Definition: Smoke: A suspension in the air of small particles produced by combustion.
This lithometeor may be present either near the Earth’s surface or in the free atmosphere. Viewed through smoke, the Sun appears very red at sunrise and sunset, and shows an orange tinge when high in the sky. Smoke from relatively nearby cities may be brown, dark grey or black. Smoke in extensive layers originating from fairly near forest fires scatters the sunlight and gives the sky a greenish-yellow hue. Evenly distributed smoke from very distant sources generally has a light greyish or bluish hue. When smoke is present in large quantities, it may be distinguished by its smell.
When the lithometeor “smoke” is present in the free atmosphere, it is, by convention, distinguished from clouds of smoke (clouds from fires or clouds resulting from industry) by its diffuse appearance and by the absence of any discernible outlines.