Vehicle Emissions, Dust
The amount of vehicle exhaust in Addis almost overwhelmed me on a few occasions. I did notice myself getting a headache when we were stuck in traffic and the clouds of exhaust surrounded us. I think the mountains surrounding the city may prevent more efficient dissipation of pollution as well.
Outside the city, the air pollution was minimal. Certainly, we were able to visually see the emissions from the vehicle, but the bigger factor was the road dust. (Rainy Season had not started yet.) At some points, it did get bad enough that we had to roll up the windows. I was able to turn a Wet Wipe completely brown when I wiped the dust off my face. When I washed my hair, the first round of shampoo rinsed out grayish-brown. Because of the suds color, I actually had to check to see if the shampoo started out purple. (It started out pale green.) Second washing was a lighter gray-brown sudsing. Third washing was back to white suds.
I would definitely take the dust over the pollution, though.
However, part of my job is Environmental Management AND I live next to a State Park in a small town away from heavy industry. So, I freely admit I am a snob about air pollution.