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Resolving the Ultraviolet‐Visible Spectra for Brown Carbon: Insights Into Structure‐Dependent Light Absorption Variations and Its Potential Environmental Impacts.

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Název: Resolving the Ultraviolet‐Visible Spectra for Brown Carbon: Insights Into Structure‐Dependent Light Absorption Variations and Its Potential Environmental Impacts.
Autoři: Yao, Wenrui, Qi, Yulin, Ge, Jinfeng, Fu, Xiaoli, Xu, Zhanjie, Wu, Libin, Hu, Wei, Deng, Junjun, Fu, Pingqing
Zdroj: Journal of Geophysical Research. Atmospheres; 11/28/2025, Vol. 130 Issue 22, p1-15, 15p
Témata: RADIATIVE forcing, CARBONYL group, AROMATIC compounds, LIGHT absorption, CARBONACEOUS aerosols, ENVIRONMENTAL impact analysis, MOLECULAR structure, HETEROCYCLIC compounds
Abstrakt: Brown carbon (BrC) is a type of light‐absorbing organic carbon and its structural characteristics have significant effects on atmospheric radiative forcing and global climate change. In this work, the main absorbing components of BrC were separated into three fractions and each fraction was analyzed individually and systematically. The compositional and structural characteristics of BrC across different wavelengths were studied, and the potential BrC compounds were revealed. Overall, nearly 100 light‐absorbing compounds were identified. The result showed that aromatic and heterocyclic compounds were main contributors to BrC absorption in the wavelength from 220 to 450 nm, which play an important role in radiative forcing. Interestingly, carbonyl groups dominated the BrC absorption in the wavelength from 200 to 220 nm. Although BrC compounds have minimal direct radiative impact due to limited solar radiation at such a wavelength, it can still play important roles in atmospheric photochemistry by participating in light‐induced oxidation process and lead to severe photochemical pollution. Additionally, carboxyl‐rich alicyclic molecules and lignin‐like substances all promoted the absorptivity of BrC, and nitrogenous substituents further enhanced such a process. These results were further extrapolated to various environmental conditions, which indicated that urban BrC probably contained more carbonyl groups. Conversely, more heterocyclic substances were observed in the forest and ocean areas, which illustrated high burden of radiative forcing in these areas. Overall, our work reveals that the BrC absorption is largely dependent on their molecule properties in different wavelengths, and such a correlation can guide and facilitate the BrC absorption analysis. Plain Language Summary: Brown carbon (BrC) affects the global radiation balance through the absorption and scattering of radiation, having a significant impact on the global climate system, but the specific molecule structures affecting its light absorption remains unclear. This research analyzed the major characteristics and molecular structures of BrC by separating it into three representative fractions, and dividing them into wavelength ranges of 200–220 nm and 220–450 nm, and the specific light‐absorbing compounds as well as environmental impacts were also evaluated. By integrating their optical and mass spectrometry data, nearly 100 light‐absorbing BrC compounds were identified, among which carbonyl groups were found to be the primary contributors to the wavelength of 200–220 nm, leading to severe atmospheric photochemical pollution. While heterocyclic compounds were identified as the main contributors of 220–450 nm, significantly increasing the light absorption of BrC and influencing the atmospheric radiative forcing. Our findings provide insights into BrC compositions, structures and light absorption mechanisms, offering theoretical support for evaluating their environmental effects. Key Points: Carbonyl groups are the core structure for brown carbon (BrC) absorption in 200–220 nm, while aromatic and heterocyclic compounds dominant in 220–450 nmCondensed aromatics and lignin‐like substances can enhance BrC light absorptivity, and nitrogenous substances further promote such a processMore aromatic and heterocyclic compounds are found in forest and ocean environments, indicating the radiative forcing in these areas [ABSTRACT FROM AUTHOR]
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Databáze: Complementary Index
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Abstrakt:Brown carbon (BrC) is a type of light‐absorbing organic carbon and its structural characteristics have significant effects on atmospheric radiative forcing and global climate change. In this work, the main absorbing components of BrC were separated into three fractions and each fraction was analyzed individually and systematically. The compositional and structural characteristics of BrC across different wavelengths were studied, and the potential BrC compounds were revealed. Overall, nearly 100 light‐absorbing compounds were identified. The result showed that aromatic and heterocyclic compounds were main contributors to BrC absorption in the wavelength from 220 to 450 nm, which play an important role in radiative forcing. Interestingly, carbonyl groups dominated the BrC absorption in the wavelength from 200 to 220 nm. Although BrC compounds have minimal direct radiative impact due to limited solar radiation at such a wavelength, it can still play important roles in atmospheric photochemistry by participating in light‐induced oxidation process and lead to severe photochemical pollution. Additionally, carboxyl‐rich alicyclic molecules and lignin‐like substances all promoted the absorptivity of BrC, and nitrogenous substituents further enhanced such a process. These results were further extrapolated to various environmental conditions, which indicated that urban BrC probably contained more carbonyl groups. Conversely, more heterocyclic substances were observed in the forest and ocean areas, which illustrated high burden of radiative forcing in these areas. Overall, our work reveals that the BrC absorption is largely dependent on their molecule properties in different wavelengths, and such a correlation can guide and facilitate the BrC absorption analysis. Plain Language Summary: Brown carbon (BrC) affects the global radiation balance through the absorption and scattering of radiation, having a significant impact on the global climate system, but the specific molecule structures affecting its light absorption remains unclear. This research analyzed the major characteristics and molecular structures of BrC by separating it into three representative fractions, and dividing them into wavelength ranges of 200–220 nm and 220–450 nm, and the specific light‐absorbing compounds as well as environmental impacts were also evaluated. By integrating their optical and mass spectrometry data, nearly 100 light‐absorbing BrC compounds were identified, among which carbonyl groups were found to be the primary contributors to the wavelength of 200–220 nm, leading to severe atmospheric photochemical pollution. While heterocyclic compounds were identified as the main contributors of 220–450 nm, significantly increasing the light absorption of BrC and influencing the atmospheric radiative forcing. Our findings provide insights into BrC compositions, structures and light absorption mechanisms, offering theoretical support for evaluating their environmental effects. Key Points: Carbonyl groups are the core structure for brown carbon (BrC) absorption in 200–220 nm, while aromatic and heterocyclic compounds dominant in 220–450 nmCondensed aromatics and lignin‐like substances can enhance BrC light absorptivity, and nitrogenous substances further promote such a processMore aromatic and heterocyclic compounds are found in forest and ocean environments, indicating the radiative forcing in these areas [ABSTRACT FROM AUTHOR]
ISSN:2169897X
DOI:10.1029/2025JD044402