| 摘要: |
| 棕碳气溶胶吸收太阳辐射，影响大气光化学和地—气系统的辐射收支平衡。而棕碳气溶胶受pH显著影响，故对不同pH下棕碳光学性质的研究十分必要。通过分析四类棕碳标准品和四类实际样品在不同pH下的光吸收特征，探究pH对棕碳组分光学性质的影响。结果表明：随着pH增加，大部分棕碳标准品会出现吸光红移，其中，硝基儿茶酚和硝基苯酚更为显著。实际样品中，随着pH增加，生物质燃烧、燃煤和环境大气样品的吸光（300—500 nm）逐渐增加，而机动车尾气样品则先降后增。在365 nm处，生物质燃烧、燃煤样品的pH从3到10，吸光度增加量是环境大气样品的约1.5倍，说明其含有更高占比的硝基酚类物质。质量吸收系数（mass absorption efficiency，MAE365）分析表明，随pH增加MAE365增至约2倍（pH=10时），而埃吸收指数（Ångström absorption exponent，AAE）随pH增加显著降低。说明pH增加会增强实际样品中棕碳的吸光能力，引起吸光红移并降低棕碳的波长依赖性。研究表明pH会对棕碳组分的光学性质有重要影响，在棕碳气溶胶气候和环境效应评估模型中应加以考虑。 |
| 关键词: 棕碳发色团 吸光度 质量吸收系数 吸光红移 去质子化 |
| DOI：10.7515/JEE232055 |
| CSTR：32259.14.JEE232038 |
| 分类号: |
| 基金项目:国家自然科学基金项目（41925015）；中国科学院基础前沿科学研究计划（ZDBS-LY-DQC001） |
| 英文基金项目:National Natural Science Foundation of China (41925015); Key Research Program of Frontier Sciences of the Chinese Academy of Sciences (ZDBS-LY-DQC001) |
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| Effect of environmental acidity on the light absorption properties of brown carbon |
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GONG Yuquan1, 2, HUANG Rujin1, 2*, YANG Lu1, 2, WANG Ting1
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1. State Key Laboratory of Loess Science, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
2. University of Chinese Academy of Sciences, Beijing 100049, China
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| Abstract: |
| Background, aim, and scope Brown carbon (BrC) aerosol effectively absorbs solar irradiation and significantly influences radiative forcing and atmospheric photochemistry. The light absorption properties of BrC are largely influenced by atmospheric environmental factors, such as pH; however, the mechanisms underlying this effect remain inadequately understood. This study examines the impact of pH on the absorption characteristics of individual BrC chromophore species from standard compounds and the bulk BrC of source and ambient samples. Different source samples emission traces of indicative BrC chromophore varied widely, resulting in large differences in source sample absorbance. Thus, the pH dependence of BrC light absorption from different sources can be explained based on the chromophore species. This mechanistic understanding of pH-chromophore interactions paves the way for developing multiscale models integrating molecular-level chemistry with regional atmospheric dynamics to better quantify BrC’s role in climate systems. Materials and methods Four types of common atmospheric BrC chromophores (nitrocatechols, nitrophenols, methoxyphenols, and benzoic acids) and four types of practical samples (winter atmospheric samples, vehicle emission samples, biomass combustion, and coal combustion samples) were selected to investigate the effect of pH on absorbance. The influence of pH on the mass absorption efficiency at 365 nm (MAE365) and the Ångström absorption exponent (AAE) of the practical samples was also evaluated. Results The findings indicate that solution pH had a significant impact on the absorbance of both chromophoric standards and practical samples. When the pH increased from 7 to 10, the MAE365 of the practical samples doubled, while AAE exhibited a noticeable decline. Discussion The results indicate that phenolics containing nitro groups (e.g., nitrocatechols and nitrophenols) exhibit higher absorbance compared to benzoic acid and methoxyphenol, with their abundance varying more significantly with changes in pH. Additionally, findings reveal that the light absorption peaks of BrC chromophores undergo a redshift as pH increases, with nitrophenol exhibiting the most pronounced shift. BrC from different sources contains various types of chromophores, leading to differing degrees of pH influence. Among the analyzed samples, biomass combustion samples appear more sensitive to pH variations, suggesting a greater presence of nitro-phenolic compounds. In contrast, vehicle emission samples display strong light absorption under acidic conditions, indicating the presence of substances such as benzoic acid that enhance light absorption in acidic environments. Conclusions This study confirms the substantial effect of pH on the absorbance of BrC standards, particularly nitro-phenols. The absorbance of combustion samples (wheat, rice, and coal) increases significantly with rising solution pH, with absorbance at 365 nm doubling when pH increases from 7 to 10. Vehicle emission samples exhibit a pattern of initial absorbance decline followed by an increase as pH rises. The MAE365 of all practical samples approximately doubles when pH is raised from 7 to 10. Recommendations and perspective The findings highlight the significant influence of pH on the absorbance of various BrC standards and practical samples, offering a basis for evaluating pH-induced changes in atmospheric radiation. Future research should focus on gaining deeper insights into the dynamic effects of environmental factors on the absorption properties of BrC. |
| Key words: BrC chromophores absorbance mass absorption coefficient absorbance redshift deprotonation |
