Chemistry Department, Boston College, Chestnut Hill, Massachusetts, United States.
Environ Sci Technol. 2013 Jun 18;47(12):6349-57. doi: 10.1021/es401043j. Epub 2013 Jun 6.
Brown carbon (BrC), which may include secondary organic aerosol (SOA), can be a significant climate-forcing agent via its optical absorption properties. However, the overall contribution of SOA to BrC remains poorly understood. Here, correlations between oxidation level and optical properties of SOA are examined. SOA was generated in a flow reactor in the absence of NOx by OH oxidation of gas-phase precursors used as surrogates for anthropogenic (naphthalene, tricyclo[5.2.1.0(2,6)]decane), biomass burning (guaiacol), and biogenic (α-pinene) emissions. SOA chemical composition was characterized with a time-of-flight aerosol mass spectrometer. SOA mass-specific absorption cross sections (MAC) and refractive indices were calculated from real-time cavity ring-down photoacoustic spectrometry measurements at 405 and 532 nm and from UV-vis spectrometry measurements of methanol extracts of filter-collected particles (300 to 600 nm). At 405 nm, SOA MAC values and imaginary refractive indices increased with increasing oxidation level and decreased with increasing wavelength, leading to negligible absorption at 532 nm. Real refractive indices of SOA decreased with increasing oxidation level. Comparison with literature studies suggests that under typical polluted conditions the effect of NOx on SOA absorption is small. SOA may contribute significantly to atmospheric BrC, with the magnitude dependent on both precursor type and oxidation level.
棕色碳（BrC），可能包括二次有机气溶胶（SOA），可以通过其光学吸收特性成为重要的气候强迫因素。然而，SOA 对 BrC 的总体贡献仍未得到很好的理解。本文研究了 SOA 的氧化水平与其光学性质之间的相关性。SOA 是在没有 NOx 的情况下通过 OH 氧化气相前体在流动反应器中生成的，这些前体被用作人为（萘、三环[5.2.1.0（2,6）]癸烷）、生物质燃烧（愈创木酚）和生物源（α-蒎烯）排放的替代物。SOA 的化学成分通过飞行时间气溶胶质谱仪进行了表征。利用实时腔衰荡光声光谱法在 405nm 和 532nm 处测量，并利用甲醇提取滤膜收集的颗粒（300nm 至 600nm）的紫外-可见光谱法测量，计算了 SOA 的质量比吸光系数（MAC）和折射率。在 405nm 处，SOA 的 MAC 值和虚折射率随着氧化水平的增加而增加，随着波长的增加而减小，导致在 532nm 处几乎没有吸收。SOA 的实折射率随着氧化水平的增加而降低。与文献研究的比较表明，在典型的污染条件下，NOx 对 SOA 吸收的影响很小。SOA 可能对大气 BrC 有显著贡献，其大小取决于前体类型和氧化水平。
