What makes hazy skies look white, and how big must the specks be?
Research question: What makes smoke, dust or sea-salt skies look whitish instead of blue, and how big do particles have to be before they wash out the blue?
The records show that sky light looks blue because it is scattered, and the document attributes this to Rayleigh scattering 1. The document ties the whiteness of clouds to a different process, Mie scattering, but the facts provided do not apply that explanation to smoke, dust or sea-salt skies 2. Fine particles matter most for total optical extinction because they scatter light efficiently 3. In Tianjin haze, the aerosol scattering coefficient rose to about 0.665 per km from about 0.213 per km on non-haze days 8, and higher PM2.5 makes multiple scattering more pronounced 7. The facts do not give a particle size at which blue is washed out, and the newest fact is from 2018, roughly eight years before October 2026 7.
Sources
"la luz en el cielo se dispersa, y por ello se ve azul, y no negro; el cielo se ve azul o naranja cuando el Sol está en el horizonte, porque se recibe la radiación dispersada (dispersión de Rayleigh)"Dispersión
"el hecho de que las nubes sean blancas también se debe a la dispersión (dispersión de Mie)"Dispersión
"Fine particles are particularly important in total optical extinction because of their high mass scattering efficiency and absorption cross-sections."Particle size distributions of wildfire aerosols in the western USA
"Atmospheric aerosols influence the global radiation balance by directly scattering and absorbing solar radiation."Particle size distributions of wildfire aerosols in the western USA
"The results show that fine particles played important roles in controlling visibility in Tianjin."Effect of Aerosols on Visibility and Radiation in Spring 2009 in Tianjin, China (2012)
"When the mass concentration of PM2.5 is constant, the larger the geometric mean of the particle diameter is, the larger the visibility is."Study on the relationship between PM2.5 concentration and visibility in Beijing based on light scattering theory (2018)
"The result shows that the higher PM2.5 concentration is，the more obvious the multiple scattering effect is."Study on the relationship between PM2.5 concentration and visibility in Beijing based on light scattering theory (2018)
"The average extinction coefficient and scattering coefficient of atmospheric aerosols were 0.253 1/km and 0.213 1/km in non-haze days, while 0.767 1/km and 0.665 1/km in haze days."Effect of Aerosols on Visibility and Radiation in Spring 2009 in Tianjin, China (2012)