  We have simulated atmospheric effects such as fog and smoke in laboratory
environment to simulate depolarisation due to atmospheric effects during a free
space optical communi- cation. This has been used to study noise in two
components of quaternary encoding for polarization shift keying. Individual
components of a Quaternary encoding, such as vertical and horizontal as well as
45$^\circ$ and 135$^\circ$ , are tested separately and indicates that the depo-
larization effects are different for these two situation. However, due to a
differential method used to extract information bits, the protocol shows
extremely low bit error rates. The information obtained is useful during
deployment of a fully functional Quaternary encoded PolSK scheme in free space.
