Ghosting Behind Picture Frame
This image shows the effect of proximity on the efficiency of the deposition. The closer the
frame to the wall the heavier the deposit.
"Ghosting" refers to the darkening of areas on the walls or ceiling due to the deposition of particles at
specific locations. These locations are typically areas of local air turbulence or areas where the distance
between two surfaces is small so that the net force of diffusion on small particles is toward the surfaces.
In this case the darkening is due to the proximity of two surfaces, the picture frame and the wall. The picture
was hung on the wall so that the top of the picture frame was farthest from the wall. The base of the picture
frame rested directly on the wall. The wall had a slight texture so the actual contact points were few. Notice
that the ghosting is darker at locations where the picture fame got closer to the wall. The effect shown here
required 25 years to form. Ghosting will appear much more quickly if the turbulence is greater and if there
is more soot in the environment.
Significance in the Environment: