To what extent is Ebola airborne? (aerosols)
Interesting question and hard to answer definitively. First of all: It seems still pretty clear that the major (and by far most important) infection route comes from direct contact with infected people or their body fluids and that aerosol transmission is of far less significance. Ebola is infecting cells of the immune system (mostly macrophages and dendritic cells) which are located in the skin which makes the route through the respiratory organs pretty uneffecient, but it is possible.

However, there are reports for Ebola transmissions (or at least unclear cases in which a direct contact could be excluded), which suggest that the aerosl transmission is possible. There are reports of Ebola infections which spread among experimental animals between infected and non-infected (and without direct contact) control groups. This has been observed between rhesus monkeys and pigs. It was also possible for the pigs to infect non-human primates (see references 1-4 for details). 

This results should be seen with some caution: At least for pigs an Ebola infection seems to be pretty much different than one in humans. There it looks more like a respiratory disease with all what comes along with it: Extended sneezing and coughing - which makes a lot of aerosol droplets. See reference 3 for the original paper and 5 and 6 for a summary and a classification. I think it is also possible that anatomical differences to the humans make such an infection route easier or harder.

Finally there are some reports of infected people which had no direct contact to people (see reference 7). However, this is rare and mostly restricted to people which where involved in health care for infected persons. These people come in close contact to the infected people which raises their chance of getting infected by aerosols. This underlines the importance for health care workers to get the right protective equipment.

References:


Transmission of Ebola virus (Zaire strain) to uninfected control
monkeys in a biocontainment laboratory.
Replication, Pathogenicity, Shedding, and Transmission of Zaire
ebolavirus in Pigs
Transmission of Ebola virus from pigs to non-human primates
Aerosol exposure to Zaire ebolavirus in three nonhuman primate
species: differences in disease course and clinical pathology
Pig-to-monkey Ebola: is there something in the air?
New paper on Ebola–no primate-to-primate transmission seen
Ebola Hemorrhagic Fever, Kikwit, Democratic Republic of the Congo,
1995: Risk Factors for Patients without a Reported Exposure