Photochemical degradation affects the light absorption of water-soluble brown carbon in the South Asian outflow

Light-absorbing organic aerosols, known as brown carbon (BrC), counteract the overall cooling effect of aerosols on Earth’s climate. The spatial and temporal dynamics of their light-absorbing properties are poorly constrained and unaccounted for in climate models, because of limited ambient observations. We combine carbon isotope forensics (δ13C) with measurements of light absorption in a conceptual aging model to constrain the loss of light absorptivity (i.e., bleaching) of water-soluble BrC (WS-BrC) aerosols in one of the world’s largest BrC emission regions—South Asia. On this regional scale, we find that atmospheric photochemical oxidation reduces the light absorption of WS-BrC by ~84% during transport over 6000 km in the Indo-Gangetic Plain, with an ambient first-order bleaching rate of 0.20 ± 0.05 day−1 during over-ocean transit across Bay of Bengal to an Indian Ocean receptor site. This study facilitates dynamic parameterization of WS-BrC absorption properties, thereby constraining BrC climate impact over South Asia.

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Sources and light absorption of water-soluble brown carbon aerosols in the outflow from northern China

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-19625-2013 ◽

2013 ◽

Vol 13 (7) ◽

pp. 19625-19648 ◽

Cited By ~ 1

Author(s):

E. N. Kirillova ◽

A. Andersson ◽

J. Han ◽

M. Lee ◽

Ö. Gustafsson

Keyword(s):

Light Absorption ◽

Radiative Forcing ◽

Climate Models ◽

Large Fraction ◽

Regional Climate ◽

Northern China ◽

Water Soluble ◽

Cloud Formation ◽

Carbonaceous Aerosols ◽

Brown Carbon

Abstract. High loadings of anthropogenic carbonaceous aerosols in Chinese air influence the air quality for over 1 billion people and impact the regional climate. A large fraction (17–80%) of this aerosol carbon is water soluble, promoting cloud formation and thus climate cooling. Recent findings, however, suggest that water-soluble carbonaceous aerosols also absorb sunlight, bringing additional direct and indirect climate warming effects, yet the extent and nature of light absorption by this water-soluble brown carbon (WS-BrC) and its relation to sources is poorly understood. Here, we combine source estimates constrained by dual-carbon-isotope with light absorption measurements of WS-BrC for a March 2011 campaign at the Korea Climate Observatory at Gosan (KCOG), a receptor station in SE Yellow Sea for the outflow from N. China. The mass absorption cross-section (MAC) of WS-BrC for air masses from N. China were in general higher (0.8–1.1 m2 g−1), than from other source regions (0.3–0.8 m2 g−1). We estimate that this effect corresponds to 13–49% of the radiative forcing caused by light absorption by black carbon. Radiocarbon constraints show that the WS-BrC in Chinese outflow had significantly higher amounts of fossil sources (30–50%) compared to previous findings in S. Asia, N. America and Europe. Stable carbon (δ13C) measurements indicated influence of aging during air mass transport. These results indicate the importance of incorporating WS-BrC in climate models and the need to constrain climate effects by emission source sector.

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Brown carbon in the continental outflow to the North Indian Ocean

Environmental Science Processes & Impacts ◽

10.1039/c9em00089e ◽

2019 ◽

Vol 21 (6) ◽

pp. 970-987 ◽

Cited By ~ 10

Author(s):

Srinivas Bikkina ◽

Manmohan Sarin

Keyword(s):

Indian Ocean ◽

Soluble Fraction ◽

North Indian Ocean ◽

Water Soluble ◽

Gangetic Plain ◽

Brown Carbon ◽

Water Soluble Fraction ◽

The North ◽

Continental Outflow ◽

Indo Gangetic Plain

In this paper, we synthesize the size distribution and optical properties of the atmospheric water-soluble fraction of light-absorbing organic carbon (brown carbon; BrC) in the continental outflow from the Indo-Gangetic Plain (IGP) in South Asia to the North Indian Ocean.

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Light absorption properties of elemental carbon (EC) and water-soluble brown carbon (WS–BrC) in the Kathmandu Valley, Nepal: A 5-year study

Environmental Pollution ◽

10.1016/j.envpol.2020.114239 ◽

2020 ◽

Vol 261 ◽

pp. 114239 ◽

Cited By ~ 3

Author(s):

Pengfei Chen ◽

Shichang Kang ◽

Lekhendra Tripathee ◽

Kirpa Ram ◽

Maheswar Rupakheti ◽

...

Keyword(s):

Light Absorption ◽

Elemental Carbon ◽

Water Soluble ◽

Kathmandu Valley ◽

Absorption Properties ◽

Brown Carbon

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Measurement Report: Optical properties and sources of water-soluble brown carbon in Tianjin, North China: insights from organic molecular compositions

10.5194/acp-2021-1045 ◽

2022 ◽

Author(s):

Junjun Deng ◽

Hao Ma ◽

Xinfeng Wang ◽

Shujun Zhong ◽

Zhimin Zhang ◽

...

Keyword(s):

Optical Properties ◽

Biomass Burning ◽

Light Absorption ◽

Radiative Forcing ◽

North China ◽

Water Soluble ◽

Formation Mechanisms ◽

Chemical Compositions ◽

Brown Carbon ◽

Near Ultraviolet

Abstract. Brown carbon (BrC) aerosols exert vital impacts on climate change and atmospheric photochemistry due to their light absorption in the wavelength range from near-ultraviolet (UV) to visible light. However, the optical properties and formation mechanisms of ambient BrC remain poorly understood, limiting the estimation of their radiative forcing. In the present study, fine aerosols (PM2.5) were collected during 2016–2017 on a day/night basis over urban Tianjin, a megacity in North China, to obtain seasonal and diurnal patterns of atmospheric water-soluble BrC. There were obvious seasonal but no evident diurnal variations in light absorption properties of BrC. In winter, BrC showed much stronger light absorbing ability since mass absorption efficiency at 365 nm (MAE365) (1.54 ± 0.33 m2 g−1), which was 1.8 times larger than that (0.84 ± 0.22 m2 g−1) in summer. Direct radiative effects by BrC absorption relative to black carbon in the UV range were 54.3 ± 16.9 % and 44.6 ± 13.9 %, respectively. In addition, five fluorescent components in BrC, including three humic-like fluorophores and two protein-like fluorophores were identified with excitation-emission matrix fluorescence spectrometry and parallel factor (PARAFAC) analysis. The lowly-oxygenated components contributed more to winter and nighttime samples, while more-oxygenated components increased in summer and daytime samples. The higher humification index (HIX) together with lower biological index (BIX) and fluorescence index (FI) suggest that the chemical compositions of BrC were associated with a high aromaticity degree in summer and daytime due to photobleaching. Fluorescent properties indicate that wintertime BrC were predominantly affected by primary emissions and fresh secondary organic aerosol (SOA), while summer ones were more influenced by aging processes. Results of source apportionments using organic molecular compositions of the same set of aerosols reveal that fossil fuel combustion and aging processes, primary bioaerosol emission, biomass burning, and biogenic and anthropogenic SOA formation were the main sources of BrC. Biomass burning contributed much larger to BrC in winter and at nighttime, while biogenic SOA contributed more in summer and at daytime. Especially, our study highlights that primary bioaerosol emission is an important source of BrC in urban Tianjin in summer.

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Size-resolved measurements of brown carbon and estimates of their contribution to ambient fine particle light absorption based on water and methanol extracts

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-18233-2013 ◽

2013 ◽

Vol 13 (7) ◽

pp. 18233-18276 ◽

Cited By ~ 3

Author(s):

J. Liu ◽

M. Bergin ◽

H. Guo ◽

L. King ◽

N. Kotra ◽

...

Keyword(s):

Organic Carbon ◽

Light Absorption ◽

Fine Particle ◽

Elemental Carbon ◽

Fine Particles ◽

Water Soluble ◽

Rural Site ◽

Brown Carbon ◽

Methanol Extracts ◽

Carbon Absorption

Abstract. Light absorbing organic carbon, often termed brown carbon, has the potential to significantly contribute to the visible light absorption budget, particularly at shorter wavelengths. Currently, the relative contributions of particulate brown carbon to light absorption, as well as the sources of brown carbon are poorly understood. With this in mind field measurements were made at both urban (Atlanta), and rural (Yorkville) sites in Georgia. Measurements in Atlanta were made at both a central site and a road side site adjacent to a main highway near the city center. Fine particle brown carbon optical absorption is estimated based on Mie calculations using direct size resolved measurements of chromophores in filter extracts. Size-resolved atmospheric aerosol samples were collected using a cascade impactor and analyzed for water-soluble organic carbon (WSOC), organic and elemental carbon (OC and EC), and solution light absorption spectra of water and methanol extracts. Methanol extracts were more light-absorbing than water extracts for all size ranges and wavelengths. Absorption refractive indices of the organic extracts were calculated from solution measurements for a range of wavelengths and used with Mie theory to predict the light absorption by fine particles comprised of these components, under the assumption that brown carbon and other aerosol components were externally mixed. For all three sites, chromophores were predominately in the accumulation mode with an aerodynamic mean diameter of 0.5 μm, an optically effective size range resulting in predicted particle light absorption being a factor of 2 higher than bulk solution absorption. Fine particle absorption was also measured with a Multi-Angle Absorption Photometer (MAAP) and seven-wavelength Aethalometer. Scattering-corrected aethalometer and MAAP absorption were in good agreement at 670 nm and Mie-estimated absorption based on size-resolved EC data were within 30% of these optical instruments. When applied to solution measurements, at all sites, Mie-predicted brown carbon absorption at 350 nm contributed a significant fraction (20 to 40%) relative to total light absorption, with highest contributions at the rural site where organic to elemental carbon ratios were highest. Brown carbon absorption, however, was highest by the roadside site due to vehicle emissions. The multi-wavelength aethalometer did not detect brown carbon, having an absorption Ångstrom exponent near one. Although the results are within the estimated Aethalometer uncertainties, the direct measurement of brown carbon in solution definitively shows that it is present and this Mie analysis suggests it is optically important in the near UV range in both a rural and urban environment during summer when biomass burning emissions are low.

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Water-Soluble Brown Carbon in Atmospheric Aerosols from Godavari (Nepal), a Regional Representative of South Asia

Environmental Science & Technology ◽

10.1021/acs.est.9b00596 ◽

2019 ◽

Vol 53 (7) ◽

pp. 3471-3479 ◽

Cited By ~ 31

Author(s):

Guangming Wu ◽

Kirpa Ram ◽

Pingqing Fu ◽

Wan Wang ◽

Yanlin Zhang ◽

...

Keyword(s):

South Asia ◽

Atmospheric Aerosols ◽

Water Soluble ◽

Brown Carbon

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Variation in carbonaceous and ionic species at a rural receptor location in the eastern Indo-Gangetic Plain

10.5194/egusphere-egu21-7205 ◽

2021 ◽

Author(s):

Bijay Sharma ◽

Anurag J. Polana ◽

Jingying Mao ◽

Shiguo Jia ◽

Sayantan Sarkar

Keyword(s):

Organic Carbon ◽

Forest Fires ◽

Ionic Species ◽

Water Soluble ◽

Photochemical Oxidation ◽

Carbonaceous Aerosol ◽

Charge Ratio ◽

Gangetic Plain ◽

Post Monsoon ◽

Indo Gangetic Plain

The Indo-Gangetic Plain (IGP) is one of the world&#8217;s most populated river basins housing more than 700 million people. Apart from being a major source region of aerosols, the IGP is affected by transported aerosols from the Thar Desert, forest-fires and open burning of crop waste from central India. Studies have been carried out to understand the aerosol chemical composition and optical properties in source regions of IGP but knowledge is severely lacking for receptor locations viz. eastern IGP (eIGP). To address this, the present study reports the seasonal variability of carbonaceous and ionic species in ambient PM2.5 from a rural receptor location (Mohanpur, West Bengal) along with insights on aerosol acidity, its neutralization and potential source regimes. A total of 88 PM2.5 samples collected during the summer, post-monsoon and winter seasons of 2018 were analyzed for SO42-, NO3-, Cl-, Na+, NH4+, K+, Ca2+, Mg2+, F-,PO43-, water-soluble organic carbon (WSOC), organic carbon (OC) and elemental carbon (EC) fractions. Sulfate, nitrate and ammonium (SNA) were the dominating ionic species throughout the seasons (67-86% out of the total ionic species measured). Significant positive Cl- depletion in summer (49&#177;20%) pointed towards influx of marine air while negative depletion in post-monsoon and winter suggested a biomass burning (BB) source, which was further supported by concentration-weighted trajectory analysis. Strong acidity was found to be highest during post-monsoon (141&#177;76 nmol m-3), followed by winter (117&#177;36 nmol m-3) and summer (40&#177;14 nmol m-3) with significant differences between summer and the other seasons. Neutralization factor (Nf) and equivalent charge ratio of cation to anion (RC/A) revealed that summertime aerosols were neutral in nature while those of post-monsoon and winter were comparatively acidic with NH4+ being the major neutralizing agent throughout the seasons. Correlations between WSOC and OC fractions (OC1, OC2, OC3 and OC4) suggested secondary formation of summertime WSOC (WSOC vs OC3: r=0.48, p<0.05) via photochemical oxidation of volatile organic carbons (VOCs) while that of post-monsoon (WSOC vs OC1, OC2, OC3: r=0.45-0.62, p<0.05) and winter (WSOC vs OC1, OC2, OC3: r=0.58-0.68, p<0.05), both primary and secondary pathways seem important. To elucidate the role of BB, we looked into the two components of EC i.e., char-EC (EC1-PC) and soot-EC (EC2+EC3). The percent contribution of char-EC to EC was 65&#177;17%, 90&#177;10% and 98&#177;1% during summer, post-monsoon and winter, respectively. Along with this, char-EC/soot-EC ratios of 2.3&#177;1.8, 17.6&#177;16.4 and 50.3&#177;18.6 during summer, post-monsoon and winter, respectively, and significant correlations of the same with the BB-tracer K+ (post-monsoon: r=0.78, p<0.001; winter: r=0.64, p<0.01) indicated the importance of BB emissions in constraining carbonaceous aerosol profiles during post-monsoon and winter.

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Optical and chemical properties of wintertime light-absorbing aerosols in the eastern Indo-Gangetic Plain, India

10.5194/egusphere-egu2020-655 ◽

2020 ◽

Author(s):

Supriya Dey ◽

Archita Rana ◽

Prashant Rawat ◽

Sayantan Sarkar

Keyword(s):

Organic Carbon ◽

Light Absorption ◽

Mass Concentration ◽

Chemical Properties ◽

Water Soluble ◽

Chemical Extraction ◽

Aerosol Formation ◽

Gangetic Plain ◽

Indo Gangetic Plain ◽

And Chemical Properties

Light-absorbing carbonaceous aerosols such as black and brown carbon (BC and BrC) and humic-like substances (HULIS) have pronounced effects on the earth&#8217;s radiative balance and tropospheric photochemistry. In India, large heterogeneities exist for BC and organic carbon (OC) emission inventories, which necessitates regionally-representative ground-based measurements. Such measurements are spatially scattered for BC, rare for BrC and non-existent for HULIS. This severely limits a robust understanding of the optical and chemical properties of these aerosols, and consequently, their climate effects. To address this issue, the present study reports optical and chemical properties of wintertime (December 2018-February 2019) BC, BrC and HULIS at a rural receptor site in the highly polluted eastern Indo-Gangetic Plain (IGP), India. A 7 wavelength aethalometer was deployed to measure time-resolved BC mass concentration, and absorption coefficients (babs) and Angstrom exponent (AE) of BrC. Separation of aqueous and organic BrC (BrCaq and BrCorg) and HULIS fractions via a multi-step chemical extraction procedure followed by optical measurements (UV-Vis, fluorescence and FT-IR), and supplementary measurements of OC, water-soluble organic carbon (WSOC) and ionic species led to better insights into the potential chromophore composition and their relative importance in constraining aerosol optical properties.The daily averaged BC mass concentration was 15.4&#177;9.5 &#956;g m-3 during winter, where the biomass burning (BB) contribution was 25&#177;5%. The diurnal profile of BCBB and BrC light absorption coefficient (babs_BrC) showed a prominent morning peak (0700-0800 H) characterized by mixed fossil fuel and biofuel emission and a gradual increase towards night due to enhanced primary BB emission from cooking activities and lowering of the mixing depth. The regionally transported BB plume from northwestern IGP contributed substantial BC and BrC to this receptor location in the eastern end of the corridor, which was supported by concentration-weighted air mass trajectories (CWTs).The BrCorg light absorption at 365 nm (babs_BrC_org) was almost 2 times compared to that of BrCaq (babs_BrC_aq) (36&#177;7.1 vs 18.3&#177;4.3 Mm-1), which suggested a dominance of non-polar polyconjugated BrC chromophores. This was also supported by the increasing trend of water-insoluble BrC from 49&#177;10% at 365 nm to 64&#177;21% at 550 nm, with averaged contributions of 49&#177;8% at 300-400 nm and 67&#177;9% at 400-550 nm, respectively. A strong correlation between WSOC and NO3- (r=0.78, p<0.01) and WSOC and NH4+ (r=0.63, p<0.01) indicated the possibility of nighttime secondary organic aerosol formation. A prominent fluorescence peak at ~409 nm for BrCaq confirmed the presence of HULIS, and babs_BrC_aq was dominated by the low-polarity HULIS-n fraction. AE of individual HULIS fractions increased by 7-36% towards the more polar HULIS-a and highly-polar water-soluble organic matter (HPWSOM) compared to the less polar HULIS-n for the 300-700 nm range. Distinct FTIR peaks at 3400 cm-1, 1710 cm-1 and 1643 cm-1 suggested abundance of C-H, C=O and C=C functional groups, respectively, in the BrC chromophores. Overall, it appeared that the regionally transported BB plume significantly enriches BrC and HULIS in the eastern part of the IGP corridor. &#160;&#160;

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Atmospheric evolution of molecular-weight-separated brown carbon from biomass burning

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-7319-2019 ◽

2019 ◽

Vol 19 (11) ◽

pp. 7319-7334 ◽

Cited By ~ 27

Author(s):

Jenny P. S. Wong ◽

Maria Tsagkaraki ◽

Irini Tsiodra ◽

Nikolaos Mihalopoulos ◽

Kalliopi Violaki ◽

...

Keyword(s):

Molecular Weight ◽

Biomass Burning ◽

Light Absorption ◽

Laboratory Experiments ◽

Atmospheric Transport ◽

Water Soluble ◽

Brown Carbon ◽

Atmospheric Lifetime ◽

Radiative Balance ◽

Considerable Uncertainty

Abstract. Biomass burning is a major source of atmospheric brown carbon (BrC), and through its absorption of UV/VIS radiation, it can play an important role in the planetary radiative balance and atmospheric photochemistry. The considerable uncertainty of BrC impacts is associated with its poorly constrained sources, transformations, and atmospheric lifetime. Here we report laboratory experiments that examined changes in the optical properties of the water-soluble (WS) BrC fraction of laboratory-generated biomass burning particles from hardwood pyrolysis. Effects of direct UVB photolysis and OH oxidation in the aqueous phase on molecular-weight-separated BrC were studied. Results indicated that the majority of low-molecular-weight (MW) BrC (<400 Da) was rapidly photobleached by both direct photolysis and OH oxidation on an atmospheric timescale of approximately 1 h. High MW BrC (≥400 Da) underwent initial photoenhancement up to ∼15 h, followed by slow photobleaching over ∼10 h. The laboratory experiments were supported by observations from ambient BrC samples that were collected during the fire seasons in Greece. These samples, containing freshly emitted to aged biomass burning aerosol, were analyzed for both water- and methanol-soluble BrC. Consistent with the laboratory experiments, high-MW BrC dominated the total light absorption at 365 nm for both methanol and water-soluble fractions of ambient samples with atmospheric transport times of 1 to 68 h. These ambient observations indicate that overall, biomass burning BrC across all molecular weights has an atmospheric lifetime of 15 to 28 h, consistent with estimates from previous field studies – although the BrC associated with the high-MW fraction remains relatively stable and is responsible for light absorption properties of BrC throughout most of its atmospheric lifetime. For ambient samples of aged (>10 h) biomass burning emissions, poor linear correlations were found between light absorptivity and levoglucosan, consistent with other studies suggesting a short atmospheric lifetime for levoglucosan. However, a much stronger correlation between light absorptivity and total hydrous sugars was observed, suggesting that they may serve as more robust tracers for aged biomass burning emissions. Overall, the results from this study suggest that robust model estimates of BrC radiative impacts require consideration of the atmospheric aging of BrC and the stability of high-MW BrC.

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The evolutionary behavior of chromophoric brown carbon during ozone aging of fine particles from biomass burning

10.5194/acp-2019-805 ◽

2019 ◽

Author(s):

Xingjun Fan ◽

Tao Cao ◽

Xufang Yu ◽

Yan Wang ◽

Xin Xiao ◽

...

Keyword(s):

Biomass Burning ◽

Light Absorption ◽

Climate Models ◽

Fine Particles ◽

Average Molecular Weight ◽

Absorption Capacity ◽

Correlation Spectroscopy ◽

Relative Distribution ◽

Fluorescent Properties ◽

Brown Carbon

Abstract. Biomass burning (BB) emits large amounts of brown carbon (BrC), however, little is known about the evolutionary behavior of BrC produced by BB (BB-BrC) in atmospheric processes. In this study, the transformation of levels and the chromophoric characteristics of BrC in smoke particles emitted by the burning of rice straw (RS), corn straw (CS) and pine wood (PW) under O3 aging are investigated. The O3 aging induced the reduction of light absorption and fluorescence for the BB-BrC, suggesting the decomposition of chromophores and fluorophores. These changes were accompanied by a decrease of aromaticity, average molecular weight and the light absorption capacity for the chromophores, and an increase of humification for the fluorophores. The excitation emission matrix combined with a parallel factor analysis revealed that protein-like components (C3) were predominantly decomposed by O3 aging, while the relative distribution of a humic-like component with highly oxygenated chromophores (C4) gradually increased. In general, the humic-like substances (C1+C2+C4) were transformed to be the most abundant fluorophores for all the BB-BrC samples, which accounted for 84 %–87 % of the total fluorophores in final O3-aged BB-BrC. Two dimensional correlation spectroscopy (2D-COS) was performed on the synchronous fluorescence, which suggested that the RS- and CS- BrC exhibits the same susceptible fluorophores changes upon O3 aging. It showed that O3 firstly reacted with protein-like fractions (263–289 nm), and then with fulvic-like fractions (333–340 nm). In comparison, the changing sequence of susceptible fluorophores in the PW-BrC to O3 were in the order of fulvic-like with shorter wavelengths (309 nm) > protein-like fluorophores (276 nm) > fulvic-like fluorophores with longer wavelengths (358 nm). The 2D-FTIR-COS analysis showed conjugated C=O and aromatic C=C and C=O groups were the most susceptible functional groups to O3 aging for all BB-BrC. Moreover, it also revealed a consistent sequential changes, which is in the order of aromatic OH, conjugated C=O groups and aromatic C=O, aromatic COO−, and finally lignin-derived C-C, C-H and C-O groups. Our results provide new insights into the evolutionary behavior of the chromophoric and fluorescent properties of BB-BrC during O3 aging. They have important implications for the heterogeneous oxidation of BB emission to form BrC, and are of great significance for improving the accuracy of climate models and source apportionment models parameterized by the optical properties of BrC.

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