An atmospheric aerosol of sufficient concentration to be visible. The particles are so small that they cannot be seen individually but are still effective in visual range restriction. The Blue Ridge Mountains of the Eastern United States have a haze caused by the natural emissions of hydrocarbons (mostly isoprene-see below) which are oxidized and form aerosols. [Graedel, T.D. and Paul Crutzen. Atmospheric Change: an Earth system perspective; 1993; Freeman Press.]
