The skies here are red, the CA Mega Fires are creating massive amounts of smoke. I made a wearable Air Quality monitor that has two arm bands that display environmental status: Temperature, Barometric pressure, Humidity. A Honeywell HPM Series Particle Sensor monitors air quality. It is a laser-based sensor which uses the light scattering method to detect and count particles in the concentration range of 0 μg/m3 to 1,000 μg/m3 in a given environment. The top picture was taken in my backyard, near Berkeley, CA, September 9, 2020 in mid afternoon. The AirQ readings are for 2.5 and 10 Particles - pretty good compared to recent days. Red skies caused by upper atmosphere smoke. Smoke particles are much larger than gas molecules, and instead better scatter the long wavelengths of red light. This is known as Mie scattering. When particle concentrations get really high, Mie scattering can dominate over Rayleigh scattering meaning we see the daytime sky as red rather than blue.