The boundary surface in the atmosphere between a haze layer and the relatively clean, transparent air above; the top of a haze layer. This “line” usually exists near the base of a temperature inversion that prevents the upward spreading of the haze particles. It is frequently a very distinct discontinuity and is particularly striking when viewed from an aircraft that is either just passing through it or is flying high aloft with the sun above the horizon. In the latter case, glare due to the upward scattering of sunlight from the haze can produce a very limited cone of visibility. See also haze horizon.