Moosmüller Hans, Arnott W Patrick
Division of Atmospheric Sciences, Desert Research Institute, Nevada System of Higher Education, Reno, NV 89512, USA.
J Air Waste Manag Assoc. 2009 Sep;59(9):1028-31. doi: 10.3155/1047-3289.59.9.1028.
Light scattering and absorption by particles suspended in the atmosphere modifies the transfer of solar energy in the atmosphere, thereby influencing global and regional climate change and atmospheric visibility. Of particular interest are the optical properties of particles in the Rayleigh regime, where particles are small compared with the wavelength of the scattered or absorbed light, because these particles experience little gravitational settlement and may have long atmospheric lifetimes. Optical properties of particles in the Rayleigh regime are commonly derived from electromagnetic theory using Maxwell's equations and appropriate boundary conditions. The size dependence of particle scattering and absorption are derived here from the most basic principles for coherent processes such as Rayleigh scattering (i.e., add amplitudes if in phase) and incoherent processes such as absorption (i.e., add cross sections), at the same time yielding understanding of the upper particle size limit for the Rayleigh regime. The wavelength dependence of Rayleigh scattering and absorption are also obtained by adding a basic scale invariance for particle optics. Simple consequences for particle single-scattering albedo ("whiteness") and the optical measurement of particle mass densities are explained. These alternative derivations complement the conventional understanding obtained from electromagnetic theory.
悬浮在大气中的粒子对光的散射和吸收会改变大气中太阳能的传输，从而影响全球和区域气候变化以及大气能见度。特别令人感兴趣的是瑞利区域内粒子的光学特性，在该区域中，粒子相对于散射或吸收光的波长较小，因为这些粒子几乎不会发生重力沉降，并且可能在大气中具有较长的寿命。瑞利区域内粒子的光学特性通常是根据电磁理论，利用麦克斯韦方程组和适当的边界条件推导出来的。这里从诸如瑞利散射（即同相时相加振幅）等相干过程以及诸如吸收（即相加截面）等非相干过程的最基本原理出发，推导了粒子散射和吸收的尺寸依赖性，同时得出了对瑞利区域内粒子尺寸上限的理解。瑞利散射和吸收的波长依赖性也是通过为粒子光学添加基本的尺度不变性而得到的。文中解释了粒子单次散射反照率（“白度”）的简单结果以及粒子质量密度的光学测量方法。这些不同的推导补充了从电磁理论获得的传统理解。
