Knight Jamie W, Egan Joanna V, Orr-Ewing Andrew J, Cotterell Michael I
School of Chemistry, University of Bristol, Cantock's Close, Bristol, U.K. BS8 1TS.
School of Chemistry, University of Leeds, Woodhouse Lane, Leeds, U.K. LS2 9JT.
J Phys Chem A. 2022 Mar 10;126(9):1571-1577. doi: 10.1021/acs.jpca.2c00532. Epub 2022 Feb 23.
Understanding the optical properties of micrometer-scale light-absorbing aerosol particles is of paramount importance in addressing key challenges in atmospheric and physical chemistry. For example, the absorption of solar radiation by atmospheric aerosols represents one of the largest uncertainties in climate models. Moreover, reaction acceleration within the unique environments of aerosol droplets cannot be replicated in bulk solutions. The causes of these reaction rate enhancements remain controversial, but ultrasensitive spectroscopic measurements of evolving aerosol optical properties should provide new insights. We demonstrate a new approach using cavity ring-down spectroscopy that allows the first direct spectroscopic quantification of the continuously evolving absorption and scattering cross sections for single, levitated, micrometer-scale particles as their size and chromophore concentration change. For two-component droplets composed of nigrosin and 1,2,6-hexanetriol, the unprecedented sensitivity of our measurements reveals the evolving real and imaginary components of the refractive index caused by changes in concentration as 1,2,6-hexanetriol slowly evaporates.
了解微米级吸光气溶胶颗粒的光学特性对于应对大气化学和物理化学中的关键挑战至关重要。例如，大气气溶胶对太阳辐射的吸收是气候模型中最大的不确定性之一。此外，气溶胶液滴独特环境中的反应加速无法在本体溶液中复制。这些反应速率增强的原因仍存在争议，但对不断演变的气溶胶光学特性进行超灵敏光谱测量应能提供新的见解。我们展示了一种使用腔衰荡光谱的新方法，该方法能够首次直接对单个悬浮微米级颗粒在其尺寸和发色团浓度变化时不断演变的吸收和散射截面进行光谱定量。对于由nigrosin和1,2,6 -己三醇组成的双组分液滴，我们测量前所未有的灵敏度揭示了随着1,2,6 -己三醇缓慢蒸发，浓度变化导致的折射率实部和虚部的演变。
