Why are distant mountains grey?

Question

I have read this question:

Where in the atmosphere is the blue light scattered?

where John Rennie says:

For the same reason, distant mountains keep their color. Also, the distant mountains don't increase the amount of blue light from other directions much simply because the intensity of light reflected from distant mountains into our eyes is vastly smaller than the intensity of light coming directly (or just with Rayleigh scattering) from the Sun to our eyes. And even if it were not smaller, e.g. when the Sun is right below the horizon and the mountains are needed, we won't be able to easily distinguish that the blue sky actually depends on the mountains.

Now I do not understand, because to me, distant mountains seem to grey out, whereas John Rennie says they do not. He says that light coming from distant mountains has a much lower intensity, then light that is coming from the atmosphere with Rayleigh scattering. Now which one is right? Do distant mountains grey out, or is that just an illusion of fog?

Question:

1. Which one is right, do distant mountains grey out or not, is it really that they seem to lose color (then to go grey), or is it just fog?

2. Why are distant mountains greyed out, is it Rayleigh scattering or is it pollution in the air?

Answer 1

The quote you've chosen should be read in the context of why mountains don't look red. Instead, they generally do have mostly the same color. You shouldn't read into this answer that they appear identical in all conditions.

The gray shift you view over long distances is due to the presence of aerosols, not Rayleigh scattering. Certainly many instances of high aerosol concentration come from atmospheric pollution, but it's not the only source. Biological and geological sources are also found.

NY Times article on the Blue Ridge mountains

NOAA article on Haze over portions of the United States