Light scattering, airborne dust

Real Time Measurement of Particle Size Distribution of Airborne Cotton Dust by Light Scattering... 

Beautiful blue skies and pink-color sunsets are direct consequences of the existence of an atmosphere. Sunlight scattered by gaseous molecules around our planet is responsible for the blue color of the sky. When we look at sunless sky, the light we observe is mainly scattered light. On the other hand, particulate matter also scatters light but toward the red side of the visible spectrum, and therefore small airborne dust particles produce a spectacular pink-reddish color. In this chapter we discuss the location, composition, and some properties of our atmosphere. 

---