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Light scattering by small particles H. C. van de Hulst
Publisher: Dover Publications

Due to the fact that large molecules or particles move slower than small molecules a defined correlation function results. Cloud particles are large enough to scatter any color of light that falls on them. Larger particles scatter light at relatively smaller angles than light scattered from smaller particles. To overcome this limit, in 1928, Edward Hutchinson Synge came up with an idea of imaging things too small for the naked eye. Potential methods to quantify total particles, such as Dynamic Light Scattering (DLS), Asymmetric Field-Flow Fractionation Using Multi- Angle Light Scattering Detection (AFFFF-MALS); Electrospray Differential Mobility (ES-DMA) and a flow cytometry method (using the Virus Counter) .. [2] Rayleigh scattering, named after the British physicist Lord Rayleigh, happens when light is scattered off particles of material that are much smaller than the wavelength of the light. The amount of light scattered is a function of the size of the particle relative to the wavelength of light falling on it. DLS measures the scattered light of a sample in very short time periods and correlates the data. When light beams interact with particles suspended in air, some of the energy is scattered, which means the light beam changes direction, and usually color as well. Consequently, even though it has mostly been developed for non-enveloped small size viruses (20 nm) this technique is a potential interesting tool for influenza-VLP quantification and characterization. Because clouds are made of billions of small water droplets and ice crystals.