Aerial perspective is the term given to the effect created when objects are viewed through the atmosphere. Dust, smoke, or moisture particulates suspended in the atmosphere viel what we see in the distance. Generally hills or whatever else we are viewing through the layer of atmosphere become lighter in tonal value, and cooler in temperature.
In the Canadian Rockies, this effect is virtually unnoticeable on a very clear day and at a high altitude due to thin atmosphere and virtually no particulates, whereas in coastal locations there is often mist, fog, etc., that creates cooler and lighter distant vistas.
Of course, this changes again when you are in an area where dust particulates gather in the air with moisture droplets. The dust hanging in the air (or whatever other pollutant may be present) creates a warmer distant color than if there was just moisture present. Are you confused yet? There is an elegant solution: paint what you see.
I find the tendency is to paint the distant hills darker and warmer than they actually are. Be aware of this tendency and look again. Harder. Believe your eyes – it’s only your mind that plays tricks.
Happy painting all,