Wildfire smoke is made of particles large enough to scatter away blue light and let red, orange and yellow pass through, and that same physics turned the sky over an evacuation near Toledo the color of an old photograph

Smoke is, after all, mostly just tiny particles suspended in air. On a clear day, the sky is blue because air molecules are small, far smaller than the wavelength of visible light, and that mismatch in scale matters enormously. Wildfire smoke is bigger — not in any way you’d notice by eye, but at the scale that matters for light, where smoke particles are large enough to change which wavelengths get scattered. As Miriam Guthrie puts it on weather.com, “since smoke particles are larger than air molecules, they cause longer wavelengths to scatter even more.” So the sky isn’t only losing blue light to scattering, it’s losing additional blue light to outright absorption, on top of the scattering effect already at work.