The uncertainty associated with carbonaceous aerosols in climate models becomes an obstacle to evaluating their harmful environmental effects. Brown Carbon (BrC) has recently become an eye-catching carbonaceous aerosol in ambient air because of its strong light absorption properties. The optical properties of soluble BrC are well studied in South Asia, one of the largest emitters. However, the absorption property of strong light-absorbing insoluble BrC is highly uncertain because of their complex mixing. Besides, the simultaneous apportionment of light-absorbing carbonaceous aerosol constituents as a function of wavelengths is seldom explored. The present study aims to study mass as well as apportionment of absorption properties of Black Carbon (BC) and different BrC chromophores using a multi-wavelength thermal-optical carbon analyzer over the least explored Eastern part of India to fill the knowledge gap. The output suggested that the primary emission sources dominate the carbonaceous aerosol mass; thus, the primary emission reductions will be helpful in improving the local air quality. The BrC is the dominant light-absorbing carbonaceous aerosol in the ultraviolet wavelengths. Besides, significant light absorption by BrC chromophores in near-infrared wavelengths (up to ∼50% of total aerosol absorption) suggested the absorption by BrC in longer wavelengths cannot be neglected. The insoluble fraction of BrC (Tar-BrC), which has a property identical to BC, contributes significantly to light absorption and is more than 50% of total absorption by aerosols in shorter ≤635 nm wavelengths. The present study also revealed that the contribution of Tar-BrC is more pronounced in the Indo-Gangetic Plain (IGP) outflow region than in the IGP emission source regions.

中文翻译：

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印度恒河平原流出区大气碳质气溶胶的质量和光吸收特性

气候模型中与碳气溶胶相关的不确定性成为评估其有害环境影响的障碍。棕碳（BrC）由于其强光吸收特性，最近成为环境空气中引人注目的碳质气溶胶。可溶性 BrC 的光学特性在最大的排放国之一的南亚得到了深入研究。然而，强吸光不溶性BrC由于混合复杂，其吸收性能具有很大的不确定性。此外，很少探索光吸收碳质气溶胶成分作为波长函数的同时分配。本研究旨在使用多波长热光碳分析仪在印度东部勘探最少的地区研究黑碳 (BC) 和不同 BrC 发色团的质量以及吸收特性的分配，以填补知识空白。结果表明，主要排放源在碳质气溶胶质量中占主导地位；因此，初次减排将有助于改善当地的空气质量。 BrC 是紫外线波长中主要的吸光碳质气溶胶。此外，BrC 发色团在近红外波长下的显着光吸收（高达气溶胶总吸收的 50%）表明 BrC 在较长波长下的吸收不可忽视。 BrC 的不溶部分 (Tar-BrC) 具有与 BC 相同的特性，对光吸收有显着贡献，在较短的 ≤635 nm 波长中占气溶胶总吸收的 50% 以上。本研究还表明，Tar-BrC 的贡献在印度恒河平原（IGP）流出区域比 IGP 排放源区域更明显。