Supplementary material to "Contributions of nitrated aromatic compounds to the light absorption of water-soluble and particulate brown carbon in different atmospheric environments in Germany and China"

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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Supplementary material to "Emission factors and light absorption properties of brown carbon from household coal combustion in China"

10.5194/acp-2016-1090-supplement ◽

2017 ◽

Author(s):

Jianzhong Sun ◽

Guorui Zhi ◽

Regina Hitzenberger ◽

Yingjun Chen ◽

Chongguo Tian ◽

...

Keyword(s):

Light Absorption ◽

Coal Combustion ◽

Emission Factors ◽

Absorption Properties ◽

Brown Carbon ◽

Supplementary Material

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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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Supplementary material to "Chemical composition, structures, and light absorption of N-containing aromatic compounds emitted from burning wood and charcoal in household cookstoves"

10.5194/acp-2020-594-supplement ◽

2020 ◽

Author(s):

Mingjie Xie ◽

Zhenzhen Zhao ◽

Amara L. Holder ◽

Michael D. Hays ◽

Xie Chen ◽

...

Keyword(s):

Chemical Composition ◽

Light Absorption ◽

Aromatic Compounds ◽

Supplementary Material

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The optical properties and in-situ observational evidence for the formation of brown carbon in cloud

10.5194/acp-2021-945 ◽

2021 ◽

Author(s):

Ziyong Guo ◽

Yuxiang Yang ◽

Xiaodong Hu ◽

Xiaocong Peng ◽

Yuzhen Fu ◽

...

Keyword(s):

Optical Properties ◽

Absorption Coefficient ◽

Light Absorption ◽

Cloud Water ◽

Water Soluble ◽

Substantial Contribution ◽

Supporting Evidence ◽

Brown Carbon ◽

Light Absorption Coefficient ◽

Free Particles

Abstract. Atmospheric brown carbon (BrC) makes a substantial contribution to aerosol light-absorbing and thus the global radiative forcing. Although BrC may change the lifetime of the cloud and ultimately affect precipitation, little is known regarding the optical properties and formation of BrC in the cloud. In the present study, the light-absorption properties of cloud droplet residual (cloud RES) were measured by coupled a ground-based counterflow virtual impactor (GCVI) and an Aethalometer (AE-33), in addition to the cloud interstitial (cloud INT) and ambient (cloud-free) particles by PM2.5 inlet-AE-33, at Mt. Tianjing (1690 m a.s.l.), a remote mountain site in southern China, from November to December 2020. Meanwhile, the light-absorption and fluorescence properties of water-soluble organic carbon (WSOC) in the collected cloud water and PM2.5 samples were also obtained, associated with the concentration of water-soluble ions. The mean light-absorption coefficient (Abs370) of the cloud RES, cloud INT, and cloud-free particles were 0.25 ± 0.15, 1.16 ± 1.14, and 1.47 ± 1.23 Mm−1, respectively. The Abs365 of WSOC was 0.11 ± 0.08 Mm−1 in cloud water and 0.40 ± 0.31 Mm−1 in PM2.5, and the corresponding mass absorption efficiency (MAE365) was 0.17 ± 0.07 and 0.31 ± 0.21 m2·g−1, respectively. A comparison of the light-absorption coefficient between BrC in the cloud RES/cloud INT and WSOC in cloud water/PM2.5 indicates a considerable contribution (48–75 %) of water-insoluble BrC to total BrC light-absorption. Secondary BrC estimated by minimum R squared (MRS) method dominated the total BrC in cloud RES (67–85 %), rather than in the cloud-free (11–16 %) and cloud INT (9–23 %) particles. It may indicate the formation of secondary BrC during cloud processing. Supporting evidence includes the enhanced WSOC and dominant contribution of secondary formation/biomass burning factor (> 80 %) to Abs365 in cloud water provided by Positive Matrix Factorization (PMF) analysis. In addition, we showed that the light-absorption of BrC in cloud water was closely related to humic-like substances and tyrosine/proteins-like substances (r > 0.63, p < 0.01), whereas only humic-like substances for PM2.5, as identified by excitation-emission matrix fluorescence spectroscopy.

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Measurement report: Long emission-wavelength chromophores dominate the light absorption of brown carbon in Aerosols over Bangkok: impact from biomass burning

10.5194/acp-2021-175 ◽

2021 ◽

Author(s):

Jiao Tang ◽

Jiaqi Wang ◽

Guangcai Zhong ◽

Hongxing Jiang ◽

Yangzhi Mo ◽

...

Keyword(s):

Biomass Burning ◽

Light Absorption ◽

Linear Regression Analysis ◽

Multiple Linear Regression Analysis ◽

Water Soluble ◽

Emission Wavelength ◽

Brown Carbon ◽

Molecular Weights ◽

Secondary Formation ◽

Combustion Emission

Abstract. Chromophores represent an important portion of light-absorbing species, i.e. brown carbon. Yet knowledge on what and how chromophores contribute to aerosol light absorption is still sparse. To address this problem, we examined soluble independent chromophores in a set of year-round aerosol samples from Bangkok. The water-soluble chromophores identified via excitation-emission matrix (EEM) spectroscopy and follow-up parallel factor analysis could be mainly assigned as humic-like substances and protein-like substances, which differed in their EEM pattern from that of the methanol-soluble fraction. The emission wavelength of chromophores in environmental samples tended to increase compared with that of the primary combustion emission, which could be attributed to secondary formation or the aging process. Fluorescent indices inferred that these light-absorbing chromophores were not significantly humified and comprised a mixture of organic matter of terrestrial and microbial origin, while these inferences exhibited a refutation with primary biomass burning and coal combustion results. A multiple linear regression analysis revealed that larger chromophores that were oxygen-rich and highly aromatic with high molecular weights, were the key contributors of light absorption, preferably at longer emission wavelength (λmax > 500 nm). Positive matrix factorization analysis further suggested that up to 60 % of these responsible chromophores originated from biomass burning emissions.

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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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Measurement report: PM<sub>2.5</sub>-bound nitrated aromatic compounds in Xi'an, Northwest China – seasonal variations and contributions to optical properties of brown carbon

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-3685-2021 ◽

2021 ◽

Vol 21 (5) ◽

pp. 3685-3697

Author(s):

Wei Yuan ◽

Ru-Jin Huang ◽

Lu Yang ◽

Ting Wang ◽

Jing Duan ◽

...

Keyword(s):

Organic Carbon ◽

Seasonal Variations ◽

Light Absorption ◽

Aromatic Compounds ◽

Radiative Forcing ◽

Northwest China ◽

Individual Species ◽

Brown Carbon ◽

Mass Fractions ◽

Different Seasons

Abstract. Nitrated aromatic compounds (NACs) are a group of key chromophores for brown carbon (light-absorbing organic carbon, i.e., BrC) aerosol, which affects radiative forcing. The chemical composition and sources of NACs and their contributions to BrC absorption, however, are still not well understood. In this study, PM2.5-bound NACs in Xi'an, Northwest China, were investigated for 112 daily PM2.5 filter samples from 2015 to 2016. Both the total concentrations and contributions from individual species of NACs show distinct seasonal variations. The seasonally averaged concentrations of NACs are 2.1 (spring), 1.1 (summer), 12.9 (fall), and 56 ng m−3 (winter). Thereinto, 4-nitrophenol is the major NAC component in spring (58 %). The concentrations of 5-nitrosalicylic acid and 4-nitrophenol dominate in summer (70 %), and the concentrations of 4-nitrocatechol and 4-nitrophenol dominate in fall (58 %) and winter (55 %). The NAC species show different seasonal patterns in concentrations, indicating differences in emissions and formation pathways. Source apportionment results using positive matrix factorization (PMF) further show large seasonal differences in the sources of NACs. Specifically, in summer, NACs were highly influenced by secondary formation and vehicle emissions (∼ 80 %), while in winter, biomass burning and coal combustion contributed the most (∼ 75 %). Furthermore, the light absorption contributions of NACs to BrC are wavelength-dependent and vary greatly by season, with maximum contributions at ∼ 330 nm in winter and fall and ∼ 320 nm in summer and spring. The differences in the contribution to light absorption are associated with the higher mass fractions of 4-nitrocatechol (λmax⁡= 345 nm) and 4-nitrophenol (λmax⁡= 310 nm) in fall and winter, 4-nitrophenol in spring, and 5-nitrosalicylic acid (λmax⁡= 315 nm) and 4-nitrophenol in summer. The mean contributions of NACs to BrC light absorption at a wavelength of 365 nm in different seasons are 0.14 % (spring), 0.09 % (summer), 0.36 % (fall), and 0.91 % (winter), which are about 6–9 times higher than their mass fractional contributions of carbon in total organic carbon. Our results indicate that the composition and sources of NACs have profound impacts on the BrC light absorption.

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