[imd321 (OP)]

If I stood on top of a building, faced forward, and shouted, would the sound travel an equivalent distance  up and down or is there anything which would limit its movement up e.g gravity, air pressure etc.

[flr]

See a calculator:
http://www.csgnetwork.com/atmossndabsorbcalc.html

[Soul Surfer]

Sound does tend to deviate from a straight line path as it passes through the atmosphere.  this deviation depends on the temperature pressure and moisture content of the atmosphere.  On clear bright summer days horizontal sound tends to deviate upwards making it appear quieter and helping us to hear the skylarks  on cold heavy oppressive winter days with an inversion sound transmitted upwards can be bent back to ground level making distant sounds louder.  I used to live near Heathrow airport and in conditions like this we could occasionally hear aircraft on the ground.   The wind can also affect the propagation of sound

[yor_on]

Nice link flr.
==
And cool explanation Soul Surfer