In section 52 of "Song of Myself" in lines 7-8 it states: "I depart as air..." What do these lines mean? I need to know what...

To find the meaning of lines in poetry, it is good to look at what comes before and after, and to look at the poem's message as a whole.  In the lines 3-6, Whitman says that "the last scud of day holds back for me...it coaxes me to the vapor and the dusk."  He feels pulled by the rain and clouds (scud) to become one with the air, and so he answers that call, and "departs as air" (which is a simile), and symbolically lets his spirt or feelings "become" the air.  In the next line, he says that he effuses his flesh in eddies and drifts it in icy jags (metaphors for his symbolic "transformation" into being like nature again; eddies and icy jags refer to an icy ocean current). 

A common theme through this poem is Whitman comparing himself to nature (in lines 3-4 he compares himself to a hawk, in lines 9-10 he gives himself to the soil).  He ends it by saying that if you ever want to find him look in nature, and there his essence will be.  I hope that this helps!