Extinction Cross Section Measurements for Single Aerosol Particles Confined to a Linear Electrodynamic Quadrupole Trap

摘要：气溶胶粒子既能散射又能吸收太阳和地面辐射，其中散射对大气有冷却作用，吸收对大气有增温作用。辐射与吸收气溶胶粒子的相互作用是目前全球气候模式中最大的不确定因素之一。因此，将开发一种新技术，使其能够准确测定弱吸收和强吸收气溶胶粒子的辐射对全球气候的影响。Cotterell等人报道的空腔衰落光谱（CRDS）测量，确定了0.5-1 Tm尺寸范围内颗粒的非吸收气溶胶颗粒的折射率（RI）值，精度为0.1%。然而，由于使用贝塞尔光束（BB）光阱产生的光致力作用于粒子上，限制吸收气溶胶粒子被证明是困难的。在这个项目中，将开发一个利用线性电动四极（LEQ）陷阱的CRDS装置，允许精确捕获吸收粒子。新技术的准确性将通过与已建立的蒸发有机和吸湿性无机物种的测量结果进行比较来验证。然后将开始确定吸收气溶胶颗粒（即棕色碳）的RI的散射和吸收成分。项目的后期阶段可能允许探索混合状态、形态和处理（例如氧化老化）对气溶胶粒子光灭的依赖。

Abstract:Aerosol particles can both scatter and absorb solar and terrestrial radiation, with scattering having a cooling effect on the atmosphere and absorption a warming effect. The interaction of radiation with absorbing aerosol particles is currently oneof the largest uncertainties in global climate models [1]. Therefore, a new technique will be developed allowing accurate determination of the effect of irradiation of both weakly and strongly absorbing aerosol particles on global climate.Cavity ring-down spectroscopy (CRDS) measurements reported by Cotterell et al., determined refractive index (RI) values for non-absorbing aerosol particles to an accuracy of 0.1% for particles in the 0.5-1 Tm size range [2]. However, confinementof absorbing aerosol particles proved difficult, owing to photophoretic forces acting on the particles created by the Bessel beam (BB) optical trap employed. During this project, a CRDS set-up utilising an linear electrodynamic quadrupole (LEQ) trap will be developed allowing precise trapping of absorbing particles. The accuracy of the new technique will be validated by comparison with well established measurements of evaporating organic and hygroscopic inorganic species. Work will then begin to determine both the scattering and absorption components of the RI of absorbing aerosol particles, namely brown carbon (BrC) species. Later stages of the project may allow exploration of the mixing state, morphology and processing (e.g. oxidative ageing) dependency of aerosol particle light extinction.