Key Laboratory of Aerosol Chemistry and Physics, State Key Laboratory of Loess and Quaternary Geology , Institute of Earth Environment, Chinese Academy of Sciences , Xi'an 710061 , China.
CAS Center for Excellence in Quaternary Science and Global Change , Xi'an 710061 , China.
Environ Sci Technol. 2019 Nov 5;53(21):12389-12397. doi: 10.1021/acs.est.9b03406. Epub 2019 Oct 9.
The light-absorbing properties of atmospheric brown carbon (BrC) are poorly understood due to its complex chemical composition. Here, a black-carbon-tracer method was coupled with source apportionments of organic aerosol (OA) to explore the light-absorbing properties of primary and secondary BrC from the North China Plain (NCP). Primary emissions of BrC contributed more to OA light absorption than secondary processes, and biomass burning OA accounted for 60% of primary BrC absorption at λ = 370 nm, followed by coal combustion OA (35%) and hydrocarbon-like OA (5%). Secondary BrC absorption was high in the early morning and later decreased due to the bleaching of chromophores. Nighttime aqueous-phase chemistry promoted the formation of secondary light-absorbing compounds and the production of strongly absorbing particles. Source analysis showed that the NCP region was the most important source for primary and secondary BrC subtypes at the study site. The mean direct radiative forcing for BrC was 0.15 W m (0.11 W m and 0.04 W m for the primary and secondary fractions, respectively). This study provides new information on the optical properties of primary and secondary BrC and highlights the importance of atmospheric oxidation on BrC absorption.
由于大气棕色碳（BrC）的复杂化学成分，其光吸收特性了解甚少。在这里，采用黑碳示踪法与有机气溶胶（OA）源分配相结合的方法，来探索来自中国华北平原（NCP）的一次和二次 BrC 的光吸收特性。BrC 的一次排放对 OA 光吸收的贡献大于二次过程，在 λ = 370nm 处，生物质燃烧 OA 占一次 BrC 吸收的 60%，其次是煤燃烧 OA（35%）和烃类 OA（5%）。由于发色团的漂白作用，二次 BrC 吸收在清晨较高，后来降低。夜间水相化学促进了二次光吸收化合物的形成和强吸收颗粒的产生。来源分析表明，NCP 地区是研究地点一次和二次 BrC 亚型的最重要来源。BrC 的直接辐射强迫平均值为 0.15 W m（一次和二次分别为 0.11 W m 和 0.04 W m）。本研究提供了有关一次和二次 BrC 光学性质的新信息，并强调了大气氧化对 BrC 吸收的重要性。
