NOAA Earth System Research Laboratory, Chemical Sciences Division, 325 Broadway, Boulder, CO 80304, USA.
Proc Natl Acad Sci U S A. 2012 Sep 11;109(37):14802-7. doi: 10.1073/pnas.1206575109. Epub 2012 Aug 27.
Biomass burning (BB) contributes large amounts of black carbon (BC) and particulate organic matter (POM) to the atmosphere and contributes significantly to the earth's radiation balance. BB particles can be a complicated optical system, with scattering and absorption contributions from BC, internal mixtures of BC and POM, and wavelength-dependent absorption of POM. Large amounts of POM can also be externally mixed. We report on the unique ability of multi-wavelength photo-acoustic measurements of dry and thermal-denuded absorption to deconstruct this complicated wavelength-dependent system of absorption and mixing. Optical measurements of BB particles from the Four Mile Canyon fire near Boulder, Colorado, showed that internal mixtures of BC and POM enhanced absorption by up to 70%. The data supports the assumption that the POM was very weakly absorbing at 532 nm. Enhanced absorption at 404 nm was in excess of 200% above BC absorption and varied as POM mass changed, indicative of absorbing POM. Absorption by internal mixing of BC and POM contributed 19( ± 8)% to total 404-nm absorption, while BC alone contributed 54( ± 16)%. Approximately 83% of POM mass was externally mixed, the absorption of which contributed 27( ± 15)% to total particle absorption (at 404 nm). The imaginary refractive index and mass absorption efficiency (MAE) of POM at 404 nm changed throughout the sampling period and were found to be 0.007 ± 0.005 and 0.82 ± 0.43 m(2) g(-1), respectively. Our analysis shows that the MAE of POM can be biased high by up to 50% if absorption from internal mixing of POM and BC is not included.
生物质燃烧 (BB) 将大量黑碳 (BC) 和颗粒有机物质 (POM) 排放到大气中，对地球辐射平衡有重要贡献。BB 颗粒可能是一个复杂的光学系统，具有 BC 的散射和吸收贡献、BC 和 POM 的内部混合物以及 POM 的波长依赖性吸收。大量的 POM 也可以是外部混合的。我们报告了多波长光声测量对干燥和热脱除吸收的独特能力，以分解这种复杂的波长依赖性吸收和混合系统。对科罗拉多州博尔德附近的四英里峡谷火灾的 BB 颗粒的光学测量表明，BC 和 POM 的内部混合物将吸收增强了 70%。数据支持 POM 在 532nm 处的吸收非常弱的假设。404nm 处的增强吸收超过 BC 吸收的 200%，并且随着 POM 质量的变化而变化，表明存在吸收性 POM。BC 和 POM 的内部混合吸收对总 404nm 吸收的贡献为 19(±8)%，而 BC 单独贡献 54(±16)%。约 83%的 POM 质量是外部混合的，其吸收对总颗粒吸收 (在 404nm 处) 的贡献为 27(±15)%。在整个采样期间，POM 在 404nm 处的虚折射率和质量吸收效率 (MAE) 都发生了变化，分别为 0.007±0.005 和 0.82±0.43m(2)g(-1)。我们的分析表明，如果不包括 POM 和 BC 内部混合的吸收，则 POM 的 MAE 可能会偏高 50%。
