Smoke colour

Having one’s home on a wildfire Evacuation Alert is a stressful experience — but, it would be worse having one’s home on a wildfire Evacuation Order.

Portraits of Local Wildlife:
My presentation is this evening.

The fire prompting the alert does not look very threatening in the picture, below. However, it was taken on Sunday, after a day of both water bombing and rain. Earlier extensive flames and candling were intimidating. 

The fairly thin smoke on this occasion does allow the sighting of interesting colour variations: bluish against a dark background; reddish against a bright background. Much of the smoke is composed of small carbon particles, yet it is not the colour of carbon that is controlling the appearance. Rather, it is the smallness of the particles that preferentially scatters (deflects) the bluish light (just as do molecules in the atmosphere).

The light coming through the smoke seen against the bright sky has lost some of the shorter (bluish) wavelengths and so looks reddish. However, against the dark mountainside, there is little transmitted light, and the smoke is seen primarily by scattered light and so appears bluish.

The colour of the smoke is not due to the material composing it, but rather to the small size of the particles. The result is that the colour depends upon how the smoke is illuminated.