how to generate a list of distinct scalar values from a column which type is array

Dear all,

given a column which type is for instance varchar(20)[], is it possible via
SQL to generate the list of distinct scalar values?

e.g.:
col1
row 1: (aaa, bb, c)
row 2: (dddd, eeee)
row 3: (aaa, eeee)

the query should return:

aaa
bb
c
dddd
eeee

if not, I guess the approach is to use stored procedure. Any code
snippet/suggestion?

Thanks, Sergio