Aerosol is a fascinating word because it's a direct Spanish cognate of the English word, making it instantly recognizable. However, its usage in the song is quite poetic and unexpected.
Juanes sings, "Llevo tu voz en mi voz Grabada con aerosol" (I carry your voice in my voice Recorded with aerosol). This creates a vivid and somewhat surreal image of a voice being
"Vía Láctea" turns missing someone into engineering. Juanes packs her into his gear like a fellow astronaut would: "Llevo el prisma de tus ojos" ("I carry the prism of your eyes"), "En mi casco de astronauta" ("in my astronaut helmet"). Her kiss is stuck to him the same practical way: "Tu beso fantasma pegado en mi labio inferior" ("Your ghost kiss stuck to my lower lip"). He doesn't cry so much as malfunction: "A veces llora mi piel" ("Sometimes my skin cries"), "Cuando se empaña de anhelo" ("when it fogs with longing"). It reads like a visor fogging up in the cold, not like sadness.
By the chorus the whole night sky is just her name repeated. "Vía láctea" ("Milky Way") stands alone for four lines in a row, more chant than lyric, before he settles on the one thing he still believes: "Y sé que te vuelvo a encontrar" ("And I know I'll find you again").