Hi - as an ATCO I'd prefer to have any smoke plume at the departure end. This would allow pilots to have a look and decide if they were going to depart through it, with the luxury of sitting on the ground making the decision! Also the departure climb angle will be much steeper than the 3 degree glidepath for arrivals - so departures would climb above it much quicker. Finally, departures have the option of making a turn to avoid it if necessary - they could do this within a mile or so of the runway, whereas inbounds are committed to being on the centreline for (at the very least) 4 or 5 miles.