Traditional charcoal making is a true ecological disaster, comparable to strip mining or slash-and-burn agriculture. Trees from old growth forests and rainforests are cut, then piled into mounds and slowly smoldered. Out of every 5 pounds of trees, about one pound of charcoal is produced. The rest is turned into gases (carbon dioxide, volatile hydrocarbons, tar and whatnot) and released into the air.
The data on the pollution from the traditional charcoal making is taken from an excellent paper published in the Journal of Geophysical Research, vol. 206, and represents the average of the Kenyan earth mound data presented there.