Abstract. Brown carbon aerosol (BrC) is one major contributor to atmospheric air pollution in Europe, especially in winter. Therefore, we studied the chemical composition, diurnal variation, and sources of BrC from 17^th February to 16^th March at a rural location in southwest Germany. In total, 178 potential BrC molecules (including 7 nitro aromatic compounds, NACs) were identified in the particle phase comprising on average 63 ± 32 ng m⁻³, and 31 potential BrC (including 4 NACs) molecules were identified in the gas phase contributing on average 6.2 ± 5.0 ng m⁻³ during the whole campaign. The 178 potential BrC molecules only accounted for 2.3 ± 1.5 % of the total organic mass, but can explain 11 ± 11 % of the total BrC absorption at 370 nm, assuming an average mass absorption coefficient at 370 nm (MAC₃₇₀) of 9.5 m² g⁻¹. A few BrC molecules dominated the total BrC absorption. In addition, diurnal variations show that gas phase BrC was higher at daytime and lower at night. It was mainly controlled by secondary formation (e.g. photooxidation) and particle-to-gas partitioning. Correspondingly, the particle phase BrC was lower at daytime and higher at nighttime. Secondary formation dominates the particle-phase BrC with 61 ± 21 %, while 39 ± 21 % originated from biomass burning. Furthermore, the particle-phase BrC showed decreasing light absorption due to photochemical aging. This study extends the current understanding of real-time behaviors of brown carbon aerosol in the gas and particle phase at a location characteristic for the central Europe.

中文翻译：

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德国农村的棕色碳气溶胶：来源、化学成分和昼夜变化


摘要。棕碳气溶胶（BrC）是欧洲大气空气污染的主要来源之一，尤其是在冬季。因此，我们从2月17日 ^th 至3月16日 ^th 在德国西南部的一个农村地区研究了BrC的化学成分、昼夜变化和来源。总共，在平均包含 63 ± 32 ng m ⁻³ 的颗粒相中鉴定出了 178 个潜在的 BrC 分子（包括 7 种硝基芳香族化合物，NAC），并鉴定了 31 个潜在的 BrC（包括 4 个 NAC）分子在整个活动期间，气相平均贡献 6.2 ± 5.0 ng m ⁻³ 。 178 个潜在的 BrC 分子仅占总有机质量的 2.3 ± 1.5 %，但可以解释 370 nm 处总 BrC 吸收的 11 ± 11 %，假设 370 nm 处的平均质量吸收系数（MAC ₃₇₀ g ⁻¹ 。一些 BrC 分子主导了 BrC 的总吸收。此外，昼夜变化表明，气相 BrC 白天较高，夜间较低。它主要通过二次形成（例如光氧化）和颗粒与气体的分配来控制。相应地，颗粒相BrC白天较低，夜间较高。二次形成在颗粒相 BrC 中占主导地位，占 61 ± 21 %，而 39 ± 21 % 则源自生物质燃烧。此外，由于光化学老化，颗粒相 BrC 显示出光吸收减少。这项研究扩展了目前对中欧特征位置的棕色碳气溶胶在气相和颗粒相中的实时行为的理解。