that biomass burning, fossil fuel combustion, secondary formation, and fugitive dust are the major sources of BrC in the city, accounting for 55 %, 19 %, 16 %, and 10 % of the total BrC of PM2.5, respectively.

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Analysis of aerosol properties at recent (2015-2018) high PM concentration events in two super-mega cities, Seoul and Beijing

10.5194/egusphere-egu2020-20979 ◽

2020 ◽

Author(s):

Yesol Cha ◽

Chang-Keun Song

Keyword(s):

Air Pollution ◽

Optical Properties ◽

East Asian ◽

Optical Characteristics ◽

High Concentration ◽

East Asian Region ◽

Asian Region ◽

Physical Chemical ◽

Mega Cities ◽

Aerosol Properties

To meet public concerns of health caused by the high concentration of PM highly raised, this research has been done to find out unique physical, chemical, and optical characteristics of aerosols in the case of recent four years high PM concentration events over the East Asian region, especially in Korea and China. Severe air pollution over the East Asian region has occurred by the rapid development of urban areas and industrialization. Also, the meteorological conditions in East Asia are strongly correlated with a high concentration of air pollution and seasonal variation of aerosols. There are three types of aerosol properties (physical, chemical, and optical property), and each property is essential to understand the characteristics of regional and seasonal high PM concentrations. This research has been done to find out unique physical, chemical, and optical characteristics of aerosols in the case of high PM concentration events, especially in two super-mega cities (Seoul and Beijing) of Korea and China, by using various observations measured during recent four years. To analyze those characteristics of aerosols at high concentration events occur, various measurement data are used, like ambient surface air monitoring data (for physical properties) from national network in both Korea and China, Intensive Monitoring Data (for chemical properties), AERONET, GOCI satellite (for optical properties), and meteorological data during recent years (2015 &#8211; 2018). This study can provide observational evidence to confirm that each different region has different physical, chemical and optical characteristics of aerosol with the different time periods. The comprehensive results analyzed from this study and integrated methodologies suggested in this study might be useful to make a better in-depth understanding of the relations between various aerosol properties in certain regions and periods.&#160;&#160;Key words : Aerosol, High concentration events, Physical/Chemical/Optical Properties of aerosols

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Exploring the observational constraints on the simulation of brown carbon

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-635-2018 ◽

2018 ◽

Vol 18 (2) ◽

pp. 635-653 ◽

Cited By ~ 44

Author(s):

Xuan Wang ◽

Colette L. Heald ◽

Jiumeng Liu ◽

Rodney J. Weber ◽

Pedro Campuzano-Jost ◽

...

Keyword(s):

Optical Properties ◽

Transport Model ◽

Model Simulation ◽

Radiative Transfer Model ◽

Transfer Model ◽

Observational Constraints ◽

Aircraft Measurements ◽

Radiative Effect ◽

Brown Carbon ◽

Direct Measurements

Abstract. Organic aerosols (OA) that strongly absorb solar radiation in the near-UV are referred to as brown carbon (BrC). The sources, evolution, and optical properties of BrC remain highly uncertain and contribute significantly to uncertainty in the estimate of the global direct radiative effect (DRE) of aerosols. Previous modeling studies of BrC optical properties and DRE have been unable to fully evaluate model performance due to the lack of direct measurements of BrC absorption. In this study, we develop a global model simulation (GEOS-Chem) of BrC and test it against BrC absorption measurements from two aircraft campaigns in the continental US (SEAC4RS and DC3). To the best of our knowledge, this is the first study to compare simulated BrC absorption with direct aircraft measurements. We show that BrC absorption properties estimated based on previous laboratory measurements agree with the aircraft measurements of freshly emitted BrC absorption but overestimate aged BrC absorption. In addition, applying a photochemical scheme to simulate bleaching/degradation of BrC improves model skill. The airborne observations are therefore consistent with a mass absorption coefficient (MAC) of freshly emitted biomass burning OA of 1.33 m2 g−1 at 365 nm coupled with a 1-day whitening e-folding time. Using the GEOS-Chem chemical transport model integrated with the RRTMG radiative transfer model, we estimate that the top-of-the-atmosphere all-sky direct radiative effect (DRE) of OA is −0.344 Wm−2, 10 % higher than that without consideration of BrC absorption. Therefore, our best estimate of the absorption DRE of BrC is +0.048 Wm−2. We suggest that the DRE of BrC has been overestimated previously due to the lack of observational constraints from direct measurements and omission of the effects of photochemical whitening.

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Review of ‘Significant seasonal changes in optical properties of brown carbon in the mid-latitude atmosphere’

10.5194/acp-2019-952-rc2 ◽

2019 ◽

Author(s):

Anonymous

Keyword(s):

Optical Properties ◽

Seasonal Changes ◽

Brown Carbon

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